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METHODS AND STANDARDS

FOR ENVIRONMENTAL MEASUREMENT

Proceedings of the

8th Materials Research Symposium

Held at the National Bureau of Standards

Gaithersburg, Maryland 20234

September 20-24, 1976

William H. Kirchhoff, Editor

institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued November 1977
Library of Congress Cataloging in Publication Data

Materials Research Symposium, 8th>Gaithersburg, Md., 1976. Methods and, standards for environmental measurement. (NBS special publication ; 464)

Supt. of Docs, no.: C 13.10:464

1. Pollution —Measurement—Congresses. 2. Environmental

monitoring—Congresses. I. Kirchhoff, William H. II. United

States. National Bureau of Standards.

Office of Air and Water Measurement. III. Title. IV. Series: United States. National Bureau of Standards. Special publication ; 464. TD177.M37 1976 628.5 76-608384

National Bureau of Standards Special Publication 464

Nat. Bur. Stand. (U.S.), Spec. Publ. 464, 659 pages (Nov. 1977)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $11

Stock No. 003-003-01704-3
FOREWORD

The Office of Air and Water Measurement of the National Bureau of Standards' Institute

for Materials Research has responsibility for coordinating the NBS program in air and water

pollution measurement. This program consists of a nearly 70 man-year effort utilizing the resources of 12 technical divisions in both the Institute for Materials Research and the

Institute for Basic Standards. In addition, the Institute for Basic Standards administers

a 30 man-year effort in developing standards for noise pollution measurement. Although the

technical results of our efforts are directed to a broad cross section of scientists and

engineers charged with environmental measurements, NBS devotes nearly 30 man-years of

effort to assisting other Federal agencies with special environmental measurement problems

related to each agency's mission.

The objectives of the Air and Water Measurement Program at NBS are to provide measurement standards such as Standard Reference Materials, to develop new and improved measurement

methods to support these standards, and to provide and evaluate chemical and physical data

needed to relate accurately environmental emissions to environmental quality. In a sense,

we at NBS do not view ourselves as environmental specialists. We are not a regulatory

agency. Rather, we are measurement scientists concerned with the reliability of all

measurements and particularly with those measurements which affect national policies.

The effectiveness of the NBS program in air and water measurement depends critically

upon our perception of measurement needs and the usefulness of standards in meeting those

needs. Thus, a major goal of this symposium was to illuminate problems associated with air

and water measurements. The topics chosen for inclusion in the Symposium ranged from the

role of Standard Reference Materials in Environmental Measurement to the Application of

Laser Technology to Air Pollution Measurement. These topics were chosen either because

there is not yet a consensus regarding the applicability of a technology or because the

technology is still in an early stage of development.

Although we are not ourselves environmental specialists, we nevertheless recognize the

importance of living in harmony with our natural resources. We hope that our present and

future activities will contribute to a better understanding of the relationship between

man's activities and the environment and more reliable methods for achieving this harmony.

The active participation of over 350 scientists in this Symposium reflects the commitment

of the technical community to our common goal.

JOHN D. HOFFMAN, Director

Institute for Materials Research

III
PREFACE

This publication comprises the formal proceedings of the 8th Materials Research Symposium, "Methods and Standards for Environmental Measurement." The topics chosen for inclusion

in this symposium were those which were in any early stage of development or those which were of particular concern and interest at the time of the symposium. Because of the rapid

changes expected to take place in our knowledge and understanding of these topics, timely

publication of the proceedings was particularly important. For this reason, this volume

consists of extended abstracts rather than full papers on the state of the art in environmental measurements and standards. Readers interested in more details concerning a particular topic are urged to contact the appropriate author for more information.

The format for the symposium consisted of review papers for each topic presented in a morning plenary session followed by simultaneous afternoon sessions of contributed and

invited papers on particular aspects of each topic. Each session was organized by an individual knowledgeable in the topic of the session. The plenary lecturers and session

organizers were selected with the guidance of an ad hoc program committee consisting of

individuals actively involved in air and water pollution measurement. In addition to the

presented papers, a panel discussion on certification of water analysis laboratories was

held. Each panel member represented a particular point of view: a Federal regulatory

agency, the U. S. Department of Commerce, a state regulatory agency, the industrial sector

and the professional chemist. The opening remarks of each panel member are included in

these published proceedings.

It should be noted that throughout these proceedings certain commercial equipment,

instruments or materials are identified in order to specify adequately experimental procedure. In no case does such identification imply recommendation or endorsement by the

National Bureau of Standards, nor does it imply that the material or equipment identified

is necessarily the best available for the purpose.

The success of a symposium such as this depends on the enthusiastic participation of

many dedicated individuals. Many members of the technical division and the staff of the

Institute for Materials Research helped in many ways. Several individuals were involved

with the symposium from its inception. Ronald B. Johnson and Robert F. Martin of the

Institute for Materials Research and Sara J. Torrence of the Office of Information Activities

provided the fiscal and administrative management of the symposium including the accommodations, social programs, and logistics. In the Office of Air and Water Measurement,

Barbara Watkins and Carol Grabnegger gave tirelessly of their time and good humor before

and during the symposium and in the preparation of the final proceedings.

A special commendation is deserved by Dr. James R. McNesby, who led the Air and Water

Pollution Program at NBS since its inception until August 1976 when he left NBS to take an appointment at the University of Maryland. It is through his leadership that NBS has found

itself firmly rooted in environmental measurement and the success of this symposium is

testimony to the success of that leadership.

Finally, and most importantly, the contribution of Eileen Myers as program coordinator

is gratefully acknowledged. Those who participated in the symposium are well aware of the

role she played in ensuring that all deadlines were met and that all problems were smoothly

sol ved.

WILLIAM H. KIRCHHOFF, Acting Chief

Office of Air and Water Measurement

IV
ABSTRACT

This book presents the Proceedings of the 8th Materials Research Symposium on "Methods

and Standards for Environmental Measurement" held at the National Bureau of Standards,

Gaithersburg, Maryland, on September 20 through September 24, 1976. The Symposium was sponsored by the NBS Institute for Materials Research in conjunction with the Office of Air

and Water Measurement.

The volume contains extended abstracts of the invited and contributed papers in topics

of concern at the time of the symposium: Accuracy, the analysis of trace organic compounds

in water, multielement analysis, the physical and chemical characterization of aerosols,

in situ methods for water analysis, the application of laser technology to atmospheric

monitoring, ambient air quality monitoring, the chemical characterization of inorganic and

organometal 1 ic constituents, reference materials for environmental measurement and finally,

environmental laboratory certification and collaborative testing.

Key Words: Accuracy; Aerosol; Air; Collaborative Testing; Laboratory Accreditation;

Laser Technology; Multielement Analysis; Pollutants; Speciation; Standard

Reference Materials; Trace Organics; Water

V
CONTENTS

Page

Foreword j j j Preface ly

Abstract V Keynote Address XV

Part I. ACCURACY

Accuracy - An Industrial Viewpoint

William 0. Fitzgibbons 3

Ultraviolet Photometer for Ozone Calibration

Arnold M. Bass, Albert E. Ledford, Jr., and Julian K. Whittaker 9

Accuracy of Ozone Calibration Methods

Richard J. Paur 15

Interrelationships Between Primary Calibration Standards for Nitric Oxide, Nitrogen

Dioxide and Ozone as Applied to Test Gas Atmospheres Generated by Gas Phase

Titration

Donald G. Muldoon and Anthony M. Majahad 21

An Analysis of the Measurement Accuracy and Validity of Results from the Charcoal

Tube Sampling Technique

Gerald Moore 37

Achieving Accuracy in Environmental Measurements Using Activation Analysis

Donald A. Beaker 43

A Comparison of Factors Affecting Accuracy in Atomic Emission and Atomic

Absorption Spectrometry Using a Graphite Furnace for Trace Metal Analysis in

Water

M. S. Epstein, T. C. Rains and T. C. 0 'Haver 47

Improved Accuracy in Background Corrected Atomic Absorption Spectrometry

Andrew T. Zander and Thomas C. 0' Haver 53

Standard Addition Uses and Limitations in Spectrophotometric Analysis

Robert Klein, Jr. and Clifford Haah ^1

Part II. DETERMINATION OF TRACE ORGANIC POLLUTANTS IN WATER

Unmet Needs in the Analysis of Trace Organics in Water

William T. Donaldson 69

GCIR--A Versatile and Powerful Tool for Analysis of Pollutants

Leo V. Asarraga

The MSDC/EPA/NIH Mass Spectral Search System

S. R. Heller 75

Methods for Analysis of Trace Levels (pg/kg) of Hydrocarbons in the Marine

Envi ronment

S. N. Chesler, B. H. Gump, H. S. Hertz, W. E. May and S. A. Wise 81

Potential Carcinogens in Water: GC/MS Analysis

Ronald A. Hites 87

VI
Page

A New Simple Method for the Recovery of Trace Organics from Water

T. D. Kaazmarek 91

Determination of Trace Organic Pollutants in Water by Spectrophotofl uorescence

After Treatment with Activated Carbon

Joseph G. Montalvo, Jr. and Ching-Gen Lee 97

Polyurethane Foam Plugs for Concentration of Trace Quantities of Benzo(a)pyrene

from Water

J. Saxena, J. Kozuahowski and D. K. Basu 101

Part III. MULTIELEMENT ANALYSIS

Thousands of Metal Analyses per Man Day--A Reality in U.S. EPA's Central Regional

Laboratory: Multielement (23) Analysis by an Inductively Coupled Argon Plasma

Atomic Emission System (ICAP-AES)

Richard J. Ronan and Garry Kunselman 107

Multielement Analysis of River Water

R, Sohelenz 1"I3

Multielement Analysis in Rainwater

J. G. van Raaphorst, J. Slanina, D. Borger and W. A. Lingerak 121

Quantitative Multi-element Analysis of Environmental Samples by X-Ray Fluorescence

Spectrometry

P. A. Pella, K. Lorher, and K. F. J. Heinriah 125

Multielement Analysis of Air and Water Pollutants in Gold Mines by Thermal and

Epi thermal Neutron Activation

C. 5. Erasmus^ J. Sargeant, J. P. F. Seltsahop and J, I. W. Watterson

A Multielement-Direct Reading Method for the Spectral Analysis of Sediment Leachates

M. M. Moselhy, D. W. Boomer, J. N. Bishop and P. L. Diosady 137

High Efficiency Solvent Extraction of Trace Elements in Aqueous Media with

Hexaf 1 uoroacetyl acetone

Morteza Janghorbani, Max Ellinger and Kurt Starke 151

Determination of Trace and Minor Elements in the Combustible Fraction of Urban

Refuse

William J. Campbell, Harold E. Marr, III and Stephen L. Law

''^^

Part IV. PHYSICAL CHARACTERIZATION OF AEROSOLS

Physical Characterization of Aerosols

K. T. Whitby ''65

Measurement of Aerosol Size Distribution with a Particle Doppler Shift

Spectrometer

Hon Chabay 175

Instrumental Analysis of Light Element Composition of Atmospheric Aerosols

Edward S. Macias "I^^

X-R-D Analysis of Airborne Asbestos Preparation of Calibration Standards

M. Fatemi, E. Johnson, L. Birks, J. Gilfriah and R. Whitlook

VII
Page

Respirable Ambient Aerosol Mass Concentration Measurement with a Battery-Powered

Piezobalance

Gilmore J. Sem 191

A Cascade Impaction Instrument Using Quartz Crystal Microbalance Sensing

Elements for "Real-Time" Particle Size Distribution Studies

D. Wallace and E. Chuan 199

A Limitation on Electrical Measures of Aerosols

W. H. Marlow 213

The Use of a Modified Beta Density Function to Characterize Particle Size

Distributions

Alan S. Goldfarb and James W. Gentry 219

Part V. WATER ANALYSIS

In-situ Monitoring with Ion-Selective Electrodes--Advantages and Pitfalls, or What the Instructions Didn't Say

Richard A. Durst 229

Problems of Mercury Determination in Water Samples

Sunao Yamazakij Yukiko Dokiya and Keiichiro Fuwa 233

Sampling for Water Quality

Willie R. Curtis 237

Monitoring Bacterial Survival in Seawater Using A Diffusion Chamber

Apparatus In-situ

George J. Vasconcelos 245

Clean Laboratory Methods to Achieve Contaminant-Free Processing and Determination

of Ultra-Trace Samples in Marine Environmental Studies

C. S. Wong^ W. J. Cretney, J. Piuze and P. Christensen 249

A Modified Procedure for Determination of Oil and Grease in Effluent Waters

G. M. Rain and P. M. Kerschner 259

Variability of Trace Metals in Bed Sediments of the Po River: Implications

for Sampling

M. T. Ganzerli-Valentini, V. Maxia, S. Meloni, G. Queirazza and E. Smedile 263

Part VI. APPLICATION OF LASER TECHNOLOGY TO ATMOSPHERIC MONITORING

Application of Laser Technology to Atmospheric Monitoring

A. Mooradian 277

Laser Monitoring Techniques for Trace Gases

William A. McClenny and George M. Russwurm 287

Long-Path Monitoring with Tunable Lasers

E. D. Hinkley and R. T. Ku 291

Development of a Two Frequency Downward Looking Airborne Lidar System

J, A. Eckert, D. H. Bundy, and J. L. PeaaocK. 295

VIII
Page

Remote Analysis of Aerosols by Differential Scatter (Disc) Lidar Systems

M. L. Wright, J. B. Pollaak and D. S. Colbum 301

Dial Systems for Monostatic Sensing of Atmospheric Gases

E. R. Murray, J. E. van der Laan, J. G. Hawley, R. D. Hake, Jr., and M. F. Williams. 305

Coherent Anti -Stokes Raman Scattering in Gases

J, J. Barrett 315

Highly Selective, Quantitative Measurement of Atmospheric Pollutants Using Carbon

Monoxide and Carbon Dioxide Lasers

D. M. Sweger, S. M. Freund and J. C. Travis 317

Part VII. CHEMICAL CHARACTERIZATION OF AEROSOLS

Chemical Characterization of Aerosols; Progress and Problems

William E. Wilson 323

Detection of Individual Submicron Sulfate Particles

laaoov Mamane and Rosa G. de Pena 327

An Analysis of Urban Plume Particulates Collected on Anderson 8-Stage Impactor

Stages

Philip A. Russell 335

Size Discrimination and Chemical Composition of Ambient Airborne Sulfate

Particles by Diffusion Sampling

Roger L. Tanner and William H. Marlow 337

The Identification of Individual Microparticles with a New Micro-Raman

Spectrometer

E. S. Etz and G. J. Rosasco 343

A Compact X-Ray Fluorescence Sulfur Analyzer

L. S. Birks, J. V. Gilfriah and M. C. Peokerar 347

The X-Ray Identification and Semi-Quantification of Toxic Lead Compounds Emitted

Into Air by Smelting Operations

Peter F. Lott and Ronald L. Foster 351

Flameless Atomic Absorption Determinations of Cadmium, Lead and Manganese in

Particle Size Fractionated Aerosols

Mark E. Peden 367

Part VIII. AIR POLLUTION MEASUREMENT

Ambient Air Quality Monitoring

George B. Morgan 381

Applications of Remote Monitoring Techniques in Air Enforcement Programs

Francis J. Biros 387

IX
Individual Air Pollution Monitors

S. C. Morris and M. Granger Morgan 391

Intercalibration of Nitric Oxide/Nitrogen Dioxide/Ozone Monitors

D. H. Stedman and R. B. Harvey 393

A Reactive Gas Generator

Wing Tsang and James A. Walker

Semiconductor Gas Sensor Equations for Predicting Performance Characteristics

S. M. Toy ^'^^

Monitoring Non-methane Hydrocarbons in the Atmosphere by Photoionization

J. N. Driscoll

A Study of Vertical Diffusion in the Atmosphere Using Airborne Gas Chromatography

and Numerical Modelling

R. S. Crahbe ^'^

In-situ Quantitation of Background Halofluorocarbon Levels

L. Elias 435

Origin and Residence Times of Atmospheric Pollutants: Application of ^'+C L. A. Currie and R. B, Murphy 439

Part IX. CHEMICAL CHARACTERIZATION OF INORGANIC AND ORGANOMETALLIC CONSTITUENTS

Chemical Characterization of Inorganic and Organometal 1 ic Constituents

Robert S. Braman 451

Analytical Techniques for the Study of the Distribution and Speciation of Heavy

Metals in Aquatic Systems

H. J. Tobsohall, N. Lawkowski and K. Kritsotakis 459

Inorganic Speciation of Copper in Estuarine Environments

David Burrell and Meng-Lein-Lee 461

Use of Ion-Specific Electrodes in Studying Heavy Metal Transformation in Aquatic

Ecosystem

5. Ramamoorthy and D. J. Kushner 467

Electrochemical Studies of the Methyl mercury Cation

Richard A. Durstj F. E. Brinakman, Kenneth L. Jewett, and John E. Doody 473

An Element-Specific Technique for the Analysis of Organometal 1 ic Compounds

Y. K. Chau and P. T. S. Wong 485

Chroma tography-Atomic Spectroscopy Combinations. Applications to Metal Species

Identification and Determination

Douglas A. Segar and Adrianna I. Cantillo 491

Changes in the Chemical Speciation of Arsenic Following Ingestion by Man

Erie A. Crecelius 495

The Determination of Lead in Aqueous Solutions by the Delves Cup Technique and

Flameless Atomic Absorption Spectrometry

Haleem J. Issaq 497

X
Part X. THE STATUS OF REFERENCE MATERIALS FOR ENVIRONMENTAL MEASUREMENT

Page

The Status of Reference Materials for Environmental Analysis

John K. Taylor 503

Reference Type Samples for Water/Waste Analyses in EPA

John A. Winter 509

The Preparation and Analysis of a Trace Elements in Water Standard Reference Material

J. R. Moody, H. L. Hook, P. J. Paulsen, T. C. Rains, I. L. Barnes, and M. S. Epstein. 5]5

The Standard Fineparticle

Brian H. Kaye 519

Thin Film Standards for X-Ray and Proton Induced X-Ray Fluorescence

D. N. Breiter, P. A. Pella and K. F. J. Heinrioh 527

Reference Materials for Automotive Emissions Testing

Theodore G. Eokman 53]

Long Term Investigation of the Stability of Gaseous Standard Reference Materials

E. E. Hughes and W. D. Dorko

Standard Reference Materials for the Analysis of Organic Vapors in Air

Barry C. Cadoff 541

Working Reference Materials for Lead Contamination Analyses of Air and Water

Alfred C. Eakert, Jr. and Dennis M. Mongan 545

Part XI. COLLABORATIVE TESTING

Collaborative Testing of Air Pollution Methods

John B. Clements 555

Inter! aboratory Comparison of Neutron Activation and Atomic Absorption Analyses of

Size-Classified Stack Fly Ash

J.M. Ondov, R.C. Ragaini, R.E. Heft, G.L. Fisher, D. Silberman, and B.A. Prentice.. 565

Collaborative Testing of a Continuous Chemi luminescent Method for Measurement of

Nitrogen Dioxide in Ambient Air

John H. Margeson, Paul C. Constant, Jr., Michael C. Sharp, and George W. Scheil. . . . 573

Collaborative Testing of EPA Method II Joseph E. Knoll, M. Rodney Midgett, and George W. Scheil 575

Evaluation of Interl aboratory Comparison Data by Linear Regression Analysis

Donald E. King 581

Potential Enforcement Uses of Emission Test Collaborative Studies

Louis Paley and Walter S. Smith 597

XI
Part XII. AIR POLLUTION, WATER ANALYSIS

Page

Ion Chroiiiatography--A New Analytical Technique for the Assay of Sulfate

and Nitrate in Ambient Aerosols

James D. Mulikj Ralph Puckettj Eugene Sawioki^ and Dennis Williams 603

The Use of a Gas Chromatograph-Microwave Plasma Detector for the Detection

of Alkyl Lead and Selenium Compounds in the Atmosphere

Donald C. Reamer, Thomao C. 0 'Haver, and William H. Zoller 609

The Dutch National Air Pollution Monitoring System - A Focal and Reference Point

T. Schneider 613

Analysis and Calibration Techniques for Measuring of Airborne Particulates and

Gaseous Pollutants

I. Delespaul, H. Peperstrate and T. Rymen 617

Factors Governing the Contents of Metals in Water

D. J. Swaine 625

Effects of Water Soluble Components of Refined Oil on the Fecundity of the

Copepod, Tigriopus Japoniaus

Colin Finney and Anthony D'Agostino 627

Part XIII. CHEMICAL CHARACTERIZATION OF AEROSOLS

A Comparison of Electron Microscope Techniques for the Identification of Asbestos

Fibers

C. 0. Ruudy P. A. Russell, C. S. Barrett, and R. L. Clark 635

Determination of Reducing Agents and Sulfate in Airborne Particulates by

Thermometric Titration Calorimetry

L. D. Hansen, D. J. Eatough, N. F. Mangelaon and R. M. Izatt 637

Determination of Acidic and Basic Species in Particulates by Thermometric

Titration Calorimetry

D. J. Eatough, L. D. Hansen, R. M. Izatt, and N. F. Mangelson ^^3

Single-Particle Analysis of the Ash From the Dickerson Coal-Fired Power Plant

John A. Small and William H. Zoller 651

Laser-Raman Monitoring of Ambient Sulfate Aerosols

R. G. Stafford, R. K. Chang, and P. J. Kindlmann 659

Chemical Characterization of Particulates in Real Time by a Light Scattering

Method

C. C. Gravatt 669

XII
Part XIV. LABORATORY ACCREDITATION - PANEL DISCUSSION

Page

The National Voluntary Laboratory Accreditation Program

T. R. Young 675

The National Laboratory Certification Program for Water Supply

Charles Hendr-iaks 677

Laboratory Accreditation

C, Eugene Hamilton

Certification of Water and Wastewater Laboratories: A Professional Chemists

View

E. Gladys Swope 685

Lessons to be Learned from Clinical Laboratory Accreditation

William F. Vincent ; 689

XIII

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

METHODS AND STANDARDS FOR ENVIRONMENTAL MEASUREMENT

Honorable George E. Brown, Jr.

Chairman, Subcommittee on the Environment and the Atmosphere

Committee on Science and Technology

U.S. House of Representatives

Washington, DC 20515, USA

Measurement: The First Step

I am genuinely pleased to be here this morning with such a distinguished gathering of

specialists in the field of environmental measurement science. It heartens me to know

that, in commemoration of the Nation's Bicentennial and the 75th Anniversary of the National

Bureau of Standards, you are being called upon to look back, review and critique past

measurement methods, then emerge with a strong, enlightened vision of future directions.

It is a doubly fitting occasion for you to assess and substantiate old approaches to

environmental measurement, while also proposing totally new ones. I would like to commend

this as a very timely effort. All too often this past year, in celebration of the Nation's

Bicentennial, we have failed to recall that our success and affluence have not been achieved

without sacrifices, one of which has been the well-being and purity of our "space ship"

Earth. Now is the time that we as a Nation, and as a world community of nations, are considering, reaffirming and expanding our goals for reclaiming and guarding a highquality environment.

This reaffirmation has been tempered by the realization that environmental goals must

he balanced with, hut not compromised by, other eTiergy and economy-related objectives.

The goals have been legitimitized by persuasive new evidence of health effects, such as the correlation of cancer to environmental factors in a majority (60-90 percent) of all cases. They have been influenced by the prediction of drastic global repercussions of

seemingly minor actions, such as the release of halocarbons from common spray cans.

The focus of the past has been on regulations to cure existing environmental degradation.

Now is the appropriate time to think of the future: to strive for regulations and incentives

to prevent the spread of this increasingly pervasive disease. In either case, the need

for environmental measurement cannot be overemphasized. Whether controlling pollution, or preventing it, we must be able to identify all environmental contaminants and document the

nature and extent of their damage to public health and welfare.

As entrepeneurs in the field of environmental measurement, you are constantly subjected

to conflicting pressures. On the one hand, quality control measures stress the need for

accuracy, reliability, and intercomparabi 1 ity of data and techniques. On the other, you

are exhorted to produce inexpensive, practical instruments on short order, for immediate

use in the field. I must admit that these diverging interests are incorporated into

existing pollution control legislation, which often sets deadlines for compliance with

regulations, calls for use of "economically achievable" technology, and stipulates that

the best, most reliable scientific data be used to justify policy decisions.

Can these diverging interests be balanced? Can you, as specialists, overcome your

preference for sophisticated, specialized approaches? This dilemma was experienced by a researcher conducting the epidemiological study of sulfur oxides (known as CHESS), for the

Environmental Protection Agency. Apparently, measurement methods which were used under

controlled laboratory conditions were not suited to widespread application in the field.

The accuracy of the data suffered as a consequence. Therefore, I urge you to keep in mind

the need to extrapolate from lab to field methods.

XV
It is n^y belief that we are dealing with a heirarahy of needs. It might be useful to

imagine a pyramid of instrument types: the narrow apex represents the most accurate,

sophisticated apparatus which can be designed, the broad base the array of more rugged,

field equipment used to conduct daily monitoring and measuring tasks. The validity of the

field data hinges upon the inherent accuracy of those "top" instruments, to which the

simpler instruments have been standardized. Thus, it is of primary importance to attain

the g,oal of accurate measurement and analysis before attempting to compare and qualify the

data collected under varying conditions. However, that data must be collected; we cannot

afford to put off establishing a firm foundation of "baseline" knowledge any longer.

Thus, an equal and simultaneous effort must be made to diversify and expand the base of our pyramid. This range of instruments, tightly-knit by measures to verify the accuracy

of each component, is what you must seek to develop.

The concern at the top of this pyramid is to arrive at standardized calibration

points, accurate and reliable characterizations of environmental contaminants in each of

the different media. These will then serve as reference points upon which to base all

analytical methods.

As scientists, you constantly deal with physical limitations of environmental measurement methods. In fact, you are dedicated to exploring, defining, minimizing, and, when

possible, eliminating them. Thus, you are well aware that all data is qualified by levels

of confidence and probability. You recognize that no number is significant, and subsequently worthy of being recorded, without an estimate of its accuracy. While there is no need for me to reiterate these points to this technical audience, I must remind you that

far too often, in practice, they are not considered. Too many people, espeaially lawyers

and legislators, believe the numbers generated by saientists without reservation. So,

rather than exhort you to present information accurately to society (which I assume you

already do), I would like to emphasize the need for the inclusion of caveats whenever data

is released, circulated, and interpreted.

Let me explain why. In too many instances, the naive faith in unqualified numbers

has led decisionmakers to promote regulations and policies whose justification was later

seriously questioned, or whose implementation was eventually frustrated.

This was the case back in 1970, when the authors of the Clean Air Act Amendments

mandated a 90 percent removal of oxides of nitrogen (NOx) from automobile emissions. This

drastic regulation was based upon measurements which, unbeknownst to these politicians, were seriously in error and consequently distorted the health risks. Subsequent data has

tended to re-confirm the wisdom of the original requirement for a 90 percent reduction in

NOx, ^^'^ ^o*" different reasons.

As this single example, one of a regrettably large number of similar ones, illustrates, more effort should be channelled into doaumenting the need for accurate measurements. Users

of environmental data must be advised of its potential weaknesses. Unless they are,

public officials may continue to formulate strategies whose undeniable repercussions upon

the economy and public's health may not be warranted. But this one example points out

another aspect of how scientific data is used. Frequently, the right decision is made for

the wrong reasons. The guess for NOx was either good, or lucky. In any case, those who

use scientifically generated numbers to support their own policy perspectives frequently

distort data to bolster their case. This is normal practice in politics.

Even the most seemingly trivial measurements strengthen the first link in the long

chain of environmental action: usually it begins with the discovery and quantification of

a "pollutant." The next step, based upon the measurement of exposure-effect relationships,

enables society to determine the need to reduce or remove the substance in question.

Finally, measurements are needed to monitor compliance and the effectiveness of pollution

control requirements.

In dealing with the accuracy of environmental data, the stakes are high: We cannot

risk endangering public health, nor can we justify the economic costs of overprotecting

it. Industry should not delay investing in technology to ameliorate pollution, but neither

can it afford to waste its scarce resources on innovations of dubious effectiveness.

XVI
It strikes me that there are strong parallels between the objectives of this scientific

"meeting of minds" and those of the House Subcommittee on the Environment and the Atmosphere,

which I chair. Let me clarify this comparison somewhat. The Subcommittee was formed less

than two years ago, in order to coalesce oversight over federal environmental research and

development efforts under a single House Committee. Its major responsibilities include

evaluating the state of knowledge on environmental matters and considering ways to optimize

the use of research resources.

Similarly, you have been called together to oversee the status of environmental

measurement techniques and standards. While we legislators are generally concerned that

adequate research is being done to insure the timely abatement of pollution, our intuition

is not enough: we would be paralyzed without the technical advice of specialists such as yourselves. So, we hold hearings to provide the crucial interface between the political

and technical spheres.

The Subcommittee's findings have been most disturbing: There is a dearth of comprehensive baseline data and long-term, basic research in almost every case of environmental

concern, on a wide spectrum of pollutants, particularly under chronic, low-level conditions.

Yet, the federal resources are not presently focused on these areas, but are skewed toward

short-range, "crisis-oriented", applied environmental research. In many cases, (such as that of sulfates), existing levels of contamination are definitely found to be harmful to

human and ecological health, yet we lack the capability to measure and monitor many

deleterious substances in air, water and food our satisfaction {i.e., accurately,

inexpensively, and speedily).

Since it is apparent that the technical foundation of environmental knowledge is

frequently unreliable, and unquestionably piece-meal, it is essential to delineate on a high

priority basis what additional data are needed. We need to expand and upgrade the current

data base, using refined techniques, but we can no longer continue to do this haphazardly.

If the situation I have depicted is not bleak enough, couple it with the scenario

described by the Office of Technology Assessment (OTA) in a recent study of the Office of

Research and Development (ORD) in the EPA: Authority for developing and standardizing

valid analytical methods is scattered throughout the federal agencies. While the EPA's

"equivalency" program is a step in the right direction, there still is no designated

central standardizing procedure. This provides fertile ground for bureaucratic rivalries

and for cumbersome, time-consuming procedures which seriously delay the introduction,

acceptance and utilization of improved instrumentation.

Thus, it is also essential to standardize the definitions of problems, and the methods

and results of environmental research and monitoring, in order to coalesce local, state

and regional efforts into a coherent, usable whole.

The question is: who will accept these responsibilities? Scientists, legislators,

health experts and government officials, industrial representatives and the public all

must voice their concerns and preferences. Can this mul tidi scipl " varied input be

coordinated within the present federal structure?

At this point, some legislators and government officials might be tempted to proffer

the stock solution: an increase in funding. However, I will have to risk my popularity by

saying that this approach is neither politically sound, nor scientifically ethical. It does no good to infuse a body with new blood unless the circulatory system is functioning.

Considering the tightness of the federal environmental research (R&D) budget, we must

first make a credible attempt to make better use of what we already have. We must address

the issues: the direction, quality, priority, and logic of the federal programs to

attain the legislated environmental goals.

XVII
As the OTA study additionally notes, the numerous Government agencies which are involved in this effort, are not integrated. Clearly, the challenge of the future is to

create explicit responsibility within the federal structure for the coordination and

evaluation of environmental research and development activities.

I might add that this challenge is not new, but has been conveniently side-stepped

for some time. Since a major campaign issue this year is the reorganization of the

Executive branch, it is time to exploit it. If this momentum does indeed exist, you here

today, among others, will have a major responsibility to channel your solutions into this

endeavor.

In a closing note, let me return to a comment I made earlier concerning the need to

focus on the prevention of future crises. A major focal point of any reorganization

effort must be the development of an "early warning system". This has become increasingly

apparent, expecially as issues of overwhelming global significance are being raised.

The depletion of ozone is a classic, and perhaps the most immediate international

environmental problem. The release of halocarbons in even a single location on the globe

could ultimately endanger the well-being of the world's population. The realization that

increased skin cancer or massive crop damage may lag decades behind the cause of ozone depletion makes it critical to detect subtle changes before adverse effects occur. Only

then can credible policies for prevention be proposed. International cooperative research

and monitoring efforts will require close partnership, full disclosure of techniques and

their limitations, and intercomparability of results. These are problems you will have to

deal with, before the control policies of any one country will be adopted by the world

community of nations.

I have outlined some of the responsibilities which you, in providing the means towards

achieving a high quality environment, have towards society. Let us make those first steps

count!

XVIII
Part I. ACCURACY

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

ACCURACY - AN INDUSTRIAL VIEWPOINT

William 0. Fitzgibbons

The Standard Oil Company

Research and Engineering Department

Warrensville Laboratory

Cleveland, Ohio 44128, USA

1 . Scope

The scope of this paper deals primarily with the industrial viewpoint of accuracy. We are dealing with non-professional union personnel. They are analyzing water samples and

doing stack sampling. Ambient air will not be dealt with here because ambient air sampling

and analysis is analogous to weather forecasting. Ambient air analysis is the concern of

the whole community. It deals with all air pollution sources, not just industry alone and

therefore it should be the responsibility of the government.

In environmental analysis, we are dealing primarily with empirical and not absolute

measurements. Analyses such as dichromate oxidizables; oxygen depletion after five days in

a 300 ml glass bottle; stuff stuck on a fiberglass filter; freon extractable non-volatile

compounds at test conditions; steam distil lable material which reacts with AAP; and finally

total Kjehldahl nitrogen. All of these techniques are empirical tests, and only one, total

Kjehldahl nitrogen, admits to the fact that it is the total nitrogen obtained under the

specific test conditions.

Why do we have these source and empirical analyses? We have them because the regulations are based on source and effluent standards. In other words, the allowable emissions

are based on the results obtained using an empirical test on a survey of many installations.

Recently, there has been a trend from source and effluent standards to stream and toxic

effluent standards. Because of this switch we are going to have to go to absolute test

methods. These are methods which measure absolute values. Examples of absolute test

methods include metal analyses, temperature, organic carbon, chloride, sulfate and fish

toxicity.

Before we precede further, it is important that we define what we mean by accuracy,

precision, bias, reproducibility, and repeatability. Figure 1 is a drawing of a target. In the center of the target is the right answer. What we are trying to do is get all of our

shots in the bull's-eye. Unfortunately that is not the real world. In figure 2 you see that

the shots are all very close together but they are not anywhere near the bull's-eye. This

is an inaccurate result, but quite precise. Figure 3 is a drawing of the shots which, on the average, are centered around the bull's-eye. The shot identified as A is the first test

done by the chemist. As you can see it was very accurate. Unfortunately most times they

stop there, and we never find, how unprecise a result is. In figure 4 you will see that all

of the shots are very close together, and they are located in the bull's-eye. They are very

precise and very accurate. The distance away from the bull's-eye from all of the shots is a measure of the bias. Reproducibility is the difference of results obtained by two different

laboratories. Repeatability is a measure of how well any particular analyst can repeat

himself.

3
Figure 3. Target drawing, accurate, not

precise results.

4

Figure 4. Target drawing, accurate and

precise results.
2. Steps Involved in Obtaining Accuracy

A. Sampling

About one-half the problem of obtaining accuracy is getting the sample. In fact in

many cases it is one-half the cost. It is particularly true when you are dealing with stack

sampling. The object is to have the sample represent the effluent.

B. Method selection

The first step is to find out what is available. Generally this is done by a literature search starting with the American Public Health Association (APHA) Standards Methods,

ASTM, or the EPA Manual. The second step is to determine what you are going to do with the

results. In some cases regulations specify the test method which you should use. You must

check to make sure the scope of the method covers the applications which you intend to do.

Find out who is going to run the test. You may need a completely different test if it is

going to be run by a Ph.D. than if it is to be run by an operator. Lastly, you need to be

concerned with what is going to be done with the results. In many cases the analytical test

is different, depending on what is to be done with the results. Is it to be used for

designing pollution control equipment, is it to be used for NPDES requirements, or is it to

be used for performance evaluation?

The third step is to compare your results with another test method; that is, independent

confirmation. An example is work we did with cyanide and fish toxicity. The ASTM and APHA

cyanide methods indicated very high cyanide levels. On the order of ten times the media

tolerance limit (TLp^) for fish. We put fish in the tank and the fish lived in straight

effluent. Thus, we deduced that what we were measuring was not cyanide but in fact was rather an interference. After much investigation we found that the test method was measuring thiocyanide as cyanide but thiocyanide isn't toxic. This work points out what we now

call the "Spike Recovery Fallacy." Spike recovery will not identify matrix interferences.

They will simply tell you whether or not you can recover the amount you spiked.

The last step in obtaining an accurate method is to have it written so it can be

evaluated. It must be clearly written in an acceptable format.

C. Training

Our experience has been that serial training is bad. Train from the method and use a teacher whose main job is to train. Do not use the person who is running it to train the

next person. This institutes everyones short cuts, and by the time the third person is

training there is very little semblance between what is done and what the written method

says.

An analyst is qualified at the end of training, not by the fact that he has attended 4,

8, or 12 hours or days of training, but rather the fact that he has demonstrated an ability

by running unknown samples or by showing he is able to do the procedure. This ability must

be demonstrated by running test knowns and effluents, and getting results within the es- tablished precision and accuracy of the method. Documentation of this ability supports the

fact that this analyst is trained and capable of getting the right answer.

D. Internal quality assurance

Internal quality assurance has been broken into two phases. Phase I is the portion

which is normally done by a reputable analyst. This includes the preparation of blanks,

standardization, calibration, and replication. The cost of doing Phase I Internal Quality

Assurance is, in most cases, included in running the procedure. A blank almost always needs

to be run if for no other reason then to set up the colorimeter.

5
Phase II in our internal quality assurance program is a programmed system of duplicates

and spike recoveries. It may or may not be known to an analyst which samples are duplicates

or spikes. The point is that it is not a police system, but is a self-controlled system

wherein the analyst is running his own internal quality assurance program. There are two

examples of this, the EPA Quality Assurance Manual points out the Shewhart and cusum techniques. Our experience has been that the Shewhart technique has been much better than the cusum technique for our environmental analysis quality assurance program. Quality assurance

is applicable to stack sampling, primarily in the sense of knowing what to look for, of

running blanks, and calibrating your equipment.

E. External quality assurance

External quality assurance involves at least three different programs. One of them is

round-robin audits. A central lab prepares samples, and ships them out. Each laboratory

analyzes them, the results are sent back, and tabulated. A report is sent to each lab

showing how they compared to the known and with other analysts.

A second very important portion of external quality assurance is to have your analysts

and analyses checked by independent laboratories. This is about the best and maybe the only

way to do stack sampling analytical quality control. Have a contract organization come in

and run a side-by-side sample. This does two things. First, it points out to management

the cost involved with having an outsider come in, and second, it shows them that stack

sampling is a pesty job no matter who does it.

The third external quality assurance program we use is watch audits. Someone from the

central lab, probably one of the teachers, comes to each lab and watches the analyst go

through the technique. He checks that the analyst is not doing any shortcuts and checks the

standard curves. Are they up to date? This is done in our company annually for every

analyst doing environmental sampling.

F. Trouble-shooting

Basically this step involves solving problems which are identified in other areas, such

as method selection, or the internal or external quality assurance programs. The cure is

what is defined as trouble shooting.

3. Costs Involved With Accuracy in Environmental

and Analytical Quality Control

There is a mass of literature available from the regulatory agencies and their contractors on analytical quality control. I am sure that the costs are significant. In many

cases the analytical quality control data is useful to us. Projects such as ASTM-Project

Threshold are also involved. Costs associated with analytical quality control are large.

The costs are those associated with our corporation which involves three refineries, two

large petrochemical complexes and four quite small petrochemical complexes.

A. Sampling

The cost associated with sampling ranges from $100 to $35,000. One hundred dollar

sampling locations are generally used for grab type water effluent samples or process gas

samples. It costs $35,000 to install a stack sampling platform and sampling connections on

a fluid cat cracker at one of our refineries. On an average, it costs us about $10,000 per

effluent to install sampling and flow measuring equipment to take a composite sample,

preserving it with five kinds of preservatives so that the results are acceptable for the

National Pollutant Discharge Elimination System (NPDES) monitoring program.

6
B. No analytical quality control

Seventy thousand dollars per year per effluent is the cost for NPDES testing for an effluent guideline source with 14 parameters. This $70,000 per year per effluent does not

make one gallon of gasoline. What is even worse, it doesn't improve the environment, it

merely tells us in an accurate way where we are.

C. Methods selection

The costs associated with this step vary between $500 and $50,000. The simple non- controversial methods generally cost $500 or less. Basically what we are doing is evaluating an existing method with which we are familiar, to find out whether it has applicability

to a new source. On the other hand there are complex problems which may cost between

$10,000 and $50,000. Cyanide: in 1974-1975 we spent $42,000 for method evaluation on the

cyanide analysis. Oil and grease analysis: method development cost us $29,000 in the last

two years. On the stack sampling side, we spent $16,000 working up the H2S method. Other

examples with significant costs have been the FSUOD method (first stage ultimate oxygen

demand). Hexavalent Chrome is another quite simple technique where we have spent significant

amounts of money simply to select a method which will work in our effluent and involved

selecting a method from only three possible sources.

D. Training

A total cost on a corporate basis is only $5,000. This includes only the teachers

cost, it does not include the cost of the analyst being trained. The cost on a per analyst

basis is $850. More assistance is needed here. The training manuals don't work very well

in training the kind of people we are trying to train. You need films or videotapes, some training technique like television which can get the point across.

E. Internal quality assurance

Phase I internal quality assurance costs are included in the basic "no analytical

quality control" costs. In other words, the $70,000 per year per effluent includes our Phase I or "expected" analytical quality control.

The costs of Phase II analytical quality control are dependent on the number of samples.

The EPA says that you can run one replicate and one spike with each ten samples. If you're

running three samples a week as required by your NPDES permit, that means a replicate every

three weeks. Obviously that is not a very workable program. The estimate, based on one sample and one spike every ten samples, in the Analytical Quality Control Manual is 30

percent. Our actual costs have been shown to be more like 100 percent or approximately

$50,000 per installation. Initially, the costs were more than 100 percent. After the

program was debugged and they got started, it dropped to a 55 percent increase. It's

maintained at about 65 percent. The reason is that less time is required for set-up and

data digestion as the program becomes more familiar. However, more time is spent in finding

causes of problems. In other words, more time is spent trouble-shooting.

F. External quality control

On a corporate basis our cost for this, program is $16,000 a year. This is only the

corporate cost, it does not include the cost for running the control samples in the various

installations. This is independent of the size of the company, or the number of the labs,

except when you're talking about trouble-shooting. The more labs you have the more troubles

and the more challenges. We're just getting started in the trouble-shooting. In the past we have had many analyst problems to be solved. We are now getting into methods problems.

We are not in a position to estimate the cost of trouble-shooting.

7
4. Justification or Environmental Analytical Quality Control Program

There are four basic reasons to be used as justification. It keeps us out of trouble

with regulatory agencies. Secondly, it avoids bad publicity in an industry that must sell

to the public. Third, it keeps regulatory agencies "honest". This is not to imply that

they are dishonest, but rather, it makes them think about the methods that they are proposing. The most important reason, which is number 4 is that it reduces capital and operating

costs. The first three justifications are hard to put dollar and cents values on. Bad

press does effect the image of an industry that is selling to the public. The one that

sells the program is that it does reduce capital and operating costs.

Following are four case histories involving instances wherein an analytical quality

control program reduced or eliminated capital or operating costs. The first one involves

oil and grease removal. Monitoring using the freon gravimetric technique showed that there

was excessive oil and grease in the effluent. The engineers brought out a variety of

equipment designed to remove oil by gravity techniques from water. None of these techniques

reduced the oil content of the effluent significantly. We went back and evaluated the

method doing all of the steps involved with methods selection. We found that the oil and

grease that we were measuring by that technique was not oil and grease in the classic sense

but rather an organic material which is soluble in water, but was also quite soluble in

freon. We were able to show that there were other methods of removing this soluble organic

and no oil and grease equipment was purchased. The reason being there was no oil or grease

problem.

the second instance involves suspended solids. Analytical results indicated excessive

suspended solids in the effluent, yet when compared to a neighboring domestic sewage treatment plant which had about one-half the suspended solids levels, the turbidities were

equivalent. A little detective work showed that each installation was using a different

fiberglass filter. Both types of filters were evaluated on both effluents. One of the

filter types resulted in suspended solids values approximately 50 percent of those obtained

by the other type of fiberglass filter. Incidentally, both types of fiberglass filters are acceptable according to the EPA Manual. By this change from one type to another type of

suspended solids filter the NPDES suspended solids limit were met and final filtration was not required. The estimated capital cost for final filtration for this installation would

have been $900,000. That expenditure was not made.

Variability reduction is another example. Much waste treatment design is based on a maximum load. One of the results of an analytical quality control program is a reduction in

variability. Much of the effluent variability turns out to be analytical rather than

process. It is a known fact that equipment costs for 50 to 70 percent reductions are much

less than that required for 90 to 95 percent. By reducing the variabil ity^ a cost savings is

realized by reducing the level of treatment required while still meeting effluent limits.

The last case in point involves cyanide. The proposed effluents regulations were issued

a while ago and they included cyanide. The analytical method was found to be inaccurate and

the cyanide in refinery effluents is present as complex, and relatively non-toxic, cyanide,

and not free cyanide. Since that time, the proposed toxic effluent regulations have been

withdrawn.

In conclusion, accuracy is expensive, but worth it. A million dollar lab, with all the

fancy equipment, and highly educated people, with all the credentials, does not mean that

their analytical result is right.

Only the right answer is accurate. The right answer is assured with an Analytical

Quality Assurance program.

8
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

ULTRAVIOLET PHOTOMETER FOR OZONE CALIBRATION

Arnold M. Bass, Albert E. Ledford, Jr., and Julian K. Whittaker

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

In order to provide a facility for photometric ozone measurements, we have designed

and constructed a double-beam photometer for ozone concentrations in the range 0.025 to

1.0 ppm. The sample path length of this instrument is approximately 300 cm. The instrument measures changes in ozonized-air sample transmissions of mercury radiation at 253.7 nm where the photoabsorption cross-section of ozone has been well determined.

Radiation at wavelengths other than 253.7 nm from the mercury lamp is removed by passing

the light through narrow-band interference filters. The light is collimated and passed

through a beam splitter which directs approximately equal intensity beams through the two

cells. Clean air flows through one cell into the ozone generator and then the ozonized air

flows through the second cell. The light beams are recombined on the face of a photomultiplier tube used in the photon counting mode. A rotating chopper allows the two beams

to be detected sequentially so that the transmissions of the two cells may be directly

observed.

Tests indicate that measurements may be made at the 0.05 ppm level with a precision of

10 percent or better. Ozone calibration data with the 3-meter photometer agreed within 1 and 2 percent with gas phase titration and UV photometric O3 measurements respectively made

at the EPA laboratories in Research Triangle Park, North Carolina.

2. Experimental

The oxidation of iodide to iodine by ozone, in a properly prepared solution of potassium iodide, is the basis for the reference method specified by the Environmental Protection

Agency [1]^ for the calibration of atmospheric monitors. Recent comparative measurements

[2] of the specific iodometric methods have raised serious doubts as to the accuracy and

reproducibility of the iodometric calibration procedures. The report of the California Air

Resources Board [2] recommended that oxidant analyzers in California should be calibrated

by a UV photometric method rather than by the iodometric method and in May 1975 this recom- mendation was accepted for the state monitoring network. At the present time the U. S. Environmental Protection Agency is considering two candidate methods, gas phase titration

and ultraviolet photometry as replacements for the 1 percent neutral -buffered potassium

iodide procedure which is the current Federal Reference Method for calibration of pollutant

monitors [1].

In order to provide a facility at NBS for the measurement of ozone concentrations,

independently of gas phase titration based on a nitric oxide standard, it was decided to

set up an ultraviolet photometer [3] that would have the desired sensitivity for ozone measurements at ambient concentrations. The desired performance for the photometer was to

^Figures in brackets indicate the literature references at the end of this paper.

9
be able to measure ozone concentrations over the range 0.05 to about 1.0 ppm with an accuracy of at least 0.005 ppm over the entire range.

The photometric measurement method is based on the application and the validity of the

Beer-Lambert Law:

T - T ^vn / -273 cPkL x ,^^

where

:

c is given in ppm (parts per million by volume)

k = 308.5 cm-^ atm"i (base e) is the ozone absorption coefficient [4] at 253.7 nm, 273

K, and 1 atmosphere

L is the path length, cm

P is the total pressure, atm.

T is the temperature of the cell, K I/Iq is the transmittance (Tr) of the sample.

The design of the photometer is based principally on the accuracy requirement, 10 percent at 0.05 ppm. The quantities k, L, P, T appearing in the equation are all known or can

be measured to within 1 or 2 percent. Thus the accuracy of the concentration measurement

is mainly determined by the accuracy of the transmittance measurement. The error in the

transmittance measurement may be expressed as

Ac _ ATr ^1

c Tr '^ iinTr (2)

It was estimated that the transmittance measurement could be made with a precision ATr/Tr

of about .0005 by using photon counting. For a concentration of 0.05 ppm these conditions

imply a transmittance of 0.995 which can be achieved in an absorbing path of approximately

3 meters.

The design that was selected for the photometer is shown in figure 1. It was decided

that a double-beam arrangement would provide greater precision in the measurement through

elimination of the effect of variability of the UV source. The cells of the photometer are made of ^h in diameter Pyrex pipe; teflon gaskets are used to make vacuum-tight seals for

the fused silica windows. The light from a low pressure mercury discharge lamp is passed

through a narrow-band interference filter in order to isolate the 253.7 nm emission line.

The light is collimated by a fused silica lens and passed through a partially-transmitting

neutral density filter which serves as a beam splitter. The two beams then pass through

the two absorption cells. Adjustable aperture stops limit the diameter of the beams to ensure that there are no reflections from inner walls of the cells. The light beams emerge

from the cells and are recombined on the face of a photomul tipl ier tube by another partially

reflecting filter.

10
irO

H

O

UJH

LU Q

I <

Figure 1. Ultraviolet photometer for ozone calibration.

n
The differential UV absorption method of photometry adopted for O3 concentration mea- surements requires the precise and accurate measurement of two light intensities--one for

each cell. It was decided to use photon counting techniques for these intensity measurements

using a UV sensitive tube with excellent single photo-electron resolution. If such a tube

is cooled to about -20°C, the dark count rate is a few counts per second. Utilizing highspeed electronics and very precise timing methods it is possible to obtain accurate, and

statistically well-characterized, pulse counts corresponding to incident light intensity on the photomultiplier. This method may be preferable to analog techniques which are more subject to instability, drift, and uncertain amounts of non-linearity.

The Hg vapor lamp is energized either by a lOKHz square-wave power oscillator or by

a 60Hz high voltage transformer. Light passing through each sample cell is alternately

allowed to fall on the photomultiplier by means of a light chopper. A chopper blade with

a single hole is driven by a hysteresis synchronous motor at a preselected rate--chosen

to be unrelated to any harmonic or subharmonic of the line frequency (approximately 23 Hz).

Light emitting diode-phototransi stor pairs are used to sense the position of the chopper.

The signal from the phototransistor triggers a discriminator to start the timing and

counting cycle for each sample tube.

A logic system, triggered by the discriminators controls the pulse counters associated

with each sample tube. In order to ensure precise counting times as the photomultiplier

is exposed to each tube, an electronic gate is used to ensure that the photomultiplier is

fully (and not merely partly) exposed to the light beam passing through the sample.

The photomultiplier tube which must be selected for gain, low dark count rate and, most

importantly, negligible afterpul sing, detects the photons as they arrive. This type of

tube, with outstandingly good single photon resolution, is essential for this measurement.

The pulse output from the photomultiplier is amplified 100 times by direct-coupled

amplifiers and the pulses are detected by a high-speed pulse amplitude discriminator.

Pulse counting is performed by conventional 100 MHz pulse counters and a rough guide of

overall pulse rate is provided by a rate meter.

Counting time is determined by a preset counter which counts the revolutions of the

chopper blade past the LED phototransistor pairs. At the end of a counting interval, the

results are printed out and the sequence repeats.

House air, dried and filtered, flows through one cell ("reference cell"), then into

an ozone generator [5] from which ozonized air flows through the second cell ("sample

cell"). The measurement is made by comparing the ratio of the signals transmitted by the

two cells in the presence and in the absence of ozone. This provides the transmi ttance

(Tr = I/Io)> and the ozone concentration is determined by application of the Beer-Lambert

Law, as discussed above. Since the mercury lamp is viewed simultaneously through both

cells, fluctuations in lamp intensity do not affect the measurement. Any impurities

present in the air stream will be observed in both cells and will not interfere with the O3

determination.

The performance of the photometer has been determined over the ozone concentration

range 0.020 to 1.500 ppm. At each of the measured concentrations the standard deviation

was less than 0.005 ppm. In order to compare the photometer with the other methods of

calibration, a Dasibi commercial photometer was calibrated against the NBS laboratory

photometer. The Dasibi instrument then served as a transfer standard for interconnecting

the measurements made by the different methodologies in different laboratories.

Multiple analyses were made at several concentrations, and a linear regression

analysis of the averaged data can be written as:

[03],|w - (1.020 ± .004) [OsJnA'; " (0-00^ ± -002)

12
For additional comparative data the NBS Dasibi instrument was transported to the EPA

Research Triangle Park facility. Simultaneous O3 comparisons were made by Dr. J. A. Hodgeson of the Office of Air and Water Measurement, NBS, at the EPA Environmental

Monitoring and Support Laboratory, where concurrent evaluations of the gas phase titration

method (GPT) and a modified Dasibi photometer [5] were being performed. From these measurements the following relationships were obtained:

^^sW.EPA = (^-^^ - '^°3]uv,NBS ^ *

t03]uv,EPA = (0-98 ± 0.01) [03]uv,NBS

Thus the agreement between UV photometric and gas phase titration measurements is excellent.

Comparisons between UV photometry and iodometry, using either neutral phosphate buffered KI or boric acid buffered KI, show a much larger discrepancy. This discrepancy is currently

being examined in detail.

References

[1] Reference Method for the Measurement of Photochemical Oxidants Corrected for Interferences due to Nitrogen Oxides and Sulfur Dioxide, Federal Register 2§_, 8195-8197

(30 April 1971).

[2] (a) Comparison of Oxidant Calibration Procedures, Report of the Ad Hoc Oxidant Measurement Committee of the California Air Resources Board, Sacramento, CA

(20 February 1974).

(b) DeMore, W. B., Romanovsky, J. C, Feldstein, M., Hamming, W. J., and Mueller, P. K.

,

Interagency comparison of iodometric methods for ozone determination, in Calibration

in Air Monitoring, ASTM Special Tech. Publ. 598, 131-143 (Philadelphia 1976).

[3] Clements, J. B. Summary Report: Workshop on Ozone Measurement by Potassium Iodide

Method, EPA-650/4-75-007, 36, U. S. Environmental Protection Agency, Washington, DC

20460, February 1975.

[4] The value of k used in this work (308.5 cm"^tm"M is based on an evaluation by

R. Hampson and D. Garvin of measurements reported in the published literature:

(a) Inn, E. C. Y. and Tanaka, Y., J. Opt. Soa. Am. 43, 870 (1953).

(b) Hearn, A. G., Proa. Phys. Soa. 78, 932 (1961).

(c) DeMore, W. B. and Paper, 0., J. Phys. Chem. 68, 412 (1964).

(d) Griggs, M., J. Chem. Phys. 4£, 857 (1968).

(e) Simons, J. W. , Paur. R. J., Webster, H. A., and Bair, E. J., J. Chem. Phys. 59_,

1203 (1973).

(f) Becker, K. H., Schurath, U., and Seitz, H., Int. J. Chem. Kinet. 6, 725 (1974).

[5] Hodgeson, J. A., Stevens, R. K. , and Martin, B. E., ISA Trans.. U_, 161 (1972).

[6] Paur, R. J., Baumgardner, R. E., McClenny, W. A., Stevens, R. K. , Status of Methods

for the Calibration of O3 Monitors, extended abstract .presented before the Division of

Environmental Chemistry, ACS Meeting, April 1976, New York.

13
1
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

ACCURACY OF OZONE CALIBRATION METHODS

Richard J. Paur

U.S. Environmental Protection Agency

Research Triangle Park, North Carolina 27711, USA

1. Introduction

The calibration of monitors for measuring ambient ozone concentrations presents

special problems because the instability of ozone makes it impossible (at least for the

present time) to prepare a certified ozone standard. Therefore, ozone must be generated in

a dynamic calibration system and assayed each time a monitor is to be calibrated.

The U. S. Environmental Protection Agency is considering candidate methods as replacements for the 1% neutral -buffered potassium iodide procedure (40 CFR Part 50, Appendix D)

that is the current Federal Reference Method for assaying ozone in a dynamic calibration

system. Two candidate methods, gas phase titration (GPT) and ultraviolet photometry (UV

photometry), have been used for determining ozone concentrations for some time and are generally accepted as valid methods. A third method, 1% boric acid buffered potassium

iodide (BKi) '"11^, is new and is in the preliminary stages of evaluation.

2. Discussion

The precision of these candidate methods is estimated by repeated determinations of

the O3 output from a stable ozone generator while simultaneously verifying the stability of

the generator by other methods. Owing to the lack of an ozone standard at the concentration

range of interest, the accuracy of the procedures used for the assay cannot be individually

verified.

The approach taken to insure that the assay methods provide reliable estimates of the ozone concentration is based on a comparison of results of two or more methods with the

following characteristics:

1) The methods should be accurate at concentrations where the O3 can be determined

manometrical ly.

2) The methods should be precise, i.e., the 95 percent confidence interval should ideally

be no larger than ±5 percent of the ozone concentration.

3) The methods must be based on different measurement principles.

4) Extension of the methods to low concentrations should be well-based in theory.

5) The methods should have a sensitivity of at least 2 ppb.

6) The sources of probable error in the methods should be easily identifiable.

Figures in brackets indicate literature references at the end of this paper.

15
The accuracy of the UV photometric procedure is dependent on the accuracy with which

the absorptivity of ozone, the transmi ttance of the ozone sample, and the optical pathlength

through the ozone sample can be measured. The optical pathlength in a typical absorption

cell can be measured to within 0.5 percent of the length without difficulty. Depending on one's choice of equipment, the transmi ttance of the sample can be measured to within 1 part

in 10^ to 1 part in 10^. Critics of the UV photometric method have questioned the accuracy

of the ozone absorptivity at 254 nm, however, a review of the literature (Table 1) indicates

that the value of 134 atm-^cm"^ used in this work is probably accurate to within 1.5 percent

Table 1

Ozone Absorptivity

Ref

.

Workers a, atm"^cm-i, base 10 Method

[2] Inn and Tanaka (1953) 133 Manometry

[3] Griggs (1968) 132 Manometry

[4] Becker Schwrath and Seitz 135 Manometry

(1974)

[5] Hearn (1961) 134 Decomposition Stoichiometry

[6] DeMore and Raper (1964) 135 Decomposition Stoichiometry

[7] Clyne and Coxon (1968) 136 (250 nm) GPT

For most of the experimental work reported in this paper, the UV photometer used was a modified [8] Dasibi (1003-AH) instrument.

The precision of the Dasibi photometer is generally significantly better than the

stability of the ozone generator/flow system. In experiments employing flow control units

(Tylan FC-260) to control the air flow through the ozone generator, the precision of the

photometer is approximately 1 ppb (one standard deviation of 20 consecutive measurements)

over the range 150-700 ppb. In experiments utilizing pressure regulators and needle valves

for flow control, the precision decreases to 1 percent of reading over the range 100-1000

ppb.

The Dasibi photometer appears to be a reliable instrument; however, one malfunction

(leakage of the solenoid valve which directs either the ozone containing sample or refer- ence air to the absorption cell) would cause erroneous readings. Most other malfunctions

of this instrument result in an obvious failure of the system.

Gas phase titration [9] is based on the reaction of nitric oxide with ozone described

by the equation:

nNO + mOg ^ mN02 + m02 + (n - m)NO (1)

The GPT system is set up to minimize competing reactions such as oxidation of NO by O2 and

reaction of NO2 with O3. Under these conditions the decrease in NO is assumed to be equal

to the amount of ozone originally present in the reaction mixture.

The GPT apparatus used to obtain the data presented in this paper consisted of teflon

tubing, stainless steel needle valves for flow control, bubble meters for flow measurement,

any of several commercial NO analyzers, an ozone generator, and a single piece of glassware

containing the reaction chamber, capillaries for splitting the air stream and the dilution

chamber. The design reduces the probability of leaks while providing a relatively compact

system.

The accuracy of the procedure is dependent on the accuracy with which the NO concentration is known; this in turn relies on the accuracy with which the NO cylinder concentration

and the NO and air flow rates are known. The NO cylinder used in the experiments reported

was either an NBS SRM (Ser. # RSG-30-8002) or a cylinder whose concentration was determined

16
by comparison with the SRM cylinder. Certification of the SRM placed the 95 percent confidence limits on the SRM NO concentration at ±1.1 percent of the 46.3 ppm nominal concentration. The flow measurements of the NO and air streams were estimated to be accurate to

±1.5 percent. Response of the NO analyzers was found to be linear to within the accuracy

of the test procedure.

The short term (few hours) reproducibility of the GPT apparatus was better than 10 ppb over the range 150 to 100 ppb; however, due to the length of time required to make the GPT

measurements, it is likely that at least part of the differences in the GPT data is due to

drift in the O3 generator output.

Combination of the errors in the GPT and UV photometry techniques as implemented for

these studies indicate that the two systems would have to yield answers that differ by more

than 2.5 percent before the discrepancy would be significant. Since these two methods are based on entirely different measurement principles, they do not tend to be affected in the same way (i.e._, give erroneous high or low readings) because of such problems as low

quality zero air or faulty flow measurements. Therefore, a calibration system that employs

both GPT and UV photometric assay systems should provide mean ozone concentrations accurate

to within ±2 percent if the UV photometric and GPT values agree to within 2.5 percent.

For the equipment used in this work, the assay systems agreed (figure 1) within the

2.5 percent range over concentrations from 150 ppb to 700 ppb (higher concentrations were

not considered to be of interest).

In a preliminary evaluation, the third method considered--the boric acid potassium

iodide method--was compared to the Dasibi photometer used above. The BKI is similar to the

1% neutral -buffered potassium iodide except that it uses O.IM boric acid instead of the

phosphate buffer system. For fifty data points (20 at 500 ppb, 6 at 250 ppb and 15 at

120 ppb), the average ratio of BKI results to photometric results was 1.015 with a standard

deviation for the ratio of 3 percent. If further tests of the BKI confirm these early

results, the BKI will be able to provide a third check on the accuracy of the calibration

system.

17
0 100 200 300 400 500 600 700 800

03. PPB (UV PHOTOMETER)

Figure 1. Comparison of GPT and UV ozone determinations.

18
References

[1] Flamm, D. L., Personnal communication on iodometric ozone calibration study carried

out at Texas A&M University under EPA sponsorship.

[2] Inn, E. C. Y., and Tanaka, Y., J. Opt. Soo. Amer. 43, 870 (1953).

[3] Griggs, M. J., Chem. Phys. 49_, 857 (1968).

[4] Becker, K. H., Schurath, U., and Seitg, H., Internal. J. Chem. Kinetics, VI, 725

(1974).

[5] Hearn, A. G., Proa. Phys. Soo. 78, 932 (1951).

[6] DeMore, W. B. and Raper, 0., J. Phys. Chem. 68, 412 (1964).

[7] Clyne, M. A. A. and Coxon, J. A., Proa. Roy. Soo., A3Q3 , 207 (1968).

[8] Paur, R. J., Baumgardner, R. E., McClenny, W. E., and Stevens, R. K. , ASTM Symposium

on Calibration Problems and Techniques, August 5-7, 1975, University of Colorado,

Boulder, Colorado.

[9] Rehme, K. A., Martin, B. E., and Hodgeson, J. A., Tentative Method for the Calibration

of Nitric Oxide, Nitrogen Dioxide, and Ozone Analyzers by Gas Phase Titration, EPA

Report EPA-R2-7 2-246, (March 1974).

19

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

INTERRELATIONSHIPS BETWEEN PRIMARY CALIBRATION STANDARDS FOR NITRIC OXIDE,

NITROGEN DIOXIDE, AND OZONE AS APPLIED TO TEST GAS ATMOSPHERES

GENERATED BY GAS PHASE TITRATION

Donald G. Muldoon and Anthony M. Majahad

Environmental Research and Technology Inc.

Concord, Massachusetts 01742, USA

1. Introduction

Environmental Research and Technology, Inc. (ERT) currently operates and maintains

over 200 ambient air quality monitoring stations. These monitoring sites are predominately

located in the northeastern quadrant of the United States. At many of these AIRMAP^ (an

acronym for the ERT, Air Monitoring, Analysis, and Prediction system designed to provide

information concerning air quality in a region and the effect of various meteorological

conditions on air quality) sites, chemi 1 uminescence NO/NOx continuous analyzers are in use.

In the development of an overall quality assurance and maintenance program in support

of this effort it became evident that a Gas Phase Titration System (GPTS) was needed for

both calibration and functional testing (converter efficiency checks, etc.) of this equipment.

A number of commercially available systems were evaluated but none could meet the

special requirements of a system that would be used in the routine operations of a highvolume (10-20 units under test at one time) calibration laboratory. The required system

should be capable of generating stable concentrations of NO and NO2 with a maximum degree

of reproduceabi 1 i ty at a sufficient output volume.

Such a Gas Phase Titration System was constructed incorporating the following features:

1. Clean air system capable of delivering suitable quantities of clean dilution air with

a background of NO, NOo , and O3 less than 2 parts per billion.

2. Precision electronic mass flow controllers for both dilution air (0.2-20.0 SLM) and

cylinder NO/N2 mixtures (0.2-100 SCCM).

3. A modified high output ozone generator with temperature (35 ± 0.5°C) and voltage (110

Vac ± 1 percent) control. A micrometer adjustable drive mechanism to adjust the

sleeve position of a stable low-pressure mercury lamp assembly (at constant dilution

air flow rate) to vary the O3 concentration.

4. Suitably sized reaction chamber (150 cc) and mixing bulb. (150 cc) assembly housed in

a temperature controlled cabinet (35 ± 0.5°C) to carry out the gas phase reaction.

5. An all glass-Teflon manifold and delivery system with suitable sampling ports for a NO/NO^ analyzer, O3 analyzer and iodimetry (Neutral Buffered Potassium Iodide)

bubbling apparatus.

After the preliminary functional testing of the apparatus was completed, a series of

intercal ibration tests, between the applicable National Bureau of Standards reference

materials (NO2 permeation devices (SRM-1629), NO cylinders (SRM-1683), AS2O3 (SRM-83c), and

Na2C20i+ (SRM-40h)), were conducted to determine the most effective calibration technique to

be used with the GPT system.

21
In the course of the evaluation of the Gas Phase Titration System two other intercalibrations were performed:

A. NBS gravimetrical ly calibrated NOo permeation devices vs the Griess-Sal tzman NO2

bubbling procedure (ASTM D1607-69).

B. NBS prototype reference ozone generator vs chemil uminescent O3 monitor with calibration

based on three different transfer standard (NO dilution, NO2 permeation devices and

lodimetry)

.

2. Experimental

A complete modular description of the Gas Phase Titration System used for these

experiments is contained in Appendix A.

For each experimental set of GPT data, an initial NO concentration of approximately

0.90 ppm was generated by appropriate dilution of a high concentration NO/N2 cylinder with

dilution air. The flow rates of both the dilution air and NO/N2 mixture were controlled

precisely by electronic flow controllers calibrated by reference techniques.^

At all times a chemi luminescence NO/NOy analyzer (Thermo Electron 14B) and O3 chemiluminescence analyzer (McMillan 1100) were used to monitor the output of the GPT system.

The O3 monitor was independently calibrated by bubbling the output of the system's ozone generator using the rpfcrence (NBKI) technique^ and transferring this calibration to

the monitor.

The NO2 channel of the NO/NOx monitor was independently calibrated using NO2 test gas

atmospheres generated by a permeation tube assembly incorporating an NBS NO2 permeation

device.

The NO channel of the NO/NOx monitor was also independently calibrated by dynamic

dilution of NO/No test cylinders. The calibration of these test cylinders were periodically

verified by a transfer standard technique- using an NBS certified^ NO/N2 gas mixture.

For a given experimental set of GPT data, the NO/N2 cylinder flow rate and the dilution

air flow rate were kept constant. The O3 concentration was increased incrementally from

0.000 ppm until an excess O3 concentration was detected by the system's O3 monitor. The O3

generation was accomplished by appropriate adjustment of the sleeve position of the O3

generator.

The NO, NO2, NOx (NO + NO2) and O3 instrument output voltage for each test point was recorded. The O3 value at each test point with no NO/N- flow was also determined.

The concentration at each test point of NO, NO2, NOx + NO2) and O3 could then be

calculated from the output voltage and appropriate calibration constant.

Two other intercal ibration experiments were also performed during the evaluation of

the Gas Phase Titration System.

A. Wet chemical determination of the NO2 output of permeation tube assembly by GriessSaltzmann procedure (ASTM D1607-69). The NO2 concentration determined by bubbling the

^See table 1 for reference calibration techniques.

2Conc Test Cvl = Cone NBS Cert Cvl INSTRUMENT NO RESPONSE TEST CYL

Lone lest Lyl Lone NBS Cert Lyl fNTTTOEFfnTO'ETl^E^MsTYT"

22
Table 1

ERT gas phase titration system calibration and verification techniques

O

u

air

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23
output of a NO2 permeation tube assembly incorporating an NBS permeation device using

the Griess-Sal tzmann procedure was compared to the NO2 concentration calculated from

the NBS permeation rate and dilution flow rate for a number of test atmospheres.

These experiments were conducted to verify the calibration of the NO2 permeation

devi ces

.

B. Evaluation of a prototype NBS reference O3 generator. A prototype NBS reference O3

generator, 2 low pressure mercury vapor lamp type, was received in our laboratory for

evaluation while our experiments were in progress.

The O3 output of this device was controlled by manual adjustment of the UV lamp sleeve

position (keeping the dilution rate constant).

The Gas Phase Titration System's O3 monitor was used to monitor the output of the

prototype O3 generator at 9 test points. The NBS designated O3 concentrations were then

compared to the O3 concentration as measured by the instrument based on three different

transfer standards:

a. NO dilution

b. NO2 permeation

c. lodimetry

3. Results and Conclusions

This calibration technique is based on the rapid gas phase reaction between nitric

oxide (NO) and ozone (O3).

NO + O3 -> NO2 + O2 (1)

Under proper experimental conditions, the following relationships are applicable due

to the stoichiometry of the reaction.

NO2 =03= ANO (2)

NO2 = NO2 generated by gas phase reaction

O3 = O3 consumed by gas phase reaction

aNO = NO consumed by gas phase reaction, [i.e., initial NO concentration - final NO

concentration.

)

Also if a classical GPT plot of NO output (Y-axis) vs O3 concentration (X-axis) is made,

the concentration of the NO/N2 cylinder may be calculated from the following relationship:

Cone of NO/N2 Tank - D x bo^ (3)

D

= Dilution Factor = Flow Rate (Air) .Flow Rate (NO/N2)

Flow Rate (NO/N2)

bQ^ = X intercept = equivalent O3 concentration, [i.e., equivalent NO concentration)

^NBS Ozone Generator #19 supplied by Region I, EPA.

24
A typical Gas Phase Titration plot is presented in figure 1. A comparison of the

NO/N2 cylinder concentration determined from this set of experimental data points as compared to the NO/N2 cylinder concentration determined from NO transfer standard techniques

is presented in table 2. These results indicate that the two calibration techniques are equivalent within experimental error.

Table 2

Determination of NO/N2 cylinder concentration by gas phase titration

and by comparison to NBS standard cylinder

A Classical Gas Phase Titration^

(A. M. Majahad/02.24. 76)

O3 Sleeve"" Percent PPM

Setting NO O3

000.0 86.4 OoOOO

lOOoO 75.9 0.125

200.0 58.7 0.299

250.0 49.8 0.388

300.0 39.6 0.490

325.0 34.1 0.535

350.0 29.4 0.580

375o0 24.5 0„615

42S„0 15.8 0„710

475.0 7.4 O08OO

500o0° 3.8 0.835

525.0^ 1.3 0.893

550«0° 0.5 0.925

^Flowrates: NO/N2 =36.1 SCCM

AIR = 8.950 SLM

'^Not included in Linear Regression

due to bend in curve (Figure ] )

NO/N2 Cylinder Concentration

Comparison

Technique Standard Cone (PPM NO)

Gas Phase Titration AS2O3 (SRM-1683) 217

Transfer Standard NO (SRM-83c} 214

Calculations

Linear Regression Analysis of GPT:

y = rnx + b where; y = FPMO3

°3 X = %N0

m = slope (PPM0 3/%N0)

b = equivalence point (PPMO3)

03

PPM O3 = -0„0099 (%N0) + 0.872

NO/N2 Cylinder Concentration Determination:

Cmh = D X b v^;here : C = PPM NO ^NO 03

D = Flow^.^ ^ F1°'^N0/N2

P1°^N0/N2

b = 0.872 PPMO3

Cj^Q = ^^^^56 T'^ ^ 0.9:72 = 217 PPM NO

25
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If all three outputs (NO, NO2 and O3) associated with Gas Phase Titration are calibrated using independent standards, then the interrelationships among these standards can

be determined.

26
Test data in table 3a indicates that, within experimental error, the three aformenti oned

calibration techniques are equivalent and any one of them could be used as the primary

calibration technique for a gas phase system. (The converter efficiency of the NO/NOx

analyzer would have to be 100% in order to use a NO2 permeation device as the primary

standard.

)

Table 3a*

Interrelationship of NBS primary calibration standards

for a typical gas phase titration (D. G. Muldoon/04-28-75)

ANO = NO2 = O3

PPM ANO PPM NO2 PPM O3 Average

SRM-1683 SPJ^I-1629 SRM-83C ANO + NO2 + O3

Setpoint PPM NO (No Dilution) (Permeation) (NBKI) 3

0^ 0.924 0.000 0.000 0.000 0.000

1 0„895 0.029 0.041 0.036 0.035

2 0.843 0.081 0.097 0.089 0.089

3 0.746 0.178 0.197 0.196 0.190

4 0.695 0.229 0.247 0.247 0.241

5 0.641 0.283 0.307 0.304 0.298

6 0.589 0.335 0.349 0.347 0.344

7 0.534 0.390 0.404 0.396 0.397

8 0.491 0.433 0.440 0.441 0.438

9 0.441 0.483 0.483 0.492 0.486

10 0.394 0.530 0.533 0.544 0,5 36

Average 0.270 0.282 0.281 0.278

^Flow Rates: NO/N2 =17.5 SCCM

Air = 5.121 SLM

^Corrected for background NO and NO2

Table 3b*

Linear regression coefficients for GPT curves

PPM X = M(PPM NO) + b

X Slope

(m)

Equivalence

Point (b)

STD Error of

Estimate (S^^)

Correlation

Coefficient (r)

ANO -1.000 0.924 9.0 X

10"'' -0.9999

NO2 -0.989 0.929 7.4 X 10"^ -0.9991

O3 -1.009 0.941 5.8 X

10"-^ -0, 9995

*see figure 2 for graphical representation of Table 3a and 3b.

27
PPM STD

- ANO

o = 03

28
4. Other Results and Conclusions

A. Test data presented in table 4 demonstrated that a chemi 1 uminescent O3 monitor can be

calibrated using Gas Phase Titration Techniques as well as the reference NBKI

methodol ogy

.

Table 4

National Bureau of Standards Ozone Generator Evaluation

Date: November 20, 1975 Location: ERT, Concord, Mass.

Instrument: McMillan 1100 (#6396) Calibration: O3 Output from GPT (NBKI

Verification)

Sleeve

Position

NBS

Designated

PPM O3

Observed

PPM O3

(a)

Observed

PPM O3

(b)

Observed

PPM O3

(c)

Average

ERT

PPM O3

90 ^ ^0.495 0„462 0„443 0.473 0.459

0 AoO f\ Aid 0.410 0 . 408 0 „ 391 0.418 0 „ 406

70 0o357 0.343 0„329 0,351 0o341

60 0.300 0.288 0.276 0.295 0.286

50 0„244 0.238 0.228 0.244 0.237

40 0„192 0.187 O0I79 0.191 O0I86

30 0.141 0.138 0.132 0.141 0.137

20 0.092 0.091 0„087 0.093 0o090

10 0.042 0o041 O0O39 0.042 0.041

Off 0.000 0.000 0.000 OoOOO 0.000

(a) NBKI Transfer Standard (AS2O3)

(b) Permeation System Transfer Standard (NO2 Permeation Device)

(c) Gas Phase Titration Transfer Standard (NO/N2 Cylinder)

(d) Assuming linearity, this designated concentration does not conform.

B. Test data presented in table 5 demonstrates that NO2 determinations based on the

Griess-Saltzman procedure (ASTM-D1607-69) overestimate the actual NO2 concentration.

The experimental evidence indicates that although the Griess-Sal tzman procedure is

very reproduceabl e , the Saltzman empirical factor (0.72 mole NaN02 produces the same azo-dye color as 1 mole NO2) should be neglected when working at ambient concentrations, i.e. J less than 1.0 ppm NO2.

29
Table 5

Evaluation of NBS NO2 permeation devices (SRM-1629)

PERI1EATI0N

nFVTPF

NUMBER

NBS DESIGNATED

(PPM NO2)

ASTM D- 1607-69

nRSFRVFD

(PPM NO2)

a STOICHIOMETRIC

(PPM NO2)

0^Q-J 1.1 7 n 1 87 n 748 nw •

11 7Q/ I7

L* » X 0 0 y) m Loo

H- 0 -L J. n 1 Q6 0 770 W , 1' 4

H 0 ~ J. J. 0w • ^?7/ 0 U • i y D

48-11 0.125 0. 172 0.124

45-7 O0I22 0.168 0.121

45-7 0.122 0.177 0.127

45-7 0. 122 0.173 0.124

1

i

^Griess-Sal tzman empirical factor neglected.

It is the opinion of the authors that Gas Phase Titration techniques should be used

for the calibration of chemi luminescence NO/NOx analyzers and that the primary calibration

of the gas phase system be based on dilution of NO/N2 cylinders traceable to NBS standards

This technique is the simplest and most practical approach.

Also, there is no reason why chemi 1 uminescent O3 monitors could not be calibrated

using the same techniques. This would eliminate the necessity of using the very difficult

iodimetry techniques.

5. Future Work

Work is currently underway at ERT to incorporate a current-controlled ozone generatio

apparatus into the gas phase titration system. This modification will allow pre-programme

multipoint Gas Phase Titration calibrations to be performed routinely.

Also, as stable, low concentration (<10 ppm) SO2/N2 and NO2/N2 mixtures are now commercially available, feasibility studies are also being conducted by the authors to

determine if the Gas Phase Titration system may be used as a dynamic dilution system to

generate pre-programmed, stable concentrations of SO2 and NO2. As with the Gas Phase

Titration system, it is anticipated that the calibration of these commercial cylinders wil

be traceable to NBS reference materials.

Appendix A

GPT Air Supply

The Clean Air Supply used for the ERT Gas Phase Titration System consists of two mail

sections. Figures 3 and 4 show the components of the system.

30
Q>

Q>

Qy

(2>-

(H

Qy

) M

0-

Qy

3

o

Z

O

o

UJz

<

Q.

-tx-

'—txJUJ

cc<

Q.

Q.

o

31
SZ

o

o

$o

o

LU I

z

o

o

o

o

I. Clean/Dry Air Delivery System (Figure 3)

A. Compressor

1. Ken og-American , Inc.

Model #452TV

B. Water/Oil Vapor Drop-out

1. Wilkerson #51024

2. Schrader #3532-1200

C. Filter/Drop-out Filters

1. Rego #8822 K-Y

32
D. Oil Vapor Trap

1. Wilkerson #5102-4

E. Regulator

1. Rego #1682

a. 0-200 PSIG

F. Meatless Dryer

1. Pure-Gas #P-HF-200-l 20E21

7

a. Special Combination Dessicant:

- 70% Molecular Sieve

- 30% Charcoal

b. Purge Orifice #200-404-24

G. Moisture Indicator

1 . Matheson #465

H. Regulator

1. Wilkerson #R1 0-03-000

I. Moisture Indicator

1. Matheson #465

J. Regulator

1. Bastian-Blessing #88021-Y

K. High Pressure Particulate Filter

1. Millipore #XX45 047 00

2. Filter Membrane

a. Millipore Hydrophobic, 0.45 pm, 47-mm dia, (Aquapel #HAHP 047 00)

L. Manifold

1 . 1/4" Copper Tubing

II. GPT Flow Control System (figure 4)

A. Clean/Dry air is delivered to the GPT flow control devices at a working

pressure 40-50 PSIG. This allows a maximum flow of 20 LPM. Figure 4 shows

the main components of the flow control assembly.

1. An ON/OFF Ball Valve is needed to isolate the GPT from the Clean/Dry

Air System.

2. A pressure regulator is required to reduce the air stream pressure to

the flow controllers.

3. An ultraviolet light assembly is used to remove NO from the Clean/Dry

Air (Ultraviolet products, #11 SC-1 with SCT-1 Transformer/Power Supply).

NO is converted to N02.

4. The NO2 is removed from the Clean Air by the scrubber. This consists

of a mixture of molecular sieve, activated charcoal, and silica gel.

5. A final particulate filter (see I. K. ) is used to remove any substances

remaining in the Clean/Dry air.

III. Mass Flow Controllers

A. The dilution air is monitored and controlled using a Tylan FC-202. The

range is 0-20 LPM.

B. NO/N2 flow is regulated using a Tylan FC-200. The range is 0.2-100 cc/min.

C. Both mass flow controllers are connected into a control box (Tylan RO-733).

The flows are set via potentiometers and are observed on a digital readout

display.

IV. Reaction Chamber

The GPT system consists of an environmentally controlled reaction chamber. This

apparatus provides the required temperature, mixing, and ozonating for a gas-phase

titration. Figure 5 shows the configuration of the reaction cabinet. The ozonator

utilizes a double-helix-thread adjustable sleeve which shields the U.V. lamp (Ultraviolet Products, Inc., Special SOG-2 ozone generator). The lamp housing assembly

contains an Alzac reflector and Suprasil flow tube. The flow tube was modified to

increase the diameter to 25 mm, which increases the output of O3. The lamp sleeve

position is set with a micrometer control dial (Amphenol #1314).

33
34
The air flow that passes through the ozonator assembly is obtained by splitting

the inlet dilution air in a ratio of approximately 1 to 10. A stainless steel "T" with 1/4 in o.d. tubing inlet and outlet and a 1/8 in. o.d. outlet for the ozone air

is used to split the air stream. The length of the 1/8 in. o.d. split required a series of trial and error experiments to obtain the necessary amount of clean air to

pass through the ozonater's flow tube.

The ozone is injected into an all glass mixing "T" and reacts with a stream of

NO/N2 gas. The resultant gas mixture is then passed into a 155 cc Kjeldahl mixing

bulb. The bulb and glass "T" are connected by Clinches of 1/2 in. I.D. corrugated

Teflon (Penntube Plastics CT-Flex).

The NO/NO2/N2 gas mixture then mixes with the remaining dilution air via another

all glass "T". The gases were then further mixed in a second Kjeldahl mixing bulb

with corrugated Teflon tubing connections. The gases are then allowed to exit via

the CT-flex tubing into an all-glass/Teflon manifold assembly.

The entire ozonator and mixing apparatus is housed in an insulated cabinet with

a temperature control environment. The use of a thermistor (Omega #0-90-UUA-32J4,

•2252 ohms 0 25°C) with a proportional set-point temperature controller and Triac

power control (Action Instruments Co., Inc., #'s 2020 and 3020) provides a temperature

range from 25-50°C ± 0.5°C. This temperature is monitored by a 3 in. dial display

thermometer (Brooklyn Thermometer Co., Inc. #5204). The heat is obtained from 3 100-

watt heating mats (Cole-Palmer Instrument Co. #3125) cemented to the chassis of the

GPT system cabinet. The use of two metal muffin fans (Panmotor #4505) insured constant

temperature circulation. Two indicator lamps are employed to show the firing of the

heating pads.

The dilution air and NO/N2 flow controllers were connected to the rear of the

GPT via stainless steel Swagelok fittings. The outlet was connected to an allglass/Teflon manifold assembly via 6 feet of 1/2 in. o.d. CT-flex corrugated Teflon

tubing.

V. Manifold

The manifold system consists of 6 specially fabricated 1 in. o.d. glass manifolds.

Each glass manifold contains four 1/2 in. o.d. ports and two 3 in. x 13 mm o.d. ends.

The ports provide the means to sample the NO/NO2/O3 gas stream. This is accomplished

by heat-shrinking 1/4 in. o.d. Teflon tubing into the ports.

The ends of the individual manifolds are connected via force fitting of CT-flex

Teflon. The entire manifold assembly stretches 30 feet and is able to accommodate 24

NOx and/or O3 instruments. The manifolds are vented into the facility's exhaust duct

system to prevent noxious gas build-up in the Air Quality Instrumentation Laboratory.

The authors wish to express their gratitude to Mr. Robert Michaud and

Dave Goldstein for their help in the construction of the experimental apparatus.

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. {Issued November 1977)

AN ANALYSIS OF THE MEASUREMENT ACCURACY AND VALIDITY

OF RESULTS FROM THE CHARCOAL TUBE SAMPLING TECHNIQUE

Gerald Moore

MDA Scientific, Inc.

Park Ridge, Illinois 60068, USA

1. Introduction

Atmosphere monitoring for contaminant gases and vapors using the charcoal tube sampling

technique is becoming more widespread, particularly because of the increased activity of

OSHA in recent years in generating exposure standards for a growing number of different

substances. The basics of the method are well described in the paper published in the

American Industrial Hygiene Association Journal [1]^ and currently is the recommended

technique for measurement of a wide variety of organic solvents in industrial hygiene

applications. Typically, the NIOSH recommended design of charcoal tube is employed together

with a small battery operated personal sampling pump, a variety of which are available from

different manufacturers (figure 1). The use of an adsorbent material such as charcoal

provides a convenient and compact system for personnel exposure monitoring and a variety of

other adsorbents are also coming into use for other applications where charcoal is not the

most suitable adsorbent. In the absence of more specific monitoring techniques, it can be

expected that this sampling method will remain in widespread use for many years despite the

known limitations and scope for inaccuracies, many of which have been documented by other

authors. The technique is relatively complex comprising of two distinct stages--sample

collection and subsequent analysis by gas chromatography in the laboratory. Careful consideration is needed to determine where errors can occur and how best to correct them.

2. Sources of Errors and Inaccuracies

A comprehensive study and analysis of a large number of samples was carried out by

NIOSH and published as a report [2]. This report clearly shows the extent to which errors

can occur and analyzes some of the reasons for these errors. Of particular significance

are the so-called "outlier" results which were eliminated from the final analysis in the

report but which serve to indicate that gross inaccuracies can occur even with supposedly

well-trained staff. The report also shows that the precision of results is markedly

inferior at low contaminant concentrations.

Analysis of the technique shows that there are five main areas where errors can occur,

all contributing to an overall lack of precision. These are identified as: (1) variations

in tube manufacture, e.g., different grades and batches of charcoal used and variations in

pressure drop which can affect sampling rate; (2) the stability of sampling flow rate which

can affect the accuracy of determination of total sample volume as well as biasing the

total exposure determination; (3) the means of determining the total sample volume drawn

through the charcoal tube--this is shown to be strongly dependent on the type of pump used;

(4) the desorbtion efficiency and variations in this parameter with different loadings of

contaminants on the charcoal; (5) the standardization of the gas chromatograph which is

used to perform the final measurements.

^Figures is brackets indicate literature references at the end of this paper.

37
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38
Each of these factors and its contribution to the total error sum is discussed.

Certain types of errors can occur without necessarily affecting the reliability of results

since they are systematic and will apply equally to the standardization process and the

sample measurement. Other sources of error are inherent and can only be minimized to ensure good overall measurement accuracy. The validity of results is directly related to

the precision which can be achieved and is critical where the results are used for standards

compliance purposes. The shortage of trained personnel in the industrial hygiene field

requires that where possible all monitoring techniques should be capable of yielding good

results even in unskilled hands.

3. Some Ways to Improve Validity and Precision

Four specific areas where improvements can be made are discussed: (1) The use of

replicate sampling which allows true "outlier" samples to be eliminated, assists in determining where gross errors have occurred in the procedure and allows averaging of results to

obtain greater precision (figure 2). (2) The use, with sampling pumps, of an improved

design with particular reference to accurate determination of total sample volume (figure

3). (3) The definition of controlled sampling parameters for each individual contaminant,

taking into account optimum tube loading, the effect of sampling mixtures and the influence

of environmental factors, such as humidity. A study has. been made of the basic data which

are currently available and this has been brought together on one chart to form a common reference for all users of the charcoal tube sampling technique. (4) Greater control of

the procedures for the gas chromatograph in analysis stage with particular emphasis on repeatability and care in standardization. The need for more user oriented GC equipment

and the potential advantages of thermal desorbtion are discussed.

4. Conclusions

The author concludes that significant improvements in overall precision are possible.

The technique as presently used is certainly capable of determining contaminant concentrations to within ±10 percent of actual in the hands of "skilled users," but gross inaccuracies can occur with less skilled users or on an uncontrolled random basis due to the

large potential for unrecognized errors. Improvements in pump design, (figure 4), the use of replicate sampling and controlled sampling parameters will contribute to more reliable

routine determinations by all users, but especially in industry where laboratory trained

staff are not always available. The author believes that an overall accuracy of ± 10 percent should be the goal for all users, while recognizing the fact that ±20 percent is

probably adequate for general purpose industrial hygiene measurement. Greater control

becomes far more significant when considering the use of other adsorbent materials which

can be expected to become more commonplace during the next few years. These materials

typically have much weaker adsorbtion characteristics and are more critical as regards to

sampling rate. There is a need for further study in this respect.

The author concludes that the charcoal tube sampling method is convenient and viable

for use on a routine basis provided that some additional attention is paid to adequate

control in the areas discussed. The technique may be gradually superceded by other methods

such as diffusion operated "badges" or specific personal monitors, but until that occurs

all users should at least be attempting to get the best possible precision and validity of

results from this proven technique.

39
Figure 2. Replicate sampling assembly

40
Figure 3. Functional diaqram accuhaler personal sampling pump.

41
Figure 4. Accuhaler personal sampling system,

References

[1] White, L. D. , et at., A Convenient Optimized Method for the Analysis of Selected

Solvent Vapors in the Industrial Atmosphere, AIHA Journal 31 225-232 (March-April

1970).

[2] Reckner, L. R., Sachdev, J., Collaborative Testing of Activated Charcoal Sample Tubes

for Seven Organic Solvents, NIOSH Technical Information, HEW Publication No. (NIOSH)

75-184, June 1975.

42
; NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

ACHIEVING ACCURACY IN ENVIRONMENTAL MEASUREMENTS USING ACTIVATION ANALYSIS

Donald A. Becker

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234, USA

1 . Introduction

The analytical technique of activation analysis has found widespread acceptance and

usage for environmental trace element measurements. In particular, the capability for

multielement determinations, high sensitivity, and non-destructive analyses have been

important in this regard. However, to consistently achieve accuracy in environmental

analyses requires careful attention to detail and use of well characterized facilities.

Activation analysis can best be described by separation into its essential parts:

sampling and sample handling, irradiation, chemical separation (if used), and counting.

Each of these component parts should be optimized to provide acceptable accuracy, always

considering the end use for the data obtained. The effect of each of these components on the overall analytical accuracy is considered in more detail below.

A. Sampling and sample handling

The first consideration in any analysis is whether the sample to be analyzed is truly

representative of the material of interest. Lack of a truly representative sample results

in imprecision or inaccuracy (or both) in the final determination, which is due not to the

analytical technique, but to the original unrepresentative sample. Aqueous or moist

matrices are particularly difficult to sample and store due to problems of adsorption,

absorption, desorption, and leaching, both with container walls and any solid matter

present.

Once a valid sample is obtained, it must usually be stored, processed, or sub-sampled.

Each process undertaken before irradiation increases the possibility of contamination.

The statement that activation analysis is generally free from "blanks" primarily refers to

reagent blanks. The only sample which can closely approximate a blank-free system is the one which can be irradiated as a single integral piece, then subsequently heavily etched

to eliminate surface contamination and contamination beneath the surface due to recoil

from nuclear reactions occurring from surface contaminants. (Treatment with several

different etchants is recommended to reduce the possibility of redeposition of the contamination back onto the fresh surface.) All processing of subsampling which occurs should

be made under clean conditions using noncontaminating implements and containers. Contamination is a particularly difficult problem for physical processing of solid samples {e.g.^

grinding, cutting, pulverizing, eta.), or for liquid samples.

There are many papers in the literature which indicate that some types of environmental

samples undergo changes in structure and chemical state even when dried at room temperature.

This should not have a great effect on the total trace element content in most cases, but

43
if speciation, organic extractable trace elements, etc., are of interest, any form of

drying may invalidate the sample. A recent extensive survey of the literature on sampling,

sample handling and long term storage goes into much greater detail on the techniques and

problems involved [1]^.

B. Irradiation

The choice of the irradiation source obviously affects the sensitivity, detectabi 1 ity,

and selection of trace elements of interest. In addition to this, the specific characteristics of the irradiation source and the degree to which it has been evaluated play a large part in determining the final result of the activation analysis. Several factors

which affect the accuracy and precision of reactor activation analysis are discussed

below.

Most irradiation facilities have a significant variation in the neutron flux within a single irradiation container. For example, the author has measured variations of more

than 40 percent along the length of a cyclindrical polyethylene "rabbit" ('^S cm), and over

20 percent across the diameter of such a container ('^2.5 cm). It is considerably worse

when these two effects are present in the same facility.

For high reproducibility and accuracy, each sample should be monitored during irradiation. A simple method for accomplishing this is to attach small bits of a pure metal

foil to the irradiation container, which are later removed and counted to provide a normalization factor. The elements copper (for short or medium length irradiations) and iron

(for long irradiations) have been found to work well.

Other problems during irradiation include variations in the neutron energy spectrum,

production of interfering nuclear reactions, and neutron self shielding. The methods and

problems in reactor characterization have been addressed more completely elsewhere [2].

C. Radiochemical separations

The judicious use of an appropriate radiochemical separation can often change a marginal trace element determination into a simple and effective one, often with greatly

improved accuracy and precision. While the use of radiochemical separations does require

the services of a chemist, and usually one with experience in such separations, the

advantages which accrue are well worth the increased time and effort needed. The use of

modern semiconductor detectors has also made group radiochemical separations an important

tool in activation analysis, especially for very low level trace analysis.

Some of the problems affecting accuracy and precision in radiochemical separations

include sample dissolution difficulties (incomplete dissolution and losses during dissolution); inadequate carrier exchange with the sample trace element(s); volatilization

losses (during prei rradiation processing, during the actual irradiation, when opened after

irradiation, and especially during sample dissolution before carrier exchange); adsorption

effects on containers (irradiation container, dissolution container, or separation con- tainer); quality of the separation procedure itself (single element, multiple element,

complicated procedures, etc.); and finally, chemical yield measurements (reproducibility,

with quantitative yields highly desirable).

Each of the above aspects can introduce a random or systematic bias into the procedure,

and thus should be carefully evaluated and tested before being accepted as a reliable and

reproducible procedure.

Figures in brackets indicate the literature references at the end of this paper.

44
However, even with all of the cautions mentioned above, the use of radiochemical

separations in the activation analysis program affords the capability for achieving the

theoretical sensitivity for almost all elements, rather than for only the few very favorable cases. This capability is not to be taken lightly.

D. Counting

In order to complete the analysis, the radiation emitted from the induced radioactivity in the sample must be accurately determined. Basically, most activation analysis

detection systems consist of a single photon detector [Ge(Li), Ge, or Nal(Tl)] and associated electronics, with a sample positioning device of some sort. With such a system, a variety of sample radioactivity levels and sizes can be counted rather easily. The

requirements for analytical accuracy and precision for each individual determination will

to a certain extent prescribe the care with which the sample is evaluated. In general,

however, the attainment of a resonable accuracy and precision requires the analyst to at

least be aware of potential errors in detection systems. What is often not realized is

that even relatively small differences between sample and standard, or from sample to

sample, in any one of many variables can result in a significant bias in the detected

count rates.

In a previous publication, the systematic biases associated with photon counting in

activation analysis [3] was described in detail. For purposes of discussion, these biases were separated into eight sub-groups as follows: sample configuration; sample positioning;

sample density; sample homogeniety and the effects due to activating particle flux

inhomogeniety ; photon intensity; radioisotopic purity; photon peak integration techniques;

and errors in nuclear constants. Since the first subgroup mentioned, sample configuration,

is both rather important and often ignored, it will be discussed briefly here also.

Differences in source configuration between samples or between sample and standard

can be a significant source of analytical error. Most analysts do not realize that, even

at 5 cm away from a 13 percent Ge(Li) detector, a 1 mm difference in average height will

induce a systematic bias of approximately 3 percent. Therefore, a sample and standard

which vary by 5 mm in height (2,5 mm in average height) will have a bias of approximately

7 percent. This is in addition to all the other errors connected to the analysis, both

random and systematic. These errors are much greater when sample positioning is closer to

the detector.

E. Reference materials j;'

One valid way to assess matrix-derived errors in any analytical system is through the

use of reference materials. These reference materials are usually carefully studied

materials which have documented homogeniety and elemental composition. There are varying

levels of integrity associated with these materials, depending on their origin, but they

all have one thing in common. They attempt to match, as exactly as possible the matrix

composition of some class of material usually encountered in real life. A reference

material which has been analyzed for one or more characteristics, and is issued by a recognized standards organization or a national laboratory, may be referred to as a certified reference material. The confidence connected to such a material is, of course,

directly related to the degree of confidence placed in the certifying organization.

Reference materials provide the opportunity for the activation analyst to check or calibrate, in their own laboratory, the accuracy and precision of their entire analytical

system. In the ideal case, this is accomplished by analyzing a reference material, having

the same or a similar matrix as the samples, to determine whether the known or "true"

value is obtained. Any deviation from this known value is a measure of the uncertainty of

the analytical system. When independent replicates of the reference material have been

analyzed, the range of values obtained indicates the precision of the analytical system,

while the deviation of the average analytical value from the "true" value indicates the

accuracy of the system. If the value obtained is significantly different from the "true"

value, the analytical system should be examined carefully to determine the source of the

45
error. In some cases, no "true" value is available for the reference material, and

therefore only a precision value can be obtained. Reference materials of environmental

matrices are available from several sources.

2. Conclusion

In conclusion, the effective use of standards and reference materials offer an import

ant opportunity to continually evaluate the last three components of activation analysis,

in order to control or eliminate errors. Evaluation of the first component, sampling and

sample handling, is much more difficult to detect and evaluate, since in most cases each

environmental sample is unique and cannot be reproduced. However, rather than assume complete acceptance or total confidence in their results, the activation analyst should

continually strive for the best methods and techniques possible, consistent with the

required costs.

References

[1] Maienthal , E. J. and Becker, D. A Survey of Current Literature on Sampling, Sampl

Handling and Long Term Storage for Environmental Materials, NBS Techniaal Note 929,

Government Printing Office, Washington, DC (1976).

[2] Becker, D. A. and LaFleur, P. D., Characterization of a Nuclear Reactor for Neutron

Activation Analysis, J. Radioanal. Chem. 19, 149 (1974).

[3] Becker, D. A., Accuracy and Precision in Activation Analysis--Counting, Proceedings

of Nuclear Methods in Environmental Research, University of Missouri, Columbia,

p. 69 (1974).

46
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

A COMPARISON OF FACTORS AFFECTING ACCURACY IN ATOMIC EMISSION

AND ATOMIC ABSORPTION SPECTROMETRY USING A GRAPHITE FURNACE

FOR TRACE METAL ANALYSIS IN WATER

Michael S. Epstein and Theodore C. Rains

Institute for Materials Research

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Thomas C. 0' Haver

Department of Chemistry

University of Maryland

College Park, MD 20742

1. Introduction

The determination of the trace metal content of water samples, whether it be for

establishing criteria for drinking water or for studying the chemistry of the oceans,

requires an extremely sensitive analytical technique. The concentration of many trace

metals in water is in the yg/1 range and below, introducing the problem of contamination

and/or loss during storage and analysis. The ideal analytical technique should thus combine

sensitivity, precision and accuracy with a minimum of sample manipulation.

Such an analytical technique is atomic spectroscopy. However, the sensitivity required

for the direct analysis of many metals in water by atomic spectroscopy can only be obtained

at the present state-of-the-art by the use of a furnace atomizer. Typically, these analyses

are performed using atomic absorption spectrometry CAAS). For several elements, an alternative to AAS with a furnace atomizer (GFAAS) is graphite furnace atomic emission spectrometry (GFAES). In this technique, the furnace is employed as the spectral excitation source

as well as the atomization cell, and atomic emission from excited species in the furnace is

measured [1]^.

The two techniques provide an interesting contrast in analytical methods. The methodologies utilized in the application of both GFAAS and GFAES to sample analysis are con- siderably different. Interferences in the two techniques may differ in their severity, mode

of interference (additive or multiplicative), and method of correction. In order to obtain

satisfactory levels of accuracy, proper correction methods must be used. This paper compares

the effect of various interferences and correction methods on accuracy in the analysis of

trace metals in water using GFAES and GFAAS.

2. Instrumentation

Analysis by GFAES, when performed with conventional furnace systems designed for atomic

absorption, is limited in many cases by intense blackbody radiation generated by the heated

graphite tube. When this radiation reaches the photodetector , analytical errors are introduced because of increased photon shot-noise, non-reproducibility of the blackbody emission

intensity from run to run, and the scatter of blackbody emission into the monochromator by

sample matrix components. Since the radiation from the furnace is largely continuum, the

technique of wavelength modulation can be used to reduce or eliminate errors due to scatter

Figures in brackets indicate the literature references at the end of this paper.

47
and changes in the intensity of the blackbody emission [2]. The instrumentation used for

wavelength modulation in GFAES has been detailed previously [2,3], and consists of an HGA2100 graphite furnace, a 0.5-m monochromator , and associated electronics. The monochromator

was modified for wavelength modulation by placing a vibrating quartz refractor plate mounted

on a torque motor between the entrance slit and the collimating mirror. The modulation

apparatus is driven by the sinusoidal signal from a function generator and audio-amplifier,

and the signal from the photodetector is processed by a phase-sensitive synchronous amplifier referenced to the second harmonic of the modulation frequency.

3. Discussion

Since the accuracy of an analytical technique will be a function of the number and kind

of interferences involved in its implementation, an examination of interferences encountered

in the application of GFAES and GFAAS to sample analysis is required. These interferences

can be loosely classified as either physical [4] (relating to effects caused by a physical

property of the analyte species or which change one of the physical properties involved in

the analytical measurement), chemical (relating to effects involving the chemical form of

the analyte), or spectral (relating to the isolation of the analyte radiation from radiation

due to other sources).

A. Physical interferences

GFAES analytical curves, particularly using resonance transitions, are nonlinear, in

contrast to GFAAS growth curves which are generally linear over several orders of magnitude.

The nonlinearity appears to be largely due to the design of commercial furnace atomizers and

the thermal gradient in the furnace tube, which result in self-reversal and self-absorption

of analyte emission in GFAES. Analysis by GFAES therefore requires close bracketing of

samples by standards in most cases.

The major physical interference in GFAAS is the scatter and/or absorption of source radiation by sample matrix constituents. The error due to this interference is additive and

increases as analyte concentrations decrease. Typically, correction for this interference

is performed by a continuum radiation source time-shared with the elemental line source. Scatter and absorption of analyte emission in GFAES are not as serious a problem as in

GFAAS, but correction for the interference is complicated by the nonlinearity of GFAES

growth curves. If a standard-addition correction procedure is used, chemical interferences

(which reduce the analyte atomic population and thus reduce the emission intensity) must be

distinguished from scatter or absorption (which do not effect the atomic population but

reduce the emission intensity). The effect of the two interferences on a nonlinear intensity versus concentration relationship will be different.

B. Chemical interferences

Chemical interferences in both GFAES and GFAAS result in multiplicative errors and are correctable by standard-addition procedures. Interferences due to compound formation appear

to be less severe in GFAES than in GFAAS, probably because emission intensity maxima occur

later in the atomization cycle than absorption maxima. The gas temperature in the furnace

will be higher when emission intensity maxima occur, thus decreasing compound formation

effects. On the other hand, the increased temperature appears to increase ionization

interferences in GFAES.

C. Spectral interferences

Spectral interferences in GFAES are more severe than in GFAAS. Source intensity

modulation eliminates any additive errors in GFAAS due to the blackbody emission from the

heated graphite tube and absorption line overlaps are less likely to occur than emission

line overlaps. A wavelength modulation system is required to eliminate the additive error

due to the furnace blackbody emission in GFAES. However, structure in the wavelength

distribution of the background radiation from the furnace may still interfere with GFAES

48
analysis, although wavelength modulation intensity-nulling procedures may be employed to

reduce the effect in some cases [3]. Scatter by matrix components of blackbody radiation

into the monochromator may also be considered a spectral interference in GFAES , but it is

correctable using the wavelength-modulation background-correction system.

Contamination in the graphite furnace appears to be a greater problem in GFAES, due to

the higher temperatures employed. Spectral interferences, due to the overlap of line or band emission from the sample and source with the analyte emission distribution, can occur

as in flame atomic emission. Such spectral interferences should either be resolved by

employing a smaller spectral bandpass or nulled by using the wavelength modulation system.

4. Results

A comparison of detection limits (LOD) for GFAES [2] and GFAAS [5], as well as approximate concentrations of several metals in seawater [6] and proposed Standard Reference

Material 1643 (Trace Elements in Water) [7], are shown in table 1, The concentration of

most elements in seawater is below the concentration range required for direct analysis

procedures, so preconcentration measures must be employed, with the inherent contamination

and recovery problems. An exception is barium, which can be determined directly by GFAES,

while direct determination by GFAAS is extremely difficult or impossible using a conventional atomic absorption spectrometer. The concentrations of many elements in proposed SRM

1643 are within the analytical capacity of both GFAES and GFAAS for direct analysis without

preconcentration.

Table 1. Water analysis by GFAAS and GFAES.

Approximate Elemental

Element Limits of Detection Concentrations

(pg/1)

a g/i)

GFAES GFAAS SRM 1643 Seawater

Al 0.04 0.1 80 0-1900

Ba 0.08 2 40 6 - 90

Be 2 0.06 20

Cr 0.4 0.2 16 0 04 - 2.5

Cu 0.4 0.1 15 1 - 25

Ni 4 2 50 0 1 - 2.6

Based on a 50 pi sample size.

SRM 1643 is designed to simulate elemental concentrations in natural water samples.

The concentrations of the major matrix constituents (Na, K, Ca, Mg) are in the pg/ml range

{i.e., approximate concentrations are Ca '\- 27 ug/ml , Mg a. 7 ug/ml , and Na 10 ug/ml).

Although some chemical interferences are observed, the major factor affecting accuracy is

the sensitivity of each technique for the element being analyzed. Figure 1 compares recorder

tracings of GFAES and GFAAS signals from barium and beryllium in SRM 1643. The comparison

is made at equivalent noise bandwidths of both systems under optimum experimental conditions

for both techniques. The LOD of barium by GFAES is approximately 25 times lower than the

LOD by GFAAS, while the LOD for beryllium by GFAAS is approximately 30 times lower than the

LOD by GFAES. This is clearly reflected in the comparison of signal-to-noise ratios observed

in figure 1

.

49
I

[A]

GFAES GFAAS

I

GFAAS

Figure 1. A comparison of GFAES and GFAAS signals for barium and beryllium in

proposed SRM 1643. (A) 1 ng Ba , 553.6 nm. (B) 1 ng Be, 234.8 nm.

As the matrix becomes more complex, such as in seawater, the effect of physical,

chemical and spectral interferences on analytical accuracy becomes more pronounced. However, no generalization can really be made about the analytical accuracy of GFAES versus

GFAAS, although evaluations can be made on individual elements in a particular sample. The

accuracy of each technique will depend on the element being analyzed, the sample matrix, and

the skill of the analyst in recognizing and correcting for interferences when they occur.

References

[1] Ottaway, J. M. and Shaw, F., Analyst, 100, 438 (1975).

[2] Epstein, M. S. , Rains, T. C. and O'Haver, T. C, Appl. Speatrosa . 30, 324 (1976).

[3] Epstein, M. S. and O'Haver, T. C, Speatrochim. Aota , 30B, 135 (1975).

[4] Koirtyohann, S. R., Chapter in Flame Emission and Atomic Absorption Spectrometry,

Vol. I., Dean, J. A. and Rains, T. C, Eds., pp. 295-315 (Marcel Dekker, New York,

1969).

50
[5] Perkin-Elmer Instrument Literature, HGA-2100, Feb. 1974.

[6] Parker, C. R., Water Analysis by Atomic Absorption Spectroscopy, Varian Techtron, Palo

Alto, California, 1972.

[7] Moody, J. R., Private Communication, National Bureau of Standards.

51

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

IMPROVED ACCURACY IN BACKGROUND CORRECTED ATOMIC ABSORPTION SPECTROMETRY

Andrew T. Zander and Thomas C. 0' Haver

Chemistry Department

University of Maryland

College Park, Maryland 20742, USA

1 . Introduction

The use of background correction techniques in atomic absorption spectrometry allows

the analysis of a broad range of samples with complex matrices. These techniques eliminate

the interference arising from particulate light scattering and broadband absorption by the

matrix constituents. In conjunction with carbon furnace atomizers and standard addition

methods, very low levels of analyte can be determined in complex samples with a minimum of

sample preparation and a high degree of accuracy.

Recently, attention has been focussed on the difficulty of obtaining corrections for

spectral interferences when analyzing samples with unusual or complex matrices [1,2,3]^.

As more and greater demands are placed on atomic spectrometric means of analysis, in terms

of accuracy and precision at very low levels of analyte concentration, it is important to

understand the limitations of the instruments utilized in dealing with interferences of

spectral origin.

The types of spectral interferences which are most commonly encountered in atomic

absorption are:

scattering of radiation and broadband absorption

nonanalyte absorbing lines within the spectral bandwidth

direct absorption spectral overlap.

The interference from nonanalyte absorbing lines within the spectral bandwidth is of

importance principally when a continuum source of radiation is used as a secondary source

to monitor the background, or for continuum source atomic absorption methods which use a continuum source as a primary radiation source. The high elemental selectivity of hollow

cathode lamp line sources eliminates this interference for line source atomic absorption

methods, up to the point at which this interference becomes that of direct absorption

spectral overlap.

2. Spectral Interferences and Methods of Correction

A. Scattering of radiation and broadband absorption

Reflection and scattering of incident radiation by particles in the flame and absorption by molecular species cause absorption signals which generally exhibit broadband

spectral character. Such matrix background absorption results in erroneously high analyte

absorbance readings. Figure 1 shows point-by-point absorption spectra of solutions of

Figures in brackets indicate literature references at the end of this paper.

53
wOH

Cn H

13

w

ooH

u

o

(1)

m

CO -Pc C 0) O -P •H C P o

cx

u

uO -P

tn iH

(Uo

nsc0 (D g g

(0

(0 iH rH u ti tl . ^ —ro ^ .

iH rH rw\ r ^

(0 2:

'> ">\ (-1 &^ U

o\o iH O O O tH rH < m U

o

Ln

CNJ

m

EhOM

o

W> o O

inn (M

ooo

o

54
high salt content (above 0.1 percent w/v). The nonatomic background spectra obtained have

been shown to be primarily due to molecular absorption by gaseous diatomic halide species

[3]. Scattering of the incident radiation by particles also contributes to the absorption.

These spectra vary irregularly with wavelength; however, the resolution with which such

spectra have been obtained is not sufficient to observe the presence of narrow or fine

structure.

B. Instrumental background correction methods

The instrumental background correction methods which have been developed for atomic

absorption are designed to eliminate only interferences exhibiting broadband spectral

character. The two-line correction (AALTL) and the continuum source corrector (AALBC) are methods most commonly used for background correction. Two new methods, which are still in

the development stage, are Zeeman effect atomic absorption (ZAA) and continuum source,

wavelength modulated echelle atomic absorption (CEWMAA).

For line source atomic absorption (AAL), the background can be monitored if a definite

nonresonant or nonanalyte atomic line lies apart from, but close to the analyte absorption

line. This two-line correction (AALTL), first proposed by Willis [5], will satisfactorily

correct for the background if certain conditions are met. A nonresonant analyte line, or a line from an element not in the sample, must be emitted by the source. Neon or argon fillgas lines can be used. Alternatively, another source, of an element which is not found in

the sample, can be inserted for the background measurement. The background spectral

character must be known to be the same at the second line as it is at the primary line; and

for this reason the closer the second line is to the primary line the better will be the

correction. These conditions cannot be met for all elements and matrices. In some wavelength regions, the steep slope of molecular absorption bands make it difficult to find a nonabsorbing line close enough to the analyte line to ensure an accurate background correction. It is preferable that the atomization conditions for each measurement be as similar

as possible. Even if an appropriate nonabsorbing line is available from the primary source,

the atomization conditions may change by the time the nonresonant line is tuned-in. If a different source must be used, or if a furnance atomizer is being used, duplication of the

conditions at the time of the first measurement will be even more difficult.

For AAL, the background can also be monitored with a second source of continuum radiation placed in the optical path on a time-shared basis with the primary source [4].

Continuum source correction (AALBC) affords automatic and continuous background corrected

results once the system is installed and optimized. Since only one phototube is used, it

is necessary to ensure that the two beams are exactly superimposed. This is difficult in

practice and generally leaves some miscorrection which must be tolerated. The intensity of

the two beams must be balanced. Due to the low intensities of the hydrogen or deuterium

hollow cathode lamps used, this generally requires reducing the primary source intensity by

lowering the operating current below the optimum level, or by using an extremely wide slit

width. Very wide slits may result in nonlinearity of the analytical calibration curve due

to an increase of nonabsorbable radiation from matrix atomic lines which can absorb the

continuum channel radiation [6]. It is necessary, in any case, to use a wider than normal

slit width to reduce to a negligible level the amount of analyte continuum atomic absorption

of the continuum channel. When analyzing for a number of elements the AALBC corrector must

be rebalanced for each element which often requires a tedious flame on/flame off optimization. AALBC is limited to elements which have resonance lines below about 350nm due to the

rapid decrease in intensity at higher wavelengths of the H2 and D2 continuum lamps normally

used. Continuum sources with adequate intensity at higher wavelengths can be substituted

[6]; but these are not adaptable, in a simple fashion, to the conventional AA units generally employed. The correction obtained is valid only if the background absorption at the

analyte line is the same as the average absorption over the spectral bandwith [4]; this is

not always the case. A distinct disadvantage of AALBC is that the signal-to-noise ratio

(SNR) is degraded. It is suspected that the output instability of the continuum source

adds significantly to the total noise of the system [7]. AALBC has however been used to

correct for the background from high salt content matrices up to the point at which the

high salt concentration causes severe chemical and bulk interference.

55
Hadeishi and McLaughlin [8] were the first to report on the construction of a Zeeman

effect atomic absorption spectrometer (ZAA). They used the instrument to analyze low

levels of mercury in biological samples. ZAA utilizes the splitting of a resonant wavelength into its Zeeman components, ti and a±, when the radiation source is subjected to a magnetic field, to obtain background correction. If the magnetic field is large enough,

the o± components will be outside the absorption profile. Absorption by the analyte will occur only at the -n-component; but the background absorption, of broadband character, will occur at all components. Since the tt and a± components are perpendicularly polarized, it

is possible to monitor the components separately. The difference between the logarithms of

the signals obtained from the separate components will be a background corrected analyte

signal proportional to the analyte concentration.

Up to a short time ago, ZAA was restricted to electrodeless discharge lamps as sources Redesigned hollow cathode lamps, which will operate efficiently in a magnetic field, are to

be made available by the ZAA system manufacturers to remove this limitation. The detection

limits presently obtainable by ZAA should improve when these new hollow cathodes are used.

Because of the nature of the output signal, it is not possible to describe the ZAA analytical calibration curves in terms of more familiar absorbance units [9].

ZAA can compensate for background interference beyond 90 percent diminished incident

light intensity [9]. Since the Zeeman components are only about .01 nm apart from the

analyte absorption line the background correction obtained for broadband interferences is

very good.

Wavelength modulation techniques have been found to be useful for the correction of

background interferences in atomic absorption [10]. The combination of a high intensity

continuum source and a very high resolution echelle monochromator modified for wavelength

modulated detection (CEWMAA) is well-suited to correcting for background interferences in

AA.

By modulating the wavelength of the monochromator, i.e., by rapidly scanning back and

forth over a small spectral interval, a signal proportional to the change in spectral

intensity over the interval is generated. The ac signal amplitude is proportional to the

wavelength derivative within the interval [11]. CEWMAA takes advantage of the difference

in response of different spectral distributions to wavelength modulation. If the spectral

character of the background is linear, a modulated system set to detect at twice the

modulation frequency (2F-mode), will not respond to the background signal level. For a linear, sloped background, for example on the side of a broad band, a background signal

will be generated at the frequency of modulation which will also be rejected when detecting

in the 2F-mode.

CEWMAA has several distinct advantages. Only one source is required for all elements,

eliminating the need for a library of hollow cathode lamps. Optimization of the system is

only a matter of turning on the modulator and setting a predetermined modulation interval.

The system is always operating for background correction since it is inherent in the

method. No special balancing of variables is required. An oscilloscope attachment allows

direct visual observation of the absorption which occurs. Continuum source AA techniques

have in the past suffered from poor sensitivities and detection limits. The use of a very

high resolution echelle monochromator affords spectral bandwidths close to the width of

absorption profiles, at geometric slit widths comparable in size to those normally used on medium resolution AA monochromators and good sensitivities are obtainable. Echelle mono- chromators are now available at reasonable cost; they have increased luminosity and they

are simple to use. Wavelength modulation techniques have been shown to improve signal-tonoise ratios in atomic absorption by eliminating the low frequency sources of noise which

are dominant at low concentrations, source flicker and flame transmission flicker [10, 12].

This is in marked contrast to AALBC which degrades the SNR for background corrected results

CEWMAA has the disadvantage of requiring the atomization of an analyte solution to tune-in

the analytical line. This is no more time-consuming, though, than changing a hollow

cathode lamp on a line source AA system.

56
C. Nonanalyte absorbing lines in the spectral bandwidth

Interference due to absorption of the background correction, secondary source continuum

radiation by nonanalyte absorbing lines within the spectral bandwidth has been reported

recently [6, 10]. All AA methods which utilize continuum sources, either for background

correction or as the primary source, are susceptible to this type of interference. Lists

of spectral lines lying close to commonly used analytical lines have been compiled for

those transitions which have been observed [13]. More complete wavelength tables [14] show

that most analytically useful resonance lines fall quite close to numerous lines from many

commonly encountered elements. The presence of these lines must be taken into account when

attempting trace analysis of samples with complex matrices by AALBC ro CEWMAA. The advent

of more efficient furnace atomizers, with their high elemental sensitivities and high

atomization efficiencies, make the presence of nonanalyte absorbing lines more likely. The

relative effect of these interferences will be greater due to lower levels of analyte which

are being used.

In non-background-corrected line source AA, the presence of a nonanalyte absorbing

line in the spectral bandwidth will not result in an interference because the nonanalyte

line will not absorb the analyte radiation, unless it overlaps the line. The AALTL and ZAA

methods will also be unaffected for this reason. (This lack of interelement interferences

is one of the principal advantages of AA). AALBC will not give accurate results when a nonanalyte line present in the spectral bandwidth is a strong absorber, or when the non- analyte is present in such high concentration that its absorption becomes significant.

Mi scorrection results from significant nonanalyte atomic absorption of the continuum

channel radiation. The continuum channel signal, which is subtracted from the analyte

channel signal, will be too large and will result in an erroneously low corrected absorbance. CEWMAA is less susceptible to this type of interference because the very high

resolution of the echelle monochromator eliminates all nonanalyte lines from the spectral

bandwidth, except those which directly overlap the analyte line.

D. Direct absorption spectral overlap

A direct absorption spectral overlap occurs if an element other than the analyte is

capable of absorbing the resonant radiation of the analyte.' By definition, this interference cannot be removed by using a smaller spectral bandwidth. The extent of the interference is dependent upon the degree of overlap of the lines, the absorptivity coefficient

of the interfering line, and the concentration of the interfering element. Tables of

observed and predicted spectral overlap interferences have been compiled [13]. It is

necessary to be aware of the predicted overlaps since the possibility of their occurrence

exists in complex matrices. The overlaps may never be observed due to appropriate choice

of atomization conditions; but the actual extent of their occurrence is not well enough

known to disregard them.

AALTL, AALBC, and ZAA are incapable of compensating for this type of interference.

The only recourse is to use an alternate analytical line, if one exists. CEWMAA is uniquely

suited to handling the problem of direct spectral overlap interference. The wavelength

modulation feature of CEWMAA produces harmonic response functions of the analyte and interfering lines which, when the system is set to detect in the 2F-mode, closely resemble

second derivatives. Epstein and O'Haver [15] have described a technique by which the zero- crossings of the response functions can be shifted to null-out the interfering line. The

second harmonic response function (SHRF) produced by sinusoidal ly modulating an absorption

line exhibits two zero-crossings up to the point at which the absorption profile changes

with high concentration, the positions of these inflection points do not change on a high

resolution system. On a medium resolution the positions do not change because the spectral

distribution modulated is the instrument function. If variable slits are available and the

instrument function is known (at least qualitatively) it is possible to adjust the modulation interval, the slit width, or both such that the zero-crossing of the interfering line

falls directly beneath the absorption maximum of the analyte. If variable slits are not

available and an interfering line zero-crossing lies within the analyte line zero-crossings,

the analyte absorption can be measured at the interfering line zero-crossing by shifting

the wavelength of the monochromator or by adjusting the modulation interval. Some loss of

57
sensitivity and even some loss of analytical calibration curve linearity may be experienced,

but the resultant signal will be free of any interfering component. If the loss of sensitivity or increased nonlinearity cannot be tolerated, the modulation interval can be changed

to shift the zero-crossings, but this may be at the expense of analyte signal intensity.

3. Results

Table 1 shows that CEWMAA is at least as precise and accurate as other well accepted

means of analysis. Table 2 shows that CEWMAA is more accurate than AALBC for an element

which has an analytical line near to the wavelength limit of conventional continuum source correctors (AALBC). Table 3 shows that ZAA is an accurate and precise method for analyzing

samples of complex nature. The only sample preparation necessary was dryinq, before

atomization in a carbon furnace. Table 4 shows that CEWMAA can be used to alleviate even severe direct absorption spectral overlap without recourse to separation techniques.

Sample

Tomato

1 eaves

Pi ne needles

Table 1

PPM Cu in botanicals

Spectro-

^ 1^ photometry AALTL

10.8±.l

2.9±.l

CEWMAA

11.5+.2 10.9+.1

3.2±.4 3.0±.3

Chelate exchange reaction of Cu with Zn

di benzyl dithiocarbamate in IN HC10i+.

Private communication: R. Burke and

B. Diamondstone, NBS, Gaithersburg, Md.

^Private communication: M.S. Epstein

NBS, Gaithersburg, Md.

Table 3

PPM Pb in SRM 1577 (Bovine liver)

Weight (mg) PPM Pb

1 .42 .370

2.12 .307

1 .65 .340

1.73 .356

1 .85 .341

Average .343±.023

NBS Certified .34 ±.08

Table 2

PPM Mg in Ni -based alloy

Sample AALBC CEWMAA

ASTM-3E(3ppm) 5.6 2.6

ASTM-4E(10ppm) 30.0 8.1

III

Table 4

PPM Zn in high purity Cu

Sample AALBC'

447.0

16.5

^No electrolysis

b,

AALBC

409.0±10

10.9±.5

Electrolyzed to remove Cu

CEWMAA'^

411 .0±34

10.3±.8

58
4. Conclusions

The instrumental methods of background corrections for AA which are regularly used are based upon assumptions about the background interference which are not always valid,

particularly for samples with complex matrices. Two new methods, ZAA and CEWMAA, more reliably and accurately correct for background interferences. ZAA monitors the background

very close to the resonant absorption line. CEWMAA inherently rejects broadband absorption

signals, and can be used to eliminate spectral overlaps by manipulating the modulated

waveform output.

References

[1] Marks, J. Y., Spellman, R. J., Wysocki , B., 2nd I^ational Meeting, Federation of Analytical Chemistry and Spectroscopy Societies, Paper #202, Indianapolis, 1975.

[2] Thompsen, K. C, Godden, R. G., Analyst, 101, 96 (1976).

[3] Culver, B. R. , Surles, T. , Anal. Chem. , 47^, 920 (1975).

[4] Koirtyohann, S. R. , Pickett, E. E., Anal. Chem., 37, 601 (1965).

[5] Willis, J. B., in Methods of Biochemical Analysis, Ch. Ill, editor J. D. Winefordner,

Vol. 9 of Advances in Analytical Chemistry and Instrumentation, Wi 1 ey- Intersci ence

,

New York (1971 ).

[6] Epstein, M. S., Rains, T. C, Anal. Chem., 48, 528 (1976).

[7] Ingle, J. D., American Chemical Society Centennial Meeting, Analytical Chemistry

Division, Paper #25, New York, April 1976.

[8] Hadeishi, T., McLaughlin, R. D. , Science, 174 , 404 (1971).

[9] Hadeishi, T., McLaughlin, R. D., Anal. Chem. 48, 1009 (1976).

[10] Zander, A. T., O'Haver, T. C, Keliher, P. N., Anal. Chem. 48, 1166 (1976).

[11] O'Haver, T. C, Green, G. L., Am. Lab., ]_ (3), 1 5 (1975).

[12] Elser, R. C. , Winefordner, J. D., Anal. Chem. 44, 698 (1972).

[13] Parsons, M. L., Smith, B. W. , Bentley, G. E., Handbook of Flame Spectroscopy, Plenum

Press, New York (1975).

[14] Meggers, W. F. , Corliss, C. H., Scribner, B. F., Tables of Spectral Line Intensities,

Part I and Part II, U. S. Dept. of Commerce, National Bureau of Standards Monograph

#145 (1975).

[15] Epstein, M. S., O'Haver, T. C. , Spectrochim. Acta, 30B, 135 (1975).

[16] Koizumi, H., Tasuda, K. , Anal. Chem., 48, 1178 (1976).

59

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

STANDARD ADDITION USES AND LIMITATIONS IN SPECTROPHOTOMETRIC ANALYSIS

Robert Klein, Jr. and Clifford Hach

Hach Chemical Company

Ames, Iowa 50010

1. Introduction

The method of Standard Additions (known additions or spiking) has long been used as a powerful tool for indicating accuracy in real world samples. However, the analytical literature defining uses and limitations of this technique in spectrophotometry is minimal and some erroneous conclusions have been made concerning what this technique can achieve and its

application. The purpose of this paper is to mention some of standard additions' uses,

describe the problems encountered and the limitations of which the analyst should be aware.

2. Discussion

Standard additions is performed by adding a small amount of standard solution to a previously analyzed sample and then repeating the analysis using the same reagent, instrument and technique. The amount of increase in the test result should be proportional to the

amount of standard added. This procedure should not be confused with an internal standard

method as has been recently reported in the literature [1]^. An internal standard is used in

IR, emission spectroscopy and gas chromatography to give a standard response with which to

compare the unknown. The standard is a known constant quantity of some stable substance

with an easily measured response and is not the same element or compound being tested.

Standard addition requires for maximum effectiveness that the substance added be the same as the analyte and if possible the same species. Another pitfall to be avoided is that a single addition in lieu of a calibration can be deceiving and is of questionable validity

although it does serve as a simple accuracy check. Also higher precision will be achieved

if multiple additions are performed on a sample rather than replicates of a single addition.

There are many examples of normal use of this technique as a standardization method.

Standard additions has long been used in electrochemistry because it gives more realistic

values since the unknown and standard would be measured under the same conditions. Modern

voltammetric techniques such as anodic stripping voltammetry (ASV) is very matrix-sensitive

and relies almost exclusively on standard additions for quantitation [2,3]. Orion [4] has

also described the use of known additions in potentiometric titrations with ion selective

electrodes via Gran's plot. Atomic absorption spectrophotometry

uses this method when the sample matrix is so complex that viscosity, surface tension, flame

effect, and components cannot be accurately matched with the standards [5,6]. By application

of a modified standard addition procedure to colorimetric analysis, Kloster and Hach [7] were able to simultaneously determine the sample concentration and reagent blank.

The advantage of standard additions over normal standardization is that the performance

of a specific procedure can be checked under operating conditions to detect flaws and biases

in a method. The use of a "decision tree" such as the one shown in figure 1 can in a systematic way identify the source of error. A "decision tree" serves as both a physical check on the procedure, the instrument, the reagents and the standards as well as the analyst's

technique. Also it serves as a possible chemical check on the absence or presence of interferences. Explanation of the various steps of the decision tree follows [8].

Figures in brackets indicate the literature references at the end of this paper.

61
010* SINGLE STANDARO

AOOiriOH Give TH( CORRECT

RECOVERY?

INTERFERENCES PRESENT?

OOES MULTIPLE STANOARO

AOOITIONS ON

01 WATER GIVE CORRECT RECOVERT'

IS THE fflOCfOUHE IN USE COBHECI'

OOES MUlllPlE STANDHnO

ADDITIONS ON

SAHE'lE DIVE UNIFORM INCBEBENIS;

USE CORRECT PROCEDURE

REPEAT e

ARE THE REAGENTS FORKING

PROPERir'

ANALYSIS MAY

BE CORRECT

IS INSTRiJMENT APPARATUS WORKING

PROPEBL»^

REPAIR REPLACI INSTRUMENT APPARATUS

REPEAT B

STAHDAROS

DEFECTIVE REPEAT B WITH NEW STOS

Figure 1. Decision Tree

62
Suppose a single standard addition on a sample shows incorrect recovery. A possible

cause for this may be that interferences are present. If they are known or assumed to be

absent proceed to Branch B. If interferences are known to be present proceed to Branch C. If multiple standard additions on distilled water give correct increments between additions

also proceed to Branch C, if not, proceed to Branch D. At Branch D, possible errors in the

procedure are investigated. If the procedure is found to be in error Branch B is repeated

using the correct procedure. If the procedure is found to be correct proceed to Branch E where the performance of the reagents are checked. If it is found that the reagents are defective, Branch B is repeated with new reagents. If the reagents are proven to be in good

condition, proceed with Branch H. At this point the operation of the instrument and/or

apparatus used in the performance of the test is checked. If a defect is found in the

instrument and/or apparatus, repeat Branch B upon correction of defect. If none is found,

proceed to Branch I. After demonstrating that the procedure, reagents, instrument and/or

apparatus are correct and operating properly, the only possible cause for standard additions

not functioning properly in deionized water is the standards used in performing the standard

additions or the standards used to prepare the calibration curve. A new set of standards is

obtained and Branch B is repeated.

If interfering ions are present, it may be concluded that the analysis is incorrect,

however, a close approximation of the correct result may be arrived at through the use of

multiple standard additions (Branch C). If the steps between each addition are roughly

uniform the analysis may be correct (Branch G). If the increments are not uniform proceed

to Branch F.

Examples of the effect of interferences upon the standard additions and the sample are

shown in figure 2. Plot A illustrates an interference which becomes progressively worse as the concentration of the standard increases. This type of interference may be chemically

caused or caused by an error or malfunction of the procedure, reagents or instrument.

Plot B illustrates a common chemical interference which becomes less or even zero as the concentration of the standard increases. The graph of the example shows that the first

standard addition was consumed by the interference and that the remaining additions gave the

correct incremental increase of 0.2 mg/1.

The two examples illustrate chemical interferences which most certainly mean that the

result of its first analysis of the water sample was incorrect. When this type of interference is encountered the analyst should attempt to analyze the sample with an alternate

method which, if possible, uses a different type of chemistry.

Examples of uniform increments between standard additions are shown in Plot C and D.

Plot C illustrates an interference which has a uniform effect upon the standard and

the substances in the sample. The four data points form a straight line which may be

extrapolated back through the horizontal axis. The point of intersection of the line with

the horizontal axis can be used to determine the concentration of the substance in question.

The apparent interferences may also be caused by a defect in the instrument or its standards.

Before assuming that the interference is chemical in nature. Branch B should be checked.

Plot D illustrates a problem for the analyst. The increments found are uniform and its

recovery of the standard was complete. The result of the first analysis was 0 mg/1 and the

graph plots back through 0 mg/1. If interferences are known to be present, the interference

may be present in an amount equal to the substance in question, thereby preventing the

analyst from finding the substance.

Returning to figure 1, if the standard addition gave the correct result initially, the

analyst must then determine if interfering substances are present. If interfering substances

are not present the result of the analysis prior to the standard addition is correct (Branch

K).

Thus, when a decision tree is used in conjunction with a well -characterized method, the

analyst can be relatively certain that his instrument, procedure and technique are correct

and has greatly improved his confidence in the accuracy of the data.

63
.4

mg/l ACTUALLY PRESENT mg/l STANDARD ADDED

Figure 2. Multiple Standard Additions Graph

Hach Chemical Company provides a convenient system for performing standard additions by

offering premixed, precal ibrated standard solutions (VoluetteTM Ampule Standardsj-^for

almost every important water and wastewater test parameter. Using a Hach Micromatic'

Pipet, small increments of concentrated standard may be accurately added to the sample over a range of 0.1 to 0.5 ml rather than adding a larger amount of a dilute standard solution,

making it necessary to correct for the change in volume.

^VoluetteTM are ampules of premixed, precal ibrated standard reagent chemical solutions

intended primarily for analytical laboratory use in water and wastewater testing.

64
3. Conclusion

A summary of general problem categories which may be encountered on unknown real -world

samples using standard additions and specific examples of each are described in table 1. In almost all the uses listed the method of standard additions may help the analyst determine

if problems are present that would affect the reliability of his original analysis thus

allowing him to arrive at a more accurate answer. Standard additions will not help if part

of the analyte is tied up by the interference or if the interference reacts in a similar manner as the analyte.

Thus the method of standard additions is a useful tool in that the performance of the

reagents, the instruments and apparatus, and the procedure itself can be checked for possible

error. The method has its greatest utility in demonstrating that the result of an analysis

is incorrect.

Table 1

Standard Additions: Summary of problems

Probi em : General Category

1 . Interference

a) Decreases ~ constant

b) Increases ~ constant

2. Interference prevents

test working

3. Interference changes

molar absorbtivity

4. Interference depletes

reagent

5. Reagent and/or standard

efficacy

6. Matrix effects

a) Kinetics shift

b) pH, Buffer capacity

i nadequate

c) Temperature

7. Incorrectly prepared

standards

8. Mechanical aspects of

Procedure

a) Incorrect wavelength

b) Unmatched cells

(dirty, scratched,

eta. ) c) Forgotten reagent

d) Incorrect timing

Specific Example

Fe(CN)5^ in 1 , 1 0-phenanthrol ine method

for iron

Cd in the Zincon method for Zn

Co blocks end pt. in Calmagite method

for hardness

Substituted phenols in 4-Aminoantipyrine

Colorless Cu, Cd 1 , 1 0-phenanthrol ine

complexes in method for Fe

Loss of reducing power in 1,10-phenanthroline method for Fe

Analysis of PO^ and Si02 in salt water

Cr(III) in EDTA back titration method

Will Standard

Additions be

Effective?

No

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

65
References

[1] Kloster, M. B., Amer. Lab., July, 63 (1976).

[2] Barendrecht, E., in Eleotvoanalytieal Chemistry^ Ed. Bard, A. J., p. 53, Marcel Dekker,

New York, 1967.

[3] Copeland, T. R., Skogerboe, R. K., Anal. Chem. 46, 1257A (1974).

[4] Orion Newsletters, II (11,12), 50 (1970).

[5] Varian manual, Basic Atomic Absorption Spectrophotometry, 1974.

[6] Willard, H. H., Merritt, L. L., Dean, J. A., Instrumental Methods of Analysis, p. 379,

Van Nostrand, New York, 1974.

[7] Kloster, M. B., Hach, C. C, Anal. Chem. 42, 779 (1970).

[8] Hach Chemical Co., Water Analysis Handbook, p. 1-25, 1976.

66
Part II. DETERMINATION OF TRACE ORGANIC POLLUTANTS IN WATER

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

UNMET NEEDS IN THE ANALYSIS OF TRACE ORGANICS IN WATER

William T. Donaldson

Environmental Protection Agency

Environmental Research Laboratory

Athens, Georgia 30601 , USA

1. Introduction

Addressing the unmet needs in the analysis of trace organics in water requires considering the problems to be studied and the factors that define requirements for identification

and measurement. Trace organics are of interest because some are known to be detrimental

to aquatic organisms and some are suspected of being detrimental to human health when

injested. It is therefore necessary to know which of these organic compounds are in the

aquatic environment, how they get there, what their effects are and how they can be

controlled.

2. Number of Compounds in Water

There are over 2 million known organic chemicals. In our laboratory we have observed

that the number of compounds detected in a sample of water is related to the detection

level: as the detection level decreases an order of magnitude, the number of compounds

detected increases an order of magnitude. Based on the number of compounds detected by

current methods, one would expect to find every known compound at a concentration of 10"^^

g/l^or higher. In only 5500 literature entries reporting organic compounds identified in

water, 1296 different compounds were reported. On the basis of these observations one would expect to encounter a large number of different compounds in samples from the

aquatic environment.

At present toxicologists are unable to select the most important compounds for environmental dose-response assessments. Of 6000 that have been tested for carcinogenicity, 1000

showed some carcinogenic activity. Adding to the complexity of selecting specific compounds

of interest is the difficulty in extrapolating results from laboratory tests with lower

organisms exposed at high concentrations to human health effects of concentrations encountered in the environment. Knowledge of distribution and concentration of organics in the

environment would be valuable to the toxicologists in selecting compounds for healtheffects screening.

To assure that wastewaters are treated efficiently and adequately it is necessary to

know what compounds are in raw wastes and how they are removed or transformed during

treatment. Since raw wastes contain many compounds that are not easily predicted by

considering manufacturing products and processes, these complex mixtures must be analyzed

both qualitatively and quantitatively. The same is true of the treated wastewaters.

Not all organic compounds enter the aquatic environment through discharge of industrial

and municipal wastes. Some compounds, such as agricultural chemicals, are washed from

non-point land sources; some fall from the atmosphere; and some are transformed as a result of chemical or bacterial action on other compounds present in the water. So complex

are the factors that affect transformation processes in the natural environment that

chemical analysis of environmental waters is mandated, both to learn what chemicals are there and to study the processes by which they are formed.

"i In these Proceedings 1 denotes liter, usually abbreviated L. 69
An of the factors discussed above point to the need for a cost-effective capability

to identify and measure all organic compounds, above some prescribed detection level, in

environmental samples rather than measuring concentrations of only selected compounds.

Because detection level determines the number of compounds identified in a sample,

one must select the detection level carefully. It must be low enough to reveal all important compounds but not so low that it makes the analysis unduly difficult. In drinking

water, those compounds at the highest concentrations are usually present at 10^ pg/l^or

less. At 10"'^ pg/1 the analyst's ability to separate compounds is taxed. Therefore a detection limit of 10"^ or 10"^ yg/1 is usually selected for drinking water and most lakes

and streams. A higher level would probably be selected for wastewater effluents, whose

constituents are generally more concentrated. While this need presents a formidable

challenge, the challenge can be met. Much can be accomplished toward this end with current

technology, but there are significant problems to be addressed.

3. A Proposed Approach

Samples can be collected either by "grabbing" a liter of the water of interest or by

passing a larger quantity through carbon or macroreticul ar resin accumulators. In the

laboratory, some volatile compounds are purged from the sample with inert gas and sorbed

onto a resin. The compounds remaining in water or on accumulators are extracted sequentially with appropriate organic solvents to effect a preliminary separation. Concentration

of the extracts by evaporation follows. Marker compounds for retention time and quantitation references can be added prior to concentrations.

The concentrates are injected into gas chroma tographs , or high-pressure liquid chromatographs, coupled to low-resolution mass spectrometers, which record spectra of all

separated compounds. A central computer tentatively identifies sample components by

matching their spectra with those of known compounds in a computer library. When the

computer "identifies" a compound, it also selects an appropriate marker compound for

automatic computation of concentration and relative retention time.

Spectra of compounds that are not in the computer file are listed separately by the

computer and numbered to determine their frequency of occurrence, even though they are not

identified. These compounds must be identified by the analyst, who usually generates

additional spectral information. Frequency of occurrence of unidentified compounds is a useful factor in prioritizing them for identification.

4. Research Needs

An analysis of the steps in the proposed approach reveals many unmet needs for research,

beginning with the sampling process. Grab sampling is simple enough for stable and non- volatile compounds, but improvements are needed to make certain that volatile compounds do

not escape and others do not decompose or interact during storage. The use of accumulators

raises needs for further studies to determine appropriate accumulator materials, optimum

flow rates, and removal efficiencies for all compounds or classes of compounds of interest.

Development of a sampling device to accommodate accumulators and to meter flows is an indicated need.

Solvent extraction from the accumulator or from the grab sample is often performed

without adequate optimization of extraction conditions or adequate knowledge of recoveries.

Sequential extraction from accumulators should be investigated to effect preliminary

separations. Marker compounds for quantitation and retention-time references should be

added as early in the process, as is practical, to indicate recoveries through subsequent

steps. Appropriate marker compounds must be developed for each class of compounds that

behaves differently during extraction, concentration, separation or detection.

In these Proceedings 1 denotes liter, usually abbreviated L.

70
; Concentration techniques for organic extracts are generally well established, but

much needs to be done to determine the best means of concentrating polar compounds, that

remain in the aqueous phase during solvent extraction of grab samples.

Although improvements in gas chromatography are reported continually, gas chromatography is by far the best established separation technique. Unfortunately only 10 to 20

percent of the mass of organic material in most environmental waters is amenable to gas

chromatography. Recent advancements in high-pressure liquid chromatography show con- siderable promise for separating the polar volatile and the non-volatile compounds of

moderate molecular weight.

So little is known about the nature of high-molecular-weight materials in environmental

waters that it is difficult to suggest approaches for their analysis. Obviously the

tedious task of characterizing these materials should be pursued to provide further insight

into their nature and their significance as pollutants.

Rapid-scanning, low-resolution mass spectrometers have proved to be so effective in

providing identifying spectra, that they are almost universally selected as the first-line

approach to identifying separated compounds. Computer-assisted interpretation of spectra

has advanced far enough to make it practically an integral part of organic mass spectrometry.

Currently most low-cost computerized spectra-matching programs are based on empirical

matching and, therfore, require that the spectrum of the compound to be identified be

present in the computer library of spectra. More relevant files should be developed to

further reduce cost and time for spectra matching.

For compounds that are not amenable to conventional mass spectrometry, techniques

such as atmospheric pressure ionization mass spectrometry, Fourier transform infrared

spectroscopy, nuclear magnetic resonance spectrometry and Raman spectroscopy should be

investigated for their applicability to these compounds. Information generated by these

techniques will also be helpful to the analyst in identifying compounds that can not be

identified from their mass spectra alone.

Ah initio identification of organic compounds (identifying them by piecing together

information gained in the laboratory) is tedious and costly, but some compounds will be

encountered that can not be identified by empirical mass spectra matching. Generation of

additional spectral information for these compounds is necessary. If large numbers of

such compounds are encountered, then it will be worthwhile to develop a systematic,

repetitive (although complex) approach to ah initio identification to make the process

more efficient. Full advantage should be taken of computer-assisted analytical techniques

in such a process.

5. Surrogate Methods

Obviously a comprehensive qualitative and quantitative analysis is not necessary or practical for some samples. For example, once the identities of components in an industrial

effluent are established, a GC retention time is adequate for identification. Extraction

and concentration conditions can be tailored to the particular effluent.

Municipal wastes and water supplies will vary in composition as a function of time,

and GC retention times alone do not provide reliable identities for components in these

samples. Surrogate methods may provide a means of monitoring these systems. Surrogate

methods do not measure specific chemicals; they respond to characteristics of the sample

representing significant groups of chemicals that can be considered, as groups, from the

stand point of toxicity or control. For example "purgeable organic chlorine" may be a significant parameter for water supplies, since purgeable organic compounds formed during

chlorine disinfection represent a significant percentage of the mass of organics so formed.

Conversely most compounds formed during chlorine disinfection of municipal sewage are non- purgeable, suggesting "total organic chlorine" as a parameter for consideration.

71
In neither case mentioned above is there sufficient information to establish the

usefulness of such parameters. From the standpoint of toxicity the same can be said of

Total Organic Carbon as a parameter, because TOC would be influenced largely by the concentration of humic acids and lignins in natural waters. A major problem with surrogate

methods is that not enough is presently known about the significance of the information

they produce.

6. Summary

What is needed at this time is research to improve capabilities to analyze samples

comprehensively so that the significance of trace organics in the environment can be

determined. This paper raises more questions than it answers. Hopefully these questions

will stimulate analytical chemists to seek their answers.

72
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

GCIR—A VERSATILE AND POWERFUL TOOL FOR ANALYSIS OF POLLUTANTS

Leo V. Azarraga

U.S. Environmental Protection Agency

Environmental Research Laboratory

College Station Road

Athens, Georgia 30601, USA

1. Introduction

In an earlier study [1]^, the feasibility of using the Fourier transform gas

chromatograph-i nf rared (GCIR) system for analyzing environmental pollutants was investigated.

Because of the complex chromatograms of environmental samples, the most useful method of

recording the spectra of GC effluents was found to be the sequential storage of each interferogram throughout the chromatographic run.

2. Discussion

On-line-trapping of the eluted zones and stop-flow methods have limited applications.

The time required for data acquisition and the quantity of sample needed to allow trapping

or stop-flow analysis of each component are the major limiting factors. Poor GC resolution

and high GC background also restrict the application of on-the-fly signal averaging. None

of the three methods (on-line-trapping, stop-flow, and on-the-fly signal averaging),

therefore, is completely reliable when measuring the spectrum intrinsic to the eluted

substance. This is because extraneous absorptions may be introduced into the spectrum by

GC background materials or by the coherent addition of interferograms containing different

spectral information.

The original FTS-14D spectrometer system and its GCIR accessory that were used during

the initial evaluation lacked sensitivity and data collection and storage capabilities for

the intended method of GCIR analysis. These problems were resolved with the adoption of

three major system modifications: (1) a more sensitive GCIR cell was installed, (2) the

triglycerine sulfate (TGS) detector was replaced, and (3) the necessary software and

hardware were added to allow sequential storage and the processing of interferograms

collected during the GC run.

These modifications have now been implemented and significant observations have been

reported at various stages of modification. A gain of more than an order of magnitude in

the signal to noise (S/N) ratio of GCIR spectra was reported by Azarraga and McCall [2]

when a liquid-nitrogen-cooled MCT detector was substituted for the TGS detector. The

observed gain agreed with the S/N advantage of mercury cadmium telluride (MCT) over TGS

calculated by Griffiths [3].

The critical stage in the modification involved the construction of a sensitive GCIR

cell. Work undertaken at EPA's Athens Environmental Research Laboratory resulted in the

development of a gold-coating process for small diameter glass tubes and produced the

Figures in brackets indicate the literature references at the end of this paper.

73
required infrared light-pipe (LP) for the construction of a sensitive GCIR cell. After the

incorporation of the peripheral hardware and software for GCIR data collection and processing,

results were obtained showing the sensitivity and capabilities of the GCIR system with the

modified LP. These results were reported during the Fifth Annual Symposium on Recent

Advances in the Analytical Chemistry of Pollutants in May 1975 [4]. Observations on the

effect of GC columns on GCIR sensitivity were reported during the 27th Pittsburgh Conference

in March 1976 [5].

3. Conclusion

The present GCIR system is sufficiently sensitive to yield identifiable spectra from

quantities of substances as small as 0.2 microgram. Interferograms are collected at rates

of 40, 20, and 15 per minute at 8, 4, and 2 cm-^ resolution, respectively. At these rates,

all interferograms are stored singly and sequentially throughout a 55-minute GC run. The

system, therefore, provides a complete and permanent storage of spectral information on the

chromatographed sample.

References

[1] Azarraga, L. V., and McCall, A. C, Infrared Fourier Transform Spectrometry of Gas

Chromatography Effluents, pub. No. EPA-660/2-72-0Z4 (Environmental Protection Agency,

Athens, Georgia, January 1974).

[2] Azarraga, L. V., and McCall, A. C, Fourier Transform Infrared Spectroscopy of Gas

Chromatography Effluents, 2Sth Pittsburgh Conferenae on Analytical Chemistry and

Applied Spectroscopy (Cleveland, March 1974).

[3] Griffiths, P. R., Optimization of Parameters for On-line GC-IR Using an FTS-14 Spectrometer, 25th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy

(Cleveland, March 1974).

[4] Azarraga, L. V., GCIR System with Sub-microgram Sensitivity, 5th Annual Symposium on Recent Advances in Analytical Chemistry of Pollutants (Jekyll Island, May 1975).

[5] Azarraga, L. V., Improved Sensitivity of On-the-fly CGIR Spectroscopy, 27th Pittsburgh

Conference on Analytical Chemistry and Applied Spectroscopy (Cleveland, March 1976).

74
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

THE MSDC/EPA/NIH MASS SPECTRAL SEARCH SYSTEM

S. R. Heller

Environmental Protection Agency

401 M Street S.W. (PM-218)

Washington, DC 20460, USA

1. Introduction

A large file of unique and high q^jality mass spectral data has been assembled in a collaborative effort involving the U.S. Environmental Protection Agency (EPA), the U.S.

National Institutes of Health (NIH) and the U.K. Mass Spectrometry Data Centre (MSDC).

This file of 29,936 spectra, together with the programs for searching through it has been

made available to the international scientific community via a time-sharing computer network. This "Mass Spectral Search System" (MSSS) has been in operation for almost five

years during which time an estimated 50,000 searches have been completed. Currently there

are about 200 working accounts which are using the system on a daily basis.

2. Background

The last few years has seen the gradual development primarily at NIH and EPA of a Chemical Information System (CIS) on an interactive time-sharing DEC PDP-10 which contains

several collections of data such as mass spectra, carbon nuclear magnetic resonance spectra

and x-ray diffraction data. Of all these components, the MSSS is the most highly developed

and has been operating on a commercial basis for three years. It is available on a feefor-service basis via the ADP-Network Services Inc., Cyphernetics Division computer network

which can be reached by a local telephone call throughout most of North America and Western

Europe and via Telex throughout the world.

This paper describes the MSSS and provides a' report on the status of the system.

3. Methods of Searching

As a practical matter, it is preferable that the time necessary to search through a data base be largely independent of the size of the data base. In the case of MSSS, this

is accomplished using an inverted file technique with a data base of "abbreviated" mass spectra. These are spectra in which only the two most intense peaks in consecutive gaps of

14 atomic mass units (amu) are retained. The resulting file is only about 30 percent the

size of the full file, but, as has been shown in Biemann and his group at MIT, contains

essentially all the information that was in the unabbreviated spectra. Although the

abbreviated file is used for efficient searching, the full file is also stored in the

computer in order that users may retrieve complete mass spectra to confirm identifications.

Searching through this mass spectra data base can be accomplished in a variety of

ways. These programs are summarized in table 1. Probably the most important of these

methods is the "PEAK" search. This program permits one to identify all the mass spectra in

the file that contain a specific peak (m/e value) with an intensity that falls into a given

range. The data base can be searched with a second peak and the two lists of hits are then

automatically intersected to produce a list of spectra that contain both peaks. Intensities

are not precisely reproducible in mass spectral measurements and so a range of acceptable

intensities must be created for the purposes of a search. This can be done by the user who

75
can specify upper and lower values for acceptable intensities. Alternatively, if he

specifies only one value, the program takes this value and accepts any peak whose intensity

is within ± 30 percent of it.

Table 1

Mass spectral search system (MSSS)

Current and future options

1. Peak and intensity search

2. Loss and intensity search

3. Molecular weight search

4. Code search

5. Molecular formula search

(a) complete (b) partial, stripped

6. Peak and loss search

7. Peak and molecular weight search

8. Peak and molecular formula search

9. Peak and code search

10. Loss and molecular weight search

11. Loss and molecular formula search

12. Loss and code search

13. Molecular weight and code search

14. Molecular weight and molecular

formula search

15. Complete spectrum search

(a) BIEMANN (b) STIRS (c) PBM

16. Dissimilarity Comparison

17. Spectrum/Source Print-out

18. Spectrum/source display

19. Spectrum/source plotting

20. Spectrum/source microfiche

21. Crab-comments and complaints

22. Entering new data

(a) mini-computer interface

(b) data collection sheets

23. News-news of the MSSS

24. MSDC Bulletin-literature search

25. CAS Registry Data

26. SSS-substructure search of CAS data

27. WLN

28. Molecular formula from isotope pattern

29. Molecular weight from spectral data

A different program called LOSS can be used to identify all the spectra in the file

that exhibit the loss of a given neutral mass from the molecular ion. Such a search is of

limited utility alone but it can be used in conjunction with the PEAK. This is an "and"

type of search known as PEAK AND LOSS. As might be expected, it is a very powerful means

of narrowing a search down rapidly to a few candidate spectra.

Other means by which the data base can be searched are given in table 1 and include

molecular weight, partial or complete molecular formula or code search. This last method

enables one to find all entries in the file of compounds that possess a particular functional group. The codes are a series of arbitrary multi-digit codes that are used to

define functional groups and in some cases, compound type.

Many binary "AND" combinations of these simple searches can be invoked and such combinations are generally found to act as much more powerful filters than a simple search. As

the data base increases in size, such methods of searching become much more advantageous

and with the file at its present size (29,936 spectra), we find that simple searches take

considerably more of an operator's time than a combined search such as PEAK AND MOLECULAR

FORMULA.

In contrast to the "interactive" method of search through the mass spectral data base,

there are programs (Biemann, PBM and STIRS) that will compare an unknown spectrum sequentially to every spectrum in the file. These programs retain the best fits, ranked in order

of goodness of fit. Such techniques have the advantage of being operator independent; no decision is necessary as to which peaks to enter, all the peaks are used. The disadvantage

of these methods are that they are relatively extravagant of computer time and they require

that the complete mass spectrum be entered into the system. If this has to be typed in,

this constitutes a rather discouraging preliminary.

76
The first of these problems has been countered by the development of a program which

collects and holds the spectra of unknowns. It then puts through the searching procedure

during off-peak hours, when the machine charges are considerably lower. The results of

this search are available by 8:00 a.m. on the following day, which is not inconvenient for

many workers. The second of the problems: the entering of data into the search has been overcome by the development of an interface that permits the user to couple his own mass spectrometer-minicomputer combination directly to the network computer. The search is

carried out and the answers are relayed back to the user by way of mass spectral data

flow from the mass spectrometer through the minicomputer and interface to MSSS. At present,

this type of interface can be purchased to operate with the Varian, SI-150, Hewlett-Packard

cassette and disk, INCOS and Finnigan 6000 data systems. Other manufacturers are in the

process of developing the necessary software for their computer systems.

4. Data Retrieval

The remaining programs in MSSS deal with the partial or complete retrieval of specified

mass spectra from the data base. A file of complete mass spectra is available in the

computer and one may, upon completion of a search and identification of the appropriate

ID #, use this number to obtain a printout of the full spectrum or part of it. If one is

using a terminal that is capable of plotting (such as the Tektronix 4000 series, the DEC

GT40 series, Zeta Plotter, H-P Plotter, etc. ) then a spectrum may be plotted as a bar

graph. Whether the data are reprinted or plotted, the origin of the spectrum is also given

as are experimental conditions under which it was measured.

5. Applications

During the five years that MSSS has been used on a regular basis, it has come to be of

particular value in some well identified contexts in laboratories in the academic, industrial

and government sectors. In general, the reasons for which MSSS is used are not recorded,

but examples in which the system proves to be especially helpful often become more widely

known by a number of mechanisms. That MSSS has been featured in the plot of a science

fiction novel ("The Swarm" by Arthur Herzog) can be regarded as a form of recognition,

dubious though it may be!

An early example of the value of the MSSS that was fairly well publicized involved the

treatment of a six-year old child admitted to a Denver hospital. The child had ingested

some of the contents of an unlabelled bottle of liquid and was developing symptoms of

serious intoxication. Mass spectrometry of the material by the local Denver EPA lab and

application of MSSS revealed the toxic principle to be parathion. Confirmation of this was obtained by comparison with an authentic sample and a vigorous course of treatment was commenced, all within an hour. In retrospect, there seems little doubt that the fortunate

outcome of the episode was due, at least in part, to the MSSS.

The public is unexpectedly and seriously exposed to chemicals in a host of ways, such

as oil spillage, train and truck accidents and the release of industrial waste into the

environment. Rapid and accurate identification of compounds, which are often only present

at low levels, is essential in the decision as to whether the chemicals pose a danger to

the health of the community or the environment.

The MSSS is used in a very routine way by analysts of the EPA and was involved in the

recent, widely publicized, identification of halogenated organic compounds in the water

supplies of several cities, most notably New Orleans. The analysis of the compounds in

question was carried out with a gas chromatograph coupled to a mass spectrometer, the

resulting mass spectra were examined with the help of the MSSS and well over sixty distinct

compounds were identified in this way. Final confirmation of these identifications was in

every case arrived at by a direct comparison of the experimentally obtained spectrum with

the file spectrum of the appropriate compound.

77
Identification of drugs and poisons is a task that is frequently undertaken for reasons

that range from the purely forensic to the purely medical. The sensitivity of gas

chromatography-mass spectrometry (GC-MS) and the power of MSSS make them valuable tools in

post mortem examinations. These methods are also used in local, state and federal law

enforcement laboratories in attempts to identify materials that have been seized. Adulteration of heroin with inactive "fillers" such as glucose is a very common practice. The

identity of the filler compounds in a batch of illicit heroin can be determined by GC-MS

and MSSS and often gives a key as to the origin of the heroin. For this reason, police

laboratories in several states have adopted GC-MS as a standard technique and are also

using the MSSS as a means of identifying such compounds.

Throughout the development of the MSSS, there has been a continual effort to create a computer system that is easy to use and that permits the chemist to bring into play his own expertise without requiring that he be particularly competent in the use of computers.

To this end, a comprehensive User's Guide, now being edited for its fifth edition is

made available to all MSSS users and there are, within the MSSS, many so-called "HELP"

files which a confused user can consult and hopefully, use to solve his immediate problem.

Users can and do write complaints and/or observations regarding the MSSS which are handled

by a professional who is employed for that purpose.

In terms of simplicity for the user, however, the most important element is clearly

the program itself. At any point in a session, the options available to the user are sufficient, but no more than sufficient. In each case, the computer prompts are concise

and unambiguous and as a result, it is not uncommon to observe a new user learning to use the MSSS by just exploring the programs and succeeding in carrying out searches.

At the same time, we find that more sophisticated methods of searching are used rather

little. The more direct searches do give the correct answers, albeit less efficiently, and

users are satisfied by this. The response to this, that is evolving, is to keep gentle but

continual economic pressure on users to search in the most efficient way possible. As an example, the judicious selection of ions that are used in a PEAK search usually means that

only three or four ions should be necessary to complete a search. If one uses very commonly

occurring ions, however, such as m/e 43, 57, 71, and so on, then more entries will be

needed to finish a search. Users are encouraged to select peaks by a pricing scheme which

ensures that the cost of a PEAK search is $3.00 until more than five peaks are used, at

which point the price rises to $7.00.

6. Economics

The economic basis of the MSSS is still evolving, but enough experience has been

gained to permit some observations to be made. The expense involved in assembling a data

base such as is used in MSSS is very considerable. The spectra are in general, extant, but

a surprisingly large amount of manpower is necessary to locate, check,- copy and assemble

them into a usable data base. A second important economic consideration is the cost of

storing a large data base in a computer. This cost is directly proportional to the size of

the data base.

Both these points, taken together, suggest that it is more economical to keep one copy

of the data base on disk, and make it accessible to many users via a computer network, as has been done in the case of MSSS. Multiple copies of the file will create formidable

problems in updating and will, of course, imply multiple monthly computer charges for

storage.

In the MSSS, the day-to-day expenses for file maintenance are borne by the MSDC, which

attempts to recover some of these costs from users. The latter pay a subscription fee for

admission to the system and in addition to this, they are also required to pay the computer

service company (Cyphernetics) in proportion to the extent of their use of the system. The

subscription fee is $300 per organization per year and the usage fee is fixed, but dependent upon which option is used. A simple PEAK search, for example costs $3.00 (unless more

than five peaks are entered) and other searches cost from $1.00 to $6.00; the combined

78
searches are generally the more expensive. As a consequence of program design, search

times and costs are almost independent of the size of the data base. The sequential search

discussed above normally costs $6.00 but can be run overnight, in which case the cost is

$2.00. Thoughtless use of the searching programs will increase one's costs without improving the quality of results. As an example, a search for all the spectra with an ion at m/e

43 and intensity between 10 percent and 90 percent will generate the useless result that

-some 5,0"00 spectra satisfy these criteria.

7. Use of Subsets of the Data

It is a fact that as the data base becomes larger, it is more difficult to extract

from it a small number of spectra using a given amount of data. Thus while a PEAK search

using two peaks may have given only one answer, when there were 10,000 spectra in the file,

the same two peaks might now cause the retrieval of five spectra and entry of a third peak

may well be necessary to narrow down the choices sufficiently. It also seems clear that it

is inefficient to attempt to identify compounds of low molecular weight using a file that

contains data from many compounds of much higher molecular weight. This is because the

latter spectra very frequently will contain peaks possessed by the former. For this reason,

we are presently considering the possibility of sub-dividing the file in the future.

Currently, an intersected search has the effect of sub-dividing the file or creating a small sub-file that is then searched. For example, a PEAK AND CODE search can be used to

isolate all the chlorinated compounds in the main file by invoking the proper code and then

search through them for specific spectral features. The same effect would be achieved if

all the chlorinated compounds were in a single file separate from the main data base. This

subfile would only be searched upon a specific command. The advantage of this would be

that the main file would not be "cluttered" with steroid spectra. The obvious disadvantage

is that this approach implies a prejudice of sorts on all searches of the main data base.

It is also not clear what groups of compounds would qualify for inclusion into a sub-file.

Pesticides would seem to be a fairly clear-cut group of compounds that in general, are of

interest to a relatively few people. An unambiguous definition of "pesticide" is not

available, and even if it were, the segregation of pesticides from the main file will

present a daily question for toxicologists , whose encounters with pesticides are rare, but

not unknown. A good case can be made for sub-files where proprietary information is

involved. In this case, a sub-file of such data could be assembled and used by those

authorized to do so. Other users of MSSS need not even be aware of the existence of such

sub-files.

8. Present Progress

An aspect of the MSSS that is currently receiving considerable attention relates to

the quality of the data in the file. Work is in progress to check some parts of this such

as molecular formulas and molecular weights. It is more difficult to check the quality of

the mass spectra themselves and there is also a problem that is related to the question of

redundant spectra. The whole file has not been checked by the Chemical Abstracts Service,

which has assigned CAS Registry Numbers to each compound in the file. These numbers were

then used to find the repeated appearance of the same compound. This done, the multiple

spectra were examined using a "Quality Index" computer program developed for EPA by

McLafferty and his group at Cornell. On the basis of the presence or absence of various

phenomena, a "Quality Index" (QI) was assigned to each spectrum, and this index used to

identify the inferior redundant spectra in the file. They were then removed to produce the

file of 29,936 unique spectra.

Another item that will be merged into the file within a matter of months is the

Wiswesser Line Notation for the structures. Programs have been written and are under test

that will permit an examination of the file from a structural point of view. As an example,

one might wish to identify all compounds in the file that contain a pyrrole ring and have some particular mass spectral characteristics. A program that calculates the best molecular weight from the mass spectrum has been written by Dromey at Stanford and will be made

available as a component of MSSS in the near future. A program that can analyze intensity

79
values and calculate isotope incorporations has recently been added to the pilot version of

MSSS and should become generally available soon. Finally, searching of the mass spectral

literature via the Mass Spectrometry Bulletin from 1966-1975 is now possible.

9. Summary

The purpose of this paper has been to describe the capabilities of the MSSS. The

system is now in a relatively stable form on the ADP-Cyphernetics computer network and

inquiries regarding its use are invited. We would also be pleased to learn of new sources

of mass spectral data and will be happy to acquire and process such data.

Details on obtaining an account with the Cyphernetics network can be obtained from The

Manager, Data Base Services, Cyphernetics, 175 Jackson Plaza, Ann Arbor, Michigan 48106,

telephone: 313-769-6800, or from The Manager, Cyphernetics International, J. C. van Markenlaan 3, Postbus 286, Rijswijk (Z.H.), The Netherlands, telephone: 070-94-88-66.

The author would like to thank Professor K. Biemann of MIT for providing the data base

that was originally used in the development of the MSSS. They would also like to thank all

of their colleagues who have assisted greatly in the development .of the MSSS. In particular,

they would like to thank the following: G. W. A. Milne, A. Bridy, W. Budde, H. H. Fales,

R. J. Feldmann, R. S. Heller, T. L. Isenhour, D. Maxwell, A. McCormick, J. McGuire, F. W. McLafferty, M. Springer, V. Vinton, S. Woodward, and M. Yagyda.

80
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977)

METHODS FOR ANALYSIS OF TRACE LEVELS (yg/kg)

OF HYDROCARBONS IN THE MARINE ENVIRONMENT

S. N. Chesler, B. H. Gump^ H. S. Hertz

W. E. May and S. A. Wise

Trace Organic Analysis Group

Bioorganic Standards Section

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

The low concentration of hydrocarbons anticipated in pollution baseline studies neces- sitates the development of analytical techniques sensitive at the sub-microgram per kilogram level. At this low level, the problems of analytical blanks and component recoveries

become paramount. Furthermore, analytical methods that ultimately permit the identification

of individual hydrocarbon components are desired.

Several authors have developed methods for the analysis of hydrocarbons in marine

samples [1-6]^. These methods are of three basic types: screening for total extractable

hydrocarbons [1], static headspace analysis, specific for low molecular weight hydrocarbons

[3,5], and digestion or extraction of the sample followed by clean-up, concentration and

gas chromatographic (GC) analysis of the hvdrocarbon components [2,4,6]. These methods are subject to certain limitations. The screening technique for total extractable hydrocarbons

is not sufficiently specific, i.e., it does not afford single-compound identification.

Static headspace analysis methods are suitable only for compounds of relatively high

volatility. Extraction/digestion procedures are generally lengthy, involve considerable

sample handling and usually result in considerable losses of hydrocarbons having molecular

weights of 200 and below.

An alternative scheme for the analysis of hydrocarbons in marine sediments and in

water has been developed in this laboratory. It involves dynanrlo headspace sampling and

the trapping of volatile components on a TENAX-GC packed pre-column. The trapped components are subsequently analyzed by GC or gas chromatography-mass spectrometry (GC-MS). The

non-volatile components are then analyzed by coupled-column liquid chromatography (LC).

Samples which have been collected and frozen in the field, are thawed and transferred to a headspace sampling flask in a class 100 laminar flow, clean air hood maintained in a cold

(4°C) room. They are then headspace-sampl ed for a period of four hours using scrubbed

nitrogen gas to sweep volatile components into the TENAX-GC packed pre-columns. After

headspace sampling is completed, the liquid remaining in the flask is pumped through an LC

pre-column packed with Bondapak C18. Subsequent GC or GC-MS (utilizing capillary columns)

and analytical LC are used to separate, identify and quantitate the volatile and non- volatile components of the sample.

^Present address: California State University, Fresno, CA 93740

^Figures in brackets indicate the literature references at the end of this paper.

81
Various headsapce sampling and coupled-column LC techniques have been applied in other

analysis systems, e.g. [5,7-15]. Grob [8] used charcoal as an adsorbent for headspace

sampling of drinking water. Trapped material was desorbed with carbon disulfide and

analyzed by GC and GC-MS. Zlatkis and co-workers used Porapak P, Carbosieve and TENAX-GC

as adsorbents in air pollution studies [12] and in the headspace-analysis of gases and

biological fluids [9,11]. Trapped material was desorbed by heating and transferred to a pre-column for subsequent GC and GC-MS analysis. Snyder [15] has discussed the use of

coupled-column LC techniques with Corasil-II and Porasil A for the separation of non-polar,

intermediately polar, and polar antioxidants.

The analysis of marine tissue samples for pg/kg hydrocarbon pollutants poses difficulties that the above procedure does not overcome. Most of the organic compounds present in

this matrix are of biological origin; thus a suitable chemical clean-up of the sample is

necessary in order to remove these interferences prior to actual trace organic analysis.

Such a method has been developed. It uses dynamic headspace sampling of a homogenized

tissue sample, as described above. Polar biogenic interferences are then separated from

non-polar hydrocarbons on an LC column and the non-polar fraction is analyzed by GC/GC-MS.

2. Experimental

Due to the low levels of hydrocarbons present in the samples, special caution was exercised at all stages during the collection and handling of water and sediment samples

[18]. An internal standard is added to the water samples at the time of collection. All

samples were quick-frozen in the field for return to the laboratory. Until analyzed,

samples were stored in a freezer at -10°C. For analysis, the samples were allowed to thaw

overnight in a laminar flow hood in a cold (4°C) room. They were then transferred into 2-

liter tared flasks for headspace sampling. Approximately 100 g of sediment or 750 ml of

water were taken for analysis. Approximately 600 ml of hydrocarbon-free water and 5yl of

the internal standard solution were added to the sediment samples. The internal standard

consisted of a solution of aromatic hydrocarbons, each present at a known concentration

(approximately 2ijg per 5ij1).

The inlet of each headspace sampling flask was connected to a supply of scrubbed

nitrogen gas. The exit of each flask was connected to a 6.5 x 0.6 cm (1/4 in.) o.d.

stainless steel column packed with TENAX-GC (Applied Science Laboratories, State College,

PA) which had been heated previously to 375°C for 60 minutes to remove any contaminants.

Experiments were carried out on six samples simultaneously, two of the six being a system

blank that consisted of hydrocarbon-free water plus the internal standard.

The headspace sampling procedure was as follows: the cool ('^15°C) air flow around the

TENAX-GC column was begun, the magnetic stirrer was started, and a flow of approximately

150 ml/min of pre-purified nitrogen was established through each sampling vessel. The

headspace was sampled at room temperature for two hours. Then the flasks were heated to

70°C and the headspace sampling was continued for an additional two hours.

At the end of the four-hour sampling period, each cooled TENAX-GC column was connected

for two hours directly to the nitrogen line to remove trapped water from the column (flow

rate of nitrogen = 150 ml/min). Each TENAX-GC column was then capped tightly and stored at

4°C until analyzed by GC/GC-MS.

Water remaining in the flask, following headspace sampling, was decanted into a clean

one-liter beaker which was then covered with cleaned aluminum foil. The water was then

pumped through a 6.5 x 0.6 cm (1/4 in.) o.d. stainless steel liquid chromatographic precolumn at the rate of 10 ml/min by use of a Milton-Roy Minipump. This column was packed

with a 37-50 pm pellicular (superficially porous) support with a bonded Ci e--stationary

phase (Bondapak C18--Waters Associates, Milford, MA), and was fitted on both ends with

Swagelok stainless steel reducing unions with 2-pm snubbers.

82
After the headspace sampled water was pumped through the LC pre-column, the pre-column

was attached to a liquid chromatograph capable of gradient elution. The two reservoirs of

the gradient pumping system contained degassed, redistilled, reagent grade methanol and

hydrocarbon-free water, respectively. Ten ml of water were pumped through the pre-column

to remove entrapped air. Then a 30 cm x 0.6 cm (1/4 in.) o.d. stainless steel analytical

column packed with a 10-ym micro-particulate (totally porous) support with a bonded Cjsstationary phase (pBondapak C18--Waters Associates, Milford, MA) was connected to the

outlet end of the pre-column. Elution of adsorbed compounds from the coupled columns was begun with a 30:70 (v/v) methanol -water mobile phase pumped at 3 ml/min. The gradient was programmed to increase the percentage of methanol in the mobile phase to 100 percent in 40

minutes. The effluent from the analytical column was passed through a UV photometer (245

nm) and the chromatogram was recorded. Individual fractions were collected for subsequent

analysis of the individual compounds (by UV, fluorescence and mass spectrometry).

The TENAX-GC packed pre-column was installed between the injection port and a coiled,

glass SE-30 coated, SCOT analytical column (100 m x 0.65 mm i.d. drawn and coated [19] in

this laboratory). A removable aluminum heating block, powered by a high intensity cartridge

heater and Variac, was placed around the TENAX-GC column. The first eight coils of the

capillary column were isolated from the remaining coils for cryogenic cooling to provide

thermal focusing of components released by heating the TENAX-GC column. A make-up carrier

gas was introduced directly into the detector to reduce the effective detector dead volume.

The first eight coils of the analytical column were sprayed with liquid nitrogen as the TENAX-GC pre-column containing trapped hydrocarbons was heated to 375°C for 8 minutes.

The flow rate of carrier gas through the system was 20 ml/min during this operation. Then

the flow rate was reduced to 6 ml/min, the cryogenic cooling was terminated, and the gas

chromatographic oven temperature was raised to 80°C and maintained at 80°C for 4 minutes.

For the chromatographic analysis, the oven temperature was programmed to rise at a rate of

4°C/min and hold at 275°C. A flame ionization detector was used.

A gas chromatograph-mass spectrometer computer system (Model 5930, Hewlett-Packard,

Palo Alto, CA) was used for GC-MS analysis of the samples. These analyses were performed

in an analogous manner to the GC analysis. Mass spectra were accumulated every 4 seconds

during the course of the chromatogram.

Tissue samples ('^25 g) were homogenized with an ultrasonic probe in 500 ml of

hydrocarbon-free water to which 50 g of NaOH has been added. The homogenate is headspace

sampled for 16 hours at 70°C. The TENAX trap is then dried for 4 hours and then attached

as an injection loop of a pBondapak NH2 LC column. The organic compounds on the TENAX are eluted onto the head of the LC column by passage of a pentane mobile phase. The polar

compounds are totally retained by the LC column while the non-polar hydrocarbons are eluted. The pentane effluent is then slowly evaporated to SOOyl total volume, and the

concentrated solution is quantitatively transferred to a clean TENAX column for normal

GC/GC-MS analysis.

3. Discussion

By use of the methods described, we have found system blanks for the separate water,

sediment and tissue methods that are consistently below 10-30 yg/kg. While the recovery of

internal standards from water is reproducible to '^-5-10 percent, large variances have been

observed when analyzing some tissue and sediment samples. This is postulated to be caused

by slow desorption from active sites in these types of sample matrices. Longer headspace

purging has been observed to improve the recovery and has been adopted for the tissue

methodology. The sediment and tissue analyses exhibit large (20-100 percent) standard

deviations at yg/kg hydrocarbon levels; this is due to the difficulty in obtaining a truly

homogeneous environmental sample of the complex matrix type.

83
4. Conclusions

The use of dynamic headspace sampling and coupled-column LC either alone or in combination offers a number of advantages over most of the current sample preparation techniques

for yg/kg hydrocarbon analysis of marine sediment and water samples. These techniques

require minimal sample handling, thereby reducing the risks of loss of sample components

and of possible contamination. Volatile components of the sample are efficiently separated

from the matrix in a closed system and collected in a concentrated form that is free from

large amounts of solvents and ready for GC/GC-MS analysis. The headspace-sampl ing technique

is well-suited for napthalene and substituted naphthalenes, compounds of special interest

due to their suggested immediate toxicity to marine organisms [16,17]. Analysis at the

sub-microgram per kilogram level is readily attainable by GC. High molecular weight non- volatile compounds, such as the benzpyrenes, may be readily analyzed by the coupled-column

LC technique. This latter method can be very sensitive, since trace amounts of hydrocarbons can be concentrated from very large volumes of water. The analysis is non- destructive and separated compounds may be detected by UV photometry (254 nm) or collected

and identified by other techniques.

A significant advantage derives from the fact that water is the only solvent needed

for the preparation of water and sediment samples. The use of hydrocarbon-free water

reduces opportunities for contamination of the sample by fossil hydrocarbons.

Tissue samples must be stripped of biogenic nonhydrocarbon constituents prior to

GC/GC-MS analysis. However, low blanks (<20 pg/kg) can be obtained if special care is

used in distillation of solvents and preparation of columns used in the LC clean-up.

References

[I] Brown, R. A., Searl , T. D. Elliott, J. J., Phillips, B. G., Brandon, D. E., and

Monaghan, P. H. , Proceedings of the 2972 Joint Conference on Prevention and Control

of Oil Spills, pp. 505-519, American Petroleum Institute, Washington, DC (1973).

[2] Clark, R. C. , Jr., and Finley, J. S., Proceedings of the 1973 Joint Conference on Prevention and Control of Oil Spills, pp. 161-172, American Petroleum Institute,

Washington, DC (1973).

[3] McAuliffe, C. D. , Chem. Tech. \_, 46 (1971 ).

[4] Warner, J. S., ms Special Publication t^o. 409, U. S. Government Printing Office,

Washington, DC, 1974, p. 195.

[5] Wasik, S. P., and Brown, R. L., Proceedings of the 1972 Joint Conference on Prevention

and Control of Oil Spills, pp. 223-230, American Petroleum Institute, Washington, DC

(1973).

[6] Farrington, J. W. , Teal, J. M. , Quinn, J. G. , Wade, T., and Vurns, K. , Bull. Environ.

Contam. Toxicol. 10, 129 (1973).

[7] Melpolder, F. , Warfield, C, Headington, C, Anal. Chem. 25^, 1453 (1953).

[8] Grob, K., J. Chromatog. 84, 255 (1973).

[9] Zlatkis, A., Bertsch, W. , Li chtenstein , H". , Tishbee, A., Shunbo, F. , Liebich, H. , Coscia, A., Fleischer, N., Anal. Chem. 45, 763 (1973).

[10] Versino, B. , deGroot, M. , and Geiss, F., Chromatographia ]_, 302 (1974).

[II] Zlatkis, A., Lichtenstein, H., and Tishbee, A., Chromatographia 6^, 67 (1973).

[12] Bertsch, N., Chang, R. C, and Zlatkis, A., J. Chromatog. Sci. VZ, 1 75 ( 1974).

[13] Novotny, M. , Lee, M. L., and Bartle, K. D. , Chromatographia 7_, 333 (1974).

84
[14] Snyder, L. R. , Modem Practioe of Liquid Chromatography, J. J. Kirkland, ed. , WileyInterscience, New York, 1971, pp. 232-235.

[15] Snyder, L. R. , J. Chvomatog. Sci. 8, 692 (1970).

[16] Wilber, C. G. , The Biological Aspects of Water Pollution, Charles C. Thomas, ed.

,

Springfield, IL, 1969.

[17] Blumer, M., Environmental Affaira 1_, 54 (1971 ).

[18] Chesler, S. N., Gump, B. H., Hertz, H. S., May, W. E. , Dyszel , S. M. , and

Enagonio, D. P., EBS Tech. Note No. 889.

[19] German, A. L. and Horning, E. C. , J. Chromatog. Sci. lj_, 76 (1973).

85

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

POTENTIAL CARCINOGENS IN WATER: GC/MS ANALYSIS

Ronald A. Hites

Department of Chemical Engineering

Massachusetts Institute of Technology

Cambridge, Massachusetts 02139, USA

1. Introduction

The presence of various synthetic organic compounds in the environment is a well-known

and often repeated story. Chloroform in tap water, Kepone in river water, and Red Dye No.

2 in food are compounds which have caused recent concern. In general, this increased

attention to organic compounds in the environment has resulted from the realization that 50

to 80 percent of all occurrences of cancer in man are due to environmental causes such as chemical carcinogens in our air, water, and food. Thus, it is obviously important to

identify anthropogenic chemical carcinogens, isolate their sources, and determine their

environmental fates.

This paper will be restricted to the occurrence of organic compounds in water, and it

will detail two approaches: a) study the sources and fates of those compounds known to be

carcinogenic, or b) survey suspicious sources (such as drinking water or industrial wastewater) to determine the identities of specific compounds being emitted and then study their

carcinogenic potential and environmental fate. This paper will present examples of both

approaches. The first example centers on a compound class which includes several known

carcinogens; namely the polycyclic aromatic hydrocarbons (PAH). The second example will

demonstrate the survey approach as applied to industrial wastewater sources.

2, Discussion

A. Polycyclic aromatic hydrocarbons

We have reviewed our work on this compound class at the recent Symposium on Sources,

Effects and Sinks of Hydrocarbons in the Aquatic Environment (held at American University,

Washington, DC, August 9-11, 1976), [1-8].

B. Industrial wastewaters

We are currently analyzing the wastewaters, receiving waters, and sediments of several

cooperating companies to determine the fates of industrial organic compounds. One of the

plants we are studying is a general-purpose chemical manufacturing plant located about

1.5 km from the mouth of a small river which empties into a bay. The flow rate of the

wastewater out of the plant is about 10^ gal/day, and the flow rate of the river is about

lO'' gal/day. Prior to release into the river, the wastewater is neutralized in a one million gallon equalization tank, passed through a trickling filter for biological degradation, and freed of most solids in a clarifier.

Composite and grab water samples were extracted with dichloromethane, and sediment

samples were extracted with methanol and then 3:1 benzene-methanol . The sediment extracts

were separated into hexane, benzene, and methanol fractions using column chromatography on alumina and silica gel. The samples were analyzed on a dual source (EI/CI) Hewlett-Packard

5982A GC/MS system interfaced with a HP 5933A data system. The mass spectrometer was

87
coupled to the gas chromatograph via a glass-lined jet separator held at 300°C and was operated in the continuous scanning mode under control of the data system.

A few representative compounds found in the plant wastewater, receiving waters, and

sediments are presented in table 1. Although the concentration of these compounds in the

river water was generally only a few parts per billion, analysis of the river sediment

revealed very high concentrations of some of the components; up to 0.5 percent for 2 (2'-

hydroxy-5 '-methyl phenyl )-2H-benzotriazole. Some of the compounds were even found in the

bay sediment 2.2 km from the source; this may result from transport of the contaminated

river sediment. It should be emphasized that none of the compounds given in table 1 are known to be carcinogenic.

From the results in table 1, we have concluded that normally water insoluble industrial

organic compounds can be accommodated in wastewater by interaction with high concentrations

of dissolved and suspended organic material {e.g. solvents, biological. sludge) . Dilution

of this effluent with river water seems to cause many of the organic compounds to precipitate and become incorporated into the underlying sediment. Low molecular weight compounds

are apparently rapidly lost through volatilization. These findings lead to the concern

that high concentrations of anthropogenic organic compounds in sediments may continually

repollute the water even after effluent controls are implemented.

Table 1

Representative compounds and their approximate concentrations in the

wastewater and receiving waters and sediments

Approximate concentration (ppm)

Compound

Tol uene Chlorophenol

Di-t^-butyl phenol

Methyl -3- (3' ,5 ' -di -t-butyl -4 '

hydroxy phenyl) propionate

2-Chloro-4,6-bis(isopropylamino)-s^-tri azine

2(2 ' -Hydroxy-5 ' -methyl -phenyl )

2H-benzotriazole

2(2'-Hydroxy-3' ,5'-di-t-amylphenyl )-2H-benzotriazo'ie

Wastewater

20

0.1

4

9

7

10

4.6

Ri ver Water

(75 m)

0.02

0.03

0.02

0.05

0.03

Ri ver Sediment

(75 m)

2600

1700

10

5000

1900

Estuary

Sediment

(2.2 km)

8

20

References

[1] Hites, R. A. and Biemann, W. G., Identification of specific organic compounds in a highly anoxic sediment by GC/MS and HRMS, Advan. in Chem. Sev. 147 188 (1975).

[2] Youngblood, W. W. , and Blumer, M. , Polycyclic aromatic hydrocarbons in the environment:

Homologous series in soils and recent marine sediments Geoahim. Cosmochim. Acta

39 1303 (1975).

[3] Blumer, M. and Youngblood, W. W., Polycyclic aromatic hydrocarbons in soils and recent

sediments, Science 188 53 (1975).

88
Hase, A., and Hites, R. A., On the origin of polycyclic aromatic hydrocarbons in

recent sediments: Biosynthesis by anaerobic bacteria, Geoahim. Cosmoohim. Acta 40,

1141 (1976).

Hase, A. and Hites, R. A., On the origin of polycyclic aromatic hydrocarbons in the

aqueous environment, in Identification and Analysis of Organic Pollutants in Water

(Ann Arbor Science Publ . , Ann Arbor, MI 1976).

Lee, M. L. , Prado, G. P., Howard, J. B., and Hites, R. A., Source identification

of urban airborne polycyclic aromatic hydrocarbons by GC/MS and HRMS , Biomed. Mass

S-pec, in press.

Hase, A., Lin, P. H., and Hites, R. A., Analysis of complex polycyclic aromatic hydrocarbon mixtures by computerized GC/MS, in Carcinogenesis, Vol. 1 (Raven Press, New

York, 1976).

Lee, M. L. and Hites, R. A,, Characterization of sulfur containing polycyclic aromatic

compounds in carbon blacks. Anal. Chem. (in press, October 1976).

89

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

A NEW SIMPLE METHOD FOR THE RECOVERY OF TRACE ORGANICS FROM WATER

T. D. Kaczmarek

Westinghouse Research Laboratories

Pittsburgh, Pennsylvania 15235, USA

1. Introduction

Currently there are four methods of general application for the analysis of organic

pollutants in water. These are direct sampling, solvent extraction, adsorption, and gas

sparging. This paper describes a new method which involves dissolving diethyl ether in the

water sample and then "salting out" the ether with a salt such as sodium sulfate. The

recovered ether contains representative quantities of organic pollutants originally present

in the water. So far in our investigations, contaminants with boiling points above 115°C

have been recovered; those with lower boiling points, although extracted, were not measurable because of the ether interferences.

2. Experimental

At room temperature, ether is soluble in water to the extent of about 7.5 percent.

However, through salting out, it is possible to recover at least 0.5 cm^ ether from 1.25 cm^

in 100 cm^ of aqueous sample and at least 0.5 cm^ from 5 cm^ in 1000 cm^ of aqueous sample.

It appears at present that for a given water sample size, the efficiency of the extraction

depends upon the amount of ether added rather than upon the ether recovered, if there is no significant loss of ether by evaporation during the extraction.

Ether (1.25 cm^ for 100 cm^ sample or 5.0 cm^ for 1000 cm^ sample) is added to the

aqueous sample contained in a volumetric flask filled to mark. Forty grams of anhydrous

sodium sulfate per each 100 cm^ of sample is added to a clean, dry companion volumetric

flask. The ether/aqueous sample is added to the flask containing the sodium sulfate to

well up the flask neck. The flask is then stoppered with a Teflon or polyethylene stopper

and immediately agitated to prevent caking of the salt and to hasten its dissolution. The

operation is performed in a way that will minimize ether losses. A water bath at a temperature between 25°C and 30°C may be used with caution to facilitate salt solution. After

the sodium sulfate has all dissolved and the solution cooled to about 20°C, additional

ether-containing sample solution can be added to make up the decrease in volume caused by

solution of the solid sodium sulfate. Ether will immediately begin to collect at the

surface in the flask. Within one hour, ether separation will amount to approximately

0.5 cm^. Swirling of the flask will dislodge ether globules adhering to the body of the

flask. [Within several hours Glauber's salt (Na2S0it'10H20) will crystallize within the

flask. There has been no study as to any effect, such as possible enhancement, this

crystallization would have on pollutant recovery.]

91
The salted-out ether containing the organics of interest can then be analyzed directly

without any solvent concentration, filtration or drying. There can be an annoying "scum"

formation in the ether layer. The amount of scum depends upon sample size and, perhaps the

amount of sodium sulfate used. This does not seriously interfere with removing aliquots of

ether by hypodermic syringe. However, with elimination of the scum less ether would be

necessary initially to recover 0.5 cm^ finally, since ether is entrapped by the scum. This

would improve organic pollutant detectabil ity and characterization. So far there has been

no major effort to identify the scum or its source. The situation is not improved by

solvent washing the sodium sulfate before use. For economic reasons, reuse of sodium

sulfate (recovered as solid Glauber's salt) is desirable. This recycling may also solve

the scum problem.

3. Results

In our laboratory the recovered ether has been analyzed by direct injection of up to

200 m1 into the Perkin-Elmer Model 270 Gas Chromatograph-Mass Spectrograph. With a Chromosorb 101 column, the ether matrix is eluted to atmosphere at a column temperature of 100°C;

with a Dexsil 300 column, at 75°C. Within the scope of our experience this technique will

not cause the loss of organic materials boiling at about 115°C or above. After removal of

the ether by venting as above, only a few minor, matrix effects have been seen so far.

These were not serious enough to warrant consideration of ether "purification" beyond the

quality commercially available.

The effectiveness of the method varies with different contaminants. ^ It ranges down

to at least 50 parts per billion (ppb) for individual organics in 100 cm^ of aqueous sample

and as low as 10 ppb with 1000 cm^ of sample. Standards were examined as mixtures of 3 to 6

components in water. As shown in figures 1 and 2, recovery was linear out to at least

1 part per million (ppm) with a 100 cm^ sample and out to at least 50 ppb with a 1000 cm^

sample. Typical quality of mass spectra for compound recovery at various levels is shown

in figure 3^ which also contains a reference spectra of pure material for comparison.

As previously stated, this method in its present form was not found applicable to

organic contaminants with boiling points below about 115°C. This limitation is due to the

fact that the contaminants are recovered in a diethyl ether matrix.

^Part, and perhaps all, of this would represent varying sensitivities of the analytical

instrumentation to different compounds.

^In figure 3, peaks at m/e 45, 59 and 74 are due to diethyl ether; at m/e 73 to

Dexsil 300 column bleed.

92
ccurrence Level (ppm)

FIGURE 1. RECOVERY OF ORGANICS FROM WATER

USING 100 ml SAMPLE

93
FIGURE 2. RECOVERY OF ORGANICS FROM WATER

USING 1000 ml SAKPLE

94
FIGURE 3. RECOVERY OF o-TOLUIDINE FROM WATER

AS EVIDENCED BY MASS SPECTROSCOPY

llhu lilM ..hi 1 1

1

Reference

Mass Spectra of

o-Toluidine

40 50 60 70 80 90 Too 110

JL mil ll

o-Toluidine

@ 50 ppb

JJoJ.

100 ml Sample

illlllllllll

40 60 70 80 90 100

-1110

J-i—

4

iiiklL

o-Toluidine

(a 10 ppb

1000 ml Sample

lillll illll ...hii illhl.t lL

40 50 60 70 80 90 100 110

I I I.mII i h, ihillllli I 1 1 1 . 1 1 1

.

o-Toluidine

@ 5 ppb

1000 ml Sample

40 50 60 70 80 90

Mass to Charge Ratio (m/e)

100

*-|

110

95
4. Conclusion

Currently we are investigating the use of high boiling solvents for the recovery of

pollutants boiling below about 115°C. Preliminary work has been done with diethylene

glycol monobutyl ether (DEGMBE), which is infinitely soluble in water, boils at about

231°C, and is nicely salted out of aqueous solution by Na2S04. The indications are that

compounds boiling at least as low as chloroform (61°C) can be recovered at below ppm levels

from water. Problems with DEGMBE involve the occlusion of major quantities of water in the

salted-out solvent and redistilled, inert gas sparged DEGMBE itself can yield spurious gas

chromatographic peaks, the most prominent of which is due to n-butanol

.

This general method is used routinely in our laboratories at Westinghouse for the

assay of a broad spectrum of organic materials in water. Two areas where the technique may

be especially useful is in the determination of polychlorinated biphenyls and chlorinated

pesticides in water because it is expected that extraction efficiency would be improved over present techniques. This, coupled with sensitive detectors such as electron capture,

would yield very low measurement levels.

The method presented here has at least five major advantages over presently accepted

extraction techniques:

1 . It is more rapid.

2. Extraction is not limited by the boundaries between liquid phases.

3. No subsequent solvent concentration losses can occur.

4. Contaminants can be recovered at 10 ppb levels of occurrence.

5. Because there is no solvent concentration step, there does not appear to be a need

to further purify commercial reagent grade solvent.

96
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

DETERMINATION OF TRACE ORGANIC POLLUTANTS IN WATER BY

SPECTROPHOTOFLUORESCENCE AFTER TREATMENT WITH ACTIVATED CARBON

Joseph G. Montalvo, Jr. and Ching-Gen Lee

Department of Analytical Chemistry

Gulf South Research Institute

P.O. Box 26500

New Orleans, Louisiana 70186, USA

1. Introduction

The proposed spectrophotof 1 uorescence procedure is based upon the fluorescence of

humics in water and the chromatographic principle that the major component (humics) is

indicative of column capacity when all other organic species (pollutants) are at trace

levels. The nonvolatile total organic carbon (NVTOC) in finished waters is due essentially

to humic residuals. The humics are present at relatively large (mg/1 range) and fixed

concentrations in finished waters and they result in intense and reproducible water fluo- rescence intensity (Iwf) values. The trace man-made organics in finished waters are present

at the pg/l range. From theories of mul ticomponent chromatography, it has been shown that

in systems dominated by a single bulk species, column breakthrough times of each trace

component can be expressed in relation to the breakthrough time of the major component.

2. Discussion

For these reasons it may be possible to design a fluorometry measurement system

capable of predicting the breakthrough time of any dissolve-d trace organic solute from

activated carbon beds. As compounds are identified to be hazardous, one need only determine

their rate of progress relative to the humic acids in a given carbon bed. From this one

can predict with a margin of safety the breakthrough times of selected toxins from the

column. This method would provide an "open ended" approach to the analytical problems

associated with carbon bed operations. That is, new compounds added to the hazardous list

will not require a change in the monitoring procedure.

In application of this concept, a fluorometer would be installed in the water treatment plant. A probe or probes to sample the carbon-treated water would be placed upstream

of the column exit, in the column itself. This placement is necessary because some of the

toxins will breakthrough before the humics. Thus, if water were sampled in the column

effluent until humic breakthrough occurred, it would be too late to consider toxic effects

of pollutants that had already moved through the column.

Fluorescent or humic breakthrough at a predetermined depth in the carbon bed will

signal the operator to consult a list of relative breakthrough times. From this list one

can determine specific trace pollutants that may be exiting the column. It is anticipated

that water quality data will be on hand for the drinking water entering the carbon bed.

Probably such data can be obtained from the periodic assay required by the Primary Drinking

Water Regulations. From these data the operator can quickly determine whether the specific

pollutants exiting the column and hence specific toxicity (assuming 100 percent breakthrough)

may exceed the maximum recommended levels.

97
Finally, by correlating the more sensitive I^ijp measurements with the less sensitive

and labor intensive VTOC and NVTOC in the column effluents, it may be possible to support

the hypothesis that trace organics are in fact removed by treatment that produces water

with a very low TOC. Because routine monitoring of specific trace organics may be beyond

the capability of most water utilities for some time, a highly sensitive and simple parameter such as fluorometric measurement seems an attractive supplement to existing water

quality data.

3. Results

In order to more fully understand the basic parameters associated with the use of this

approach as a control parameter for operation of activated carbon filters, the dependence

on source water characteristics was systematically studied. Results are summarized below:

A. In situ fluorescence

Fluorescence appears to be an intrinsic property of all drinking water sources due to

contamination from bioorganic fluorophors, specifically humics. This extremely important

finding means that a "spectroscopic probe" already exists in drinking water sources that

are to be subjected to activated carbon treatment.

B. Humics

For all practical purposes, the native I^^p in drinking water sources is due only to

the humics. For example, experiments were run on New Orleans tap water which had not been

treated by activated carbon. At the wavelength of optimum excitation and emission of

humics, the observed I^^p increased only 2.1 percent when the water sample was spiked with

1 ppm benzene, a good fluorophor.

C. Effect of activated carbon

At the optimum wavelength of Aex ^nd Aem> the native I^jp envelope does not change

shape when drinking water is treated with activated carbon; only the observed I^F decreases.

This finding is extremely important to the application of fluorometry as a control parameter

for monitoring activated carbon beds. The progress of the humics as an unresolved frontal zone through the column permits the application of certain chromatographic principles which

will simplify the problem.

D. Fluorescence vs. source water

The observed I^p increased as a function of source water as follows: bottled water,

treated with carbon < granular activated carbon (GAC)-treated water from tertiary stage of

sewage treatment plant < finished drinking water without carbon treatment, river source < finished drinking water without carbon treatment, ground source.

E. Fluorescence vs. pH and turbidity

The dependence of IWF on water pH was critical. In the pH range 1-13, I^ip varied by

47 percent for finished drinking water from a river source and by 212 percent for similar

water from an underground source. The dependence of IwF on turbidity in raw river water

was also quite great: Fluorescence in unfiltered water was 82 percent greater than with

the f i 1 tered water.

98
F. Precision of IWF values

The within-day and day-to-day precision of Iwp values over a five-day measurement

period expressed as coefficient of variation (CV) was about 7.8 percent for New Orleans tap

water.

G. Fluorescence-raw to finished water

Several water samples were collected from various parts of a local water treatment

plant (river source water, no carbon treatment employed) in a progressive order identical

to the path of the water through the plant. I^^p values decreased by only 14 percent from

raw to the finished water.

H. Quenching

Neither concentration quenching nor quenching of I^F by impurities in the activated

carbon was observed with New Orleans tap water.

I. Carbon-chloroform-extraction (CCE) and carbon-alcohol extraction (CAE)

The CCE and CAE techniques gave an apparent recovery of 90.8 percent of the fluorescent

organics absorbed to the carbon. This data suggests carbon bed capacity is determined by

the humic load in the water.

J. Nonvolatile organics

The bubbling of nitrogen through New Orleans drinking water for one-half hour had no effect on its I^jf values at temperatures ranging from 25-89°C. These data suggest that the

fluorophors primarily responsible for the observed I^F ^re nonvolatile organic compounds.

K. Dissolved vs. suspended organics

Filtration of finished drinking water with a millipore filter did not reduce the I^p,

indicating that the fluorescence intensity was associated with dissolved and not suspended

organics. This is in contrast to the observations with raw river water, where turbidity

did alter Ij^p.

L. Home filter units

Two "mini" carbon columns--one home filter unit containing 1 pound carbon and one containing 8 pound carbon--were evaluated with New Orleans drinking water. After approximately two hours of filtration, the filter containing 8 pound carbon reduced I^jp and TOC by

87 percent and 91 percent, respectively. The filter containing 1 pound carbon did not

measurably reduce either I^jp or TOC, suggesting bed exhaustion by the humics in the water.

These data further support the hypothesis that the humic load in the drinking water will

determine the carbon bed capacity.

M. Sensitivity

In all the above studies source waters were analyzed without preconcentration.

Furthermore, due to the extreme sensitivity of the instrument and the intense I^F signal,

the instrument was operated in its lower sensitivity range. Increased sensitivity, by a factor of 100-1000, could have been used if necessary.

99
N. Future studies

Experimentally determined carbon breakthrough times of selected toxins in the water

sources investigated will be correlated with the progress of the humic front in the carbon

bed as measured by fluorometry. Carbon contact time (bed depth), carbon type, and velocity

of water through the carbon will be varied in the studies. The calculated breakthrough

times will then be verified in a plant water treatment carbon filter.

100
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

POLYURETHANE FOAM PLUGS FOR CONCENTRATION OF TRACE QUANTITIES

OF BENZO(A)PYRENE FROM WATER

J. Saxena, J. Kozuchowski and D. K. Basu

Center for Chemical Hazard Assessment

Syracuse Research Corporation

Syracuse, New York 13210, USA

1. Introduction

An important consideration in the assessment of environmental hazards from carcinogenic

Polycyclic Aromatic Hydrocarbons (PAH) is to monitor their presence in the environment.

The low levels of PAH that can be expected in waters necessitate a preconcentration step

prior to analysis. The methods available at the present time are unattractive because of

poor recovery, and their inability to handle large sample volumes necessary for detection

of low levels of PAH.

The removal of trace quantities of benzo(a)pyrene (BaP), a major representative of

carcinogenic PAH, from water with flexible polyurethane foam plugs is reported.

2. Experimental

Radiolabel led BaP (7-10-^'+C) was used in these studies because of ease and greater

sensitivity of detection. In a typical experiment, the polyurethane foam plugs of appropriate dimension were wetted with distilled water, squeezed to expel air, and placed snugly

in a 25 mm diameter Chromaflex column. The foam plugs were precleaned with acetone, benzene

and finally distilled water. Water spiked with BaP at an environmentally significant

concentration (0.1 ppb, unless otherwise specified) was passed through the foam column at a suitable rate achieved by application of negative pressure with the help of an oscillating

type pump. The flow of water in these experiments was monitored by means of a flow meter.

For continuously monitoring the temperature of water during passage through the column, a water trap equipped with a right angle thermometer was introduced in the line between the

exit end of the column and the pump.

The concentration of radioactive BaP in the spiked water was determined by extracting

a known aliquot of the solution with benzene and counting the ^'^C-activity in the benzene

layer. The BaP retained on the foam was eluted with acetone-benzene and counted; the

retention efficiency calculated was based on the initial ^'^C-acti vity detected in water.

3. Results and Discussion

Preliminary assessment of the sorption characteristics of foam plugs was based on their ability to retain BaP from aqueous solution under static conditions. Preweighed foam

plugs were left to equilibrate in ^^C-BaP solution of various concentrations and following

a period of 4 hours the ^^C-activity remaining in the solution was measured. Based on the

initial ^^C-activity of the spiked water the amount of BaP sorbed by the foam was calculated.

Four different types of foam plugs were evaluated for their sorption characteristics.

These included polyester diSPo plugs, 50 x 38 mm, of two different densities (Scientific

Products, Inc.), polyether Identi-plugs, 45 x 45 mm, (VWR Scientific), and polyester green

U.U. 34 plugs, 50 x 38 mm (Thomas E. Forrest Co.). The foam plugs tested differed only to

a small extent in their ability to remove BaP at various concentrations under static conditions. However, Identi-plugs were chosen for further study because of their low density

101
(thereby permitting satisfactory flow rates), uniformity in foam quality from batch to

batch, and the fact that they were not colored.

The recovery of benzo(a )pyrene from 4 liters of tap water with Identi -plugs at room temperature under flow system conditions ranged between 62 and 65 percent. Under similar

conditions, the recovery of BaP from spiked distilled water was -93 percent. The decreased

retention efficiency of BaP removal from tap water was not due to the saturation of sites

on the foam by background impurities in water. This was proven by passing spiked distilled

water over a foam plug through which tap water had already been passed. This foam plug was found to retain BaP with > 90 percent efficiency. In order to optimize conditions for

efficient removal of BaP from tap water, a number of parameters were varied. These studies

are summarized below.

The retention of benzo(a)pyrene from tap water varied with the diameter of the column

used for holding the foam. The efficiency increased as the diameter of the column was decreased; the value changing from 53 percent for a 50 mm column to 73 percent for a 20 mm

column. Although squeezing the foam in a smaller column gave higher efficiency of BaP

recovery, it produced difficulty in attaining reasonable flow rates. An approximate ratio

of 2:1 between the plug and column diameter was considered the best compromise between

retention efficiency and flow rates.

The recovery was not significantly affected as the flow rates were successively

increased from 130 cm^/min to 520 cm^/min. In subsequent studies, however, a flow rate of

250 ± 10 cm^/min was used because flow rates exceeding this value resulted in the sliding

down of the foam plug in the column. Attempts to hold the plug on a support in the column

caused lowering of the retention efficiency.

The sorption of BaP on foam was also found to be pH dependent; the retention at pH 6.7

(tap water) was between 62 and 65 percent, but upon increasing the water pH to 10.0, the

retention efficiency increased to 76 percent. Lowering of the water pH below 6.7 resulted

in decrease in benzo(a)pyrene retention. The removal of free chlorine, or ions from tap

water did not significantly improve the retention efficiency.

The most dramatic effect on the recovery of benzo(a)pyrene from spiked tap water was observed when the temperature of the water was varied (fig. 1). The relationship between

BaP recovery from tap water and temperature was found to be bi phasic. The percent retention steadily increased with increase in temperature up to 40°C, but decreased with further

increase in temperature. When the temperature was increased beyond 50°C, the increase in

BaP retention was resumed until a plateau was reached starting at 60°C. The recovery of

BaP at a temperature > 60°C was approximately 87 percent.

102
10 20 30 40 50 60 70 80

Temperature of Water Passed Through Foam ( °C )

Figure 1. Effect of water temperature on recovery of benzo{a)pyrene on foam plugs. The

water was brought to the desired temperature by passing it through a glass coil (10

ft X 6 mm) which was immersed in a Haake Model FE thermostated circulator. The coil was placed inside the reservoir housing through the opening of the cover plate.

0 = Tap Water (Unfiltered), • = Filtered Tap Water, A = Distilled Water

The effect of temperature on BaP recovery from tap water is complex and probably the

consequence of many interacting factors. The initial increase appears to be linked to the

presence of suspended particles in water. This is due to the fact that such an increase

was not seen with distilled water, and that the increase was less pronounced when tap water

was millipore-filtered prior to spiking. The increased retention of BaP beyond 50°C is

observed with tap water and distilled water as well as filtered tap water, and, therefore,

appears to be linked to the foam itself. Such an increase could be attributed to a possible

change in the conformation of the polymer at higher temperature. Heat treatment of the

foam plug prior to passing spiked water (at room temperature) gave low retention of BaP.

This suggests that the temperature-induced changes in the sorption characteristics of the

foam were reversible.

In view of a significant increase in the recovery of BaP with an increase in temperature, it was decided to heat water routinely to enhance BaP retention on the foam. Further

studies were carried out at a water temperature of 60 to 65°C.

103
In an effort to further improve the efficiency of BaP retention by foam plugs, the

effect of coating the foams with chromatography phases was investigated. The chromatographic phases tested included nematic liquid crystal, SE-30 and DC-200. With the foams

coated to the extent of 5 to 10 percent by weight an increase of 4 to 9 percent in the

recovery of BaP was observed at the water temperature of 60°C. In view of only a small

increase in the retention of BaP in the presence of chromatographic phases, the foam coating

may be eluted from the foam along with BaP and interfere with analysis. The coating of the

foams was not further considered.

A study of the recovery of BaP by foam plug at various concentrations revealed that

the recovery was not significantly affected with change in BaP concentration. In the

concentration range (0.002 - 25 ppb) tested, the retention of BaP was found to be between

83 to 88 percent. The data show the applicability of foam plugs for concentrations of BaP

at wide concentration ranges.

By passing various volumes of spiked water over foam plugs, it was determined that up

to BaP 5 liters of tap water could be recovered with one foam plug with an efficiency > 85

percent. With increase in volume of spiked water passed over one foam plug, the efficiency

of BaP retention steadily decreased. The data suggested that for larger volumes of water,

the number of foam plugs must be increased. It was found that for recovery of BaP from 20

liters of water with efficiency > 85 percent a minimum of 4 plugs, 2 each in 2 different

columns were necessary.

Prior to considering foam plugs for field monitoring, it is important to assess the

stability of BaP on foam plugs. This was studied by passing known volumes of BaP spiked

tap water through the foam plugs and storing the plugs with sorbed BaP under various conditions. The plugs were analyzed for BaP after various periods of storage. The foam plugs were stored in a Chromaflex column covered with aluminum foil to prevent photodegradation.

The effect of storage at room temperature and in the refrigerator was compared. No significant decomposition or loss of BaP from foam plugs stored in refrigerator was noted up to 7 days. However, a small loss of BaP was observed when plugs were stored at room temperature.

On the basis of these results it is suggested that foam plugs following sampling water

should be cooled to 4°C during transportation to the laboratory for analysis.

The applicability of polyurethane foam plugs for concentrations of BaP from untreated

surface water was also investigated. Four liters of water was collected from Onondaga

Lake, Syracuse, N.Y. (water pH 7.5, total residue on evaporation 940 mg/1), spiked with BaP

and passed over a foam plug at 60°C. The recovery of BaP from lake water was found to be

69 percent. When the number of foams in the column was increased to two, the percent

retention on the foam increased to 81 percent with 4 liters of water. The data suggests

that for concentrating BaP from untreated-surface waters, it may be necessary to use larger numbers of foam plugs in the column to maintain higher retention efficiency.

4. Conclusion

It is concluded that polyurethane foam plugs can be successfully used for concentration

of trace quantities of benzo(a)pyrene and other PAH from water. The recovery is more or

less independent of water flow rates but depends to a great extent o.i the temperature of

the water. For efficient removal, the water temperature should be > 60°C. Under these

conditions a single foam plug placed in a 25 mm column can effectively retain PAH from up

to 5 liters of tap water. For larger volumes, the number of plugs in the column must be

proportionately increased.

Supported by Environmental Protection Agency Grant R80397702, and a grant-in-aid of

research from Niagara Mohawk Power Corporation, Syracuse, New York.

104
Part III. MULTIELEMENT ANALYSIS

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

THOUSANDS OF METAL ANALYSES PER MAN DAY - A REALITY IN THE U.S. EPA's CENTRAL REGIONAL

LABORATORY: MULTIELEMENT (23) ANALYSIS BY AN INDUCTIVELY COUPLED ARGON PLASMA

ATOMIC EMISSION SYSTEM (ICAP-AES)

Richard J. Ronan^ and Garry Kunselman

U.S. Environmental Protection Agency - Region V 1819 West Pershing Road

Chicago, Illinois 60609, USA

1. Introduction

The U.S. EPA's first Inductively Coupled Argon Plasma (ICAP) multielement direct

reader system has been in full operation for more than one and one-half years at the Central

Regional Laboratory of Region V in Chicago. This ICAP system, described here, can analyze

one sample every thirty seconds using a cycle time which includes sample rinse, 10 second

integration and TTY printout of 23 elements. (This time period assumes concentrations

typically found in surface waters and waste effluents). At this rate one might expect to

produce in an 8 hour day:

(8 h/day) (60 min/h) (2 samples/min) (23 elements/sample) = 22,080 elemental results.

Not included in this estimate are other considerations which limit actual output per man day of effort. The ICAP was investigated as a replacement for the U.S. EPA accepted method

for the analysis of metals, flame atomic absorption, and as a viable means for the analysis

of large numbers of environmental water samples. In accomplishing this, three principal

areas were focused upon. These were:

1 . Analysis of Sample

2. Preparation of Sample

3. Large Volume Data Handling

The product of the evaluation of these areas has been the generation of over 5000 high

quality quantitative results reported for a typical man day of effort. More important than

simply a large number of results reported is the high degree of quality control made possible

by the introduction of automatic data handling.

2. Analysis of Samples

The ICAP method was compared in detail to the U.S. EPA accepted method for the analysis

of metals, flame atomic absorption. Summaries of this work have been presented elsewhere

[1]^. A brief review of the fixed elements' basic performance is given in table 1. The

analysis of samples is accomplished using the Jarrell-Ash Plasma Atom Comp 750.

^Author to whom correspondence should be addressed, current address: Jarrell-Ash Division,

Fisher Scientific Company, 590 Lincoln Street, Waltham, Massachusetts 02154.

^Figures in brackets indicate the literature references at the end of this paper.

107
Table 1

Basic performance characteristics

A in D.L.^ LQD^

Element nm yg/i pg/i 7o RSD 100 pg/l

Ag 328.1 4 20 1.8 96 ± 1

Al 396.2 7 35 0.8 95 ± 1

B 249.7 3 15 0.8 100 ± 1

Ba 455.4 <1 <5 0.9 106 ± 3

Be^ 313.0 <1 <5 0.5 99 ± 1

Ca 393.4 <0.5 1 0.5 97 ± 1

364.4 989 ± 2

Cd 226.5 2 10 0.9 105 + 4

Co 238.9 4 20 1 97 ± 3

Cr 267.7 1 5 0.8 96.2 ± 0.4

Cu 324.8 1 5 1.2 95 ± 7

Fe 259.5 2 10 1.0 94 ± 2

Mg 279.6 <0.5 1 1.1 106 ± 2

Mn 257.6 1 5 1.1 99 ± 3

Mo 203.8 5 25 1.0 102 ± 2

Na^ 589.0 5 25 0.5 100 ± 1

Ni 341 .5 15 75 0.5 100 + 1

Pb 220.3 12 60 0.4 104 ± 1

Sn 190.0 12 60 1.2 105 ± 4

Ti 334.7 1 5 1.2 100 ± 1

V 309.3 1 5 1.1 99 ± 5

Y 417.8 1 5 1.0 100 ± 2

Zn 213.9 1 5 0.8 96 ± 2

"I This is the amount of material necessary to produce a signal that is two

times the standard deviation of the background noise. These data are

typical of 10 second integrations.

'^The Lowest Quantitative Determinable concentration (LQD) is five

times the detection limit.

This is a percent standard deviation for a 1 mg/1 mixed standard of all

elements run ten times with ten second integration periods. These

data are typical

.

^The system was standardized at 1 mg/1 and individual 100 mg/1 standards

were run and averaged over 8 hours to demonstrate linear range.

p Element not included in the NPDES study and subsequent acceptance because

it was added in the field one year after installation.

108
As part of this same study three approaches were made to evaluate the precision and

accuracy of the ICAP System. In the first approach, four common environmental water matrices

(distilled, lake, dirty river, and sewage effluent water) were spiked at two levels with

all metals listed in table 1. The eight samples were repeatedly analyzed for all elements

by both AA and ICAP methods for six weeks. The results showed no problems at the levels

chosen. These levels were 0.250 mg/1 to 50 mg/1 depending on element, and were chosen to

match the flame atomic absorption ideal concentration response. In the second approach

normal laboratory samples used for quality control were rerun and analyzed by the ICAP.

Twenty-two different effluent samples and duplicates which were spiked at low levels of

interest showed good agreement to flame atomic absorption. The third study involved a direct assessment of accuracy by the analysis of standard reference material supplied by

U.S. EPA (5 samples), U.S.G.S. (2 samples), and NBS (1 sample). A typical comparison of

the U.S.G.S., chosen here because it has the most elements certified, is given in table 2.

All three studies showed the ICAP System equivalent or better in the analysis of surface

and waste water than the reference method, flame atomic absorption. A detailed copy of

this study is available upon written request to the Region V Laboratory.

Table 2

USGS reference material 49 and 47

USGS^ yg/1 ICAP"^ yg/1 USGS^ pg/l ICAP^

Ag 6.4 ± 0.9 5. 7 Mg 18.3 ± 0.9^ 18 7

Al 71 ± 35 66. 4 Mn 159 ± 14 160 0

B 92 ± 29^ 113. 0 Mo 56.6 ± 4.6 62 5

Ba Ni 9.3 ± 6 k15 0

Ca 69.5 ± 2.5^ 65. 7 Pb 23 ± n 15 5

Cd 4.7 ± 1.4 6. 9 Sn

Co 5.1 ± 0.6 k4 T1

Cr 16.5 ± 6 19. 7 V

Cu 391 ± 24 379. 0 Zn 347 ± 28 346

Fe 87 ± 16 80. 0

^Reference Material 47 - cone, mg/1

^The USGS value represents the average and standard deviation of all laboratories

who participated in the Analytical Evaluation Program for Standard Reference

Water Samples 49 and 47 through May, 1975.

^All reference material run as a single blind experiment.

One problem which was noted shortly after the instrument was set up, was the existence

of stray light interferences. During the course of the development of the method described

above, these interferences were corrected by a variation of the Dynamic Background Correction scheme supplied by the vendor. The problem now has been further reduced by the

replacement of all standard Hamamatsu (R300) photomultiplier tubes used at wavelengths

below 240 nm with solar blind tubes (R427). The magnitude of the stray problem is easily

expressed in terms of the equivalent concentration, in mg/1 analyte, detected at each

analytical channel when 1000 mg/1 Ca is sprayed into the plasma. The magnitude of the

effect that is now observed while running the Ca test solution is less than 0.05 yg/l for

almost all elements listed in table 1. On the solar blind R427 channels where the stray

109
light problem has been shown to be severe, the maximum Ca effect is less than the detection

limit in all cases. For those elements which exhibit a stray light effect and do not

profit by the addition of a solar blind tube, significant improvements have been accom- plished elsewhere [2]. In Wohlers' work the spectrum is wavelength shifted during a determination and any wavelength independent shift in background (such stray light) is compensated

for by subtraction.

Six months after the original studies were completed the ICAP system was expanded by

adding Be, Na, and a monochromator to allow individual selection of different elements.

The Be and Na data are presented in table 1. Limited application to other elements using

the monochromator has produced detection limits and precision similar to the literature

[3]. In the near future the elements Li, K, Hg, As, Se and W are to be added as permanent

channel s.

3. Sample Preparation

With this analytical evaluation completed it was then possible to consider the method

of sample preparation as it impacted on sample throughput. The U.S. EPA defines by differing operations in sample preparation several types of metals in water. This discussion

will only consider total metals as defined in Section 4.1.3 of the Methods for Chemical

Analysis of Water and Wastes (1974). Under this definition of total it is necessary to

bring the acidified sample to dryness. This limitation defines the best method of high

volume sample preparation as being the block digestion approach. Two hundred samples can

be prepared by running batches of 40 samples with a metal block drilled to accept 40-200 ml

test tubes and thermally controlled to 8Q°C. With this method one person can prepare 200

samples per work day.

4. Large Volume Data Handling

The Region V Laboratory has available the following computer facilities in addition to

the dedicated PDP8 of the ICAP. The system includes: Data General Nova 840, 64 K Core,

Moving Head Disk, Fixed Head Disk and Magnetic Tape Storage. A file system was developed

that allowed the following sorts of information to be coded into the computer system:

1. Date and time of each sample run.

2. Unique Name for each sample.

3. Unique association of each element with each sample.

4. Unique definition of the sample source.

5. Class code for each sample (standard, spike, blank, reference sample, in-house

check sample, field .blank, field duplicate, house blank, house duplicate and the

like).

6. Special reference points for profiling exit slits.

With the above system we were able to run complex sets of samples, standards, blanks, and

quality control solutions and produce finished study reports of any type for any group of

samples in the files. Because every element in each sample is dimensioned, it is possible

to sort and compile a very large volume of data covering any desired time period.

The effects of these improvements are:

1. Saving of many man-years of effort.

2. Compilation of statistically significant data base from which real assessments of

quality can be judged.

3. Improved reliability in daily use.

All of the above have been achieved with the Nova 840 system.

no
References

[1] Ronan, R. J., Paper 361, 27th Pittsburgh Conference, 1976.

[2] Wohlers, C. C, to be presented at FACSS, 3rd National Meeting, November, 1976.

[3] Fassel , V. A., and Kniseley, R. N., Anal. Chem. , 46^, lllOA, 1974.

Ill

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

MULTIELEMENT ANALYSIS OF RIVER WATER

R. Schelenz

Federal Research Center for Nutrition

EngesserstraBe 20, D-7500 Karlsruhe

Federal Republic of Germany

1. Introduction

Standards for maximum permissible concentrations of some elements in drinking water

have been set by the Federal Republic of Germany at the end of 1974. For quality control

of surface and drinking water, the necessity for specific analytical methods which permit

multielement determination, even at very low concentrations, with good precision and

accuracy is evident.

Instrumental neutron activation analysis (INAA) combined with high resolution gammaray spectrometry with Ge(Li) semiconductors and computer evaluation of the recorded spectral data [1]^ is a promising technique for the simultaneous multielement determination in

water.

2. Experimental

A. Sampling

Water collection is performed with cleaned l£ polyethylene bottles with screw caps.

Prior to sampling these containers are rinsed several times with the water to be analyzed.

This procedure should prevent a possible contamination due to trace element from the inner

surface of the sample container. After rinsing the bottles they are filled with the

sampling water and allowed to stand for 10 minutes. This should adjust a sorption equilibrium of the trace elements of the collected water and the inner walls of the polyethylene

sample container. After pouring out the water the bottles are rinsed once more and then

the water to be analyzed is collected, frozen and stored at -18°C until the analysis can be

carried out.

B. Freeze-drying

Previous studies have indicated that a 1 day irradiation of 200 mg liquid water in

sealed quartz ampoules gave unsatisfactory results with respect to elemental detection

limits. A direct neutron irradiation of greater amounts of liquid water in sealed quartz

ampoules as proposed by Salbu et al [1] appeared too dangerous because of the high rate of

gaseous radiolysis products induced in the water due to the high thermal neutron flux of

the nuclear reactor FR 2 of the Nuclear Research Center of Karlsruhe. For technical reasons the irradiation of frozen samples as proposed by Brune [2] and Baudin [3] was not

possible.

^Figures in brackets indicate the literature references at the end of this paper.

113
In order to reduce statistical counting errors during gamma spectrometric measurement

of the radionuclides produced in the sample and to improve the detection limits of the

elements of interest, f reeze-drying has been utilized as a preconcentration step. This

technique has been used already by several workers for drying natural water [4-8]. In this

study the so called "spinf reezing" method according to Schmitz et dl [9] and Schneider [10] was applied.

After thawing and shaking the closed polyethylene bottles, 250 ml of the until tered

water are transferred to a precooled and siliconized glass flask. The si 1 iconization was found to prevent loss of trace elements due to sorption effect on the glass walls. To

shorten contact time of the liquid water sample with the glass walls of the flask, the

water is "spinfrozen" at -78°C. The principle of this technique is similar to that of a rotating evaporator. Care has to be taken to avoid losses of the dried material by electrostatic charging. This problem can be overcome by the installation of suitable filters and

by controlling the velocity of the sublimation process. A sieve of stainless steel with

pores of 30 pm diameter gave satisfactory results [10]. The water samples are dried for

about 24 hours to give approximately 120 mg dry matter corresponding to an enrichment

factor of nearly 2000.

Both short- and long-term neutron irradiation are used for the determination of 21 elements in the preconcentrated water samples. For long-time irradiation (flux: 1.5 x lO^^

ncm"^s~^, irradiation time: 1 d, cooling time: 7 d) to determine the elements Au, Ba, Br,

Ca, Co, Cd, Cr, Cs, Fe, Hg, La, Mo, Rb, Sb, Sc, Se, Th and Zn, 80--100 mg of the "dried

water" are weighed into specially manufactured high purity ampoules of synthetic quartz.

Possible elemental contamination of the surface of the quartz ampoules was removed by

etching (5 s) with aqueous hydrofluoric acid solution (1:1) at room temperature. Prior to

weighing-in of the samples, the ampoules are additionally cleaned by boiling them 30 min

with concentrated nitric acid. The samples are cooled to -35°C, heat sealed and irradiated

together with biological multielement standards such as NBS bovine liver (SRM 1577), NBS

orchard leaves (SRM 1571) and Bowen's kale powder.

Using purely instrumental techniques the sample is measured within the irradiation

container. Therefore the trace element impurities of the container have to be known. To

determine the amount of trace elements contributed by the irradiation container it was irradiated under the conditions given above for long-time activation. The content of 15

elements determined in the high-purity quartz are listed in table 1. Using these irradiation containers, no blank problem arises compared to the element concentrations found in

the preconcentrated water samples. For example, the influence of the Hg blank of the

quartz container [oa. 1.8 g) on a measured Hg value of 45 ng in the dry matter of 250 ml of

liquid water is approximately 0.1 ng or 0.24 percent and thus within the error resulting

from counting statistics.

Element concentration of cleaned synthetic quartz (HF etching, 5 s; HNO3 boiling, 30 min)

C. Irradiation and sample containers

Table 1

Element Content yg/kg Element Content yg/kg

Ba

Br

Co

Cr

Cs

Eu

Fe

30.0

0.09

0.2

0.7

< 0.001

< 0.01

48.0

Hg

La

Mo

Na

Sb

Sc

Se

Zn

0.06

0.13

5.9

75.0

0.01

0.01

0.2

1.9

114
For short-time irradiation (flux: 9 x lO^^ ncni"^s"^, irradiation time: 5-10 s, cooling

time: 20 min) to determine CI, K, Mn and Na, oa. 20 mg of dry matter are weighed into

specially manufactured polyethylene vials (available from Prof. Spronk, Free University of

Amsterdam, Netherlands). The elemental blank concentration of the plastic vials was determined under the conditions for the short-time irradiation. For manganese 2 ppb were found,

for sodium 30 ppb, and for chlorine 250 ppb. Potassium was not detected. The inherent

influence of the blank of the polyethylene vial is - as determined for the quartz ampoules

negligible compared to the element concentrations found in the dry matter of the water

samples. For example, the influence of the Mn blank of the polyethylene container [oa.

0.7 g) on a measured Mn value of 6.63 pg determined in the dry matter of 250 ml of liquid

water, is approximately 0.001 yg or 0.02 percent.

After a cooling period, due to the time required for transportation of the irradiated

samples to the laboratory using short-time activation and to reduce the prominent radioacti

vity of 2^Na using long-time irradiation, the activated samples are measured directly

within the irradiation containers after external cleaning with 6 N nitric acid to remove surface contamination.

D. ShieTding

The shape and height of the background may play an important role in determing the

detection limits of elements to be determined, especially when measuring low activities

Therefore a circular shielding for the semiconductor was designed and built. The

shielding materials (lead, iron, aluminum and plexiglass) are arranged with increasing

ordinal number around the detector [11]. The effect of this shielding on the composition

of the gamma spectrometric background is shown in figure 1. The upper spectrum indicates a measurement without shielding and the other spectrum a measurement with the shielding.

A considerable decrease in the pulse heights is obtained mainly in the low energy region.

without s> ielding

with stiieidtfig - ' . 1 1 .

500 woo 1500 tioV

Figure 1: Effect of the shielding on the measured gamma spectrometric background of a Ge(Li) semiconductor detector; time of measurement: constant.

E. Counting and data processing

The installed gamma spectrometry system consists of a 113.4 cm^ Ge(Li) semiconductor

(energy resolution: 2.0 kev at 1332 kev for ^°Co, peak to compton ratio: 43:1, relative

efficiency compared to a Na(Tl)J crystal: 18 percent) coupled with a 4096 multichannel

pulse height analyzer. With the aid of a computer (Hewlett-Packard, model 2100 A, 16 K

memory) and a program in "instrument basic", photopeaks are located and peak areas determined by the correlation technique [12]. Element concentration is calculated by comparing

the areas of interference free photopeaks both of sample and identically treated standard.

115
The detection limits are found to be 10"^^ to 10"^

g, depending on the element. The total

time required for analysis is 8 days; this includes irradiation, cooling, measurement and

data evaluation.

F. Test of the method

The accuracy and precision of this instrumental method has been tested by repeated

analyses of Bowen's kale powder, NBS orchard leaves and bovine liver [13]. Furthermore our laboratory participated in interlaboratory comparisons for multielement determination in

various biological materials, organized by the Analytical Quality Control Service of the

International Atomic Energy Agency (IAEA) [13-15].

3. Results and Discussion

As an example of our activities, the results of water analyses of the Neckar river,

where much industry is located, are discussed below. Between kilometers 136.5 and 175

(seen from the mouth, where the Neckar River flows into the Rhine River) 7 water samples were collected at different locations on the same day within 6 hours beginning upstream

(fig. 2). The element concentrations found for Cd, Cr, Hg, Se and Zn in the water samples

of this part of the Neckar river are given in table 2. It should be noted that the element

concentrations given refer to the weight of the liquid water samples. The actual concentrations found in the dry residue are nearly 500-times higher. This means, that no detection

problems arise in analyzing the trace element content of the "dry water". The average

deviation from the mean values given for a single determination is 10-15 percent.

Figure 2. Map of the Neckar-Enz-Rhine region •: locations of water sample collection.

116
Table 2

Content of some elements in the course of Neckar river water compared to

the standard for drinking water of the Federal Republic of Germany

km (to mouth)

Standard 136.5 Enz 137 142.5 150 172 175

Element (yg/1

)

(yg/1

)

Cd 6 <0.1 <0.1 2.4 <0.1 <0.1 <0.1 <0.1

Cr 50 9 5 6 5 5 5 3

Hg 4 0.3 0.1 0.2 0.3 0.2 0.4 0.4

Se 8 0.2 0.2 0.2 0.1 0.2 0.1 0.1

Zn 2000 41.0 56.0 33.0 29.0 18.0 45.0 28.0

The element contents determined are far below the maximum permissible concentrations

for these elements in drinking water as set by the Health Ministry (Bundesministerium fiir Jugend, Familie und Gesundheit) of the Federal Republic of Germany and below the corre- sponding recommendations of the World Health Organization (WHO). Furthermore these contents

are also below the recommended values of the European Community for surface water suitable

for preparing drinking water.

The summary of the results of the 21 elements determined in the river water are indicated in table 3. Element concentrations are given in yg/1 (equal to ppb by volume = parts per 10^). With the exception of the Cd content of the water at km 137, this element

could not be detected in the other water samples with statistical significance. Compared

to the values for the other elements at kilometer 137, shortly downstream of the mouth of

the Enz River (fig. 2), the composition of the element spectrum determined in the river

water has changed to a certain extent. At this location (km 136.5) significantly higher

levels of Ba, Cr, Fe, Th and Zn have been found whereas the concentrations of Ca, CI, La,

Mo and Na have decreased.

Table 3

Variation of element concentrations in the course of Neckar river

km to mouth

136.,5 136.8(Enz) 137 142.5 150 172 175

El ement Average concentration (pg/1)

Au 0..3 <lxl0"3 6xlC'3 9xl0"3 0.011 0.,010 6x10"3

Ba 109 142 69 36 31 41 40

Br 50 48 55 26 36 37 31

Caa 114,,2 63.5 189.6 79.0 73.4 117,,6 114.,2

Cia 28,,6 23.7 50.4 22.2 28.6 30.,5 28. 6

Co 0,,41 0.31 0.43 0.24 0.31 0.,27 0. 21 Cd <0.,1 <0.1 2.4 <0.1 <0.1 <0,,1 <0. 1 Cr 8.,7 4.5 5.9 5.2 4.9 4,,7 3. 1 Cs 0,.43 0.18 0.47 0.23 0.31 0.,58 0. 52

Fe^ 0.,28 0.1 0.11 0.07 0.07 0,,07 0. 12

Hg 0.,30 0.08 0.19 0.28 0.18 0,,35 0. 37

La 0.,19 0.16 0.48 0.08 0.11 0.,14 0. 05

Mn 42.,4 24.2 51 .6 26.5 28.4 30.,6 33. 5 Mo 1.,9 0.8 8.4 1 .4 3.2 2.,8 2. 7 Naa 24.,4 29.2 40.8 20.6 26.4 26.,1 24. 4

117
Table 3 (continued)

Rb 7.8 4.1 1.1 3 2 4.2 5.1 4.4

Sb 1 .6 20 1 .

3

0

"7 /I 74 1 .

1

1 .2 1 .

1

Sc 0.04 5x10-3 0.02 0 01 6x10-3 9x10-3 0.01

Se 0.24 0.24 0.22 0 13 0.20 0.12 0.10

Th 0.04 9x10-3 0.02 0 01 0.01 1x10-3 0.01

Zn 41 56 33 29 18 45 28

^mg/1

To illustrate these l^esults more clearly, the concentrations of some elements found at

different locations of the Neckar River are shown (fig. 3,4), are given in a logarithmic scale.

The element concentrations

137 142.5 150

km (to mouth)

172 175

250

37 142.5 150

km (to mouth)

172 175

Figure 3. Distribution of Cr, Mo and Sb Figure 4. Distribution of Fe, Mn and Zn

in the course of Neckar river water. in the course of Neckar river water.

An interesting correlation has been found for the Na and CI contents of the Neckar

River water (fig. 5). After a sharp increase between km 142.5 and 137, both the concentrations of Na and CI dropped downstream of the mouth of the Enz river at km 136.5. This

observation is in agreement with the relatively low concentrations found in Enz River water

of 29.2 pg/l for Na and 23.7 yg/1 for CI.

118
ppm

50

40

30

20

15

10-L . . "—'—

137 142.5 150 172 175

km (to mouth)

Figure 5. Correlation of Na and CI content in Neckar river water.

4. Conclusion

The data presented do not support the assumption that a pollution problem exists in

this part of the Neckar River. However, the sensitivity of the method may indicate possible

sources of pollution even if concentrations of heavy metals and other elements are below

the permissible level. Instrumental neutron activation analysis (INAA) for multielement

analysis of river water coupled with f reeze-drying of the collected water samples can be

applied as a routine method for environmental water monitoring.

Reference

[1] Salbu, B., Steinnes, E., Anal. Chem. 47, 1011-1016 (1975).

[2] Brune, D. , Landstrom, 0., Radioohem. Acta b_, 228 (1966).

[3] Baudin, G., Modem Trends in Activation Analysis, Proceedings 1976 International

Conference Vol. I, p. 94-110; (Sept. 13-17, 1976, Munic, F.R.G.).

[4] Grimanis, A. P., Pantazis, G., Papadopoulos, C, Tsanas, N., Third United Nations

International Conference on the Peaceful Use of Atomic Energy (1964).

[5] Schutz, D. P., Turekian, K. K. , Geochim. Cosmochim. Acta 29, 259 (1965).

[6] Merrit, W. F., Proceedings of International Conference on Identification and Measurement of Environmental Pollutants, 358 (1971).

[7] Schramel , P., Samsahl , K. , Int. J. Environ. Studies 37 (1973).

[8] Harrison, S. H., LaFleur, P. D., Zoller, W. H., Anal. Chem. 47, 1685-1688 (1975).

[9] Schmitz, J., Schneider, J., Vogg, H., "gwf'-wasser/abwasser 113, 318-324 (1972).

[10] Schneider, J., Z. Anal. Chem. 267, 270-273 (1973).

119
[11] Schelenz, R. , Diehl, J. F. , Aaouraay in Trace Analysis, 7th Materials Research Symposium Oct. 7-11, 1974, Natl. Bureau of Standards, Gaithersburg, MD, U.S.A.

[12] Black, W. W., Nucl. Instrum. Methods 1J_, 317-327 (1969).

[13] Schelenz, R., Fischer, E., Reports of the Federal Research Center for Nutrition,

Karlsruhe, F.R.G., Report 1976/4.

[14] Gorski, L., Heinonen, J., Suschny, 0., IAEA-Report RL/25, Jan. 1975.

[15] Gorski, L., Heinonen, J., Suschny, 0., IAEA-Report RL/28, July 1975.

120
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg , Md. (Issued November 1977).

MULTIELEMENT ANALYSIS IN RAINWATER

J. 6. van Raaphorst, J. Slanina, D. Borger, W. A. Lingerak

Energi eonderzoek Centrum Nederland

Petten, The Netherlands

1. Introduction

During the last three years the Energi eonderzoek Centrum Nederland (the Netherlands

Energy Research Foundation, former Dutch Reactor Centre) has been engaged in rainwater

analysis on a large scale for several purposes.

We are involved in a research program concerning the role of dry and wet deposition

in the Netherlands. The accuracy of sampling of rainwater is investigated by comparing

the results of some 15 rain gauges located at one spot. In the near future the variation

of the inorganic components in rainwater during rain squalls will be measured.

Some 10,000 rainwater samples were analyzed in an environmental control program of

the Dutch Government. The samples were taken on a daily and a monthly basis at 22 points

in Noord-Hol 1 and , a county comprising industrial areas in the northern part of our country.

2. Experimental

All rainwater samples are analyzed for inorganic bulk compounds such as nitrate,

sulfate, chloride, sodium, potassium, ammonium, calcium and iron, and for some trace

elements e.g. fluoride, zinc, copper, lead, cadmium and vanadium.

To suit all purposes our analytical methods must fulfill the following conditions:

1. The methods must be fast (we perform some 15,000 analyses a year).

2. The useful concentration range must be a factor of 100 at least, to cover

the differences between rainwater of industrial and rural areas.

3. Sometimes very small samples are available, so the methods are adopted

for samples of 0.5 ml

.

4. The accuracy must be typically a few percent.

The following methods are used: spectrophotometry (NO3, SOi^), potentiometry with ionselective electrodes (CI, F, NHi+), A.A.S. (Na, K, Ca , Fe and in some cases Zn and Pb), flameless

A.A.S. with a graphite furnace (Cd, Pb, Cu) and neutron activation analysis [e.g., V).

For 0.5 ml samples special spectrophotometric and potentiometric procedures were developed.

Sulfate is measured nephelometrical ly as barium sulfate according to the well known

standard method.

Nitrate is determined by a spectrophotometric measurement at 210 nm. The sample is

pumped through a special filter (consisting of active carbon on a carrier) which removes completely aromatic organic compounds. These compounds interfere as most of them have an absorbance as high as nitrate at 210 nm.

When sufficient sample (4 ml) is available, it is mixed with 5 ml of 0.2 molar

HCIO1+, pumped through the filter and the absorbance of the last 2 ml is measured. For

0.5 ml samples an adaption of Rucicka's flow-injection analysis has been developed: a

121
stream of 5 ml per minute of demi neral i zed water and of 5 ml per minute of 0.2 molar perchloric acid are mixed, the mixture flows through the active carbon filter. The sample is

injected in the water stream and the absorbance of nitrate is measured in a flow-through

cell. Peak height or peak area is measured.

Fluoride, chloride and ammonium are determined by means of ionselective electrodes.

The fluoride and chloride electrodes are quite sensitive to variation of the ion activity

of the samples and the presence of complexing agents. These interferences are minimized

by the use of a standard addition method. The response of these electrodes can be very

slow. Therefore an automated instrument has been developed which is comprised of an amplifier, a differentiator, a timer and a printer. The differentiator will inhibit a printout if

the drift of the electrode exceeds a preset level. A vessel has been developed in which

the bottom is formed by the surface of the electrode in upside down position. The solution

is homogenized by a magnetic stirrer which turns on the surface of the electrode.

The ammonium selective electrode is much less sensitive to variation of the ion

activity in the samples so the procedure of standard addition can be avoided. Electronically the signal of the electrode is converted to its anti 1 ogari thm to obtain a direct readout

in concentration units. Samples of 0.5 ml can be measured in a special vessel.

The concentration of sodium, potassium, calcium, iron and, in most cases, zinc in

rainwater are so high that measurement by A.A.S. is simple and straight forward. Iron is

often present in a chemically inert form, and a digestion with concentrated nitric acid in

a Teflon bomb at a temperature of 160°C is necessary to obtain total dissolution.

We use a dual beam-dual channel spectrometer (Jarrel-Ash) so either two metals can be

measured simultaneously or two calibration ranges are available.

Whenever sample size or concentration is a problem, a Perkin Elmer HGA 74 graphite

furnace is used. Rainwater is an excellent matrix for flameless A.A.S if the sodium content

of the samples is kept more or less on the same level. Sodium seems to diminish the signal

of some metals, especially cadmium, perhaps by changing the pattern of vaporization.

Precautions are taken by adding enough sodium to all samples. No background corrections

are necessary.

We have equipped our Jarrel -Ash-HGA 74 combination with a ASI sample changer, a fast

integrator (based on a voltage to frequency converter) and a printer for each optical

channel so two metals can be measured simultaneously. This set up may be used to perform

up to 30 determinations per hour.

A minicomputer (based on a 12 K L.5.I.) is being introduced in our laboratory for

control, measurement and calculations. This instrument can read up to 5 DVM's, check the

status of the controlled apparatuses on 16 points, count pulses and control by means of 16

relay outputs. The determinations of sulfate, nitrate, chloride and fluoride will be the

first to be automated by the use of this instrument.

3. Results

Typical values obtained in our laboratory are shown in table 1.

122
Table 1

Some results of the determination of SO4, NO 3,

5 ml samples

Ion Determined

(nephelometry)

actual value

(ppm)

4

10

20

50

observed value

(ppm)

4

9.8

19.8

51 .5

CI", F" and NHt

0.5 ml samples

actual value

(ppm)

5

10

25

50

observed value

(ppm)

4.7

9.5

24.5

49.7

NO3

(spectrophotometry)

1.5

4.2

15.3

32.0

1.6

4.3

15.1

32.2

2

7.5

20

30

1.8

7.6

20.2

30.2

Chloride 5

10

20

50

5.5

10.5

20.7

51 .5

2

5

10

20

1 .9

5.1

9.8

20.4

Fl uori de 25'

50

100

500

26'

51

101

502

25'

50

100

250

28

46

98

247

Ammonium 0.2

2

10

20

0.2

1 .8

9.4

20

0.2

2

10

20

0.2

2.0

10.2

20.3

Values for fluoride are in ppb

123

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

QUANTITATIVE MULTI-ELEMENT ANALYSIS OF ENVIRONMENTAL SAMPLES BY

X-RAY FLUORESCENCE SPECTROMETRY

P. A. Pella, K. Lorber, and K. F. J. Heinrich

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

X-Ray fluorescence spectrometry is an analytical technique currently being used to measure the trace element concentrations of many elements in environmental samples such as particulate matter collected from urban aerosols and suspended matter in polluted water.

Non-destructive analysis of ambient air aerosols requires collection of the aerosol on a suitable substrate, usually by impactor-type devices. The recent development of the

dichotomous sampler [1]^ permits collection of particulate matter and separation into a 0

to 2 ym range (fine particles) and >2 to 10 ym range (coarse particles). Collection of

these particles on thin membrane filters, which have a low trace element blank, provides

samples, which are well suited for rapid x-ray fluorescence analysis, for elements with

Z > 13 and sufficiently sensitive for monitoring applications [2]. Quantitation is

usually achieved by comparision of the x-ray emission intensities of the elements of

interest with those from thin calibration standards. That is, the specimen is so thin

that it becomes essentially transparent to the incident and fluorescent radiation. Thin

specimens are also ideal for x-ray analysis because absorption effects are usually negligible for many elemental analyses. The mass thickness of samples considered to be sufficiently transparent is typically a few hundred micrograms per square centimeter. For

such samples the concentration of an element is considered to be directly proportional to

the x-ray fluorescence intensity of the element. For elements of atomic number < 21,

however, particle size effects (mainly absorption effects) must be considered and the

appropriate corrections made. Corrections are also necessary in many cases for x-ray

absorption by the substrate when particles penetrate the substrate surface appreciably.

2. Experimental

Samples of material suspended in water can be collected on thin membrane filters by

filtration and subsequently analyzed. Analysis of dissolved trace metals, on the other

hand, does require the use of preconcentration techniques. A number of enrichment procedures have been proposed; probably the most attractive of these are the use of chelating

ion-exchange resin loaded filter papers. These include Chelex-100 (iminoacetate) and SA-2

Amberlite IR-120 which contain sulfonic acid functional groups. Some very recent work [3]

suggests that heavy metal ions can be retained (greater than 95%) from seawater samples if

calcium and magnesium ions are first removed by ion-exchange chromatography. The capacity

of these filter papers are also sufficiently high to permit collection of ions at concentrations up to 1000 ppm.

^Figures in brackets indicate the literature references at the end of this paper.

125
In the x-ray spectronietri c analysis of particulate matter, variations in particle

size composition and size can lead to systematic errors in the results if these effects

are not properly compensated. Particle size effects on the measurement result can be

eliminated by employing destructive techniques such as fusion with borax or lithium tetraborate. Fusion techniques have been used for many years for sample preparation especially

in the analysis of geological samples. Under proper conditions the samples can be fused

to form a homogeneous solid solution. There are basically three ways to prepare fused

samples for x-ray analysis. They are (a) fusing and casting, where a separate casting

operation is performed to produce a disk suitable for analysis, (b) fusion and grinding;

following solidification the fused sample is ground and pelleted, and (c) fusion and

direct solidification where the melt solidifies directly in the crucible to produce a disk

for direct x-ray analysis. With the development of the Pt-Au alloy crucible within the

past few years it has been possible to prepare fused glass disks by direct solidification

with a high degree of success. This method is currently in use in our laboratories for

the quantitative analysis of a number of different kinds of samples including the environmental samples urban dust, river sediment, and fly ash. Sample sizes typically range from

0.2 to 1.0 grams and are fused with 6.0 grams of lithium tetraborate. In the application

of fusion techniques the following variables must be considered; (a) sample type {e.g.

refractories), (b) particle size of samples, (c) fusing agent (flux), (d) sample-toflux ratio, (e) fusion temperature, and (f) fusion period. With the automated fusion

device in use in our laboratories, fusion period and temperature can be controlled.

Temperatures from 1000 to 1100°C can be attained using natural gas-air mixtures and from

1100 to 1200°C using propane-air mixtures. If necessary, the sample is first ground to at

least 200 mesh before fusing to provide optimum mixing and to minimize the fusion time.

In table 1 are listed fusion periods for fusing some typical sample types.

Table 1

Low heat cycle

{550-600°C)

Melt and fuse cycle

(1100°C)

Mix and fuse cycle

(1100°C)

Ambient cool

Air cool

Automatic Fusion

Typical sample types

Time in minutes

Cement

3-4

4

3-4

3

3

Sediments

3-4

6-8 (typ)

8 (max)

3

3

Al umina

Quartzite

(Refractories

)

3-4

12 (max)

8 (min)

3

3

TOTAL 16 23 29

Cements and dolomitic limestones represent typical easily fused non-refractory samples,

and calcined alumina and quartzite represent the more difficult to fuse refractory samples.

Samples containing chromium concentrations above 10% by weight are often difficult if not

impossible to fuse in lithium tetraborate but can be fused with lithium metaborate as the

flux agent. The low heat cycle at about 550°C expels the low temperature volatiles such

as carbon dioxide, then 2-3 minutes are required to melt the flux and start the dissolution

of the sample. Four minutes is usually satisfactory for the more easily fused samples but

the time can be extended to 12 minutes for the more' refractory type samples. Mixing at

the fusion temperature requires 3-4 minutes to a maximum of 8 minutes. Longer times can

be employed, however, during this cycle with an external timer. At the end of the fusion

cycle the crucible is allowed to cool at room temperature for three minutes. Compressed

126
air then enters the burner to promote rapid cooling. The solidified disk is removed and

ground on a 220 mesh abrasive and then polished with a fine grade of paper abrasive [e.g.

400 grit). Although the Pt-Au alloy crucible is essentially non-wetting, there is some wetting which is obvious as a concave meniscus on the solid disk. The amount of wetting

varies with sample composition and experience in other laboratories has shown that sticking

can become so severe that samples such as copper ores cannot be removed from the crucible

without cracking the disk. Some investigators [4] have added halides, notably bromides to

reduce the sticking substantially. With the addition of 2 drops of hydrobromic acid the concave meniscus is eliminated and the disk released easily from the crucible. Our results

have shown that an appreciable amount of HBr is retained in the disk and can interfere in

the analysis. We have found that after careful preparation of the inside surface of the

crucible by first polishing with metal polish followed by cleaning in 1:1 hydrochloric

acid the disk could be removed without cracking. This procedure was used for a number of

different types of samples including cements, urban dust, river sediments and minerals

successfully and minimized the need for wetting agents. Wetting may still present a problem, however, for some types of samples.

3. Results

When thick specimens are analyzed, the measured x-ray fluorescence intensities are influenced by the elemental composition of the sample. That is, the intensity of emission,

Ig, of one element, a, depends upon the concentration of all the elements present:

I3 = f(Ca, Cb, Cc, ...) (1)

A number of matrix correction procedures have been devised which require the use of samples

of known composition. In the empirical approach, one obtains interaction or influence

coefficients from the standard samples which are then used to calculate the corrected

concentration of each element in the unknown sample. Since disks can be prepared from

samples of known composition and/or synthesized with reagent compounds, the coefficients

can be easily determined. Another method often used to compensate for interelement effects

requires the addition of a "heavy absorber" [e.g. LazOs, or WO3) to both the analyte and

the standard. This technique has been used especially in the analysis of mineral samples

for elements from aluminum to iron. Because the heavy absorber attenuates the x-rays to a much greater degree than the elements excited in the sample, it is very effective in

minimizing the interelement effect. We have used this technique in the analysis of urban

dust samples and NBS-SRM 1633 Fly Ash. The analyses of the fly ash sample are in good

agreement with the NBS certificate values and those from other workers.

References

[1] Goulding, F. S., Jaklevic, J. M. , and Dzubay, T. G., EPA-650/4-74-0S0 , July, 1974.

[2] Hammerle, R. H. , Marsh, R. H. , Rengan, K. , Giauque, R. D. , and Jaklevic, J. M.

,

Anal. Chem. 45_, 1939 (1973).

[3] Kingston, H. M. , private communication.

[4] Matocha, C. K. , Halide Additions to Fusions in Platinum-Gold Crucibles to Control

Wetting, Analytical Chemistry Division, Alcoa Laboratories, Alcoa Center, Pa. 15069.

127

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

MULTIELEMENT ANALYSIS OF AIR AND WATER POLLUTANTS IN GOLD MINES

BY THERMAL AND EPITHERMAL NEUTRON ACTIVATION

C. S. Erasmus, J. Sargeant, J. P. F. Sellschop and J. I. W. Watterson

Nuclear Physics Research Unit

University of the Witwatersrand

Johannesburg, 2001, South Africa

1. Introduction

A multielement procedure for the determination of potentially harmful constituents in

air and water samples, taken from underground working areas and slimes dam sediments (from

the surface surroundings associated with the gold mining industry), is presented. The

method utilizes thermal and epicadmium instrumental neutron activation analysis based on Ge(Li) gamma-ray spectrometry and computer evaluation of recorded data, which allows up to

40 elements to be determined without any chemical treatment or extensive sample manipulation.

Industrialized countries are becoming more aware of the implications that result from

pollution of both working areas and the surrounding environment. The control of air and

water samples is of importance both to the mining industry and to those responsible for

natural fresh water resources in South Africa. The excess water pumped from gold mines can become an important source of water in densely populated and heavily industrialized areas,

where surface contamination and transmission of pollutants should be avoided and monitored.

This implies that the long term effects of harmful elements and the mechanism of their

transmission warrants investigation.

The study of trace elements in atmospheric aerosols and water samples has become a field of great emphasis in recent years. Instrumental neutron activation analysis (INAA) is

attractive for this type of study because of its high sensitivity for the simultaneous

determination of a great number of elements in environmental samples. Several reports

concerning a small number of elements have been published both for aerosols [1]^ and water

studies [2,3]. Tanner, et at. [4] stressed that the relatively high concentration of sodium

present in underground waters interferes with the INAA of many elements in such water samples.

The advantages of f reeze-drying water samples as a preconcentration step have been suggested

by Schmitz, et at. [5], while the efficiency of lyophyl ization has been investigated by

Harrison [6]. In a recent paper, Salbu, Steinnes and Pappas [7] have shown that up to 40

elements may be determined in natural fresh water by INAA.

This work demonstrates that quantitative determination, of 19 elements present in

aerosols and water from underground working areas and slimes dam sediments from surface

mining surroundings, can be performed using thermal and epithermal instrumental neutron

activation (the latter to overcome problems with high sodium content) and subsequent gamma

spectrometry with high resolution Ge(Li) detectors.

2. Experimental

Samples . The air in underground working areas of a gold mine was sampled by electrostatic precipitation onto Whatman 541 filter paper discs. Approximately 7 m^ air was sampled

at positions corresponding to the face-level of a miner during his working day. Depending

on the miner's working environment, from 1.4 mg to 3.4 mg of solid materials were collected

per aerosol. The quartz component of these samples (determined by x-ray fluorescence)

ranged from 0.08 to 0.6 mg of the total sample.

Figures in brackets indicate the literature references at the end of this paper.

129
Underground water was sampled from a gold mine situated on the Witwatersrand and 250 ml

aliquots were cautiously evaporated to dryness in new Teflon beakers. Approximately 0.7 g of dissolved solids crystallized on the bottom of each beaker and were pulverized and homogenized using an agate mortar and pestle.

Slimes dam sediments were sampled at different depths (30 cm, 60 cm, and 90 cm) of a dam still being used. Each sediment sample was pulverized and thoroughly mixed before

aliquots were removed for analysis.

A well analyzed granitic rock reference sample and dilute solutions of certain elements

{e.g.. Uranium) were included as calibration standards.

Sample preparation and irradiation . All irradiations were carried out in the ORR-type

reactor of the South African Atomic Energy Board (Pelindaba). For elements giving nuclides

with half-lives <3 hours (see e.g., table 1) the aerosols and 100 mg of the solid samples

(dissolved solids obtained from the underground water and slimes dam sediment) were sealed

in high purity polyethylene containers and irradiated for 3 minutes in the pneumatic tube

facility at a neutron flux of 3 x lO^^n cm^ s^. The remaining elements (in table 1) were determined by thermal and epithermal methods of activation. In order to compare the two

methods half of each aerosol sample and duplicates of approximately 200 mg of the solid

samples were sealed in quartz ampules. One set was sealed in aluminum cans and irradiated

for one hour in the hydraulic facility at 9 x 10^^ n cm^ s^. For epithermal activation, the

other set was incapsulated in cadmium cans of 1.5 mm wall thickness and irradiated in an epithermal flux of 1 x 10^^ n ^-i syp^bol for 20 hours.

Gamma-ray spectrometry . The activated samples were counted on 60 cm^ Ge(Li) detectors

having resolutions of 2.4 keV and 1.9 keV for the 1332 keV and 1170 keV peak of cobalt-60

and relative efficiencies of 9.5 and 10 percent. The detectors were coupled to 4000 channel

pulse-height analyzers calibrated at 1 keV per channel. Samples and calibration standards were counted at varying distances from the detector so as to optimize the compromise of

maximum precision due to counting statistics and minimum correction for dead time in the

analyzer. Dead time corrections were performed by means of a pulse generator as described

by Anders [8]. The spectra accumulated were transferred to magnetic tape for subsequent

analysis using a modified version of the Hevesy program [9]. All spectral data were nor- malized to a counting distance of 10 cm for comparative purposes.

3. Results and Discussion

Quantitative results for 19 elements determined in aerosols and water samples from

underground working areas and slimes dam sediments are reported in table 2. These results

show that high uranium contents were found in the aerosol, and particularly in the underground water and slimes dam samples. Arsenic is present in both the aerosol and sediment

samples, but before one establishes whether arsenic is present as arsenopyrite or another

(more harmful) form, no inferences should be made.

It should also be emphasized that corrections for reagent blanks (filter paper and

sample vials) were applied.

Figure 1 shows three spectra taken shortly after the 3 minute irradiation for each of

the three sample types. The peaks representing the analytical photopeaks indicated in table

1 are labeled.

In order to compare thermal with epicadmium activation, two spectra of the same sample

irradiated by these two methods and recorded at approximately the same decay time are shown

in figure 2. Elements that are better determined by that method of activation are indicated.

4. Conclusions

In the present study instrumental neutron activation analysis, using epithermal irradiation, is a very useful technique for the simultaneous determination of a great number of

elements in aerosol and water samples, from underground mining areas and samples of the

surface environs of mines.

130
Epithermal activation is shown to enhance the detection sensitivities of many elements

such as Mn, Fe, Co, Ni, Ga, As, Br, Sr, Mo, Sb, Ba, La, Sm, Tb, Ta, W, Au, Th, and U, relative

to those elements {e.g.. Ha, Sc, Cr, and Eu) mainly activated by thermal neutrons. In particular sodium and scandium, which often interfere with the thermal activation analysis

of other less sensitive elements, are subdued in epithermal activation, which allows a greater number of elements to be determined. This aspect is particularly important in the

analysis of materials with a high sodium content such as most natural waters and terrestrial

rocks from which dust (collected on aerosols) originates. It may therefore be suggested

that epithermal activation analysis become the preferred technique for air and water studies

of the environment.

Table 1

The elements found in underground air and water samples and slimes dam

sediments from gold mines.

Target Product Radio- Photopeak Underground Underground Slimes

element isotope nuclide measured air water dam

half-life E (keV) samples samples sediments

Na 2 4m-. ^^Na 1 b, U h

1 ooc

\ 6oo Q Q Q

rig ^ 'Mg n AC m 1 Ul 4

n

r nr

n

r A

1

28m m

1 "7"7n

1 / /y Y n

V

n

V n 38n m 1 O^L id 10/ n

r

nr

n

r K i ^. b h Q V Q

Ca ^^Ca 8.8 m 3080 p

n

P

n

Sc ^°Sc 83. 9 d on n 889 P n

Q Q

Cr ^^Cr 27.

8

d

o o n 320 pM

N Q

1 1 5 It-; D. /y m

o o n n

V IN n

V y 52y 7fi m111 I H OH pr N rP Mn 2.56 h 847,1811 Q Q Q

Fe 59Fe 45.

1

d 1099,1292 Q Q Q

Co 60Co 5.27 y 1173,1333 Q Q Q

Ni 58C0 71.3 d 810 Q Q Q

Cu 66CU 5.1 m 1039 P P P Zn 6 5zn 245.0 d 1115 N N N As 76AS 26.3 h 559,657 Q Q Q

Br 82Br 35.9 h 111 P P P Rb 86Rb 18.7 d 1077 Q Q Q

Ag 1 1 OmAg 253.0 d 1384 P N P Sb 12^Sb 60.9 d 1691 P Q Q

Cs is'+cs 2.07 y 796 N N P Ba i3iBa 11.3 d 496 P Q Q La i^OLa 40.3 h 1595 P Q Q

Sm 47.1 h 103 P P P Eu 12.2 y 1408 P Q Q

Tb 160jb 72.1 d 879 Q Q Q

Dy 16 50y 2.36 h 95,280 N N P Hf IBlHf 42.1 d 482 N Q N Ta 182Ta 115.1 d 1222 Q N Q

W 187W 1.0 d 686 p N P Au 19 8AU 2.7 d 412 p N P Th 233pa 27.0 d 300,312 Q Q Q

U 239fjp 2.35 d 228,278 Q Q Q

Q = quantitative value

P = presence established

N = not detected

s = seconds, m = minutes, h = hours, d = days, y = years

131
Table 2

The average results obtained by instrumental neutron activation analysis

of aerosol, water and slimes dam sediment samples.

Element a Aerosols Waters Sediments

ppm E% ppm E% ppm E%

Na 1.12% 0.8 40 0.4 0.14% 1.1

K 1.% 11 P 17 1.6 % 2.9

Sc 10 2 0.007 10 10.7 0.9

Cr P 30 N 258 0.5

Mn 745 0.3 13.3 1.0 57 0.6

Fe 7.0 % 10 11 20 2.0 % 1

Co 59 5 3.5 0.2 20 1.2

Ni 77 13 12 0.4 80 3.5

As 1.1 1 0.002 3.5 12 0.5

Rb 110 30 N 65 3.3

Sb P 5 0.001 10 1.7 1 .6

Ba 21 26 1.2 7.7 190 5

La P 1.3 0.38 2.7 27 1 .2

Eu P 25 0.02 10 0.7 4.4

Tb 6 15 0.011 2.4 0.5 6.8

Hf N N 6.8 2.3

Ta 3.7 20 N 2.0 1.7

Au (0.7) 1.7 N (0.23) 1 .8

Th 14 15 0.012 2.5 6.4 4

U 15 0.6 1.6 1.2 12 1

Results are in parts per million (ppm) unless otherwise indicated

E% = counting error

P = present but not determined

( )= estimate

N = not detected

132
0 1000 2000 3000 4000

ENERGY (keV)

Fig. 1 Spectra taken soon after 3 minute irradiation

133
10 —I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I

0 500 1000 1500 2000

ENERGY (keV)

Fig. 2(a) Conparison of spectra obtained foi' duplicate samples after

thermal and epithemal irradiation

134
10 —'—I—I—I—I

1—I—I—I—I \—I—I—I 1—I—I—I—I—I

0 500 1000 1500 2000

ENERGY (keV)

Fig. 2 (b) Conparison of spectra obtained for duplicate sanples after

thermal and epithennal irradiation

135
References

[1] Janssens, M., Desmet, B., Dams, R., and Hoste, J., J. Radioanal. Chem., 26, 305-315

(1975).

[2] Slavic, J., Draskovic, R., Tasovac, T., and Radosavl jevic, R., Isotopenpvaxis, 9^, 87

(1973).

[3] Schneider, J., and Geisler, R., Fvesenius' Z. Anal. Chem., 267, 270 (1973).

[4] Tanner, T. M., Rancitelli, L. A., and Haller, W. A., Water, Air, Soil Pollut., 1_, 132

(1972).

[5] Schmitz, J., Schneider, J. and Vogg, H., Gas-Wasserfaoh/Abwasser, 113 , 318 (1972).

[6] Harrison, S. H., LaFleur, P. D., and Zoller, W. H., Anal. Chem., 47, 1685-1688 (1975).

[7] Salbu, B., Steinnes, E., and Pappas, A. C, Anal. Chem., 47, 1011-1015 (1975).

[8] Anders, 0. U., Nual. Instrwn. Methods, 68, 205 (1969).

[9] Yule, H. P., U.S. NBS Spec. Publ. 312, 2, 115 (1968).

[10] Steinnes, E., Activation Analysis in Geoahemistry and Cosmochemistry, Uni versi tetsforlaget, Norway, 113-128 (1971).

136
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

A MULTIELEMENT - DIRECT READING METHOD FOR THE SPECTRAL ANALYSIS OF SEDIMENT LEACHATES

M. M. Moselhy, D. W. Boomer, J. N. Bishop and P. L. Diosady

Inorganic Trace Contaminants Section

Laboratory Services Branch

Ministry of the Environment

Ontario, Canada

1. Introduction

Recent developments in Environmental Chemistry and increased interest in the effects of

heavy metals on our environment have emphasized the need for mul tielemental analysis of

various types of environmental materials. One such material, lake and river sediment, has

been difficult to analyze for trace elements due to the complexity of the material, but it

remains a very important environmental sample. Sediment represents the interface between

the earth and the water, and contains not just the elements released by erosion, decay, and

other natural processes, but also contains traces of metals released by man's activities.

However, this mixture of silicates, metal hydroxides, carbonates, and organic matter, is

extremely difficult to analyze for trace contaminants.

The application of AAS [1]^ and colorimetry [2] to the analysis of leachate analysis

suffers the disadvantages associated with techniques capable of single element analysis.

The main problems are the length of time required to sequentially analyze for many elements,

and the attendant risk of losses or increases of some elements while the analyte solutions

are held. However, the application of the atomic emission spectroscopy technique to multielemental analysis of sediment leachates has been limited due to the variability of sample

composition, complexity of spectra and possible spectral, interelement and matrix interferences [4,5,6].

This report examines the application of the rotating graphite disc-high voltage spark

technique as a means for the introduction of liquid samples into the discharge zone and the

excitation of their characteristic spectra. Selection and optimization of the excitation

source and associated parameters have been detailed in a previous report [3].

2. Experimental

A 3.4 m Ebert type convertible spectrograph spectrometer was used in its direct reading

mode of operation. The high voltage condensed spark obtained from a mul ti -mode vari source

was used for spectral excitation. Control of spectrometer-source operations and monitoring

of spectral line intensities on various analytical channels was performed by a computerized

spectro-chemical controller. In this work a Jarrell-Ash rotating electrode attachment was used to support and to uniformly drive a rotating graphite disc partially immersed in the

analytical solution.

One of the channels (si it-photomultiplier-spectro-chemical controller circuit boards) was dedicated to monitoring of the 3650. 15A Hg line. Exact profiling of this line was used

to bring the other channels to profile.

Figures in brackets indicate the literature references at the end of this paper.

137
3. Optimum Operating Conditions

Source: High Voltage condensed spark.

Resistance R: 1 ohm,

Inductance 1 : 40 pH

Capacitance C: 0.005 yH

Current i: 6.25 amps; 6 breaks per half cycle

Entrance Slit: 20 y width, 4 mm height, one lens illumination

Graphite Electrodes: Counter: National AGKSP-L-3955 , 4 mm round tipped, double ended

Disc: National AGKSP-L-4075 3 mm thick, 12 1/2 mm diameter

Exposure Time: 15 sec. preburn, 15 sec. exposure

Spectral line intensity measurements: computer controlled dedicated photomultipl ier tubes

(direct reading mode).

Input-output terminal: an AsR-33 teletype was used to access the computer memory and

print out results.

Selection of the optimal excitation conditions was made by applying a sequential simplex

technique [3]. Optimization and stability of the system was confirmed by a moving plate

study.

4. Calibration of the System for Direct-Reading Operations

In a previous report [3] the rotating electrode solution technique was adopted for the

analysis of some types of environmental materials containing low concentrations of various

elements. The direct application of this method to routine spectral analysis of sediment

and sediment-like leachates has shown both spectral and interelement interferences (see

table 1). In addition a true matrix effect appeared which had a variable effect upon the

intensities of some analytical spectral lines. Routine analyses of sediments have also

shown that high concentrations of Fe, Ca, Si, Al , Mg, Mn, and for Zn are not uncommon in

these environmental materials. At such concentrations, these elements affect the overall

excitation potential and frequently cause partial overlap of spectral lines. Practice has

shown that introducing interelement corrections with the computer software provided is

adequate for subtraction of small interferences from a weak line of one element on a strong

line of the analyte element. However, this method of interference correction is not suitable

when the interfering line is relatively intense and the analytical line is near the detection

1 imit.

Table 1, Spectral and interelement interferences shown by direct

application of the rotating electrode solution technique to routine

spectral analysis of sediment and sediment-like leachates.

Zn Mn Cu Ni Cr Pb

Sample # AAS ES AAS ES AAS ES AAS ES AAS ES AAS ES

S44-27-1 gm 3. 0 3.1 1.4 1.,6 0.,47 0.6 0.,16 0,.3 0,.17 2,,1 0,,09 < .3

-0. 5 1. 64 1.5 0.7 0,.8 0,.27 0.8 0,.1 0,.6 0,.08 1,.4 0..05 < .3

28-1 3. 5 3.5 3.2 3.,8 1.,4 1.8 0..17 1

.

.1 0.,17 1

.

,7 0,.13 .3

-0. 5 2. 2 3.5 1.9 2,,3 0,,9 1.3 0,.11 1

.

,1 0.,11 1.,5 0,.12 < .3

29-1 4.,3 6.5 2.2 3,,1 1,.5 2.7 0,.22 <

,

.3 0,,23 2,,4 0..14 < .3

-0. 5 2. 4 3.3 1.1 1.,2 0,,8 1.3 0..12 0,.9 0,.14 1

,

.4 0,.09 < .3

30-1 7.,5 7.9 7.9 7,,0 0,.6 0.7 0,.34 0,.5 0,.52 2,.5 0,.37 < .3

-0. 5 3.,3 4.4 3.8 4,.2 0,.3 0.6 0,.22 0,.6 0,.25 2,.2 0..28 < .3

36-1 30 29.6 24 21,.4 3,,9 4.2 0,.47 < ,.3 0,.67 4,.3 0,.37 < .3

-0.,5 16,,6 19.9 11.5 13,.6 2,.1 2.5 0,.24 < ,.3 0,.35 2,.9 0,.22 .7

138
The application of methyl iso-butyl ketone (MIBK) extraction of the analyte solution

from 8N HCl did prove useful in removing the high Fe concentrations from the digested materials. However, this step introduced undesired effects caused by the presence of organic

materials. Consequently, the extraction step was eliminated and a method was developed for

the analysis of leachable heavy metals.

From the above considerations it was apparent that the addition of a spectroscopic

buffer reasonably provides an average excitation potential in the discharge plasma and

probably reduces the interferences caused by the possible presence of a matrix element.

From all the spectroscopic buffers normally used in matrix matching NaCl was selected for

two main reasons:

1) optimum concentrations of the low excitation potential sodium introduced into both

standard and sample solutions will balance the overall excitation potential.

2) The possible chemical reaction between the active chlorine atoms and those elements

which might produce refractory materials, could undergo a chemical reaction resulting

in the formation of volatile chlorides.

The effect of various concentrations of sodium chloride introduced into a multielement

standard solution was investigated by observing the levels and reproducibilities of the

analytical spectral line intensities. An optimal concentration of 10,000 ppm Na in solutions

was found to overcome most matrix problems.

Further to the use of spectroscopic buffer it was found that the addition of indium as an internal standard improved both the accuracy and precision. Two sets of calibration

standards solutions, which more closely approximate the concentrations found in digested

sediment samples, have been prepared. Tables 2a, b show the composition of these standards

in ppm. The selected spectral line wavelengths are shown in table 3.

Table 2a. The composition of two sets of calibration standards

solutions in ppm.

Std. #

Element 1 2 3 4 5 6 7

Al 4000 1420 2500 680 340 80 180

B 0 16 24 8 0 4 0.8 1.6

Ca 2400 4000 5600 800 400 8 80

Cd 0 16 0.8 12 1 6 4 8

Co 12 24 0 40 4 0.8 1.6

Cr 8 24 12 0 16 40 4

Cu 8 24 40 16 0 4 1.6

Mg 1600 1200 640 320 80 120 160

Mn 240 400 40 120 1 6 8 20

Ni 20 40 8 4 0 8 0 1.6

Pb 12 24 4 40 8 0 1.6

Sr 40 24 12 8 4 0 1.6

Ti 40 160 80 240 20 1 .6 8

Zn 40 24 12 8 0 8 0 4

139
Table 2b

Std. #

Element 1 2 3 4 5 6

Fe 5000 3000 1500 750 300 100

Pb 0 50 30 5 20 2

Mo 0 50 20 5 10 30

V 0 30 2 5 20 10

Ga 0 22.2 7.4 3.7 1.48 14.8

Table 3. Selected spectral line wavelengths

Element Wavelength A° Element Wavelength A° Element Wavelength A°

Al I 3092.71 Cr II 2677 18 Ni I 3414 77

As I 2349.84 Cu II 2247 0 Pb II 2203 53

B I 2496.78 Fe II 2599 49 Sr II 4077 71 Ba II 4554.03 Fe II 2714 41 Ti II 3349 04

Be II 3130.42 Ga I 4172 06 V I 4379 24

Ca II 3968.47 Mg II 2795 53 Zn I 2138 56

Background

Ca II 3179.33 Mg I 3832 31 BL 2105.5

Cd I 2288.02 Mn I 2576 10 BM 2969.9

Co I 3453.51 Mo II 2020 32 BH 3716.5

The design of the required computer program included the information necessary for full

computer control of both the standardization of the system and for analytical procedures.

Such instructions included:

1) times of preburn and exposure;

2) number and specifics of the required analytical channels:

3) background and internal standard channels;

4) intensity ratios required for standardization;

5) print-out format, priorities and concentration mode;

6) gains and offsets

Figures (1, 2, 3, 4) show the elements calibration curves shown as plots of average

intensity ratios vs concentrations in ppm.

140
Figure 1. Elements calibration curves shown as plots of average intensity ratios vs concentrations in ppm.

ppm

Figure 2. Elements calibration curves shown as plots of average intensity ratios ys concentrations in ppm.

141
J 1 1 l_ 0 4 8 12 16 20 24

C ppm

Figure 3. Elements calibration curves shown as plots of average intensity ratios vs concentrations in ppm.

0 1000 2000 3000 4000 5000

^ ppm

Figure 4. Elements calibration curves shown as plots of average intensity ratios vs concentrations in ppm.

142
The results obtained from several runs of the standards used in this calibration on various days have shown good agreement with the expected values. In general, the results

obtained on various types of real samples have shown good agreement with AAS standard analytical values. However, samples containing exceptionally high Fe, Mn, Al , As and/or Ca have

shown increased concentrations on certain analytical channels. This required an additional

step to correct for either spectral or partial interelement interferences.

The most logical approach was to run solutions of the interfering e'lements separately

at various concentration levels and to watch any possible response on the other elemental

channels. It was immediately apparent that high concentrations of Mn increased the intensity

of the chromium spectral line. Similarly, Fe affected the intensities of B, Cd, As and Cu,

Ca affected Pb, As affected Cd and Al affected Mo. Table 4 lists the interfering elements,

the affected element and its wavelength and the corresponding correction factors obtained

from R-C ppm curves.

Table 4. The interfering elements, the affect element and its

wavelength and the corresponding correction factors obtained

from R-C ppm curves

Affected Element

o Wavelength A Interfering Element Correction

Factor

Cr 2677.16 Mn 0.01460

B 2496.78 Fe 0.01110

Pb 2203.51 Al 0.00555

Cd 2288.02 Fe 0.0002

Cd 2288.02 As 0.070

As 2288.12 Fe 0.030

Mo 2020.3 Al 0.0020

Pb 2203.51 0.0002

Cu 2247.0 Fe 0.0070

With this information included in the program, the computer will start and end the

exposure, calculate the intensity ratios on different channels, multiply the concentrations

obtained on the interfering channels by the correction factor and subtract the additional

concentrations on the affected channels prior to data presentation.

143
5. Data Quality Control and Intercomparison Studies

Various points from the elements calibration curves were introduced to the program as a separate group of instructions. The day-to-day standardization compensated for possible

deviation from the optimized conditions by adjustment of the gains and offsets on all the

channels. However, it was found necessary to introduce the following steps for quality

control

:

1) A check of the spectral line intensity of the internal standard produced in each run.

2) The gains and offset values obtained after standardization should be close to one and

zero, respectively. Restandardization would then be repeated on the analytical channels

which show excessive deviation from the original values.

3) Calibration standard solutions were run after the standardization and during routine

sample analysis.

4) Runs of a blank and working sediment references in each set of samples.

5) Parallel AAS analysis of two samples per rack.

6) Each sample was to be done in two aliquots containing approximately 0.5 gm and 1.0 gm

of the sediment. This step, in addition to the back-up check, should provide a measurable

concentration range on various channels.

7) Occasional use of photographic plate recording to confirm direct-reading results.

8) To further confirm the stability of instrument performance the diagnostic computer

program can perform a white light test. The standard deviation obtained from 10 consecutive runs of the white light test gives an estimate of the performance of all analytical

channels.

9) Rotation of the refracting quartz plate installed behind the entrance slit to give a maximum response of Hg profiling channels in order to bring the analytical channels to

profile.

However, it was necessary to conduct some AAS-ES intercomparison studies on real samples

prior to routine operations. Both 0.5 gm and 1 gm aliquots of sediment material collected

from various locations around Ontario were digested in aqua regia and filtered. The filtrates

obtained were made up to volume (25 mis) by the addition of 5 mis of the indium-buffer

solution containing 250 ppm indium and 50,000 ppm sodium.

Tables 5a and 5b show intercomparison results obtained by atomic absorption spectrophotometry and atomic emission spectroscopy. The same samples were reanalyzed after spiking

with 100 ppm Al and Mg, 200 ppm Ca, 500 pm Fe and 2 ppm of the rest of the analytical train.

The percentage recoveries obtained on some elements are shown in table 6.

Table 5a. Intercomparison results obtained by atomic absorption

spectrophotometry and atomic emission spectroscopy.

Al Mg Ca Ti Co B Sample # AAS ES AAS ES AAS ES AAS ES AAS ES AAS ES

S38-19-1.0 730 925 570 613 2100 2254 1.4 2.1 1.1 <1 4.0

0.5 220 340 266 332 960 1065 0.7 1.6 0.7 <1 2.8

S39-10-1.0 44 <50 12. 1<50 <2 <1 4.7 3.5 2.2 2.1 27.5

0.5 17 <50 3. 8<50 <2 <n 2.3 1.6 1.3 <1 10.0

S40-163-1.0 50 <50 70 97 850 1002 5.5 4.7 0.50<1 <.5

0.5 24 <50 39 <50 440 537 3.9 3.7 0.46<1 <.5

S44-27-1.0 120 99 150 176 400 477 20.8 18.1 0.58<1 1.2

0.5 60 50 73 104 250 292 14.4 13.3 0.46<1 0.5

144
Table 5b

Pi 1 Ni Fe

Sample AAS ES AAS ES AAS ES AAS ES AAS ES AAS ES

5 ppm 4.7 5.5 4.1 3.3 4.4 5 0 5 1 3 4

1 5 ppm 1 'f . 0

1 1; /I

1 0 1 D 1 D ICQ 1 b . y

1 /I b

S38-19-1 6.8 7.7 18.1 16.4 5.2 6 0 5 5 5 5 9.2 8 7 1040 1068

-U . D 0. D J . 0

R0. J7 7 / . / 9 7 c0

00 (J

•5 /I 7 0 1 u 0/0

S39-10-1 1010 0.7 <2 240 0 9 1 2 0.2 <1 5090 5127

-U. b

/I QCl 0 4 yo 0. 6 <

rb U. 1 < 1 ?55R

S40-163-1 0.47 <.5 2.0 <2 0.2 0 2 0 4 0 3 0.2 <1 99 132

-0.5 0.26 <.5 1 .0 <2 0.1 < 3 0 35 0 35 0.1 <1 50 <50

S44-27-1 7.3 14.3 3.9 2.8 2.0 2 2 0. 59 0 7 0.5 <1 259 285

-0,5 5.2 6.4 2.0 <2 0.5 1 1 0. 45 0 5 0.26 <1 132 111

Table 6. Percentage recoveries obtained on some elements

after spiking with 100 ppm Al and Mg, 200 ppm Ca, 500

ppm Fe and 2 ppm of the rest of the analytical train.

% REC.

Sample # Fe Zn Ni Ti Al Mg Ca

S39-19-1 97 106 94 130 102 103

-0.5 104 115 119 87 112 129 108

S39-10-1 84 120 95 78 131 118

0.5 120 83 130 115

S40-163-1 104 112 125 90 100 116 99

-0.5 103 115 95 85 114 99

S44-27-1 94 100 109 91 112 111 103

0.5 96 104 108 95 99 116 101

AVERAGE % 100.3 108.7 112.5 95.8 98.3 121 105.8

145
Table 7 shows the average intercomparison results obtained by both AAS and ES analyses

of different digestions on different days. This set of data also provides some evidence of

the long term stability of both analysis and solutions.

Table 7. Average intercomparison results obtained by AAS and ES

analyses of different digestions on different days.

Ref. Ref. 7 Ref 11 Ref 13 Ref 14 Ref 15

Element AAS ES AAS ES AAS ES AAS ES AAS ES

Al 10.9 10.2 10 0 6 8 11 4 11. 3 9 4 10 5 Ca 23.8 23.5 25 8 23 4 274 0 348 6 4 6 5. 3 53 8 71 7 Cr 25.0 110.9 70 9 97 3 <25 16 3 <25 46 9 <25

Cu 23.4 19.2 25 3 38 3 6 6 38 3 9 8 10 66 7 82 5 Fe 25.4 18.7 24 0 15. 1 3 8 3 2 16 5 9 8 13 2 7 4

Mg 13.5 15.7 10 9 11 2 2 4 2 8 2 8 3 6 3 8

Mn 1065 911 571 324 185 128 440 374 333 247

Ni 41.4 47.7 66 54 155 4 9 8 40 5 25 6 82 6

Ti 8.4 2 1 4 0 18 7 15 8

Zn 64,0 64.9 133 2 129 5 12 0 28 5 39 6 37 7 185 210 9

The close similarity in composition of sewage sludges and sediment materials has

encouraged our laboratory to apply the internal standard-spectroscopic buffer approach to

the analysis of such materials.

Figures 5, 6 and 7 show the AAS-ES intercomparison results obtained on three different

digestions (Runs #1, 2 and 3). The data obtained in three days was then "pooled" on one

plot. The closeness to linearity is an indication of the long term stability and reproducibility of the two techniques.

146
o o o o o o o o o o

o o o o o o o o o o o o o o o o o

o in o tn o in

CM eg CM CVI

Figure 5. AAS-ES intercompari son results obtained on three different digestions.

147

Figure 7. AAS-ES intercomparison results obtained on three different digestions.

149
6, Conclusion

The method of spectroscopic buffer addition to both calibration standards and samples

provides an acceptable method for multi-elemental analysis of digested sediment and

sediment-like materials. The method is simple, relatively fast and provides the accuracy

necessary for routine "on-line" analysis of this type of environmental materials.

The authors would like to acknowledge the continuous encouragement of Mr. Gerard C,

Ronan, Director, Laboratory Services Branch.

References

[1] Theron, P. P., etal., J. S. Afr. Vet. Assoc., 44, 271, (1973).

[2] Boratynski, K. , et at., Pol. J. Soil Sei. , 6, 95, (1974).

[3] Moselhy, M. M, , Boomer, D. W., Bishop, J. N. Diosady, P. L., A paper presented at the

TARC International Symposium III, "Trace Analysis of Environmental Materials", Aug.

1976, Halifax, Nova Scotia, Canada.

[4] Cowgill, U. M., Appl. Speat., 28, 455 (1974).

[5] Scott, R. H., Kokot, N. 0., Anal, Chim. Acta, 75, 257, (1975).

[6] Scott, R. H., Kokot, N. 0., Anal. Chim. Acta, 76, 71 (1975).

150
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

HIGH EFFICIENCY SOLVENT EXTRACTION OF TRACE ELEMENTS

IN AQUEOUS MEDIA WITH HEXAFLUOROACETYLACETONE

Morteza Janghorbani ^ , Max El linger and Kurt Starke

Philipps University

Marburg/L., Fed. Rep. of Germany

1. Introduction

Widespread application of gas-liquid chromatography to analysis of trace elements in

aqueous media has been severely limited due to lack of suitable methods for converting a wide range of elements to volatile and thermally stable species. Of the converters tested,

the 6-di ketone family has shown the greatest promise [1]^. Furthermore, it has been

conclusively shown that fluorine substitution of the methyl protons enhances the volatility

of the resulting chelates, allowing column operation at reduced temperatures and greatly

enhanced sensitivities by use of electron capture detection. These advantages are, however,

said to be offset by the poor extractabi 1 ity of elements with hexaf luoroacetylacetone

(Hhfa) as compared to acetylacetone (Hacac). Unfortunately, in contrast to Hacac, no systematic study of solvent extraction of elements with Hhfa, and to a lesser extent, with

trif luoroacetylacetone (Htfa), has been reported [2]. In this communication, we present

data on comparative extraction of Sc^^ with Hacac, Htfa, and Hhfa obtained with a special

radiochemical solvent extraction device.

2. Instrumentation

A special solvent extraction device is reported in this -work based on gamma spectrometry with NaI{Tl) detection and multi-channel pulse-height analysis. This device allows:

(1) solvent extraction studies to be carried out at trace levels by use of high specificactivity tracers, (2) capability of simultaneous extraction studies of multi-element

solutions to the extent permitted by Nal(Tl) detection resolution, thus permitting studies

on synergi sti c/antagoni sti c effects of various elements to be carried outon a single

solution, (3) acquisition of the entire %E-pH curve on a single solution aliquot reducing

contamination problems and excessive use of reagents, (4) study of extraction-time behavior

at various pH values, and (5) experimentation on extraction reversibility to be conducted

easily.

The basic features of this simple device are shown in figure 1. It consists of a glass cylinder inside of which a Teflon plunger with side clearance of about 1 mm moves vertically by a motor and motion-converter mechanism. Two detectors in NaI{Tl), 2in x 2in, continuously monitor gamma radiation from the two phases and a combination electrode

measures pH of the aqueous phase. Suitable size lead shielding between the two detectors

reduces radiation cross talk (to less than 1% for 1.33 MeV radiation in the present design).

In this version of the device the two detector outputs are sequentially switched into a 1024 channel multi-channel analyzer. Thus, after any mixing period and attainment of

phase separation, the ratio of integrated counts in the photopeaks of interest between the

^Present Address: Environmental Trace Substances Research Center, Route 3, Columbia,

Missouri 65201

^Figures in brackets indicate the literature references at the end of this paper.

151
two detectors, corrected for an instrument factor, gives the needed %E data. Changing

solution pH is accomplished by addition of a small volume of acid or base as required.

Shaking time can be controlled from a few seconds on and the extent of mixing is adjusted

by controlling speed of plunger motion with the variable-motor employed.

I to motor

PreMCA amp

.

f- amp

.

5x5 Nal {T£)

T

20 Pb-shield

1

5x5 Nal (Til)

20

A

aqueous phase

to pH meter

pH electrode

38,

^Teflon plunger

16.25

.^0.1

—^organic phase

1

Fig.l-Solvent Extraction Device

all dimensions in cm

3. Extraction Data

Figure 2 shows comparative extraction kinetic data obtained for Sc3+ with the three

agents Hacac, Htfa, and Hhfa in chloroform. Note that these data were obtained with

solution buffered at pH 5.2. It appears that the extraction rate increases in the order

Hacac < Htfa < Hhfa. Although approximately two minutes are required for attaining

equilibrium for the Sc^"*" - Hacac system, 20 seconds is sufficient for Sc^"*" - Hhfa.

152
1.0

%E/%E

max

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

/ Htfa

, 'Hhfa ^

I /

/ Hacac

r hi

10 30 60 80 100 120 140

Mixing time, sec.

Fig . 2-Comparative extraction kinetics of Sc -3-diketone system

buffered at pH 5.2

Comparative extraction -pH curves for Sc^"*" and the chelating agents are shown in

figure 3 based on long (a few minutes) mixing time. From these data it appears that

extraction efficiencies of better than 90% are obtained for all the three systems. The

efficiency for Sc^"*" - Hhfa decreases drastically in neutral to basic media, most probably

due to hydroxocomplexation. This may also be the case for the other two systems at higher

pH values. An important observation to be made from these data is the apparent discrepancy

in the direction of the shift in pHh values in the series. In the absence of complicating

reactions, the Sc3+ - Hhfa curve should lie to the left of that for Sc3+ - Htfa. The

experimental curve is shifted significantly to the right; this being due to competition

from the dihydrate formation reaction.

153
100

90

80

70

60

50

40

30

20

10

,x' X x" a 0 0

• / <

I 0

/

Htfa '

I

'

(

'

I I

Hacac

Hhfa

X

I

I

IX

»X

fX

/X

/

1

'

I '

i I

I \

1

I ?

I

I '

I I

t /

PH

Fig. 3- Extraction of 40 Tig/ml Sc"^"*" with 0 . IM g-diketone in CHCl

154
100

90

80

70

60

50

40

30

20

10

(

IX

/ 0

-0 pH 4.8 - 5.1, buffered

I

\

X y —pH 2.9 - 3.2, unbuffered

\

\

V

pH 1.4 - 1.5, unbuffered

J I L J Xy I J L

20 60 100 140 180

Mixing time, seconds

220

Fig. 4-Extraction kinetics of Sc"^''"-hfa system for different pH

values

155
Extraction-time plots for the Sc^"*" - Hhfa system at three pH values are shown in

figure 4. Although the curve for the solution buffered at pH 5.2 attains a plateau, as expected for a simple extraction system, those obtained at pH values of 1.5 and 3.0 exhibit

a maximum at about 30 seconds, clearly indicating that: (1) significant dihydrate formation takes place in acid but not neutral or basic media, (2) kinetics of dihydrate formation

are significantly slower than extraction for this system, and (3) the equilibrium extraction efficiencies (corresponding to approximately three minutes) closely duplicate data

shown in figure 3, thus explaining the observed right-ward shift of the Sc^"*" - Hhfa curve. Spectroscopic data on the [Hhfa] • [Hhfa • 2H2O] system also confirm these findings.

4. Conclusions

Data presented in figure 4 indicate clearly that for elements whose extraction

kinetics are faster than the dihydrate formation reaction and whose extraction with Hacac

is efficient, Hhfa can be utilized effectively if shaking times are optimized. This would

not only allow high-efficiency extraction of such elements with Hhfa, but would also

permit group separations based on this consideration. Practical application of this

concept, however, should await establishment of detailed extraction data on the elements of

interest.

References

[1] Moshier, R. W. and Sievers, R. E., Gas Chromatography of Metal Chelates^ (Pergamon

Press, NY, 1965).

[2] Stary, J. and Hladky, E., Anal. Chim. Acta., 28, 227-235 (1963).

156
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

DETERMINATION OF TRACE AND MINOR ELEMENTS IN THE

COMBUSTIBLE FRACTION OF URBAN REFUSE

William J. Campbell, Harold E. Marr, III and Stephen L. Law

College Park Metallurgy Research Center

Bureau of Mines

U. S. Department of Interior

College Park, Maryland 20740, USA

1. Introduction

With the national focus on energy, the combustible fraction of urban refuse is being

extensively considered as a fuel supplement for coal in the generation of heat and power.

One concern regarding this fuel supplement is the possible environmental impact from trace

elements released to the atmosphere during the combustion process. The objective of these

ongoing analytical studies is to determine the concentration of major, minor, and trace

elements in the combustible fractions collected at various locations in the Bureau of Mines

urban refuse recycling pilot plant located at College Park, Md. The samples processed

through the plant are submitted by various municipalities that are considering resource recovery as an alternative to landfill or other means of disposal. Parallel studies are also underway to identify individual major contributors by analyzing separately, highcirculation newspapers and magazines plus various other types of paper and plastic products

[1]^

2. Separation of Combustibles

In the United States refuse-derived fuels will generally be separated from the glass

and metal fractions of municipal solid waste (MSW) prior to use for generation of heat and

power. Many of the MSW separation processes will include part or all of these steps incorporated in the Bureau of Mines urban refuse pilot plant [2]. This 5-ton-per-day pilot

plant consists of shredders, magnetic separators, trommels, air classifiers, cyclones, and

mineral jigs, as shown schematically in figure 1.

The products collected in the three cyclones (figure 1) consist primarily of the

lighter paper and packaging materials together with plastic film and light fabrics. The

heavier combustibles such as wood, leather, rubber, and heavy-gage plastics are concentrated

in the heavy organic product from the secondary air classifier. Most of the putrescibles and

yard waste are concentrated in the organic wastes separated out by the mineral jig. Samples

of combustibles from all five collection points in the plant are included in this study;

however, it is probable that some refuse-derived fuels will be limited to the cyclone

products. Therefore, this fraction is emphasized. Based on pilot plant data the following

percentages of the combustibles entering the plant report in the cyclone fractions: paper,

93 percent; plastics, 70 percent; fabrics, 92 percent; cardboard, 46 percent; leather and

rubber, 15 percent; wood, 14 percent; and a negligible amount of the putrescibles.

^Figures in brackets indicate the literature references at the end of this paper.

157
Unburned refuse

KEY :

*o bag house

Water to recycle ^ system

PRIMARY SHREDDER

LIGHT AIR CLASSIFIER

MAGNETIC

SEPARATOR

Very light paper ond plostic

Moqnetic metol

to detinning Nonmaqnelics

PRItl/lARY AIR CLASSIFIER

/ _ /

Massive metals

f

OMAGNETIC

SEPARATOR '^wy

Gloss, nonferrous metols and heovy orgonics

with poper and plostics

COMPACTOR _ Light paper and plost ics

Heavy

iron

wiin poper a L. Alternole — ^

Heavy

nonferrous meta I

TROMMEL

Aluminum ond

i heavy orgonics

with paper and

plostics

Gloss, nonferrous metals, heavy food and other orgonics

Figure 1. Raw refuse recovery flowsheet.

158
3. Samples and Analysis

The MSW samples for this study were collected in the District of Columbia, Baltimore

County and Montgomery County, Md., and Tampa, Fla.; MSW samples from other areas of the

United States are presently being processed. The data in table 1 represent average U.S.

values for the combustible fraction of MSW based on a 1973 survey [3]. The composition for

individual samples varies significantly depending on factors such as economic status of

neighborhood, time of year, and geographic location, particularly in regards to food and

yard wastes.

Table 1. Composition of combustible fraction of municipal

sol id waste in the U.S.

Composition, Paper fraction.

Component weight percent weight percent

Paper 50.2

Corrugated cardboard 26.7

Newspapers 18.0

Other, paperboard 13.3

Paper packaging 12.6

Office paper , 12.2

Magazines, books ' 7.6

Tissue paper, towels 5.3

Other, nonpackaging 2.9

Paper plates, cups 1 .4

Yard 17.8

Food 16.8

Plastics 5.2

Wood 4.6

Leather-rubber 3.4

Textiles 2.0

The sampling procedure for the combustible fractions from the pilot plant was designed

to obtain samples for energy- related measurements such as Btu value and ash content [4].

For the cyclone products the total accumulated sample collected in each cyclone is passed

through the secondary shredder and the secondary air classifier to obtain a more manageable

particle size. A 10 to 20 percent grab sample is then taken and progressively coned and

quartered to a final sample size of approximately 3 kilograms. A similar procedure is used

for the heavy organics fraction, whereas the organic fraction containing the putrescibles

and yard wastes is sampled periodically during the pilot plant runs. Two hundred grams of

each type of sample are then put through a Wiley mill^ to achieve a minus 2-mm particle size

for the analytical samples. The large-volume individual contributors--paper, magazines,

plastics, textiles, etc. --are prepared by reducing the entire sample to minus 2 mm in the

Wiley mill. Any noncombustible material in these samples such as staples, buttons, etc., is

removed prior to size reduction in the mill. Analysis of replicate samples of the combustible

fraction indicates that the reproducibility of the analytical sample is adequate for these

environmental impact studies. The largest variations were noted for those elements--Cu, Fe,

Ni, Pb, and Zn--that may be present as fine wires or pieces of solder and screen in addition

to their normal mode of occurrence in the combustible materials. As expected, the reproducibility between replicate samples was good for the large-volume individual contributors.

The combustible fractions and the large-volume individual contributors were analyzed by

two techniques--chemical digestion-atomic absorption spectrophotometry, and pressed pelletenergy dispersive x-ray spectrography. For the chemical -AA procedure, 4 to 5 grams of

sample are digested in nitric and hydrofluoric acid with subsequent treatment by perchloric

acid when necessary. The dissolved samples are brought to volume in a 100-ml volumetric

flask and then analyzed by flame AA procedures. Reliability of the chemical digestion-AA

method was evaluated by analyzing a National Bureau of Standards reference coal fly ash

#1633.

^Reference to specific equipment or materials does not imply endorsement by the Bureau of

Mines.

159
The pressed pellet-energy dispersive x-ray procedure was calibrated using previously

analyzed samples of both the combustible fraction and individual large contributors as secondary standards. Samples and standards were prepared by blending 3.5 grams of minus 2- mm sample and 0.5 gram of Somar mix (as a binder) in a Spex mill and then pressing into a

1 1/4-inch-diameter pellet at 30,000 pounds per inch.

Linear regression curves obtained by this procedure have correlation coefficients in

the order of 92 to 95 percent. The deviations from the regression lines were of the same order as the spread in replication values. No interelement corrections were applied to the

x-ray intensities, although there are significant variations in the composition of both the

combustibles and individual contributors. Sampling of MSW is considered to be a more important source of error than the uncorrected x-ray analytical results.

4. Results

Table 2 summarizes analytical data obtained on the combustible products of MSW collected

during operation of the Bureau of Mines pilot plant. These data are now being extended to

include other elements of environmental concern such as antimony, arsenic, bismuth, and

mercury. The Oak Ridge National Laboratory coal values in table 2 represent a specific

coal, whereas the eastern coal data are average values for a wide range of coals collected

in the Eastern United States. Because of the wide variability in both types of fuel, small

differences in concentration levels between coal and combustibles are not significant.

The approximate weight fractions of the combined cyclones, heavy organics, and organic

wastes are 0.76, 0.06, and 0.18, respectively. By limiting the combustibles used for fuel

to the cyclones fraction only, it is possible to achieve a significant reduction in the

amount of Cd, Cu, Ni, Pb, and Zn available for release to the atmosphere.

Table 2. Trace, minor, and major metals in combustible fractions and in coals.

Combustibles

Coal Cyclones Heavy organics Organic wastes

ORNL Eastern Av Range Av Range Av Range

Ag 3 < 3- 20 4 < 3- 8 < 3 < 3- 4

Al 14,670 9,600 5,500- 21 ,000 9,900 4,900-22,000 7,400 6,000- 8,600

Ba 96 94 160 < 20- 1,400 150 35- 280 170 70- 240

Be 1.3 < 2 < 2 < 2 < 2 < 2 < 2 Bi < 15 < 15 16 < 15- 27 < 15 < 15- 20

Ca 5,790 6,500 1,500- 17,500 26,000 4,400-44,000 25,000 15,000-38,000

Cd 0.64 4 < 2- 23 38 9- 70 32 6- 93

Co 4.6 20 3 < 3- 7 6 < 3- 12 5 4- 8

Cr 26.7 25 50 10- 240 180 55- 320 50 30- 85

Cu 12.2 14 190 20- 1,400 2,800 330- 6,600 690 290- 1,700

Fe 17,825 2,000 800- 5,100 5,900 1 ,100-22,000 3,000 2,400- 4,300

K 2,480 820 280- 2,000 1 ,300 510- 2,600 3,600 2,000- 4,600

Li 62 2 < 2- 25 < 2 < 2- 4 2 < 2- 6

Mg 1 ,890 1,400 560- 4,100 2,900 860- 8,600 2,500 1,800- 3,500

Mn 58 28 130 50- 480 160 50- 310 150 120- 170

Na 930 4,300 1 ,500- 11 ,000 3,100 900- 6,400 9,800 6,400-13,000

Ni 23 22 14 5- 35 85 16- 400 35 15- 50

Pb 8.2 5.9 300 90- 1 ,600 430 no- 950 1,700 310- 6,500

Sri 20 < 20- 80 35 < 20- 50 50 25- 110

Sr 15 < 10- 60 25 < 10- 60 30 10- 65

Ti 710 2,100 1,100- 4,500 3,100 100- 5,400 2,000 850- 2,800

Zn 94 25 850 150- 7,000 2,400 150- 9,300 560 330- 880

The technical assistance and advice of the Analytical Research and Service Group is

greatly appreciated, in particular Ben Haynes, John Novak, David Neylan, James McConnell,

and Margret Lang. Paul Sullivan and Harry Makar of the Secondary Resource Recovery Group

supplied the pilot plant samples in addition to many helpful comments.

160
References

Campbell, W. J., Metals in the wastes we burn, Envirormental Science and Technology,

Vol. 10, p. 436-439, 1976.

Sullivan, P. M., Stanczyk, N. H., and Spendlove, M. J., Resource Recovery from Raw

Urban Refuse, Bureau of Mines Report of Investigations 7760, 36 pages, 1973.

U. S. Environmental Protection Agency, Third Report to Congress: Resource Recovery

and Waste Reduction, SW-161, 1975.

Schultz, H., Sullivan, P. M., Walker, F. E., Characterizing Combustible Portions of

Urban Refuse for Potential Use as Fuel, Bureau of Mines Report of Investigations 8044,

26 pages, 1975.

161

Part IV. PHYSICAL CHARACTERIZATION OF AEROSOLS

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

PHYSICAL CHARACTERIZATION OF AEROSOLS

K. T. Whitby

Mechanical Engineering Department

University of Minnesota

Minneapolis, Minnesota 55455

1 . Introduction

During the past decade there has been a major revolution in the way aerosols are measured and in the understanding of their physical and chemical size distributions. It is the

purpose of this paper to review the most important findings and discuss some of the most

important implications for aerosol measurement. Size distribution characteristics and

concentrations found in various locations will be illustrated from the results of a number

of field studies.

2. General Characteristics of Aerosols at the Earth's Surface

Much evidence from a variety of field studies suggests that atmospheric aerosols are in

general multimodal, with two to three modes being observable. The mass or volume distribution

is usually bimodal with a minimum observed in the 1 to 3 ym diameter range. The particles

larger than a few microns originate from natural or man-made mechanical processes. The

mechanically produced particles are hereafter called "coarse particles". The particles

smaller than a few microns arise predominantly from condensation processes. These aerosols

smaller than a few microns are called "fine particles" . The predominant man-made source of

these fine particles is combustion or the condensation of chemical or photochemical reaction

products on nuclei from combustion.

The fine particle range may also show two distinct modes. For example, figure 1 shows

a trimodal size distribution measured 30 m from the roadway during the General Motors Sulfate

Study. The smallest mode is quite distinct in this case because the source (catalystequipped cars) emitted most of the aerosol in the 0.02 ym nuclei mode, and the accumulation

mode (middle mode) was relatively small because the background on this day was very low.

Figure 2 summarizes the nomenclature, mechanisms of formation, and removal mechanisms

for the three modes. The first mode in the vicinity of 0.02 pm diameter results primarily

from the direct emission of primary particles from combustion. The second submicron mode,

in the 0.15 to 0.8 pm range by volume, is the result of either the coagulation of primary

particles or the condensation of reaction products or water on primary particles. The third

mode, or coarse particle mode, consists of mechanically produced aerosols with the upper

size limited by classification due to sedimentation. There appears to be very little ex- change of mass under most conditions between the fine and coarse particle ranges in the

atmosphere.

Figure 2 also summarizes the various mechanisms that contribute to the formation , transformations and removal of atmospheric aerosols. Most mass is inserted in the distribution

either through the accumulation mode or through the coarse particle mode. Only under unusual

circumstances near large sources of combustion aerosol such as a freeway, or in a plume from

a stack, is appreciable mass injected directly into the nuclei mode.

Some typical values of the concentration of fine and coarse particles in the atmosphere

are shown in table 1. Because of the relative independence of fine and coarse particles,

both nonurban and urban sites have yielded widely varying ratios of fine to coarse particles.

On the average, however, the fine particles constitute between one-third and one-half of the

total aerosol mass.
GM MILFORD PROVING GROUNDS

site: GMP 15 RUN NO, : 15 TIME: 8:40 TO 9:00 HR EOT

WD: 354.9 CNC: I.02E 05 V2: 1.35 NO/NOX; 0.30 WSP: 17.0 NTM: I.03E 06 V3: 2.32 van: 1 .30 RH: 73.8 ST: 4.53E 02 V3-; 3.67 vac: 2.76

vt; 7.16 V4+: 3.49 VCP: 4.09 xio(+o)

DP iiim)

Figure 1. Trimodal volume distribution measured 30 m from the

roadway during the General Motors Sulfate Study, October, 1975.

HOT VAPOR

CHEMICAL CONVERSION

OF GASES TO LOW VOLATILITY VAPORS

PRIHARV PARTICLES

CHAIN AGGRESATES

WIND BLOWN DUST

.002 .1 I 2 PARTICLE DIAMETER, MICROMHER

TRANSIENT NUCLEI OR

AITKEN NUCLEI RANGE ACCUMULATION . RANGE

-FINE PARTICLES

MECHANICALLY GENERATED

AEROSOL RANGE

COARSE PARTiaES

Figure 2. Schematic of the principal mechanisms of formation of

a trimodal size distribution.

166
Table 1. Typical values of the concentration of fine and coarse particles in the atmosphere.

Concentration - )jg/m^(p = 1)

Fine Coarse

Location Condition Particles Particles

Los Angeles Grand average 37 30

Los Angeles

T rccWdy wina Troin treeway 77 c;q oy

Denver Grand average 16.6 232

Goldstone CI ean 4.2 10.4

Milford, Mich. Clean 1.5 3

Pt. Arguello

(seaside) Marine air 1.1 53

St. Louis Very polluted 365 114

3. Size Distribution Models for Source Related and Urban Atmospheric Aerosols

Whitby [1]^ has shown that atmospheric volume, mass and chemical size distributions can

be fitted by three independent log-normal distributions. For example, figure 1 shows a typical, distribution observed alongside of the roadway during the General Motors Sulfate

Study. The bars are the actual data from the three sizing instruments, and the solid lines are the fitted log-normal distributions.

The trimodal log-normal fitting procedure has been applied to a large number of size

distributions measured with the Minnesota Aerosol Analyzing System during the field projects

in which we have participated during the last seven years. After examining this data in some detail, Whitby and Cantrell [2] have grouped the distributions into six categories.

The modal parameters for these six distributions are presented in table 2, and the characteristics of each distribution are summarized below:

Table 2. Modal parameters and integral parameters for six

typical model atmospheric distributions.

Nuclei Mode Accumulation Mode Coarse Particle Mode Integral Parameters

DGV V V DGV V NT ST VT

Clean background 0 .35 2.1 1.5 6 2.2 5 796 40.7 6.5(

Average

background .034 1.7 .037 .32 2.0 4.45 6.04 2.16 25.9 8 .6E3 148 30.4

Background & aged urban

plumes .028 1.6 .029 .36 1 .84 44 4.51 2.12 27.4 1 .6E4 938 71 .4

Background & local sources .021 1 .66 .62 .25 2.11 3.02 5.60 2.09 39.1 4 .1E5 352 42.7

Urban average .038 1.81 .63 .32 2.16 38.4 5.7 2.21 30.8 1 .4E5 1131 69.8

Urban & sources .032 1.74 9.19 .25 1 .98 37.5 6.02 2.13 42.7 2 .2E6 3201 89.4

DGV = Geometric mean size by volume, ym

Og = Geometric standard deviation, unitless

V = Volume concentration in mode, ym^/cm^

NT = Total number concentration in distribution, no./cm^

ST = Total surface area concentration, ym^/cm^

VT = Total volume concentration, ym^/cm^

^Figures in brackets indicate the literature references at the end of this paper.

167
CI ean Background

Observed only in large clean air masses

Several hours away from combustion sources

No nuclei mode

Volume accumulation mode (VAC) < 2 ymVcm^

Average Background

Mixture of Clean Background , small amounts of aged urban plumes and local

combustion aerosol

Small nuclei mode

Volume accumulation mode (VAC) = 5 ym^/cm^

Volume coarse particles (VCP) independent of VAC and dependent on local sources of

dust

Background + Aged Urban PI umes

Average Background + a strong plume from a major urban area

Small nuclei mode determined by local combustion sources

VAC similar to that in an average urban area

VCP determined by local sources of dust

Background + Local Sources

Strong local combustion sources increase Volume nuclei mode (VAN) to the urban

concentrations of = 0.6 without much increase in VAC over background

Distribution is very dependent on nature of sources

Urban Average

Nuclei mode determined by local sources, primarily automobiles

Accumulation mode determined primarily by aged aerosol from the general area;

VAC = 30 on the average

Coarse particle mode determined by local sources

Urban + Sources

Strong local sources of combustion aerosol, e.g., automobiles, increase both

nuclei and accumulation modes

Coarse particle mode is influenced by the nature of the source. Fine particle and coarse particle sources are usually unrelated

Concentration is very variable in time.

The size distributions for which the parameters are tabulated in table 2 are plotted in

figures 3 and 4. A typical size distribution measured in the Labadie coal fired power plant

plume, located in St. Louis, is also shown in figure 4. Although both background and plume

aerosol distributions measured from aircraft in St. Louis during the Midwest Interstate

Sulfur Transport and Transformation Study (MISTT) program seem to have small nuclei and coarse particle modes most of the time, most of the aerosol mass is in the accumulation

mode.

Another characteristic that may be observed from table 2 and figures 3 and 4 is that,

except for the clean background and Labadie plume distributions, the volume of aerosol in

the coarse particle mode is relatively constant at about 30 pm^/cm^. It is seen that the

accumulation mode volume is much more closely related to anthropogenic contributions than is

the coarse particle mode.

168
Figure 3. Volume Size distributions of four background model

aerosols. Note that except for the CLEAN BACKGROUND, the

volume in the coarse particle mode is about the same.

The nuclei mode is an indicator of close (less than 1/2 hour transport time) sources of

combustion aerosol except in those cases where photochemical ly produced nuclei may be observed in relatively clean air {e.g., small accumulation mode). Number concentrations of

about 10^/cm^ of nuclei of size less than 0.01 ym have been observed in the Labadie plume

during the summer of 1976. These nuclei are apparently due to homogeneous reactions in the

plume.

The formation rate of new nuclei in a coal fired power plant plume is only about 3.5

nuclei per cm^ • sec. These nuclei contained an insignificant amount of mass compared to

the mass that condenses directly on the particles in the accumulation mode during the aerosol growth in the same plume.

4. General Mode Characteristics of the Physical Size Distribution

From modal characterization of the variety of aerosol size distributions, the following

general conclusions have been reached:

1. Nuclei mode. For very fresh combustions aerosols from clean combustion {e.g.,

alongside of a freeway), the geometric mean diameter by number (DGN) is about

0.01 vjm. For more aged aerosols, DGN may approach 0.02 ym. The geometric standard deviation (SG) is usually between 1.5 and 1.7. Except for well aged aerosols

{e.g., away from sources on the earth's surface or well above the earth's surface),

the nuclei mode accounts for most of the aerosol number and hence the Aitken

nuclei count.

169
003 .01 .1 I 10 50

Dp, fLm

Figure 4. Volume size distributions of two model urban aerosol

distributions and a typical size distribution measured in the

plume of the Labadie coal fired power plant on 8-14-1974. The

power plant plume has only the accumulation mode.

2. Accumulation mode. Average geometric standard deviation by volume (SGV) = 2.0 and

average geometric mean diameter by volume (DGV) = 0.34 pm. Also aged aerosols

have a somewhat greater SGV than fresh aerosols, the range being from about 1.8

for fresh aerosols to 2.2 for well aged aerosols. In well aged aerosols the

nuclei mode disappears into the accumulation mode by coagulation and then the

Aitken nuclei count becomes equal to the number of particles in the accumulation

mode within the experimental error of the measurements {e.g.^ about ±30%). This

situation appears to be the normal condition at altitudes greater than about 200 m and at the surface more than 50 Km from sources of combustion aerosol.

3. Coarse particle (CP) mode. The average geometric standard deviation by volume of

the coarse particle mode (SGV) = 2.3, and the average geometric mean diameter by

volume (DGV) = 5 ym. The log-normal distribution parameters are much more variable

for the coarse particle mode than for the accumulation and nuclei modes, values of

DGV having been observed between 3.5 and 25 pm. The mass concentration in the CP

mode is also quite variable, from a few to several hundred yg/m^.

An examination of the relationship between the volume of coarse particles, VCP, and the

geometric mean size of the coarse particle mode, DGVCP, shows that DGVCP is nearly constant

up to VCP = 30 um^/cm^ and equal to about 5 ym. Above 5 ym, DGVCP increases linearly with

VCP.

170
5. Chemical Size, Distributions

Improved devices for the size classification of atmospheric aerosols have produced many

new insights into the distribution of the chemical elements with respect to particle size in

recent years. Table 3 shows some recent data obtained by Dzubay and Stevens in St. Louis,

using the virtual dichotomous sampler which separates the fine and coarse particles at 2 pm.

From the table it will be noted that the elemental distribution is about the same for the

urban and rural site, indicating that the sources of the aerosol are essentially the same in

both cases. Consistent with their origin by condensation, only S and Pb are found predominantly in the fine particle range.

Table 3. Comparison of the 18-day-average percentage composition

at an urban and rural site in St. Louis, measured between August 18

and September 7, 1975, by T. G. Dzubay and R. K. Stevens of EPA.

Site 106 (Urban)

Element Fine (29 yg/m^) Coarse (22 yg/m^) Fine/Coarse

S 13% 1.3% 10

Pb 2 0.6 3.3

Ti 1 2 0.5

K 0.5 1.1 0.45

Fe 1 5 0.2

Si 1 8 0.13

Ca 0.5 8 0.06

Site 124 (Rural )

El ement Fine (29 yg/m^) Coarse (15 yig/m^) Fine/Coarse

S 12% 0.9 13.3

Pb 0.5 <0.1 5.0

Ti <0.1 0.3 0.33

K 0.3 0.9 0.33

Fe 0.3 1.2 0.25

Si 0.5 4 0.13

Ca 0.4 4 0.10

Work has begun in our group to apply the trimodal log-normal models to the distributions

of chemical elements measured during the ACHEX project in California and to other good data.

The early results from this modeling effort suggest that within the accuracy of the data,

elements like Pb, S, and Br, which one would expect to end up in the accumulation mode, can

be fitted by a log-normal distribution having the same parameters as the physical accumulation mode distribution. If this is indeed true, it supports the concept proposed by Junge

that the fine particles are usually mixed at distances beyond a few km from significant fine

particle sources.

Other elements such as Al , Fe, Si, and Ca, which come from the soil, are found in the coarse particle mode. There are a few elements (for example, CI) which are found in both

modes and have a bimodal distribution very similar to the physical distribution. The evidence suggests that for Los Angeles at least, this is because the coarse particle CI comes from the sea and the fine particle CI from auto emissions.

171
6. Liquid Content of Atmospheric Aerosols

Numerous recent studies of atmospheric aerosols have shown that in their normal state,

at normal humidities, the fine particles contain an appreciable fraction of water or other

volatile liquid. Typically the fine particles have 20% water by weight at 60% relative

humidity (R.H.) and 50% water at 75% R.H. The water content usually does not approach zero

until the R.H. decreases below 35%. The significant water content at normal atmospheric

humidities has an important bearing on aerosol measuring and sampling procedures. Among the

implications are:

° Changes in ambient humidity will cause changes in aerosol size and mass concentration.

° Changes in the ambient humidity to which collected samples are exposed will change the mass on the surface.

° Aerosols at humidities at which they are in the liquid state will not bounce on impactor stages. However, at humidities below about 25%, they may bounce. The coarse particles are usually dry and may bounce off the coarse particle stages of a cascade

impactor, only to be collected on the finer stages where the more liquid fine particles

have provided a sticky coating. This effect can cause serious distortions in the

measured physical and chemical size distribution.

° Temperature changes inside of sampling lines or instruments can cause a significant

change in the aerosol volume concentration measured.

° If the usually dry coarse particles are collected on the same surface as the wet fine

particles, as in the Hi-Vol TSP measurement, the fine particles may react with the coarse particles to change the chemical composition. For this reason, chemical species

measurements on TSP samples are questionable.

7. The Influence of Aerosol Characteristics on Measurement Techniques

In the previous sections, the influence of such aerosol characteristics as water con- tent on the suitability of measurement techniques has already been mentioned. However,

there are other physical properties which should be considered. Some of these are briefly

mentioned below.

° The fact that the number distribution of aerosols is described approximately by dN/dlog

D = constant x Dp""^ means that the number concentration decreases very rapidly with

increasing size. When designing and operating continuous particle counting instruments,

it is very important to take this into account. For example, in the case of a single

particle optical counter, the usable counting range is ordinarily limited to one decade

of size by the conflicting requirements of only one particle in the view volume versus adequate count statistics at the coarse end for a given design.

° Real aerosols have variable indices of refraction, and the coarse particles are often

irregular in shape. The sophisticated optical techniques that depend on the aerosol

being quite ideal are likely not to work very well on real aerosols.

° The great range of size of atmospheric aerosols from about 0.003 to 100 ym requires

that systems of instruments be used to cover the entire range. Better results can be

obtained with three less ideal instruments covering overlapping but adjacent ranges

than can be obtained with one expensive and elegant instrument that can only cover one decade of size. Because instrument systems, compl icate data analysis, data analysis

should be considered before instrument systems are designed. Also, the great size

range of atmospheric aerosols means that useful data can be obtained with instruments

which have only fair size resolution.

° The perishability of atmospheric aerosols means that they must often be analyzed where

they are sampled. The ability to take aerosol instrument systems to the sampling site

along with a lot of other equipment is often more important than the extraordinary

virtues of any one piece of equipment.

172
This research was supported by U.S. Environmental Protection Agency Research Grant

803851-011. The financial support of the agency is gratefully acknowledged.

References

Whitby, K. T., "Modeling of Multi-modal Aerosol Distributions", presented in the

transactions of GAF meeting, Bad Soden, Germany, October 1974.

Whitby, K. T. and Cantrell, B. K., "Size Distribution and Concentration of Atmospherio

Aerosols", presented at 82nd AICHE meeting, Atlantic City, N.J., August 1976.

173

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

MEASUREMENT OF AEROSOL SIZE DISTRIBUTION WITH A

PARTICLE DOPPLER SHIFT SPECTROMETER

Ilan Chabay

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

1. Introduction

A system has been developed at NBS which is particularly suited for testing the size

distribution produced by aerosol generators and calibrating measurements of other particle

size instruments. The technique involved is particle Doppler shift spectroscopy (PDSS)

[1]^. It has virtues of being rapid, applicable to liquid or solid particles dispersed in

a gas, covers the size range 0.5 to 100 pm radius, operable at any number density up to

about 10^ particles/cm^ , nondestructive, does not disturb the aerosol or its size distribution, inherently accurate and internally calibrating.

2. Discussion

The instrument measures size and size distribution by determining the slip corrected

Stokes Law settling velocity and the intensity of light scattered from each falling particle.

Doppler shift spectroscopy, that is, the measurement of the amplitudes and frequencies of

signals from moving sources, is used to determine the falling velocity of particles. Light

scattered out of a horizontally propagating laser beam is collected by apertures and a photodetector at a small forward angle in the vertical plane. The radiation field, which

has been Doppler shifted by the motion of the scatterers (the aerosol), interferes with

elastically scattered radiation from stationary sources to produce beat notes in the output

photocurrent at the different frequencies. A given beat frequency implies a specific

velocity which in turn implies a particle size. The relative amplitudes of the beat frequency component, after normalization by the calculated relative Mie scattering intensities

and the relative residence times spent by the particle in the observation volume imply the

relative number of particles of each size. The basic scheme of measurement is indicated in

figure 1

.

In figure 1, v is the velocity of the particle which is given by Stokes Law as v(r) = (2pg/9n)r2 plus the slip correction factor where p is the particle density, g is gravitational acceleration, n is the viscosity of air, and r is the particle radius. The scattering

vector K is defined in the drawing and is a function of the incident wave vector ko and

scattering angle. The frequency shift is given by Av = (1/2it) T • iT.

1 Figures in brackets indicate the literature references at the end of this paper.

175
176
Spherical particles of known index of refraction and density are produced by a BerglundLiu vibrating orifice particle generator [2]. The particles are introduced at the top of a 1.5 m column above the scattering chamber. The column is filled with aerosol from the

generator, then closed off by means of air-driven piston valves. As the particles then

settle through the beam, the scattered light is observed and data gathered.

For the most part, dioctylphthalate (DOP, an oil) was used in these experiments.

Recently some work has been done also on ASO3 particles.

These particles serve several purposes. The actual distribution of particles produced

by Berglund-Liu generator under various conditions has been examined. Results of characterizing the degree of monodispersity of the generator will be discussed. The use of the

particles to calibrate other instruments after passing through the PDSS will also be noted.

A polydisperse aerosol can be produced intentionally by the Berglund-Liu device. This

type of output has been used to provide calibration of the PDSS instrument. Comparison of

the photocurrent power spectrum of a wide distribution of particles with the Mie scattering

function as calculated from first principles, allows determination of the absolute size and

of the resolution measured by the PDSS.

The characteristic pattern of minima and maxima in the calculated Mie function and in

the measured size spectrum provide a clear means of determining the presence of convective

broadening and of measuring any existing slow, uniform flow rate in the chamber. The

sharpness of the extrema in the measured spectra indicated the resolution (at present, it is

less than 0.1 m with comparable accuracy). A uniform shift in positions of the measured

extrema relative to the calculated values is proportional to the velocity of uniform flow of

air through the scattering volume. It is possible to design the scattering chamber so that

there is essentially no convective flow.

This technique is currently designed for use with spherical particles of known, uniform

index of refraction and density. It is possible to adapt the calculations and measurements

to study fibers of known index and density.

Two commercial instruments, the Royco 225 with 508 plug-in unit, and the Particle

Measurement Systems model ASSP 100, were tested using the aerosol generator and the PDSS

instrument. Aerosol from the generator was passed through the PDSS instrument, measured,

then allowed to flow on directly to the Royco or PMS. This ensured that virtually the same distribution was being measured by each instrument. These preliminary tests indicated that

the readings for the Royco and PMS were consistent with PDSS data, though the resolution and

range of sizes measured with the commercial instruments were limited due to their inherent

lower resolution compared to the PDSS.

An additional corraborati ve technique that is particularly useful in determining size

of relatively monodisperse aerosols of less than 5 pm radius will also be discussed. This

technique consists of using the angular pattern of maxima and minima of light intensity in

the 1.5 m column of flowing aerosol. The Mie pattern is quite discernable by eye and

traceable by photographic microdensitometer techniques. This provides an additional check

on the size calibration of the PDSS.

3. Conclusion

The PDSS instrument built at NBS has several important features. The method of size

measurement can be calibrated from basic light scattering theory in two complementary ways:

one using the angular distribution of intensity of a monodisperse aerosol, the other using

177
the size variation of intensity at a single angle. The measurement of size distribution

then is internally calibrated with respect to size. Measurement is rapid, independent of

number density (up to a limit imposed by multiple scattering events), independent of as- sumptions regarding the width or modality of the size distribution, and capable of producing

good resolution with either liquid or solid aerosols. The primary function of this instrument is as the basic reference and calibrating system for other aerosol sizing devices. The

PDSS instrument also can be used to study the coagulation, evaporation, condensation, and

coalescence of aerosols.

References

[1] Gollub, J. P., Chabay, I., and Flygare, W.H., Appl. Optics VZ, 2838-42 (1973).

[2] Berglund, R.N. and Liu, B.Y.H., Env. Sci. and Tech. 7, 147-152 (1973).

178
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 454. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

INSTRUMENTAL ANALYSIS OF LIGHT ELEMENT COMPOSITION OF ATMOSPHERIC AEROSOLS

Edward S. Macias

Department of Chemistry

Washington University

St. Louis, Missouri 63130, USA

1. Introduction

The monitoring and control of atmospheric aerosols has received national attention and concern in the past few years due to the adverse effects of these airborne particles on visibility, climate, and health. Techniques for the study of the elemental abundances and

chemical composition of atmospheric aerosols are of prime importance in order to understand

the complex processes leading to aerosol formation in the atmosphere. No single technique

is presently available which provides a complete analysis of a particulate sample. Elemental, analysis using neutron activation analysis [1]^ and X-ray fluorescence [2] are excellent methods for analysis of elements heavier than sodium. However, except for sulfur,

these heavy elements are present only in trace quantities in typical samples of atmospheric

fine particles (dia. <3.5 ym) [3,4]. Four light elements, carbon, nitrogen, oxygen, and

sulfur, account for most of the fine particle mass. Convenient, fast and nondestructive

techniques to measure these abundant light elements are not well developed. However, such

techniques are essential to determine the mass balance of atmospheric fine particles and to

understand the chemistry of these particles.

In this paper a new nondestructive technique for the simultaneous determination of

several light elements including carbon, nitrogen, and sulfur is described. The composition

of the sample is determined by analyzing gamma rays emitted from low-lying nuclear excited

states of the stable nuclei of those elements excited by inelastic scattering of protons

impinging on the target. This method is rapid (5-10 min per determination), accurate, and

sensitive enough for the determination of elemental concentrations in ambient aerosols with

1-4 h sampling. Filters on which aerosol samples have been collected are irradiated

without pre-treatment thereby avoiding errors introduced by sample dissolution and subsequent chemical analysis. Thus the method measures the total elemental abundance in a sample not just the water soluble fraction. The gamma rays emitted from carbon, nitrogen,

and sulfur are all above 2 MeV (half thickness >16 g cm"^) therefore no sample absorption

corrections are necessary.

It is not necessary to correct for the absorption of protons in the sample for several reasons. First a 7 MeV proton beam loses less than 150 keV on passing through the filter.

The cross section for the proton inelastic scattering reaction on the nuclides of interest

does not change appreciably over these energy ranges. Secondly calibration standards are prepared in an identical manner to atmospheric aerosols which negates the need for a correction. Finally, the deposit is primarily on the front of the filter and therefore is even less effected by a slight proton energy loss.

^Figures in brackets indicate the literature references at the end of this paper.

179
2. Experimental Methods

Samples of atmospheric aerosols were collected on a Pallflex^ glass fiber filter with

thin cellulose backing using an automated two-stage sequential filter sampler (TWOMASS) [5,

6]. The filter medium was chosen for its high collection efficiency, low mass density, and

low carbon, nitrogen and sulfur content. The mass density of this filter is 2.5 mg/cm^.

The flowrate through the sampler is nominally 300 cm^/s. The total mass of the aerosol

deposit was determined with an on-line beta attenuation mass monitor [5]. Filter samples were irradiated without the cellulose backing in the external beam facility of the Washington University 135-cm sector focused cyclotron. A 7 MeV proton beam was used for carbon,

sulfur, and nitrogen analysis as a compromise between large inelastic scattering cross sections to the first excited states of ^^C, ^^N, and and small cross sections to the

first excited states of ^^0. Analysis of oxygen can be carried out with a higher energy

proton beam in a separate bombardment because the Compton scattering from the 6132 keV

gamma ray of ^^0 decreases the precision of the analysis of the other elements.

Each sample, mounted in a standard 35 mm film slide holder, was irradiated with a collimated 7 MeV proton beam in a chamber maintained at 1 atmosphere of helium as shown in

fig. 1. The irradiation chamber was built around a modified commercial 35 mm slide projector to automate the sample changing. The identity of the sample being irradiated was monitored with a closed circuit television camera. A 0.003 mm thick Havar foil served as a vacuum seal between the scattering chamber and the cyclotron beam tube. The samples were typically irradiated with a 80 namp beam for 10 min. The beam current was determined with

a digital current integrator which measures the total charge collected on the Faraday cup.

In general, inelastic proton scattering excites a nucleus to its lowest lying excited

states which decays by the emission of gamma rays. The resulting in-beam gamma-ray spectrum includes at least one gamma ray from each element of interest as shown in fig. 2.

Gamma-ray energies for some of the elements which can be analyzed by GRALE are given in

Table 1.

^Pallflex Corp., Putnam, Conn.

180

UJ

H- <

LJ

^

CL O

CO CD

^

CL

< >

O LlI

U

OJ

o

o

LxJ Q

>

IE

ro

CP

o — C\J

CO > 2

ro _

3

CO

u

:L

ro

<M

<U

Q. "o

</) (/) O o

G k. o

Ql < < o CO

Q. 3

E

c

o

o

lauuoqQ J9d sjunoQ

Figure 2. In-beam gamma ray spectrum from 7 MeV proton bombardment. The upper curve is_

from a 123 mg atmospheric aerosol deposited on a glass fiber filter. The lower curve is

from a blank filter.

182
METHIONINE CALIBRATION

30,000

o

20,000 -

10,000

1

1

1 y

CARBON

r=0.98 —

/ 1 1 1 0 20 40 60

CARBON MASS (/xg)

T

GO

10 20 30

SULFUR MASS (/xg)

10,000

CO

5000 -

80

40

5 10 15

NITROGEN MASS (/Ltg)

Figure 3. Carbon, nitrogen and sulfur calibration curves for the GRALE technique using a known mass of methionine aerosol deposited on a filter.

183
I I I I to o

^

(eUJ/BT/) NOIl VdlN3DN0D

Figure 4. Concentration of carbon, nitrogen and sulfur and total mass of fine particle

ambient aerosol plotted as a function of time. The samples were collected in 4 hour

intervals in St. Louis, Missouri, August, 1976.

184
CO

LJ

>J

o

I-

<

CL

UJ

O

(T

UJ

I

Q.<oO

O

o

in

h;<>m\\\\\\\\\\\\\\

I M

WWWVWWWW

v;a\\\\\\\\\

i\\\\\\\\\\\\\\\\ \\\\\\\\\\

wwwwww^ wwv

\svv\\\x\vm

iO

N.\

00

hin

00

00

to

to

00

o

in

inCM

to

>-<

UJ

SSVW nViOi dO iN30M3d

Figure 5. Particulate carbon, nitrogen, sulfur and oxygen (from sulfate) concentrations

from the data in fig. 4, plotted as a percentage of the total fine particle mass.

185
Table 1

Properties of nuclides observable with GRALE

El ement

Atomic

Number

Target

Isotope

Isotopi c Abundance (%) Ey(keV)^

Carbon 6 12C 98.89 4430

Nitrogen 7 99.63 2311

Oxygen 8 160 99.76 6131

Fl uorine 9 19p 100 110,197

Neon 10 20Ne 90.92 1630

Sodi um 11 23Na 100 439

Magnesi um 12 2'+Mg 78.70 1369

Al uminum 13 27A1 100 843,1013,2209

Si 1 icon 14 28Si 92.21 1780

Phosphorus 15 31p 100 1266

Sulfur 16 32s 95.0 2237

Chlorine 17 35C1 75.53 1220,1763

^Data obtained for Lederer, C. M. Hollander, J. M. , Perlman, I., Table of Isotopes,

6th ed., John Wiley and Sons, N.Y. (1967).

Gamma rays produced in the proton bombardment were detected with a 60-cm3 lithium

drifted germanium Ge(Li) detector (11.75 percent efficient relative to a 3" x 3" Nal(Tl)

detector for 1332 keV gamma rays), with energy resolution of 2.5 keV full width at half

maximum for 1332 keV gamma rays. A large volume detector was used to maximize the efficiency for the 4430 and 6131 keV gamma rays of and isq respectively. Maximum energy

resolution is not essential because the prompt gamma rays from '^'^Z, 32s, and ^^N are Doppler broadened. The output of the Ge(Li) detector was sent to a high-resolution fast

rise time preamp and linear amplifier which are able to process high count rates ('^^10,000

count/sec) without appreciable degradation of energy resolution. The amplified signals were sent to a 13-bit 200-MHz analog to digital converter (Tracor Northern). Digital

information was stored and processed in a PDP-11 mini-computer with a 28000 word memory

(Digital Equipment). The spectra were analyzed immediately after each irradiation with the

on-line computer. The intensity of each peak is determined from the integrated peak area after subtraction of background. The peak intensity was corrected for system dead time

losses (typically 20 percent) determined from the area of a pulser peak in the spectrum

produced from a 60 Hz tail pulse generator inputted at the preamp. These data were normalized to the proton beam intensity determined from the integrated current measured in the

Faraday cup. The normalized peak intensities of the filter blanks were subtracted from the

atmospheric aerosol results. The conversion of peak intensity into mass was carried out

using standard methionine aerosols as described below. Filter blanks, atmospheric aerosol

samples, and methionine aerosol standards were run under nearly identical conditions which

yielded nearly equal detector count rates. All samples were analyzed in the same way.

3. Calibration

The identification of a given element in a sample was determined on the basis of peak

energy determined for the large peaks by the use of external standards before and after

each run. The large known peaks were then used as internal standards for energy determination of the smaller peaks. The amount of a given element in a sample was determined from

186
the ratio of the peak area in the sample to the area of the corresponding peak in a standard sample of methionine aerosol (C6H11O2SN) deposited on the same type of filter. The

mass of methionine deposited on the filter was determined using a beta attenuation mass monitor [5,6].

A detailed methionine calibration was carried out over a period of several days. The

results of the GRALE analysis of carbon, nitrogen and sulfur in standard methionine aerosol

samples are shown in fig. 3. The linear correlation coefficient for all determinations is

quite good (r > 0.9). The method was cross checked by analyzing several atmospheric

samples by GRALE followed by flash vaporization-flame photometric sulfur analysis [7] of

the same sample. The results of the two techniques agree within the uncertainties of the

methods. For the analysis of atmospheric aerosol samples, only a few standard methionine

samples need be run in order to verify that the system is operating correctly. These data

must be corrected for the relative solid angle subtended by the detector determined by

counting long-lived standard radioactive sources in the sample position of the irradiation

chamber.

With the calibration curve given in fig. 3, the results are accurate to about ±15 percent. However, much of the inaccuracy is due to the normalization technique. It is

anticipated that much better accuracy will be possible by normalizing to an internal

standard. Experiments are in progress to perfect this normalization technique.

4. Field Measurements

A study of the ambient aerosol sulfur, carbon and nitrogen content was carried out in

St. Louis in August, 1976. Samples were collected in 4 hour intervals in two size fractions with a two-stage sampler (TWOMASS) but only the fine particle fraction (diam. <3.5 pm) was subsequently analyzed by the GRALE technique. The total mass of these samples was determined using a beta attenuation mass monitor during collections [5]. The results of

this analysis for a 4 day period are shown in fig. 4. These data show that the concentrations of these elements vary substantially in a time scale of a few hotirs.

In fig. 5, the data are plotted as a percentage of the total aerosol mass. The oxygen

concentration from sulfate aerosol only has been estimated by assuming all of the particulate sulfur is in the form of sulfate. These data indicate that carbon, nitrogen, sulfur

and oxygen from sulfate constitute a substantial fraction of the total aerosol mass. The

average percentage of each element for the entire 4 day period was found to be: carbon

19 percent, sulfur 10 percent, nitrogen 9 percent, and oxygen from sulfate 20 percent.

Taken together these elements account for a total of 58 percent of the fine particle mass. The total mass was determined during sample collection and therefore includes a substantial

amount of water. It should be expected, therefore, that water accounts for much of the

remaining mass. It is interesting to note that the ratio of sulfur to nitrogen is equal to

the stoichiometric ratio of these elements in ammonium sulfate.

5. Conclusions

It has been shown that the GRALE technique is a powerful nondestructive technique for

analysis of abundant light elements in atmospheric aerosols. The technique requires no sample preparation and is sensitive enough for 1-4 hour sampling intervals. The main cause

of error is the uncertainty in the normalization of the beam current. It is expected that

the use of an internal standard will remove much of this uncertainty. Another source of error is the uncertainty in the weight of the calibration standards. It has also been

shown that this technique can be used to determine the elemental concentrations constituting most of the fine particle mass.

187
The author gratefully acknowledges many helpful discussions regarding the project with

Professors Rudolph B. Husar and Demetrios G. Sarantites. The assistance of Robert Fletcher,

Thomas Fulbright, Roland Head, H.-C. Hseuh, Janja Husar, Charles Lewis, David Radcliffe,

and Bernard Smith during various phases of this work has been invaluable. This work has

been supported in part by the U.S. Environmental Protection Agency Field Methods Development Section under grant R803115.

References

[1] Zoller, W. H., and Gordon, G. E., Anal. Chem. 42, 257 (1970).

[2] Johansson, T. B., Van Grieken, R. E., Nelson, J. W., and Winchester, J. W. , Anal.

Chem. 47, 855 (1975).

[3] Dzubay, T. G. , Stevens, R. K. , Environ. Sai. Teahnol. 9, 663 (1975).

[4] Flocchini, R. G., Cahill, T. A., Shadoan, D. J., Lange, S. J., Eldred, R. A., Feeney,

P. J., Wolfe, G. W., Simmeroth, D. C, Suder, J. K. , Environ. Sai. Teahnol. V^, 76

(1976).

[5] Macias, E. S., and Husar, R. B., Environ. Sai. Teahnol. (in press).

[6] Macias, E. S., and Husar, R. B., Fine Fartiales, B.Y.H. Liu, Ed., Academic Press,

N.Y., p. 535 (1976).

[7] Husar, J. D., Husar, R. B., Stubits, P. K. , Anal. Chem. 47^, 2060 (1975).

188
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

X-R-D ANALYSIS OF AIRBORNE ASBESTOS PREPARATION OF CALIBRATION STANDARDSi

M. Fatemi , E. Johnson, L. Birks, J. Gilfrich and R. Whitlock

Naval Research Laboratory

Washington, DC 20375, USA

1. Introduction

The use of a novel x-ray diffraction technique coupled with electrostatic fiber

alignment has been demonstrated to have considerable promise for routine measurement of

the concentration of airborne asbestos collected on membrane filters [1]^. The aligned

fibers are mounted in a thin nitrocellulose film and are measured in transmission geometry

using a broad collimated x-ray beam. By measuring the x-ray intensity, with the fibers

oriented normal and parallel to the plane of the incident and diffracted x-ray beams, the

asbestos signal can be corrected for background due to both scattering and diffraction by

other non-aligned materials in the sample. Using a modified commercial x-ray spectrometer

with a Cr-target spectrographic tube operated at 1100 watts," a 500 second 3a detection

limit^ of 0.15 yg of pure chrysotile asbestos has been achieved.

2. Discussion

The x-ray measurement of the aligned chrysotile fibers is very straightforward.

However, the alignment of the fibers is affected by several physical and chemical parameters. Futhermore, unlike pure standards which are aligned aliquots from large, preweighed

quantities, the unknown field samples contain only a small quantity of asbestos, all of

which must be processed and aligned. This extention of the method from large known

standards to small unknowns requires a few modifications in the original sample preparation

and, therefore, makes the procedure more critical.

Effects of many suspected parameters on the alignment of small samples have been

investigated. The most critical are found to be the following:

1. Chemical composition of the alignment medium. The alignment medium is established

as a solution of parlodion in distilled amyl acetate. The suitable concentration of

parlodion in amyl acetate has been determined to be between .001% to .002% w/v (10 and

20 ppm). The primary function of parlodion is fiber dispersion, but once the parlodion

concentration is increased beyond .002%, good alignment is not always possible (although

on occasion it has been observed).

^Supported by the Environmental Protection Agency under Interagency Agreement

EPA-IAG-D5-0651

.

^Figures in brackets indicate the literature references at the end of this paper.

^Limit of detection C|_ in micrograms is calculated from the formula 3 Nb/(SxT) where S is

the sensitivity in counts per second per microgram, Nb is the background in counts per

second and T denotes the counting time. This definition conforms to the recommendation

by lUPAC.

189
2. Filter pore size and fiber retention. The effect of filter pore size on fiber

retention has been found to be more striking than previously thought. In investigating

this parameter, three pore sizes - 0.22 pm, 0.45 urn, and 0.8 ym were used. Sample batches were sonicated in water-Aerosol OT solution for 40, 60, and 120 minutes respectively. In a typical case, the 60-minute sonicated samples showed an average sensitivity of 5.2 c/s,yg

on 0.22 pm filter, 4.0 c/s,yg on 0.45 pm, and 2.5 c/s,Mg on 0.8 pm. The two-hour sonicated

samples showed sensitivities of 4.2 c/s,pg on 0.22 pm, 2.5 c/s,pg on 0.45 pm and ~ 1.3 c/s,

pg on 0.8 pm.

3. Radio Frequency ashing of small samples. Radio Frequency ashing of small samples

is found to be the most critical aspect of sample preparation. It is necessary to contain

the ashed samples in a small volume, such as a test tube, for dispersion in the alignment

liquid. The extent of exposure to the Radio Frequency field varies from sample to sample

depending on gas flow condition. Radio Frequency intensity, and vacuum level. This variation in exposure is not always easily controllable, and in some cases affects the amount of

ashing residue from the filter itself. The greater the ashed residue from a given size

filter, the worse the alignment, since the higher residue implies either poor, incomplete

ashing, or the transformation of the material into an unashable compound.

The most striking example of this variation in the ashed residue is seen in the case of

filters containing a large amount of asbestos (5-75 pg/cm^) which ash satisfactorily and

filters containing small amounts of asbestos (0-1 pg/cm^), which ash poorly. The latter

often shrinks into a hardened mass which is difficult either to disperse in a liquid, or to

ash further. It appears that the asbestos fibers or other particles (say, from air collection) help support the filter membrane to permit better, more uniform exposure to Radio

Frequency, which in turn reduces the ashed residue.

4. Relative humidity surrounding the alignment medium. The relative humidity

surrounding the alignment medium has also been shown to be a significant factor. At room temperature (20-22°C) the alignment is practically nonexistent for low humidities (20-

25% RH). At higher humidities (35-45%), the alignment quality improves. For still higher

humidities, alignment is possible but is accompanied by electrode corrosion. The optimum

humidity range is therefore defined as 40-45% at 20-22°C.

5. Contamination effects. Finally, it is important to note that the presence of

soluble organic and inorganic matter in the alignment medium can greatly affect the fiber

alignment. It is, therefore, essential that all rules of cleanliness be strictly adhered

to, especially in the last stages of preparation, namely, prior to dispersing the clean,

ashed samples in the alignment medium.

References

[1] Birks, L. S., Fatemi, M., Gilfrich, J. V., and Johnson, E. T., Quantitative Analysis

of Airborne Asbestos by X-Ray Diffraction: Final Report on Feasibility Study,

Environmental Protection Agency Report EPA-650/2-75-004, Jan. 1975; also nrl Report

7874, Feb. 28, 1975.

190
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

RESPIRABLE AMBIENT AEROSOL MASS CONCENTRATION MEASUREMENT

WITH A BATTERY-POWERED PIEZOBALANCE

Gil more J. Sem

Thermo- Systems Inc.

2500 N. Cleveland Ave.

St. Paul, MN 55113

1 . Introduction

In 1975, Sem and Tsurubayashi [1]^ introduced a new, portable, battery-powered instrument, the piezobalance, for near-real -time measurements of respirable aerosol mass con- centration. The instrument uses electrostatic precipitation to deposit respirable particles

down to 0.01 pm diameter onto a piezoelectric microbalance mass sensor. Primary applications

of the piezobalance include [2]

1) industrial hygiene walk-through surveys to locate industrial areas requiring better

smoke and dust control or requiring compliance measurements, 2) measurements in offices,

stores, restaurants, arenas, and other public buildings to assist in adjustment of

ventilation systems for control of tobacco smoke, and 3) outdoor measurements to

characterize human exposure to respirable aerosol while engaged in activities such as walking down the street, riding an auto or subway train, barbequing dinner in a backyard, or camping in a remote wilderness.

This paper will 1) suggest a rationale for respirable or fine particle measurements of

outdoor air, 2) review the design, operation, application and performance of the piezobalance

and 3) present some typical results.

2. Why Measure Outdoor Respirable or Fine Dust Concentrations?

Current Environmental Protection Agency regulations applicable to outdoor ambient air

are based on "total" suspended dust concentration rather than "respirable" dust concentration.

Outdoor areas are subject to a maximum yearly average of either 60 or 75 yg/m^. Daily

average concentrations must not exceed 250 yg/m^ more than once per year. The standard

measurement instrument is the hi-vol sampler with a specifically prescribed design.

Although no regulations currently exist, outdoor environmental scientists [3-8] often measure the "fine" or "submicron" particle fraction, containing primary and secondary

combustion, condensation, and photochemical smog aerosols. [3] The larger, supermicron

particles become airborne by different processes, usually involving the breakup of larger

particles, such as wind-blown and automobile-generated dusts and fly asfi. Recent data [3-

8] strongly suggests that this is a basic, nearly-universal characteristic of aged atmospheric aerosol. The particle size which divides the 2 types of particles is usually in the

1-2 ym range.

The fundamental difference in the source of the two aerosol fractions points toward a future regulation covering small particles, based either on the concentration of specific

chemical species or the combined concentration of all species.

^Figures in brackets indicate the literature references at the end of this paper.

191
Current Occupational Safety and Health Administration and Mine Enforcement and Safety

Administration regulations apply to outdoor air only where employees are working, not areas frequented by the general public. The regulations are based on "respirable" dust concentration measured by a personal lapel sampler worn by the employee during his work shift.

The definition and rationale of respirable dust, based on particle deposition in various

parts of the human respiratory system, is discussed by Lippman [9] and others. Respirable

particles are defined by the American Conference of Governmental Industrial Hygienists and

the Atomic Energy Commission as particles which pass a sampling pre-cutter with 50 percent

penetration at 3.5 pm aerodynamic equivalent diameter. Respirable particles penetrate

deeply into the respiratory system and are thus capable of harming one's health.

Since particles smaller than about 2 pm become airborne by processes much different

from those which suspend larger particles, [3] and since respirable particles cause the

greatest potential hazard to human health, some form of measurement of these particles in

the outdoor environment seems justified.

3. Why Use a Battery- Powered, Hand-carried Instrument?

Current governmental monitoring of total suspended particles in the U.S. is done at

sets of stations covering each metropolitan area. Fixed-station monitoring determines

changes in concentration within the urban cloud on a monthly or yearly time scale. However,

such stations do not usually measure the particulate exposure of the people at street level

and the currently used hi-vol sampler can provide no information about exposures with a time

scale less than a day.

The personal lapel sampler used by the Occupational Safety and Health Administration

cannot be conveniently worn by people performing normal outdoor activities. Another problem

of the lapel sampler for non-occupational sampling is that its accuracy for 10-100 pg/m^

levels, even for 5-10 hr samples, is not very good.

With the above limitations, respirable or fine particle aerosol measurements on the

street or in other public areas can best be done with a small, portable, battery-operated,

real-time sensor capable of accurate measurements from 5-10,000 pg/m^. The piezobalance is

a strong candidate for the measurement.

4. Description of the Piezobalance

Sem and Tsurubayashi [1] and Sem, et at. [2], recently described the piezobalance in

considerable detail. This section briefly reviews major points of interest.

Figure 1 is a photograph and schematic diagram of the piezobalance. A small pump sucks

1 liter per min of aerosol into the instrument. Particles greater than 3.5 pm aerodynamic

equivalent diameter are removed from the air stream by an impactor. Particles passing the

impactor are carried to an electrostatic precipitator which deposits them onto a piezoelectric

microbalance sensor oscillating at its natural frequency.

The particles on the sensor cause the natural frequency to decrease by an amount

proportional to the particulate mass. Each 10-sec frequency shift is displayed by the

digital display. Each 2-min frequency shift is converted to units of mg/m^ and displayed

digital ly.

The piezobalance includes a simple wet-sponge mechanism for wiping the particles off

the sensor when the accumulated deposit exceeds 5 pg. The cleaner operates by a manual turn

of the cleaning knob. Cleaning sponges require rewetting every 1-2 days and replacement

after 20-50 cleanings.

The sensor is a disk of crystalline, AT-cut quartz, about 13 mm diameter and 0.2 mm

thick. The crystal forces an electrical circuit to oscillate at a highly stable resonant

frequency. The frequency decreases in direct proportion to the particulate mass added and

adhering to the sensor. The practical sensitivity is about 10"^ g.

192
I

IMPACTOR PRECIPITATOR

>3.5um DEPOSIT PARTICLES <3,5pm

HERE DEPOSIT HERE

FIGURE I : PHOTOGRAPH AND AIR FLOW SCHEMATIC

DIAGRAM OF THERMO-SYSTEMS MODEL 3500

PIEZOBALANCE RESPIRABLE AEROSOL MASS

MONITOR.

193
The shift in resonant frequency Af (Hz) during sampling time At (sec) at constant

sampling rate Q (m^/sec) is related to aerosol concentration C (yg/m^j by:

C = ^^

(1) ^ SQ At ^'^

S is the mass concentration coefficient, expressed in Hz/yg, which accounts for crystal mass sensitivity, aerosol collection efficiency, and particle sensing efficiency. S is factory

calibrated for each instrument with welding smoke and is nominally about 200 Hz/pg.

Since the resonant frequency of the sensor is about 5 MHz, the measured frequency is

reduced to a more convenient range by electronically beating the sensor frequency against a reference frequency 1-3 KHz higher than the sensor frequency. The resulting mixed frequency

is the difference between sensor and reference frequencies. Af in equation 1 is the change

in mixed frequency as particulate mass is added to the sensor.

For the 50-2000 ug/m^ respirable concentration range, the piezobalance uses a 2-min,

direct-readout mode. When the operator presses the "measure" button, the pump draws Q = 1 liter/min (1.67 x 10"^ m^/sec) and the electrostatic precipitator is turned on. Sample time

begins when the operator presses the "start" button. For concentrations below 2000 yg/m^,

120-sec sample time is used; for 1-10 mg/m^, the 24-sec sample time. When sample time ends, mass concentration appears on the digital display in XX. XX mg/m^ format. Statistical

accuracy of variable concentration measurement can be greatly improved by making 5 or more

2,-min measurements at a single location.

For the 5-100 yg/m^ range, an indirect readout mode is used to obtain the highest

accuracy. A 120-second sample time is selected and two seconds after pressing the "start"

button, the mixed frequency displayed on the digital readout is recorded. The piezobalance

is operated in measure mode for about 15-30 min. Even though the piezobalance displays a concentration continuously after 2 min, it continues to precipitate particles onto the sensor. After the 15 to 30-min sample time, the "start" button is repressed and mixed

frequency is again recorded after 2 seconds. By subtracting the first mixed frequency from

the second, the difference is Af in equation 1.

The piezobalance is not a continuous monitor. It has no provision for recording data.

It cannot sense particles above 10 ym, cannot measure concentration above 20 mg/m^, and

cannot measure aerosol streams above 40 °C.

5. Accuracy of Piezobalance Measurements

Sem, et at. J [2] compared piezobalance and low-volume 47-mm filter measurements on several aerosols. Piezobalances had been previously calibrated using welding smoke. Arrangement of the test setup was found to be important for accurate, repeatable results.

Figure 2 shows results for outdoor air, oil mist, and several combustion smokes. Nearly all

piezobalance concentrations were within ±10 percent of filter measurements.

Although the operator should calibrate his piezobalance on his specific aerosol,

reasonable results can be obtained without such calibration in cases where respirable aerosol

is primarily combustion- or condensation-generated. Most outdoor aerosol below 1-2 ym

appears to fit this description. [3-8]

The piezobalance measures aerosol at ambient humidity. Most filter sampling procedures

call for drying filters before weighing. Agreement cannot be expected between piezobalance

and low-volume measurements if filters are dried before weighing. Filters used must be

highly hydrophobic, such as Millipore fluoropore membrane filters. The piezobalance will

not measure the correct concentration if relative humidity varies more than -0.5 percent

during a measurement, rarely a problem for 2-min measurements, but potentially serious for

the 15 to 30-min low concentration mode.

194
LOW-VOLUME FILTER CONCENTRATION, mg/m'

FIGURE 2; COMPARISON OF PIEZOBALANCE MEASUREMENTS

WITH LOW-VOLUME FILTER MEASUREMENTS ON

SEVERAL AEROSOLS. THE PIEZOBALANCES WERE

CALIBRATED EARLIER WITH WELDING SMOKE.'

6. Outdoor Measurements

During the past year, outdoor aerosols were measured in rural and urban areas of Utah,

Colorado, and Minnesota. Table 1 lists results of such measurements. All concentrations

were measured with the 5-100 yg/m^ data mode. At >_ 20 min, and S = 200 Hz/yg. Although no low-volume filter samples could be obtained within reasonable sample times at these low

concentrations, measured concentrations were consistent with each other and with volume

concentrations and size distributions measured by Sverdrup, et al. [10], in the Mojave

Desert in November, 1972, and recent urban measurements. Recent rural Minnesota measurements

suggest considerable variability in fine particle concentration over relatively short time

periods, probably caused by local upwind combustion sources. Some 20-min rural concentrations

approached urban street corner concentrations.

195
TABLE I Outdoor Respirable Aerosol Concentrof ions Meosured in Minnesota, Colorado, ond Utati. All Somple Periods Were 20 Minutes or Longer Unless Noted.

DATE TIME LOCATION COMMENTS

MASS

CONCENTRATION

II- 9 -75 1 1 .4 J

II- 9 -75 I5.*45

II- 10-75 I3.'45

II- 10-75 I4II5

II-10-75 17:30

II- 29-75 16.' 10

II- 29-75 16:40 5- 29-76 15:50

I9:05 19:25

19:45 20:05

5- 30-76 00: 10 09:45

10:05

10:25 10:45

ii:o5

11:25 12:05

7- 4 -76 19:15 19:35

19:55 20:15 20:35

21:20

7--5 -76 18:50

1

19:10 19:30

7- 6 -76 18:20

-23-76

18:45 I9:05

19:25 20:10 20:30

20:50

21:10 21:30 09:30

10:00

10:20 10:40

11:00

11:20

ii:4o

12:10

12:50

13:10 13:30

13:45

14:00

MONUMENT VALLEY, UT MONUMENT VALLEY, UT

NEAR NATURITA CO

NEAR NATURITA CO

100 Km S GRAND JUNCTION, CO

8Km N UNDERWOOD, MN

IN AUTO ON FREEWAY,

ROSEVILLE -MINNEAPOLIS, MN

DOWNTOWN MPLS, NE CORNER

7th-NIC0LLET, UPWIND OF BUS TRAFFIC

DOWNTOWN MPLS, NW CORNER

7th-NIC0LLET,

DOWNWIND OF BUS TRAFFIC

IN AUTO ON FREEWAY,

MINNEAPOLIS-ST PAUL, MN

DOWNTOWN ST PAUL.MN,

SW CORNER 7th-CEDAR

DOWNTOWN ST PAUL, MN,

IN PARKING RAMP

IN AUTO ON FREEWAY

ST PAUL-ROSEVILLE, MN

CLEAR, ICC, WIND W 3-8Km/h, DESERT

CLEAR, IO°C, WIND W 3-8Km/ti, DESERT

CLOUDY, 5°C, WIND N 3 Km/ti , SEMI - DESERT

CLOUDY, 5°C, WIND N 3Km/h, SEMI-DESERT

P CLOUDY, 2''C, WIND S 0-30 Km/h, RANCH

CL0UDY,-8°C, WIND NW 5Km/h, FARMYARD

CL0UDY,-8°C, WIND NW 5K m/h , FARM Y/" o

P CLOUDY, 20''C WIND SE 10-20 K m/ti , LAKESHORE

P CLOUDY, 20°C WIND SE 5 - 15 Km/ti, FARMYARD

PCLOUDY, 20°C, WIND CALM, FARMYARD

CLOUDY, I7°C, WIND CALM, FARMYARD

HAZY, 30°C, WIND E 0-3 Km/ti, FARMYARD

HAZY, 30°C, WIND SSE 10-20 Km/li, FARMYARD

P CLOUDY, 27°C, WIND W 3-8 Km/ti, FARMYARD

(RAINED Icm, WIND W TO 50 Km/h AT I7:00)

P CLOUDY, 25''C, WIND N 15-20 Km/ti ACROSS LAKE

CLEAR, 27°C, WIND SE 0-IOKm/h, URBAN FREEWAY

CLEAR, 28°C

CLEAR, 28''C CLEAR, 28°C

CLEAR, 30°C

CLEAR, 30°C

CLEAR, 30°C

CLEAR, 30°C

CLEAR, 32''C

CLEAR, 32''C CLEAR, 32°C

CLEAR, 32°C

CLEAR, 32°C

URBAN STREET

URBAN STREET

URBAN STREET

URBAN STREET

URBAN STREET

URBAN STREET

URBAN FREEWAY

URBAN STREET

URBAN STREET

URBAN STREET

URBAN PARKING RAMP

URBAN FREEWAY

55

13148

13

13

17 30

31 29

31 25

22

18 22

21

18

15

15

II8

76

18 20

7

87

3

7

3

54

2

2

36

31

20

22

25

41

33

39

49

46

44

34

90*

44

*AVERAGE OF THREE 2 MINUTE SAMPLE PERIODS.

195
References

[1] Sem, G. J. and Tsurubayashi , K., A New Mass Sensor for Respirable Dust Measurements, Am.

Ind. Hyg. Assoc. J. 36:791 (1975).

[2] Sem, G. J., Tsurubayashi, K., and Homma, K., Fiezohalanae Respirahle Aerosol Sensor:

Application and Performance, Presented at the Am. Ind. Hyg. Assoc. Annual Meeting,

Atlanta, GA, May 17-21, 1976.

[3] Hidy, G. M. , et al.. Summary of the California Aerosol Characterization Experiment, J. Air Poll. Control Assoc. 25:1106 (1975).

[4] Whitby, K. T. , Husar, R. B., and Liu, B. Y. H., The Aerosol Size Distribution of Los

Angeles Smog, J. Colloid Interface Science 39:177 (1972).

[5] Willeke, K., Whitby, K. T., Clark, W. E., and Marple, V. A., Size Distributions of

Denver Aerosol s--A Comparison of Two Sites, Atmos. Environ. 8:609 (1974).

[61 Durham, J. L., et al.. Comparison of Volume and Mass Distribution for Denver Aerosols,

Atmos. Environ. 9:717 (1975).

[7] Lundgren, D. A. and Paulus, H. J., The Mass Distributions of Large Atmospheric Particles,

J. Air Poll. Control Assoc. 25:1227 (1975).

[8] Whitby, K. T. , et al.. Aerosol Size Distributions and Concentrations Measured During

the General Motors Proving Ground Sulfate Study, Report EPA-600/3-76-03S, NTIS,

Springfield, VA (April 1976).

[9] Lippman, M., Respirable Dust Sampling, Am. Ind. Hyg. Assoc. J. 31:138 (1970).

[10] Sverdrup, G. M., Whitby, K. T., and Clark, W. E., Characterization of California

Aerosols--II Aerosol Size Distribution Measurements in the Mojave Desert, Atmos.

Environ. 9:483 (1975).

197

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

A CASCADE IMPACTION INSTRUMENT USING QUARTZ CRYSTAL MICROBALANCE SENSING ELEMENTS

FOR "REAL-TIME" PARTICLE SIZE DISTRIBUTION STUDIES

D. Wallace

IBC/Berkeleyi

Irvine, California 92664 USA

and

R. Chuan

Defense Division/Brunswick Corporation^

Costa Mesa, California 92626 USA

1. Introduction

Sampling instruments using cascaded impaction type nozzles and collection plates for

the determination of particle size distribution have been in use for many years and have

established the validity of the classical impaction nozzle theory. In many applications, a serious limitation in this type of instrument is the long sampling times required to collect

a sample of sufficient mass for accurate weighing with an analytical balance on the collection

plate. Thus, phenomena with short time constants cannot be observed because of the long

sampling times required; only integrated distributions are measured without the fine structure

of individual events.

A new instrument is available which uses the classical impaction nozzle in a cascaded

series of stages but replaces the sample collection plates with individual quartz crystal

microbalances (QCM), measuring in real-time and capable of weight resolution in the nanogram

range. With the sensitivity obtained with the QCM sensing crystals, sampling times are shortened to two minutes or less depending upon the sampled concentration, thus quasi-realtime measurements can be made while at the same time retaining the primary measurement

advantage of the impaction nozzle technique, i.e. , measurement based upon the mass and

aerodynamic diameter of the particle.

2. Impaction Theory for Particle Sizing

Particle size discrimination is obtained when using impaction flow nozzles by a combination of inertial and viscous drag forces on the particles as illustrated in figure

1. Depending upon the nozzle and plate geometry and the particle diameter and velocity on leaving the nozzle, the particle has a definite probability of striking the collection

plate. The parameter characterizing the capture probability is the Stokes Number which is

given in figure 1, along with other pertinent nozzle flow parameters. Marple and Willike [1]^

have established design criteria for the Stokes Number for 50 percent collection efficiency

as a function of nozzle-to-plate spacing, Reynolds Number , (etc, )

, which facilitates cascade

design. The controlling relationship between the 50 percent cutoff particle diameter

Dr and geometrical and flow parameters is

^50

'50

3 D. N

c Q.

1/2

(1)

^Tormerly IBC/Celesco Industries Inc.

^Formerly MSD Division/Celesco Industries Inc.

^Figures in brackets indicate the literature references at the end of this paper.

199
where Dj is the nozzle diameter, N is the number of nozzles in a particular stage, c is the

Cunningham Slip Coefficient, is the volume flow through the unit at ambient pressure and

P /P is the ratio of the nozzle pressure to ambient pressure.

Dp *NJ

"so

Figure 1. Impaction theory criteria,

To achieve the collection of low submicron particles, the design must include some combination of reduced nozzle diameters and high volume flow with the implied high nozzle

velocity, Vq, and attendant large pressure drop, aP. The high particle velocity can lead

to particle bounce and reduced collection efficiency as reported by Rao [2] but can be

essentially eliminated by the proper selection of an adhesive coating on the collection

disk, as reported by Cahill [3].

A cascade impaction instrument is now available using these design criteria in a tenstage arrangement with calculated collection efficiency curves, shown in figure 2. The 50

percent cutoff points cover the particle size range of 25 micrometers down to 0.05 micrometers. 2no
LU

CO

CN —

CO —

in —

to -

00 -

a> -

o -

LU

I-LU

UJO

DC uLU LU O

QCO <

Q o

QC

Z)

I-<

o

I-DC

ooooo o o

>o A3N3l3ldJ3 N0I1Q31103

Figure 2. Collection efficiency curves.

3. Quartz Crystal Microbalance as Weighing Technique

The use of the piezoelectric quartz crystal as a microbalance was first suggested by

Sauerbrey [4], who formulated the sensitivity equations relating crystal frequency shift to mass addition. A later perturbation analysis by Stockbridge [5] correctly accounted for

the addition of discrete mass increments and applies more directly to the use of the QCM in

this particle collection application. The crystal sensitivity to mass for 10 MHz crystals

is 713 Hz/yg. The ambient concentration of particles in the size range defined by the

stage collection curve can be determined by measuring the frequency shift rate and the

volume flow of air sampled.

201
1402.5 Af/At (2)

where C is the ambient concentration in pg/m^ of a certain particle size, Af/At is the

frequency shift rate in Hz/min and Qa is the volume flow of air sample measured at ambient

conditions in ml/min. The design volume flow is determined then by the minimum reliably

measurable frequency shift rate and the minimum desired concentration. Frequency drift

rates of one Hertz per five minute interval are easily obtained. Thus, in design, one Hertz per minute was conservatively used for the minimum signal . Minimum concentrations

per stage of Spg/m^ were chosen leading to a volume flow of approximately 250 ml/min. Once

this volume flow was chosen, the separate stage nozzles were designed for the desired

particle sizes according to Eq. (1).

4. Verification of Stage Collection Efficiencies

Calibration of a cascade instrument is made difficult by the absence of absolute

aerosol standards of accurately known size distributions. The aerosol generated for

calibration purposes must itself be characterized as to concentration and size distribution

by yet other instruments with their own particular built-in assumptions. This is particularly true of the low submicron range, which is below the range capability of commercial

aerosol generators. The alternate approach of correlation with similar instruments is

questionable since completely different collection techniques are used.

The primary area of concern is particle collection efficiency, particularly in the

submicron range where high nozzle flow velocities exist. Low capture efficiency would

permit particles to bounce off the collection plate and carry over into the following

stage. This would result in a broadening of the range of particle sizes collected in a stage and a greater uncertainty in the actual size distribution. Studies with a scanning

electron microscope tend to verify the accuracy of the calculated collection efficiency

curves shown in figure 2. The SEM photos in figures 3 and 4 for stages 5, 6, 8 and 10

verify the cut points in these stages. Very few particles are observed to be larger or smaller than the 50 percent particle diameter dimension indicated on the photograph.

Extensive agglomeration of particles occurs, with the low submicron particles forming

an effective collecting surface for subsequent particles. As evidenced by the photo in

stage 10, the mound of particles which couples to the vibrating crystal is orders of

magnitude greater than a few particle monolayers.

5. The Instrument

In the instrument shown in figure 5, the particle size range of 25 micrometers to

0.05 micrometers is measured in ten cascade stages. Each separately removable stage is a complete unit with impaction nozzle, quartz crystal microbalance and hybrid chip electronics.

Stage electronic output is thus a frequency which is amplified by electronics in the base

cabinet and can then be fed into a multiplexed printer or directly to a computer. A selfcontained pump located in the base provides a constant volume flow through the stages.

202
MAGNIFICATION 1 K MAGNIFICATION 2K

MAGNIFICATION 10K

Pp=2gm/ce

STAGE 6

MAGNIFICATION 5K

P^= 2gm/cc

STAGE 5

Figure 3. Collected particle size verification by SEM photomicrographs.

203
MAGNIFICATION 1 K MAGNIFICATION 200

MAGNIFICATION lOK MAGNIFICATION 2 OK

•<5Q=0.2Mm K^jj^ 0.05jum

Pp=29m/cc Pp=29m/cc

STAGE 8 STAGE 10

Figure 4. Collected particle size verification

by SEM photomicrographs.

204
Figure 5. Ten stage QCM cascade.

205
206
6. Field Data

The real-time measuring capability of the QCM Cascade makes possible transient measurements from airplanes or automobiles. Three studies exemplifying this technique were

performed in 1975: (1) a vertical profile of aerosol size over the Los Angeles Basin was taken from a light plane; (2) a profile of particulate size produced by a major brush fire

in the San Gabriel Mountains near Los Angeles was measured from an automobile; and (3) a light plane was used to measure power plant plume aerosol size distribution changes as a function of distance downstream from the stack.

Vertioat profile of aerosol size over Los Angeles Basin: The variation in aerosol

size distribution and total concentration is shown in figure 6 as a function of altitude

over the Los Angeles Basin on October 16, 1975. The measurements were taken from 50 feet

to 1900 feet in altitude with the well-defined bimodal aerosol size distribution shifting

as expected to greater fractions of submicron particles at the higher altitudes.

Partioulate size distribution produaed by San Gabriel Mountains brush fire: A brush

fire in the San Gabriel Mountains of Southern California produced smoke which extended over

portions of three counties in and around Los Angeles. Size distribution measurements were

taken along the freeway system beginning outside the smoke area and traversing the entire

smoke region into Orange County, The locations of the measurement points are indicated on

the map in figure 7A, along with total mass concentrations and mass mean diameters. Lines

of constant concentration are roughly indicated as interpolated from the measured data.

The size distributions presented in figure 78 began on the western edge of the smoke

with a significant amount of large particles caused by the high winds. Entering the heavy

smoke area, a trimodal distribution was observed which was common throughout the smoke

area. Preliminary analyses indicated the significant middle mode at 0.8 pm was responsible

for light scattering giving a bluish color to car headlights.

Aerial measurement of particulate size distribution in Four Corners Power Plant Plume:

Measurements were taken from a light plane of plume particulate size distribution as a function of downstream distance at the Four Corners Power Plant. This data was taken under

the direction of Dr. Rudolf F. Pueschel of the National Oceanographic and Atmospheric

Administration. The flight path and two of the measured distributions are shown in figure

8. The plume directly over the power plant has a relatively high MMD of 2.2 pm. Downstream

approximately 25 miles submicron sulfate aerosols have formed and the MMD has decreased to

0.45 ym.

207
Figure 7a. Measuring locations, total particulate concentrations

and mass mean diameters during brush fire episode of

November 24-25, 1975.

208
Dp — ju""

7

Figure 7b. Particulate size distribution during brush fire

of November 24, 25, 1975.

209

References

Marple, V. A., Willike, K. , Inertial Impaators: Theory, Design and Use, Fine Particle

Symposium, Minneapolis, MN, May 28-30, 1975.

Rao, A. K., Non-Ideal Collection Characteristics of Inertial Inrpactors. Summarized

Ph.D. Thesis, University of Minnesota, Minneapolis, MN.

Prepared statement of Dr. Tom Cahill, University of California at Davis, presented at

Aerosol Measurement Workshop, March 24-26, 1976, University of Florida, Gainesville,

FL.

Sauerbrey, G., Verwendung von Schwingquartzen zur Wagung dunner Sohieten und vur Mikro

Wagung, Zeit fur Physik, Vol. 155, pp 206-222 (1959).

Stockbridge, C. D., Resonance Frequency versus Mass Added to Quartz Crystals, Vacuum

Microbalance Techniques, Vol. 5, 1966, Plenum Press, NY, K. Behendt, ed., pp 193-206.

211

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

A LIMITATION ON ELECTRICAL MEASURES OF AEROSOLS^

W. H. Marlow

Department of Applied Science

Brookhaven National Laboratory

Upton, New York 11973, USA

1. Introduction

All aerosol measurement methods which electrically charge the aerosols in the presence

of free ions and in the absence of a strong external electric field are referred to as "electrical measures of aerosols".

Numerous such methods have been used in the past [1]^ and are currently employed.

Based upon the assumption that there is a constant, natural, background ion source,

atmospheric conductivity has been used as a measure of the presence of aerosol particles

because such particles remove the effective charge carriers from the atmosphere. Another

variety of electrical measure is the total charge acquired by the aerosol under either

natural or artificial charging conditions. Currently, the most widely cited electrical

method for aerosol size distribution analysis is the "diffusion charging mobility analysis

method" [2]. In this method the electrical current due to the controlled unipolar charging

of the aerosol is measured, while increasing mobility fractions of that aerosol are removed.

The hypothesis is that by monitoring the diminution of aerosol current as a function of

the known particle electrical mobilities removed, a measure of the aerosol size distribution

is derived.

Fundamental to all such measures of aerosol size is the assumption that any aerosol

can be put in a well-defined charge state. This note presents an examination of that

assumption. From this examination, a rigorous condition for the applicability of diffusion

charging measures of aerosol size will follow.

2. Aerosol Charge Acquisition

In the atmosphere there are numerous natural and artificial sources of available

charge. Ionization by cosmic rays and radioactive decay products from the earth supply a continuous source of bipolar (both positive and negative) background ions while concentrated radioactive sources, corona discharges, combustion, and thermionic emission in

various arrangements provide bipolar or unipolar (only a single polarity) ions. It is

known that such free ions only survive for less than ten microseconds under atmospheric

conditions before they begin participating in clustering reactions with atmospheric

trace gases [3]. The clustering pathway of a single ion is dependent in detail upon the

varieties and concentrations of such molecules as SO2, NH3, H2O, NO^, numerous organic

species, et al. [4]. As a result, the physical properties, i.e., mass and mobility of an ion cluster are also sensitive to the atmospheric trace gases. Whatever the fate of an individual ion, a spectrum of ions of differing chemical and physical properties will be

^This work was supported by the Division of Biomedical and Environmental Research, U.S.

Energy Research and Development Administration, Washington, D.C.

^Figures in brackets indicate the literature references at the end of this paper.

213
in evidence whenever a number of ions are simultaneously present. Consequently, there is no intrinsic meaning to the citation of a single ion species (or a physical property such

as mobility) as characterizing the small ions under a particular set of conditions in the

atmosphere.

The motion of an ion in the vicinity of an aerosol particle depends upon the physical

characteristics of both the ion and the particle. For the sake of mathematical traceability, the particle is usually approximated as a sphere, an approximation which is well

justified in many atmospheric circumstances. Two limiting, conceptually straightforward

cases are relevant in treating aerosol charge acquisition. One is the macroscopic or collision-dominated case wherein the ion mean free path, with respect to collision with

the neutral gaseous molecules, is very small in comparison to the particle radius. Under

such conditions, particle charge acquisition should be capable of accurate description in

macroscopic terms since the variables determining charging are accessible to macroscopic

control. The other case is the free-molecular approximation wherein the ion mean free

path is considerably larger than the particle radius. When the ion mean free path is of

the same order of magnitude as the particle radius, the ion is in the transition regime of

kinetic theory [5].

The equations for bipolar polydisperse aerosol charging by polydisperse ions can be

written as — (pP

) dt ^^jn^

pP I? j(n-l) ^ ^j(n-l)i -1 P^^ L [}^. jn • jm 1 iP + pP z B. j(n+l) ^ '^jCn+Di

i:P pP

jn

rP. i:P jm 1

+ ion equations

I'

1

number density of particles in size-class j, carrying n charges of sign p

number density of small ion species i which is of polarity p

uP^.; = volumetric acquisition rate of ion specie (i,p) by a j-sized, n-charged

particle of polarity p

B

P volumetric acquistion rate of ion specie (i,p) by a j-sized. n-charged

"^"^^ particle of polarity-p.

Properly speaking, P and I should be considered as random variables [6] with mean values as measured in the laboratory. In that case, the charging equations become stochastic

differential equations reflecting the nonuni formi ty of the ion-aerosol mixture. The

substantial and possibly important additional complications such a treatment would entail

have not yet been addressed. Therefore, the above equations will be considered as deterministic (which means that their solution is unique for a given set of initial conditions).

For the sake of clarity, only unipolar, monodisperse aerosol charging will be con- sidered below. This is expressed by setting I-P = 0 and dropping the j and p indices.

Nonetheless, the following arguments apply equally well to the bipolar case. Their conse- quences for polydisperse aerosol charging will be discussed below. The unipolar charging

equations can therefore be written

dPn

dt n-1 'n-li

U . I ni

214
In the conision-dominated case.

U . ^ U^. = vi. m m n

where fp is a factor dependent solely upon characteristics of the aerosol particle and its

charge state and y-j is the electric mobility of ion specie i. This gives

dt ^ n-1 n-1 n n' . i i

Since Ey^ 1^ is the ionic conductivity of the atmospheric segment under consideration and

is a macroscopic quantity which can be controlled to compensate for external conditions, a well-defined charge state can be achieved for the aerosol.

By similar considerations for the free molecular case,

dPn = (p ff.m. _ p ff-m. w 7 t dt ^^n-1 ^n-1 ^n ^n M ^i

where f^'_^' is again a factor dependent solely upon particle characteristics and v-j is the

mean ionic speed. This time z v-j I-j is not an obvious macroscopic variable. This implies

that aerosol charging in the "l^ree molecular regime is governed by a quantity which is

poorly defined in macroscopic terms.

If R is the particle radius and A-j the ion mean free path, the transition regime is

usually delimited as 0.25 < Kn-j < 10 where Knj = Ai/R. To understand the difficulty of

bringing an aerosol in this size range to a well-defined charge state, it is useful to

express the general volumetric charge acquisition rate as

m

f^ R X Vi

c e

In the collision-dominated regime we can then show that f^ = f^

of charge, k = Boltzmann's constant, T = temperature) and X = A-,- while in the free molecular

regime fp = fj^-m- R and X = 1. This demonstrates that in the transition regime X is

explicitly a function of ion properties and at least implicitly a function of R while

fn "

^ii^ remains a function of particle properties alone,

charging equations are

(e = elementary unit

Then X = X (R, A-; , . . . ) and the

dPn ^ ,p .tr

dt ^^n-1 ^n-1

P f^*^) R E n n

' ^

X (R, A, ) I.

Since X (R, A-j, ...) is a function about which very little is known either experimentally

or theoretically, aerosol charging in this regime is equally poorly defined.

Polydisperse aerosol charging for particles, which are all in either the collisiondominated or free molecular regimes, may still be treated experimentally by starting with

some calibration procedure wherein an ad hoc determination of the charging variables is

made. However, this procedure cannot be extended to an aerosol in which the transition

and either of the other kinetic theory regimes is included. The fundamental physical

obstacle is that charging depends upon differing parameters and the car^eful control of

one, such as conductivity, does not guarantee that another, such as E v-j 1^, will have

any clearly defined value. This difficulty is compounded by the fad that even the

215
mathematical form of X (R, X-j , ...) for the transition regime is not known.

3. Aerosol Measurement

If the atmospheric cluster ion spectrum were unique or at least clearly defined, some calibration procedure which related the peculiarities of that spectrum to the charging of

each of a variety of sizes of monodisperse aerosols could be devised. As has been discussed,

this is not the case. This means that measurements dependent upon diffusion charging made

in one set of atmospheric conditions will most li'kely have little quantitative relationship

to those taken at either another time or place unless the ionic conductivity was controlled

and comparisons were made only for particles in the collision-dominated regime.

In terms relevant to measurements made in the lower troposphere, the free molecular

regime corresponds to particles below 0.01 m radius or larger.

4. Illustrative Example

The operational consequences of the foregoing discussion can be very well illustrated

by a brief discussion of the performance of the Electrical Aerosol Analyzer or "EAA"

(Thermo-Systems , Inc., St. Paul, Minnesota) [7]. This is the field instrument based upon

the original Whitby Aerosol Analyzer that first used the "diffusion charging mobility

analysis hypothesis" for aerosol size distribution measurements.

In the EAA, the aerosol stream is first passed through a charger whose design is

intended to maintain a constant number density of ions. The most closely related parameter

which can be controlled is the ion current and this is what is actually regulated in this

device. Since the ion current is directly proportional to the ionic conductivity, the EAA

does produce a well-defined charge distribution upon the largest particles of the aerosol,

which are in the collision-dominated regime. General agreement has thus been found between

the EAA and optical particle counters when both devices have been properly calibrated.

Similarly, in a study to determine the role of cluster ion variability on the performance

of the EAA [8], a statistical analysis of data showed narrow confidence intervals for

parameters related to charging of particles in or near the collision dominated regime.

Conversely, that same study showed that at a 90% confidence interval the particle current

due to the transition regime particles were broad and could vary over almost an order of

magnitude.

A mathematical model for the ideal EAA has been constructed and computed. This model

includes six sizes of particles and six species of cluster ions and incorporates the

essential features of constancy of total small ion conductivity in the charger and classification of particles according to their electrical mobility. Variability of the cluster

ion spectrum produced in the charger corona is included by weighting the ion distribution

among the species represented in differing ways. Ion removal is accomplished either by

collision with an aerosol particle or by removal due to the constant ion current. Table 1 gives the cal cul ational inputs and results. N(R) is the number density of sampled particles

of R micrometers and the headings "Successive Numerical Flux Differences" give the

differences in fluxes of charges carried by particles between successive total flux measurements according to the EAA's operational parameters. The first is zero because of the

omission of particles under 0.005 ym from the model. The fourth and higher differences

are each equal in the two cases presented here because the corresponding particles were computed as if they were all in the collision dominated regime due to the inavailability

of any reasonably accurate expression for U^^ that included the image force for particles

of 0.05 ym radius. The ionic fractions from the corona were chosen as being representative

of plausible real variations in the ion spectrum that can occur in the presence of differing

fractions of atmospheric trace gases that may occur under field conditions. As a result,

a 70% discrepancy in the flux differences corresponding to the transition regime charged

particle flux is computed. By comparison the "diffusion charging mobility analysis,

hypothesis" predicts that the numbers are equal.

216
Table 1

Numerical results of mathematical model of EEA performance

N(R): N(.005) = 10*^ N(.Ol) = 7 x 10^ N(.05) = 5 x

10^*

N(.l) = 10"^ N(.5) = 500 N(l.O) = 50

Ion Index i 1 1 4 5^ 6_

Mass (AMU) 69 73 88 109 148 279

Mobi 1 i ty

(cm2/V-sec) 2.2 2.1 2.0 1.8 1.5 1.0

Mean free path

(ym) 0.022 0.020 0.018 0.015 0.011 0.0056

Case 1

Ionic fraction

from corona 0.10 0.10 0.10 0.10 0.20 0.40

Ionic fraction in

charging region 0.062 0.065 0.068 0.076 0.18 0.55

Successive numerical flux differences

0.0 1.0 X 10^ 1.4 x 10^ 2.4 X 10"*

Case 2

Ionic fraction

from corona 0.40 0.20 0.10 0.10 0.10 0.10

Ionic fraction in

charging region 0.33 0.17 0.091 0.10 0.12 0.18

Successive numerical flux differences

0.0 1.7 X 105 2.3 X 10^ 2.4 x 10^

5. Conclusions

The foregoing discussion indicates that the physics of the process of charge acquisition by an aerosol particle dictates that a rigorous condition exists for giving any

aerosol a well-defined charge distribution if the particles can all be assumed to have

similar physical properties. The condition is that all the particles be in the collisiondominated region (x-j/R < 0.25) and that the cluster ion conductivity be held constant.

For smaller particles, no such conditions are possible nor is any laboratory calibration of the process meaningful due to the variable and indeterminate nature of the cluster

ions which are central to the charging process.

The meaning of these results for current instrumentation is that quantitative comparison of data acquired at different times or places is not possible. The methods have

meaning as relative measures of size distribution, in one location and over a time span,

during which the atmospheric trace gases may be considered to be constant. These conclusions will be elaborated upon in a series of papers now in preparation.

217
References

[1] Israel, H., Atmospheric Electricity, Volume I (translated by D. Ben Yaakov and Baruch

Benny), Israel Program for Scientific Translations Ltd. (1971), NTIS TT67-51 394/1

.

[2] Whitby, K. T. , and Clark, W. E., Electrical Aerosol Particle Counting and Size

Distribution Measuring System for the 0.015 to ly Size Range, Tellus 1_8, 573 (1966).

[3] Mohnen, V. A., Discussion of the Formation of Major Positive and Negative Ions Up to

the 50 km Level, Pure and Applied Geophysics 84, 141 (1971).

[4] Castleman, A. W. , Tang, I. N., Munkelwitz, H. R. , Clustering of Sulfur Dioxide and

Water Vapor About Oxonium and Nitric Oxide Ions, Science 1 73 , 1025 (1971).

Huertas, M. L., Marty, A. M. , Fontan, J., On the Nature of Positive Ions of Tropospheric

Interest and on the Effect of Polluting Organic Vapors, J. Geophys. Res. 79_, 1 737,

(1971).

Kadlecek, J. A., Ion Molecule Reactions of Atmospheric Importance: Positive Ion

Clusters Involving BOi, NE^, SO2J Ion Induced Aerosol Formation, Publication No. 263,

Atmospheric Sciences Research Center, State University of New York at Albany, 1974.

[5] Marlow, W. H., and Brock, J. R. , Unipolar Charging of Small Aerosol Particles,

J. Coll. Inter. Sci. 50_, 32 (1975).

Bird, G. A., Molecular Gas Dynamics, (Clarendon Press, Oxford, 1976).

[6] Sedunov, Y. S., Physics of Drop Formation in the Atmosphere (translated by D. Lederman

and edited by P. Greenberg), John Wiley and Sons (1974).

[7] Liu, B. Y. H., Whitby, K. T. , Pui , D. Y. H., A Portable Electrical Analyzer for Size

Distribution Measurement of Submicron Aerosols, Air Poll. Contl. Assoc. Journal 2A_,

1067 (1974).

Liu, B. Y. H. and Pui, D. Y. H. , On the Performance of the Electrical Aerosol Analyzer,

J. Aerosol Science 6_, 249 (1975).

[8] Marlow, W. H. , Reist, P. C, Dwiggins, G. A., Aspects of the Performance of the

Electrical Aerosol Analyzer Under Nonideal Conditions, J. Aerosol Science 7_, 457

(1976).

218
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

THE USE OF A MODIFIED BETA DENSITY FUNCTION TO CHARACTERIZE

PARTICLE SIZE DISTRIBUTIONS

Alan S. Goldfarb

Continental Oil Company

Baltimore, MD 21226, USA

James W. Gentry

University of Maryland

College Park, MD 20742, USA

1. Introduction

The physical properties of an aerosol system are strongly dependent upon the size of

the aerosol particles. In general, particulate matter is polydisperse and in order to

describe a system of particles, the distribution of particle sizes must be specified. It

is convenient to be able to specify the distribution of a system of particles in the form

of a mathematical function. A mathematical function that has had a high degree of success

in describing the distribution of particle sizes is the log normal probability function.

This function is commonly used to characterize the size distribution of atmospheric particles and emissions from stacks. The log normal probability function has the advantage

that only two parameters, the median diameter and the geometric standard deviation, are required to define it and the cumulative distribution plots as a straight line on logarithmic probability coordinate graph paper [1]^. In addition, if the distribution by mass

is a log normal function, the surface area distribution and the number distribution are also log normal with the same geometric standard deviation.

2. Discussion

Inherent shortcomings of the log normal probability function are that it is a symmetrical function and implies the presence of particles of sizes from 0 to infinity.

Particle size distribution data frequently indicate a maximum and/or minimum particle

size for the sampled particulate system. Sometimes the characteristics of the instrument

used to sample and size particles have an upper and lower limit of particle size. In other

instances, the particles may have passed through a particle collecting device with 100%

efficiency of collection for certain sizes. For example, a cyclone has a high efficiency

of collection of large particles (>5 microns) and thus the distribution of particles

leaving a cyclone will tend to be asymptotic towards an upper size limit. This is shown in

figure 1

.

A membrane filter has a 100% efficiency of collection of particles larger than its

pore size and a high efficiency of collection of small particles due to diffusion within

the pores of the filter. Thus particles leaving the membrane filter have a narrow distribution and tend to be asymptotic towards an upper and lower size limit. This is shown

in figure 2.

T Figures in brackets indicate literature references at the end of this paper.

219
Figure 1. The effect of a cyclone on a log normal

distribution of particles.

A modified Beta probability function has been defined which asymptotically approaches

an upper and lower size limit. The cumulative distribution of the beta probability

function has the shape of an 'S' on logarithmic probability coordinate graph paper. The

modified beta probability function is defined by

where

In

' rmin

In

^"^^^ rmin

0 < X < 1

rmax and rmin are the maximum and minimum particle size respectively and a and b are parameters

of the function.

220
Figure 2. The effect of a filter on a log normal

distribution of particles.

By varying the values of the parameters a and b the function can be negatively skewed,

symmetrical, positively skewed, or simply the uniform distribution. Thus it has the potential

for describing a wide variety of particle systems.

Sampling data are fitted to the modified beta function by a trial and error procedure.

Trial parameter values are used to calculate values of the cumulative distribution and the

calculated values are compared with the actual data as the sum of the squares of the differences

between the actual value and the calculated value. The procedure is repeated with

new parameters until the error is minimized. The direct search method of Hooke and Jeeves

[3] is used to choose the parameter values for trial. If the maximum and minimum particle

sizes are unknown, their values may also be varied in the trial and error procedure. An

improvement in the fit of the beta distribution to a set of experimental data results if the

maximum and minimum particle size is allowed to vary along with the parameters a and b in

the search for the best distribution to fit experimental data.

The above described procedure was used to fit a beta distribution to the calculated

distribution of particles leaving a cyclone and a filter. The beta distribution was found

to describe the particle size distributions better than the log normal distribution. This

is illustrated in figures 3 and 4.

221
70

10

zo

(E

UJ

(-

UJ2 I

. <a

til

i~\—

r

"1

I I I I I I I

1—r~r

o ^

/

/

/

/

/

/

/

o/

/

/

0.1 /

1_0/A

A"

0.03 —

_1_1 L

— ACTUAL DISTRIBUTION O LOG NORMAL FIT A BETA FIT

I I I I

0.1 2 10 30 50 70 90 98 CUMULATIVE PERCENT LESS THAN SIZE

i

Figure 3. Comparison of fit of log normal distributions

and beta distribution to particles leaving a cyclone.

A cascade impactor is a device that separates particles in an air stream into two or more size classifications by inertial separation. It is commonly used to measure the cumulative

mass-size distribution of particles in the atmosphere and of emissions from stacks.

Cascade impactors consist of consecutive stages with progressively finer orifices

through which the sampled gas passes. An obstruction after each stage forces the gas to

change direction before passing through the next orifice. Particles that cannot change

direction with the air stream will impact on the obstruction. The progressively finer

orifices cause the velocity of the gas and entrained particles to increase and progressively

finer particles are collected on each successive obstruction.

Ideally, each stage of an impactor would collect all particles larger than a certain

size and none smaller. The fraction of the total mass of particles that escape being collected

on the stage would represent the cumulative mass distribution fraction for that "characteristic"

size. In real impactors, there is overlap in the particle sizes collected by the different

stages and the collection efficiency of a real impactor stage as a function of particle size

is described by an S-shaped curve.

222
I 0

a.<

1.0

0-03 -

i~i 1 I I I I I I I r

¥

o /

-- ACTUAL DISTRIBUTION O LOG NORMAL FIT A BETA FIT

_1_J I

I I _L J l_L

0.1 2 10 30 50 70 90 98 CUMULATIVE PERCENT LESS THAN SIZE

99.9

Figure 4. Comparison of fit of log normal distribution and

beta distribution to particles leaving a membrane filter.

In analyzing impactor data, it is common practice to determine a characteristic diameter

of the particles collected on each stage. If the mass of uncollected particles larger than

this diameter is equal to the mass of collected particles smaller than this diameter, the

real impactor captures the same mass of particles as the ideal impactor. Often, the characteristic diameter is specified as that diameter for which the stage has a 50% collection

efficiency.

This procedure can lead to a false size distribution curve.

An improved method for obtaining an estimate of the size distribution curve from cascade

impactor data has been developed. The method involves assuming a functional form of the

particle size distribution and using the direct search technique of Hooke and Jeeves to

locate the parameters of the distribution which, when applied to an analog of the cascade

impactor, will result in stage mass accumulations comparable to that accumulated by the

stages of the real impactor.

223
The Mass of particles, M, collected on the mth stage of the impactor is calculated by

r m-l

M„ = / V {] - S.)S f (r, a.)dr (2)

Jq J

where Sj and Sm are the collection efficiency of impactor stages j and m respectively and

fpCr, aj) is the initial particle size distribution.

A comparison between the size distribution curve obtained by a characteristic diameter

approach to interpretation of cascade impactor data and that obtained from the above described

procedure is illustrated in table 1. Figure 5 is a graphical illustration of the comparison.

0.1 0.5 2 10 30 50 70 90 98 99.5 99.9

CUMULATIVE PERCENT MASS < PARTiCLE DIAMETER

Figure 5. Comparison of two methods of fitting cascade imoactnr

data to a log normal distribution function.

The analog method was used to interpret cascade impactor data obtained from an oil

fired boiler stack [2] and a coal fired boiler stack [4]. The experimental data were fitted

to a log normal distribution and a beta distribution. In both instances the beta distribution

provided a better fit to the experimental data. Figures 6 and 7 illustrate the results of

these calculations.

224
Table 1. Comparison of two methods for analyzing cascade impactor data.

Original Distribution (log normal)

Calculated Distribution

Characteristic Diameter Method

Cascade Impactor Analog Method

Median

Particle Size

0.36 microns

0.30 microns

0.35 microns

Standard

Deviation

4.05

4.50

4.50

99-8

96

90

70 -

50

30 -

I 0 -

0.2

01

1 1 I r 1 r

•CONNECTS EXPERIMENTAL DATA CALCULATED COLLECTION ASSUMING O LOG NORMAL DISTRIBUTION X BETA DISTRIBUTION

J L I I I I _L

STAGE NUMBER

Figure 6. Comparison of actual cascade impactor collection

of particles from an oil fired boiler with calculated

collection.

225
—I—I—I—I—I \ I I 99.8 -

X

a.

CONNECTS EXPERIMENTAL DATA

2 ~ CALCULATED COLLECTION ASSUMING — O LOG NORMAL DISTRIBUTION

Q 5 _ X BETA DISTRIBUTION

0.1 — 13 5 7 9

STAGE NUMBER

Figure 7. Comparison of actual collection of fly ash dust from a pulverized coal boiler in a cascade impactor with calculated

col lection.

References

[1] Fuchs, N. A., The Mechanics of Aerosols, Pergamon Press, Oxford (1964).

[2] Gentry, J. W. and Goldfarb, A. S., Particulate Size Distributions for Emissions from

Oil Fired Combustion Equipment, Paper Presented at the 65th Annual Meeting of the

A. I.Ch.E. , New York (1972).

[3] Hooke, R. and Jeeves, T., [J. Assoc. Comp. Mach.], 8, 212 (1961).

[4] Schulz, E. J., Engdahl , R. B., and Frankenberg, T. T., (Submicron Particles from a Pulverized Coal Fired Boiler), [Atmospheric Environment], 9_, 111-119, Pergamon Press

(1975).

226
Part V. WATER ANALYSIS

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg , Md. (Issued November 1977).

IN-SITU MONITORING WITH ION-SELECTIVE ELECTRODESADVANTAGES AND PITFALLS, OR WHAT THE INSTRUCTIONS DIDN'T SAY

Richard A. Durst

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

Ion-selective electrodes have demonstrated unique features for the continuous and

direct monitoring of a variety of ionic and gaseous species in solution. Sensors are now commerically available for about two dozen ions and several gases (see table 1), including

such environmentally important species as cyanide, fluoride, nitrate, copper, cadmium,

lead, hydrogen sulfide, sulfur dioxide, chlorine and nitrogen oxide. By means of indirect

electrode techniques, the number of species that can be measured is greatly increased

(table 2), but usually at the price of increased analytical complexity.

Table 1

Commercially available ion-selective electrodes

Cations

Acetyl chol ine Lead

Mercury

Potassi um

Si 1 ver

Zinc

Univalent

Divalent

Arsenic

Cadmi um Calcium

Chromi um Copper

Hydrogen

Anions

Bromide

Carbonate

Chloride

Cyanide

Fluoride

Fluoroborate

Iodide

Ni trate

Perchlorate

Phosphate

Sul fate

Sulfide

Thiocyanate

Neutral (gases)

Ammonia

Carbon dioxide

Chlorine

Hydrogen sulfide

Oxygen

Sulfur dioxide

Nitrogen oxides

229
Table 2

Examples of indirect determinations

Aluminum

Boron

Barium

Bromine

Carbonate

Chelating agents

Chlorine

Chromate

Cobal

t

Cyanate

Epoxy groups

Hydrazine

Iron

Lanthanum

Magnesi urn Mercaptans (Thiols)

Molybdate

Nickel

Oxalate

Oxidizing agents

Reducing agents

Sulfate

Tungstate

Zinc

2. Advantages

While direct potentiometry by ion-selective electrode is not a highly precise analytical

technique, with relative precision on the order of about ±0.5 percent at best, it does

have a number of significant advantages over most other analytical techniques for real-time,

in-situ monitoring.

For example, depending on the electrode type, concentration range, and direction and

magnitude of the concentration change, these sensors exhibit response times varying from

fractions of a second to several minutes. Such response times are consistent with the

requirements for most analytical monitors, both for purely monitoring applications and

where corrective actions must be taken. Also of considerable importance in monitoring and

control situations is the continuous nature of the measurement. Instead of batch sampling

and analysis, these sensors can be built into systems which continuously measure one or more chemical species. An example of such a system for water quality measurement might

include sensors for pH, dissolved oxygen, fluoride, and hardness.

Since ion-selective electrodes are logarithmic readout devices, their response, and

consequently their precision, is constant over most of their dynamic operating range which

may extend six or eight orders of magnitude. While this range is sufficient for most

applications, such as monitoring fluoride levels in drinking water or cyanide in plating

baths, some of the electrodes lose sensitivity at analytically significant levels. For

example, the heavy-metal ion-selective electrodes (cadmium and lead) are of little use below about 20 ppb (-10"^ mol/1), while the copper electrode can, under ideal conditions,

function down to about 1 ppb (-10"^ mol/1). At the present state of the art, it is

unlikely that these sensors can be used for field monitoring of these ions at normal

ambient levels.

Another advantage of ion-selective electrode measurement systems (as opposed to

photometric techniques) is their ability to function in intensely colored or even opaque

solutions and, under certain circumstances, even turbid solutions although some problems

may be encountered in multiphase solutions. However, in many cases, time-consuming separations such as filtration and distillation can be eliminated and chemical pretreatment of

the sample solution may be unnecessary.

Finally, when compared to most other modern instrumental methods of analysis, the

equipment required for potentiometric studies is quite simple and relatively inexpensive.

Consequently, portable battery-operated systems are available for field studies, such as the environmental monitoring of water quality.

Another feature of these sensors may be either an advantage or a disadvantage depending

upon the analytical application. This is the unique characterization of these electrodes

that they sense ionic activity rather than concentration. For example, in studies of

chemical equilibria, it is necessary to make measurements of the activity of the species

involved. However, in most analytical situations, except for speciation studies, the

230
total concentration of the component is needed, especially if correlation with other

analytical techniques is required. Although readout in either parameter is possible, the

control of solution parameters requires a sound knowledge of the chemistry of electrolytes.

In general, ion-selective electrodes can provide concentration data, both free ion and

total, by means of methods such as titration, standard addition, and ionic strength

buffering.

3. Pitfalls

While the advantages of these electrodes are widely known and appreciated, the problems

associated with using them can be a serious source of error, not to mention aggravation.

Perhaps the subtitle, "What the Instructions Didn't Say," is unfair to the manufacturers

who often do provide considerable information and assistance on using their electrodes. A more appropriate subtitle, from the manufacturers' point of view, might be, "When all else

fails, read the instructions!" Unfortunately, most users approach the application of ionselective electrodes with great anticipation, assuming that since they have used the pH

electrode without problems, why should analogous ion-selective electrodes be any different.

This approach often leads to considerable disappointment because the potential sources of

difficulty are almost as varied as the sensors and the samples. Besides instrumental

problems with the readout devices, several common causes can be identified: interferences

and/or "fouling" of the electrodes, sample matrix effects {e.g., ion strength changes or

the presence of complexing agents), reference electrode instability, and improper calibration

of the measurement system. Other examples of problems and their possible causes are given

in table 3.

Table 3

Examples of problems and possible causes

Problem: Out-of-range reading.

Causes : Defective meter; function switch in wrong position; electrode(s) not

plugged in properly; defective electrode(s)

.

Problem : Unstable readings (noise).

Causes : Defective meter; reference electrode junction clogged; improper grounding

of meter or stirrer; high solution resistance; static electricity; air

bubbles blocking membrane or junction; poor electrical connections.

Problem : Drift

Causes : Temperature variation; fouled membrane; incorrect reference electrode

filling solution; variations in illumination.

Problem : Sub-Nernstian response.

Causes : Standards contaminated or incorrectly prepared; ionic strength variations;

defective electrode (depletion of exchanger or leakage); temperature error.

Problem : Incorrect answer on "knowns"

Causes : Computation or graphing error; function switch in wrong position; incorrect

standards or concentration units used; unforeseen interference.

9^1
How can these problems be anticipated and either eliminated or minimized in order to

reduce their associated errors? First and foremost, a good knowledge of solution chemistry

and thermodynamics is essential. Nothing really sophisticated, just good, basic chemistry

that we all should have learned (and retained) as undergraduates. This is because ionselective electrodes are sensitive to only the free (hydrated) ions in solution, and any

other solution components which affect the ionic activities will also affect the apparent

ionic concentrations. For example, in the case of fluoride analyses, interferences such

as H"*", Al3+, and Fe^^ will result in negative errors unless they are masked by appropriate

chemical agents. On the other hand, since these electrodes are not specific for the ions

of interest, they may give positive errors when electrode interferences are present.

Consequently, a knowledge of the composition of the sample solution and the appropriate

means of masking interferences are necessary before attempting to use these sensors.

Instrumental problems can occur with any of the three components of the system:

meter, indicator electrode, or reference electrode. In general, meter malfunctions are rare and easily detected by applying known potentials to the meter and observing its

response. When the problem is due to a malfunction in one of the electrodes, the first

question is which one and, second, why. Generally, problems with the indicator electrode

are due to interferences which poison the membrane, or depletion of the liquid ion-exchanger

which results in sub-Nernstian behavior. More likely, electrode problems will occur with

the reference electrode and are often due to blockage of the liquid junction which results

in noisy signals and drifting potentials. In choosing the proper reference electrode,

consideration must be given to the type of junction, the salt-bridge solution composition,

and temperature effects.

Finally, no matter how perfect the measurement system and solution conditions, it is

not possible to get accurate results if the electrode system is not calibrated properly.

Ideally, the calibrating solutions will have a matrix identical to the sample solutions.

If the matrix is too complex or variable, it is often more convenient to perform the

analyses by a standard addition procedure which obviates the need for a separate calibration scheme.

4. Summary

Ion-selective electrode sensors can be a useful and convenient means for the continuous

monitoring of selected species, but only if the potential pitfalls are recognized and

eliminated. If this is not done, the results will be meaningless and, even worse, the

analyst may not realize that the data are erroneous. More than any other modern analytical

technique, ion-selective electrodes have brought chemistry back to analytical chemistry.

232
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

PROBLEMS OF MERCURY DETERMINATION IN WATER SAMPLES

Sunao Yamazaki, Yukiko Dokiya and Keiichiro Fuwa

Dept. of Agricultural Chemistry, Fac. of Agr.

The University of Tokyo

Bunkyoku, Tokyo, Japan, 113

1 . Introduction

The development of cold vapor flameless atomic absorption enabled us to determine an amount as small as 0.1-1 ng of Hg. However, the specific properties of Hg which enable

sensitive analyses, also cause errors in Hg analysis. For water samples three factors are assumed to be the cause of the loss: 1) vaporization from the surface of the water or from

polyethylene containers; 2) adsorption on the surface of the containers; and 3) susceptibility

to biological activities. Literature references dealing with mercury determination in water

samples are listed [l-5]2.

2. Discussion

First, some model experiments are carried out using radioactive tracers 203Hg and ^^In,

in order to understand the behavior of trace amounts of Hg and Zn added to natural and

artificial water samples. As shown in figure 1, -o^^g decreases rapidly from distilled

water, pond water and sea water but slowly from artificial sea water. On the other hand,

^^Zn decreased from pond water only.

The mechanism of these losses is studied by successively measuring the radioactivity

after sampling in polyethylene test tubes and also by cutting the polyethylene walls of the

containers after removal of the sample solutions. In distilled water about 40 percent of Hg

is found almost uniformly distributed on the surface of the walls of the containers, whereas

in pond water the bottom shows greater concentrations of Hg indicating that some co-precipitation with other materials such as biological entities, occurred. In pond water Zn is also

found at the bottom part which might be explained by the same reasoning. In sea water, Hg

behaved similarly as in pond water, except that the vaporized amount is as much as 60 percent.

Next, the effectiveness of preservatives was studied using the same tracer method. The

results are summarized in figure 2. The addition of cysteine with 0.1 N HCl as well as the

addition of Au with 0.1 N HNO3, which has been proposed by NBS workers, are proved to be

effective.

The natural background of Hg in sea water is assumed to be in the range of 0.01 - 0.7 ppb. As the concentration is very low, even the cold vapor flameless atomic absorption

method is not sensitive enough. Therefore, long quartz absorption cells are used for this

purpose.

^Present address: Dept. of Chem., Faculty of Science, The University of Tokyo.

^Figures in brackets indicate the literature references at the end of this paper.

233
Days

Figure 1. Behavior of 203Hg(|-..|) and ^''ZniO 0) (1-5 ppb)

added to (1) pond water, (2) sea water, (3) distilled water and

(4) artificial sea water. 100 ml polyethylene containers were

used.

The detection limit of this method is as low as 0.05 ng Hg, the lowest value determined

is about 0.5 ng Hg. The results tested with reference materials from NBS and Sagami Central

Research Lab shown in table 1, are in satisfactory agreement.

Table 1. Determination of Hg in standard solutions.

NBS-SRM 1642

Sagami Central Research Lab

Certified

Found

1 .18±0.05 ppb

1 .09±0.05 ppb

Calculated 12.40 ppb

Found 12.70±0.40 ppb

Found 12.48±0.13 ppb

(measured after dilution x 100)

234
c

o

o

0)

100

50

-(A

(2)

J.

a>

u

o

o

o

100 -"vQ*- >^ -A50

I

I

I

I

(3)

15

(4)

-Qk

15

Days

Figure 2. Effect of preservatives on the loss of 203Hg(i ppb) (1) pond

water, (2) sea water, (3) distilled water and (4) artificial sea water.

(•) no preservatives, (a) 1 mM cysteine, () 1 mM cysteine + O.IN

HCl, (a) 10 ppb Au, and (0) 10 ppb Au + O.IN HNO3.

References

Dokiya, Y., Yamazaki, S., and Fuwa, K., Environ. Lett. ], 551 (1974).

Dokiya, Y., Yamazaki, S., Ashikawa, H., and Fuwa, K., Spectroso. Lett. ]_, 551 (1974).

Yamazaki, S., Dokiya, Y., and Fuwa, K., 34th Forum of Jap. Anal. Chem. (Muroran)

(1 973).

Yamazaki, S., Dokiya, Y., Hayashi, T., and Fuwa, K., Annual Meeting of Agr. Biol.

Chem., (Tokyo) (1974).

Watanabe, T., Dokiya, Y., Toda, S., Fuwa, K., Annual Meeting of Jap. Chem. Soc.

CSagami) (1976).

235

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

SAMPLING FOR WATER QUALITY

Willie R. Curtis

Northeastern Forest Experiment Station

Forest Service

U.S. Department of Agriculture

Berea, Kentucky 40403, USA

1. Introduction

Many parameters of water quality are affected by man and his use of the land. Even

in a natural environment, water quality is not constant over time.

We are passing quickly from having a surplus of land to having competing demands for

the same land. We need to predict the effects of all these demands and their interactions

upon the land and its associated resources. Only when we can do this, will we be able to

manage our land and water resources for the greatest benefit. Much of the needed information can be obtained through study and observation of the streamflow and water quality

from small watersheds.

Any land use, but especially surface mining, affects water quality. Freshly exposed

rock is subject to rapid breakdown, and undergoes many chemical reactions. Sulfuric

materials found in coal and associated rock strata are the principal producers of the acid

found in mine drainage. Pyrite and marcasite, both sulfides of iron, oxidize when exposed

to air and water to form iron sulfate and sulfuric acid. Secondary reactions between the

sulfuric acid and organic and inorganic materials produce other chemicals often found in

acid mine drainage.

The amounts of acid, iron, and other pollutants in drainage from a particular surface

mine will vary, depending upon the rate of flow, extent of area disturbed, distance from

the stream system, amount and quality of precipitation, type of geologic materials encountered, temperature, and vegetative cover. Therefore, the chemical composition of mine

drainage cannot be accurately determined from a "one-shot" sample. Continuous or periodic

sampling, for a period of time that depends upon the objectives, is required.

Samples cost money. So do errors. The objective of this paper is to provide some

basis for designing a sampling program that will satisfy current and anticipated needs for

data on the chemical quality of water affected by surface mining. The aim is to make

enough observations to obtain the desired information--no more, no less.

Good technique is the basic requirement; results obtained with poor technique are of

little value and may be biased. It is most important to obtain a representative sample of

the flow. This may best be achieved by following these basic rules: Take samples where

the water is homogeneous; avoid skimming the surface or bottom of the discharge channel;

take samples at midstream at approximately one-half stream depth, if possible. Bottles

used for sampling should be clean and should have-a label for identifying the sample.

They should be rinsed several times with the water to be sampled before they are filled to

reduce the possibility of contaminating the sample from the container. The bottle should

be filled completely, leaving no air space, and sent to the laboratory for analysis as quickly as possible.

237
Methods of collecting and analyzing water samples are well documented [1,2,5]^ and

will not be discussed here. Rather, the remainder of this paper will be devoted to the

frequency of sampling, particularly of first- or second-order streams that drain basins

where there is surface mining.

The frequency of measurement at each sampling site will depend on the variability of

each variable and the desired error of estimate. The USGS has long used daily sampling

for the usual comprehensive chemical -qual ity investigation [2], but monitoring the effects

of surface mining on small headwater streams may not require such frequent sampling.

Chemical data from six first-order streams draining both mined and unmined watersheds

in eastern Kentucky have been analyzed to determine what sampling regimen is necessary to

characterize the stream quality. The most commonly used estimates are the sample averages

and the regression coefficients. Once the statistics have been estimated within satisfactory limits, additional observations will have little value except for detecting changes in

water quality due to long-term natural changes or to specific changes in land use. We are interested in detecting changes in water quality that result from surface mining. To do

this we need to determine either the mean concentration of some substance or a regression

equation using some easily measured variable. Our objective is to make an accurate

estimate of the chemical parameters with the fewest and least expensive measurements.

2. Discussion

Specific conductance can be measured rather simply and at low cost. It has long been

accepted as a measure of the total concentration of ionized material in solution [5]. For

most natural waters the specific conductance, in micromhos per cm at 25°C, multiplied by

0.65 approximates the total dissolved solids in milligrams per liter [2]. For an unmined

study watershed we found values of 0.52 to 0.62, and for surface-mined watersheds, values

ranging from 0.61 to 0.84.

It is interesting to note that the factor increased with time after mining. The

average values for Jenny Fork, an unmined watershed, are compared with those for Miller

Branch and Mull ins Fork, both mined watersheds, in this tabulation:

Water Year^ Jenny Fork Miller Br. Mull ins Fork

1970 0.57 0.61 0.63

1971 .61 .66 .65

1972 .60 .67 .68

1973 .62 .70 .68

1974 .52 .69 .71

1975 .57 .81 .84

^Water year extends from Nov. 1 through Oct. 31.

Plottings of specific conductance against the concentration of ionized constituents

in water from both mined and unmined watersheds generally show a linear relationship

(figure 1 )

.

^Figures in brackets indicate the literature references at the end of this paper.

238
++

X

Oi

CO

in

m

CM

CO

IT

>-

CO

Ti- cs

II

<

X

LO

COm

CO

LO

cvi oq

Ln

CM

I

in

I

CO

II

o

CO oCM

CO

o

CM

"

<

I—o

oC-3

C_3

C-9 LU

Q.

CO

CO CM »-

i/9i/\i sanos QBAiossia ivioi

Figure 1. Specific conductance plotted against total dissolved solids for Jenny Fork

and Miller Branch for water year 1975.

239
Concentrations of many chemicals in water from both mined and unmined watersheds were

found to be correlated with specific conductance. It correlates quite well with SO^, Ca,

Mg, and HCO3 (table 1). Sulfate has been found to be one of the most important indicators

of stream pollution from mining activity; correlation coefficients for it range from 0.651

to 0.991. Specific conductance is poorly correlated with Zn, Al , Fe, Na, K, and Mn.

Regression equations are shown in table 2. In all cases the Y-intercept is higher for the

mined watershed.

Table 1

Correlations between specific conductance and ionized constituents, by water years

Water year HCO3 SO'4 Ca Mg

Jenny Fork (unmiined watershed)

1969 .905 .883 .919 .816

1970 .843 ,815 .833 .887

1971 .799 .818 .829 .736

1972 .810 .985 .991 .991

Miller Branch (mined watershed)

1969 .984 .969 .809

1970 .654 ,906 .951 .899

1971 .651 .919 .682 .579

1972 .711 ,878 .765 .953

1975 .743 ,609 .852 .874

Table 2

Regressions of specific conductance on some dissolved constituents in streams

draining mined and unmined watersheds for water year 1972

Watershed Correlation

Name Status Constituent Regression equation coefficient

Jenny Unmined Ca Y = -1 .628 + 0.083X 0.989

Miller Mined Ca Y = -1 .789 + 0.066X .765

Jenny Unmined Mg Y = -0.284 + 0.042X .987

Miller Mined Mg Y = -2.461 + 0.065X .953

Jenny Unmined 50^ Y = -8.683 + 0.379X .985

Miller Mined Y = -27.369 + 0.396X .878

For each water year and for each chemical element tested, the 52 weekly analyses were

separated into an odd-numbered and an even-numbered set. The sets were paired. This made

26 pairs, representing biweekly data, on which paired T-tests were performed. Then to

eliminate bias the first value was dropped and the remaining values paired as before and

tested by the T-test. No statistically significant differences were found. Therefore,

sampling twice monthly appears to be adequate for headwater streams in eastern Kentucky.

Tests for the seven water years from 1969 to 1975 indicate that any one of those

years would have given good estimates of water quality from the unmined watershed.

Seasonal differences and trends can be established with monthly sampling, as evidenced

by the plot in figure 2. Moving averages of three values, with the middle value double

weighted, smooth the curve and allow trends to show more clearly. This method of smoothing

can be used for any sampling interval selected.

240
3 o92 iv i/\io/saHi/\in aoNVionoNOO ouiOBds

Figure 2. Specific conductance for Jenny Fork, showing the relationship of different

sampling intervals during water year 1972.

241
Figure 2 also shows that monthly (4-week) samples defined quite well the specific

conductance of water flowing from an unmined watershed. Plots of mineral constituents

show essentially the same thing, i.e., that monthly sampling is generally adequate to

define baseline water quality data. The same thing has been noted for the mined watersheds.

Figure 1 shows how we can determine the influences of a particular land use, in this case surface mining, on the quality of water in streams that drain that land. In the

lower left are data from an unmined watershed. Not only is there a difference in the

slope of the regression line, but there is a large difference in actual values. Plotting

the same variables for both these watersheds before mining showed a similar slope in the same value range.

From plots of the 95 percent confidence interval in figure 3, it can be seen that

after a certain point adding samples results in only a small decrease in the interval.

For example, the 95 percent confidence interval width for Jenny Fork is 1.23 mg/1 for 12

analyses, 0.87 for 26 analyses and 0.56 for 52 analyses. Because the concentrations of

maay chemicals change seasonally, sampling must be spread over a year. Similar computations

can be made for any variable of interest and an optimum sampling interval can be defined

to meet any requirement.

242
1/9I/\I HIQIM IVAUHINI 33N3QldN03

Figure 3. Number of analyses plotted against 95 percent confidence interval width for

magnesium, for Jenny Fork and Miller Branch for water year 1972.

243
3. Conclusion

In general, sampling should be based on the relation between specific conductance and

the concentration of ionized constituents. When the relationships are defined, sampling

can be reduced to a frequency that will detect trends in ion concentration. Biweekly

sampling for 1 year before surface mining should be adequate to define the regression

equation if conductance is the independent variable. Monthly samples should normally be

enough to detect trends. In some cases quarterly sampling may be enough.

It would be better to sample through the complete range of stream discharge and to use discharge-weighted concentrations, but that procedure may be too expensive for routine

water quality monitoring. Biweekly to monthly sampling on a fixed schedule will generally

be adequate to define the effects of surface mining on water quality.

References

[1] Standard Methods for the Examination of Water and Wastewater, American Public Health

Association, American Water Works Association and Water Pollution Control Federation,

13th ed. Publ. Off., Am. Public Health Assoc., Washington, DC (1971).

[2] Brown, E. , Skougstad, M. W., and Fishman, M. J., Methods for collection and analysis

of water samples for dissolved minerals and gases, Teah. Water-Resour. Invest. B. 5, Chap. 160, U. S. Geo! . Surv. (1970).

[3] Hem, J. D., Study and Interpretation of the Chemical Characteristics of Natural Water,

U.S. Geol. Surv. Water-Supply Pap. 1473, 2nd ed. 363 (1970).

[4] MacKicham, K. A. and Stuthmanu, N. G., Freliminary Results from Statistical Analysis

of Water Quality in Selected Streams of Nebraska. U.S. Geol. Surv. Open file rep.

Lincoln, Neb., 35, illus., (Oct. 24, 1969).

[5] Rainwater, F. H. and Thatcher, L. L., Methods for Collection and Analysis of Water

Samples, U.S. Geol. Surv. Water-Supply Pap. 1454, 301, illus. (1960).

244
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

MONITORING BACTERIAL SURVIVAL IN SEAWATER USING

A DIFFUSION CHAMBER APPARATUS IN-SITU

George J. Vasconcelos

Environmental Protection Agency

Seattle, Washington 98103, USA

1. Introduction

Efforts to simulate the natural aquatic environment have led to the development of a membrane enclosed diffusion chamber capable of allowing interaction and exchange between

microorganisms in the chamber and the outside environment. Although there is considerable

evidence suggesting that enteric bacteria do not survive extended periods outside the

intestinal tract, the factors affecting their short-lived viability are varied and complex.

To help resolve this problem, a microbiological survival chamber for in-situ environmental

studies was developed.

2. Apparatus

The apparatus consists of three main parts or units (fig. 1): (1) the chamber unit

itself, (2) a supportive base unit to cradle the chamber, and (3) a stirring mechanism for

Figure 1. Monitoring bacterial survival in seawater using a Diffusion Chamber Apparatus in-situ.

245
continuous internal agitation. The detachable chamber unit was constructed entirely of

autoclavable polycarbonate to permit steam sterilization for 15 minutes at 15 lbs. psi. A

small Teflon coated stirring pellet placed inside the chamber prior to sterilization provided the necessary internal movement when magnetically coupled to the electric DC motor

positioned below. The stirring mechanism was included in the apparatus to ensure a homogenous cell suspension within the chamber and simultaneously enhance solution-transport

through the membrane sidewalls by decreasing the internal Nernst film at the membrane-water

interface. To stabilize, orient, and physically protect the membranes of the chamber,

plastic guide fins and a nose cone were attached to the supportive base unit.

3. Discussion

Workers in the past have utilized dialysis sacs or bags made of regenerated cellulose,

cellophane, parchment and other materials to culture microorganisms in aquatic systems.

Unfortunately, these membranes vary in thickness and can undergo changes in porosity upon

hydration; all of which limit the size of molecules that can enter and leave the system.

Because of the rapid development in microf il tration technology, dialysis bags have given way

to rigid chambers and rings that support microporous filter membranes (or membrane filters)

fabricated from mixed cellulose esters, asbestos, or plastic.

During evaluation of the chamber diffusion, experiments were conducted using a variety

of filter membranes. These included regular (150 m) and ultra thin (25 ym) cellulosic

membranes from Millipore Corp. and polycarbonate membranes (10 urn) from Nuclepore Corp. The

ultra thin cellulosic membranes tested provided rapid diffusion but were too fragile for

field work. Consequently, only the regular cellulosic (Millipore, HAW P-047-00) and polycarbonate (Nuclepore, N-040-CPR-047-00) membranes were subjected to further evaluation.

Seawater diffusion experiments were designed to compare the solute permeability of both

membranes, with and without internal agitation, using sodium fluorescein and glucose as test

substances. Standard concentrations of both substances were injected into the chambers with

a syringe and withdrawn similarly at 12 hour intervals. Results showed that polycarbonate

type membranes were superior to cellulosic membranes with regard to solute permeability,

requiring less time to achieve a given percent exchange between the chamber contents and

outside environment. Internal agitation lessened the time necessary for this exchange. In addition, after 10 days exposure to seawater, the cellulosic membranes became exceedingly

brittle and crumbled easily upon finger contact. Since then, other investigators have

confirmed that cellulosic membranes undergo biodegradation in seawater as a result of

microbial enzymatic activity.

To demonstrate the applicability and general usefulness of the chamber apparatus,

experiments were conducted with eight representative species of bacteria all recently isolated

from environmental sources. These included five opportunistic pathogens and three indicators of water quality. Of the three bacterial indicators, Streptoooaaus faecalis was found to persist longer than either member of the coliform group. The survival characteristic

of this organism is thought to bs related to the electrolyte content of seawater, but no mechanism has yet been proposed. The five pathogens examined included Klebsiella pneumoniae,

Staphylocoocus aureus and Fseudomonas aeruginosa. With the exception of the latter organism,

little variation in viable count was observed between these pathogens over a seven day

period. By far the most dramatic diversity in survival was shown with Vibrio parahaemolytiaus

(a true marine pathogen) was compared to Esaheriohia coli (control) and Salmonella enteriditis

.

In this experiment, E. aoli fatalities were much higher in comparison to the salmonella

pathogen it was intended to represent.

Bacterial viability in seawater is influenced by a multitude of environmental factors,

among which are temperature, salinity, pH and availability of nutrients. The study was conducted over a period of a year and rearranging the data on a seasonal basis revealed that

the survival of E. aoli was definitely a function of water temperature. As seasonal temperatures rose, so did fatalities, clearly showing an inverse relationship between survival and

water temperature.

246
4. Conclusion

If low temperatures can prolong the life of enteric bacteria in seawater, then the

curtailment of wastewater disinfection during the cold winter months would seem inadvisable

for many coastal regions. This would be particularly true of those areas used extensively

for the production and harvesting of fish and shellfish. Considering the wide variation in

the persistence of both indicator organisms and enteric pathogens, marine waters receiving

treated wastes should be evaluated more closely. Because of its improved design and performance,

the survival chamber described in this presentation would be a useful tool in evaluations of

this type.

247

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977)

CLEAN LABORATORY METHODS TO ACHIEVE CONTAMINANT-FREE PROCESSING AND

DETERMINATION OF ULTRA-TRACE SAMPLES IN MARINE ENVIRONMENTAL STUDIES

C. S. Wong, W. J. Cretney, J. Piuze^ and P. Christensen

.Ocean Chemistry Division

Institute of Ocean Sciences

Victoria, B.C., Canada, V9A 3S2

and

P. G. Berrang

Seakem Oceanography Ltd.

Victoria, B.C., Canada, V8Z 1B2

1. Introduction

Reported baseline concentrations of some trace metals in open-ocean waters have been

generally decreasing over the years as is indicated in table 1. It is likely that a large

part of the data on trace metal concentrations found in the literature is worthless [1]^,

being only indicative of the level of contamination, since careful interlaboratory calibration exercises [2] have demonstrated that rigorously clean sampling, handling and analytical

techniques will produce accurate data.

Table 1

Baseline concentrations of some trace metals in open-ocean waters

reported in the last 35 years

Reference Units Cd Cu Pb Zn

Compiled Data

Sverdrup et al., 1942 [25]

Goldberg, 1965 [26]

Brewer, 1975 [27]

yg/kg

yg/^

present

0.11

0.1

10

30.5-

4

0.03

0.03

5 10

4.9

B. Recent Original Data

Zirino and Healy, 1971 [28] yg/5,

Chester and Stoner, 1974 [29] yg/£ 0.07

Eaton, 1976 [30] yg/kg 0.06

0.8

1.7

1.4

^Present address: Environment Canada, Peches et Sciences de la Mer, Quebec, Canada, GIK 7X7

^Figures in brackets indicate the literature references at the end of this paper.

249
This paper reviews briefly the methods used by the Ocean Chemistry Division in obtaining trace analysis data and puts particular emphasis on the description of a pair of portable shipboard clean laboratories, which we believe to be the first of their kind used for

marine work. The discussion will pertain to the analysis of ultra-traces of metals and

petroleum or petroleum-like hydrocarbons in sea water since this work is plagued by a myriad of contamination problems because of the extremely low concentrations involved.

2. A Unified Approach to Ultra-Trace Analysis in Sea Water

Although workers have published fairly detailed information on specific aspects of

ultra-trace analysis such as sampling, storage, or clean laboratory techniques, very few

have described a unified approach to obtaining meaningful data in sea water. By a unified

approach, we mean one that would include reducing the probability of contamination as much

as possible in all of the following steps:

- on shore laboratory manipulations including precleaning and packaging of sampling

equipment for use on shipboard

- obtaining samples at sea

- shipboard handling and sample workup

- storage and preservation of samples

- instrumental methodology

There has been a tendency to dissociate the sample collection from the chemical analysis [3].

In ultra-trace analysis, the dirtiest step is going to most affect the accuracy, so that

all of the above steps must be carefully examined for contaminating influences. Even extraordinary efforts of cleanliness spent on one step of the analysis may be negated by contamination in another.

A. Contamination-free sampling and handling on an oceanographic vessel

When collecting and handling sea water samples for ultra-trace analysis, one must keep

in mind that contamination lurks in every corner of a ship and in the surrounding surface

waters. Possible sources of metals or hydrocarbons include:

- the ship itself, as most parts are made of metal, which is either exposed or coated

with paints containing metals and oils or plasticizers

- grease and oil on the ship

- smoke, fumes, sewage, garbage, lubricants and fuel released to the air or sea by the

ship

- the hydrographic wire, messengers and weights

- materials used in the construction of the oceanographic samplers themselves

- the sea surface microlayer, which is enriched in both metals and hydrocarbons [4]

Surprisingly, for a long time oceanographers did not seriously concern themselves with

such problems, even though many of them had been pointed out twenty years ago [31]. Thus,

sampling and shipboard handling techniques have been the weakest links in marine ultratrace analysis. Improved techniques have been designed in recent years in order to curb

contamination.

250
1) Sampling techniques

We have employed a number of hand collection methods using small launches away from

the mother ship. These methods minimize the contamination, but they cannot be used unless

the sea is very calm. These methods moreover yield only shallow samples and are not well

suited for collecting large numbers of samples.

Pumping systems of bulk samplers attached to a hydrowire can be used on a ship. Not

all pumping systems or bulk samplers are suitable for obtaining sea water for ultra-trace

analysis. Somewhat different sampling equipment moreover is required for ultra-trace

hydrocarbons than for ultra-trace metals.

a. Ultra-trace metal samplers

Most pumping systems for ultra-trace metal sampling are too contaminated [5] and the

clean ones, such as those using peristaltic pumps and acid-cleaned Teflon tubing, cannot be

used to obtain very deep samples. We have been using PVC^ Niskin bottles with Tefloncoated stainless steel coil springs and with all other sources of metals removed [6]. The

bottles are acid-cleaned and used with stainless steel hydrowire, messengers and weights.

These samplers, however, and the newer models replacing them such as the Top-Drop Niskin

[5] and the Go-Flo Sampling Bottle [7], are not entirely satisfactory because they pass

through the surface open and/or they are made of PVC, a possible source of zinc and copper

among other metals [8]. Clean samplers which penetrate the surface of the ocean in a closed position should soon be available for ultra-trace metal analysis. Patterson and co- workers have been testing a super-clean deep ocean water sampler [9,10]. Seakem Oceanography

Ltd. has developed a Teflon and nylon sampler of different design [11].

b. Ultra-trace hydrocarbon samplers

Pumping systems have been used successfully for dissolved hydrocarbon gases [12] but

their utility has not been demonstrated for polycyclic aromatic hydrocarbons or other high

molecular weight hydrocarbons. As in the case of ultra-trace metal analysis, bulk samplers

should not pass through the surface slick open and should be built of contaminant-free

materials. The Blumer Organic-Free Water Sampler [13], consisting of an aluminum pressure

casing with a glass liner, is available commercially [14]. We have been using this sampler

with a few modifications [15], one of which is a long inlet tube as an aid in getting

samples uncontaminated by oil originating from the hydrowire or the outside surface of the

sampler itself.

2) Shipboard handling techniques

a. An answer to shipboard contamination - a seagoing clear laboratory

In many instances, a certain number of operations should be performed on sea water

samples immediately after collection. These operations include subsampling, acidification,

spiking, filtration, preconcentration, extraction, etc. Traditionally, these operations

have been carried out in the wet laboratories of oceanographic vessels, thus being subjected

to contamination as discussed earlier. In order to avoid contamination at this stage in

ultra-trace metal work, it has been suggested that sea water be handled in plastic enclosures

away from other activities. A similar approach could be used in ultra-trace hydrocarbon

work. Instead, we have chosen to use portable seagoing laboratory modules, complete with

^Polyvinyl chloride

251
clean room sections, which can be hoisted and bolted on to decks of different research

vessels. The modular concept has been used before for GEOSECS, but only involved portable

wet laboratories rather than clean laboratories. Our shipboard laboratory modules con- stitute clean enclaves in a dirty environment.

b. Shipboard laboratory modules

(1) Description of the Ocean Chemistry Division modules

Our two shipboard laboratory modules (fig. 1) are identical in construction. Each

module, including its steel lifting and support frame, has overall dimensions (4.72 m length x 2.63 m width x 2.55 m height) which were dictated in a large part by the oceano- graphic vessels available to our Division. The gross weight of each module is about 3200 kg.

Steel lifting and support frames completely box in the modules. When a module is moved to or from a ship, lifting slings for a crane are attached to brackets in the four top corners

and the module is hoisted from above. The rigidity of the frame prevents the module from

twisting and buckling under its own weight. A steel mounting platform, which conforms to

the curvature of the deck, is used with the module on the two most used oceanographic

vessels. The frame, mounting platform and deck are bolted securely together. On other

ships, which are used occasionally, the frame is welded to leveling brackets which are in

turn welded to the deck.

The walls and ceiling of each module are made of 8.26 cm wide panels which have a foamed polyurethane core bonded between an inner and outer skin of steel prefinished with a white baked-on epoxy coating. The floor consists of galvanized sheet metal over plywood.

The underside is sprayed with an asphalt coating and the upperside coated with epoxy paint.

The paint surface is covered with a self-adhesive Teflon-over-vinyl laminate. The outer

doors are solid core with white baked-on epoxy paint over steel. The internal walls, doors

and panels are constructed of wood and are coated with white epoxy paint. All of the doors

are provided with rubber seals.

The bench tops throughout the modules are made of wood with a skin of 316 stainless

steel sink. Besides the usual 115 V, 15A circuits, each module is provided with two 208 V,

35A circuits. Conduits and electrical outlets are wall mounted and coated with epoxy

paint. Incandescent lighting is used throughout.

The configuration of the air systems is consistent with a desire to use a little

potential working space as possible and a necessity to place air intake and exhaust ports

high on the modules to protect them against sea water breaking across the deck.

In the preparation room, entering air is passed through a small non-resinous fiber

filter in a protected port. Exiting air is vented through a 2.8 m^/min (100 cfm) fan.

This arrangement assures adequate air exchange in the small preparation rooms and also

provides a slight negative pressure so that air would tend to travel into the preparation

room from other parts of the module.

The combination change room, air lock and air shower is, we believe, a reasonable

compromise to reduce space use. The air shower is provided by compressed air being forced

through perforations along the length of a pipe located in each corner. Air from the

shower is drawn into the main air system of each module.

The clean room in each module is serviced by an air filtering and recirculating system.

Air from the change room, clean room and outside enters a small plenum above a 95 percent

efficient basket filter of dimensions 61.0 cm x 61.0 cm x 305 cm. After passing through

the basket filter, the air travels through an activated charcoal filter of the same dimensions, air-cooling coils, and a 28.3 m^/min (1000 cfm) squirrel cage fan. The filtered air

enters the clean room from beneath the bench via an opening which provides space for mounting a 76.2 cm x 61.0 cm x 30.5 cm HEPA^ filter (not yet installed). Manipulations requiring

^High efficiency particulate air.

252

the cleanest conditions are carried out in one or two VLF'+ hoods (61.0 cm x 61.0 cm) placed

in a space provided for them or other bulky floor-standing equipment. A positive air

pressure and fresh air make-up is provided by two interlocked variable speed fans.

(2) Use of shipboard laboratory modules containing clean rooms

A shipboard laboratory module such as the ones described will only be used efficiently

if, at all times, concern for contamination problems is shown by such precautions as wearing

the proper clothing, cleaning equipment properly and using sufficiently purified chemicals.

The proper operation of shore clean laboratories, which has been very well summarized by

Patterson and Settle [9], is directly relevant to shipboard clean laboratories.

B. Storage of samples at sea

Although some trace analyses can be completed on shipboard, there is still a need for

storing the majority of samples at some stage of analytical procedure. Generally, the

stage at which a sample is stored at sea is determined by a desire to maintain sample

integrity as well as by time and space constraints. Handling samples for ultra-trace

analysis in a modular clean laboratory allows us to minimize the ill effects of storage.

Sea water samples for ultra-trace metal analyses can be filtered and acidified immediately

in the clean room. Sea water samples for ultra-trace hydrocarbon analyses are sometimes

extracted on shipboard and the less space consuming extracts brought back to the shore

laboratory.

With the flexibility that a shipbeard clean laboratory provides, we- can often avoid

problems related to contamination from container materials or loss of substances of analytical interest by adsorption or absorption by container materials [8,16,17].

C. Shore-based clean laboratory techniques

Even though contamination problems during shipboard handling have only recently been

recognized, analysts in shore-based laboratories have been aware of these problems for a long time [18,19] and the need for special clean rooms and ultra-clean techniques in trace

analysis is now acknowledged [9,20,21,22]. We have been following accepted criteria of

cleanliness as closely as possible although our clean laboratories are only temporary and

hence of modest cost. Our trace element clean room, for instance, consists of about 12 m^

of laboratory floor space which is completely enclosed in polyethylene sheeting. An air

filtration system mounted in the plenum above ensures a slight positive pressure in the

clean room relative to the rest of the laboratory. The system consists of a 95 percent

efficient (particles > 1 ym) bag filter, activated carbon filters and a propeller fan

delivering air at a rate of about 20 m^/min. The handling of samples in ultra-trace work

is carried out in Class 100 VLF hoods.

D. Instrumental analysis

Most analytical instruments used in ultra-trace work are too sophisticated to operate

routinely on shipboard. Often they require more space than is readily available, more power than the ship can spare, drawers of spare parts and an electronics technician standing by. Although a few days of instrumental down time may be tolerable in a shore-based

laboratory, it may mean the loss of valuable data on a ship since oceanographic cruises

generally operate within a tight schedule. We have adopted a policy of doing as much of an analysis as is practicable in the shipboard laboratory modules and completing them in our shore-based clean rooms, where some of our instruments, such as the GC/MS and the anodic

stripping unit, are set up.

'^Vertical laminar flow.

254
E. Some of our data illustrative of a unified approach to ultra-trace analysis of sea water

The plot shown in figure 2 was obtained in the fluorimetric analysis of extracts of

sea water of the Southern Beaufort Sea. The study zone contained a mixture of Mackenzie

River water, ice water and Arctic ocean water. The plot shows a correlation (r = 0.75)

between the concentration (in chrysene equivalents) of fluorescent extractable compounds

(FEC) and salinity. We feel we have successfully reduced general contamination influences,

which would be expected to have a levelling effect on the data, to a point where the

correlation shown in figure 2 appears.

In the case of trace metal analysis, a recent study [23] conducted in the waters of

the Strait of Georgia, British Columbia, using clean laboratory methods, yielded the

background data presented in table 2. Results compare very favorably with the more recent

values in table 1, especially when one considers that the results in table 2 are for

estuarine waters.

Table 2

Background concentrations of some trace metals in estuarine waters

of the Strait of Georgia, B.C. [23]

Metal

Component

Measured

Number of

Samples^

Range of

Concentrations

[ug/kg]

Average

Concentration

[ug/kg]

Analytical

Technique

Cd dissolved 22 0.01 - 0.05 0.02 ASV (TFE)^

Cu dissolved 22 0.20 - 0.98 0.50 ASV (TFE)

Pb dissolved 22 0.04 - 0.28b 0.15 ASV (TFE)

Pb total 10 0.04 - 0.13 0.07 ID^

Zn dissolved 22 0.33 - 1.74 0.89 ASV (HMDE)

^Samples taken at depths ranging from 1 to 200 meters

One value of 0.55 not included

^Differential pulse anodic stripping voltammetry with a thin film rotating glassy

carbon electrode

Isotope dilution mass spectrometry

^Differential pulse anodic stripping voltammetry with hanging mercury drop electrode

3. Conclusion

"The analytical results should characterize the original system and not one that is a modification created by the analytical processing" [24].

255
256
References

[1] Hume, D. N., Fundamental Problems in Oceanographic Analysis, Analytical Methods in

Oceanography, Gibb, R. P., Jr., Ed., 1-8, -Hdvanaes in Chemistry Series 147, American

Chemical Society, Washington, DC (1975).

[2] Participants of the Lead in Seawater Workshop, Inter-laboratory Lead Analyses of

Standardized Samples of Seawater, Marine Chemistry 2, 69-84 (1974).

[3] Burrell, D. C, Atomic Spectrometric Analysis of Heavy - Metal Pollutants in Water,

87-100, Ann Arbor Science, Michigan (1974).

[4] Duce, R. A., Quinn, J. G., Olney, C. E., Piotrowicz, S. R., Ray, B. J., and Wade,

T. L., Science 176^, 161-153 (1972).

[5] Segar, D. A. and Berberian, G. A., Trace Metal Contamination by Oceanographic Samplers,

Analytical Methods in Oceanography, Gibb, R. P., Jr., Ed., 9-15, Advances in Chemistry

Series 147, American Chemical Society, Washington, DC (1975).

[6] Wong, C. S. and Berrang, P. G., Lead in Sea Water, Reference Manual for Ocean Chemistry

Sampling Techniques, unpublished manual, Pl-PlO, Institute of Ocean Sciences, Victoria,

British Columbia V9A 3S2 (1976).

[7] Go-Flo Sampling Bottle Model 1080, Data Sheet No. 108-75A, General Oceanics Inc.,

Florida 33127.

[8] Robertson, D. E., Role of Contamination in Trace Element Analysis of Sea Water, Anal.

Chem. 40, 1067-1072 (1968).

[9] Patterson, C. C. and Settle, D. M. , The Reduction of Orders of Magnitude Errors in

Lead Analyses of Biological Materials and Natural Waters by Evaluating and Controlling

the Extent and Sources of Industrial Lead Contamination Introduced During Sample

Collecting, Handling and Analysis, Accuracy in Trace Analysis: Sampling, Sample

Handling, Analysis, LaFleur, P., Ed. Vol I, 321-351 , ms Spec. Pub. 422,

U.S. Government Printing Office, Washington, DC 20404 (1976).

[10] Patterson, C. C. and Schaule, B., California Inst, of Technol . , personal communication

(1976).

[11] Berrang, P. G., New Samplers for the Ultra-Trace Analysis of Heavy Metals and Hydrocarbons, unpublished manuscript.

[12] Sigalove, J. J. and Pearlman, M. D., A Continuous Ocean Sampling and Analysis System,

Undersea Technology, 24-26 (March 1972).

[13] Clarke, R. C, Jr., Blumer, M., and Raymond, S. 0., A Large Water Sampler, RuptureDisc Triggered, for Studies of Dissolved Organic Compounds, Beep-Sea Res. 14^, 125-

128 (1967).

[14] Blumer Organic-Free Water Sampler Model 1730, Data Sheet No. 173A, Benthos, Inc.,

Mass. 02556.

[15] Cretney, W. J., Operation of the Blumer Organic-Free Water Sampler, Reference Manual

for Ocean Chemistry Sampling Techniques, unpublished manual, H5-H6, Institute of Ocean

Sciences, Victoria, British Columbia V9A 3S2 (1976).

[16] Robertson, D. E., The Adsorption of Trace Elements in Sea Water on Various Container

Surfaces, Anal. Chim. Acta 42, 533-535 (1968).

257
Gordon, D. C, Jr. and Keiser, P. D., Estimation of Petroleum Hydrocarbons in Seawater

by Fluorescence Spectroscopy: Improved Sampling and Analytical Methods, Tech. Report

No. 481, Bedford Institute of Oceanography, Dartmouth, Nova Scotia (1974).

Thiers, R. E., Separation, Concentration, and Contamination, Trace Analysis, Yoe,

J. H. and Koch, H. J., Jr., Eds., 637-666, J. Wiley and Sons, New York (1957).

Pinta, M., Detection and Determination of Trace Elements, translated from French

(Dunod, Paris (1962)) by Bivas, M., Israel Program for Scientific Translations Ltd.,

430, Ann Arbor Science Publishers, Ann Arbor (1966).

Blumer, M., Contamination of a Laboratory Building by Air Filters, Contam. Control 4_, 13-14 (1965).

Tolg, G., Extreme Trace Analysis of the Elements - I. Methods and Problems of Sample

Treatment, Separation and Enrichment, Talanta 1489-1521 (1972).

Mitchell, J. W., Ultrapurity in Trace Analysis, Anal. Chem. 45, 492A-500A (1973).

Wong, C. S., Berrang, P. G., and Erickson, P. E., Data Report for Cruise 0C-76-IS-001

,

Contract DSS File Ref. 5508. KF832-5-SP009B, Department of Environment, Ocean and

Aquatic Affairs, Pacific Region, Ocean Chemistry Division, Victoria, British Columbia

(March 1976).

Ciaccio, L. L., Ed., Water and Water Pollution Handbook, Vol. I, vii. Marcel Dekker,

New York (1971).

Sverdrup, H. U., Johnson, M. W. , and Fleming, R. H., The Oceans: Their Physics,

Chemistry, and General Biology, Prentice-Hall, New Jersey (1942).

Goldberg, E. D., Minor Elements in Sea Water, Chemical Oceanography, Riley, J. P. and

Skirrow, G., Eds., Vol. I (First Edition) 163-196, Academic Press, London (1965).

Brewer, P. G., Minor Elements in Sea Water, Chemical Oceanography, Riley, J. P., and

Skirrow, G., Eds., Vol. I (Second Edition) 415-496, Academic Press, London (1975).

Zirino, A. and Healy, M. L., Voltammetric Measurement of Zinc in the Northeastern

Tropical Pacific Ocean, Limnol. Oceanogr. 1_6, 112-11?> (1971).

Chester, R. and Stoner, J. H., The Distribution of Zinc, Nickel, Manganese, Cadmium,

Copper, and Iron in Some Surface Waters from the World Ocean, Mar. Chem. 2, 17-32

(1974).

Eaton, A., Marine Geochemistry of Cadmium, Mar. Chem. 4_, 141-154 (1976).

Cooper, L. H. N., J. Mar. Res. ]]_, 128-132 (1958).

258
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

A MODIFIED PROCEDURE FOR DETERMINATION OF OIL AND GREASE IN EFFLUENT WATERS

G. M. Hain and P. M. Kerschner

Cities Service Oil Company

Cranbury, NJ 08512, USA

1. Introduction

There are currently three procedures listed in EPA's "Manual of Methods for Chemical

Analysis of Water and Wastes" for the determination of oil and grease in effluent waters.

The methods listed are:

Storet 00550 - Oil and Grease, Total Recoverable, Soxhlet Extraction

Storet 00556 - Oil and Grease, Total Recoverable, Separatory Funnel Extraction

Storet 00560 - Oil and Grease, Total Recoverable, Infrared

All three are based on extraction of the contaminants with a suitable solvent such as carbon tetrachloride or FreonR 113 followed by quantizing the amount of oil and grease

extracted. The methods differ either in mode of extraction or the quantitative method of

measurement.

2. Discussion

Storet 00550 collects the oil and grease on a diatomaceous-silica filter, followed by

a Soxhlet extraction of the filter cake with FreonR 113. The Freon^ 113 is distilled from

the extract and the residue weight is a measure of contaminants present.

Storet 00556, as the title implies, uses three successive extractions with Freon^^ 113

using a separatory funnel. As in the previous procedure, solvent is distilled from the

extract and the residue weight is a measure of contamination.

Storet 00560 uses the separatory funnel procedure for extraction but the degree of

contamination is determined by a standard infrared procedure.

All three procedures require considerable time and manpower and suffer other limitations

as well. The distillation step in the first two limit them to relatively non-volatile

hydrocarbons boiling above 70°C, and the multiple steps give rise to sample loss.

The three methods were tested by a single laboratory (MDQARL) on a sewage dosed with

a No. 2 fuel oil and Wesson oil.

Based on this testing, precision and accuracy statements are given with the method

write up.

Storet 00550 - Soxhlet extraction gave an 88 percent recovery with a standard deviation

of 1 . 1 mg

.

Storet 00556 - Separatory funnel extraction gave a 92 percent recovery with a standard

deviation of 0.9 mg.

259
Storet 00550 - Infrared gave a 99 percent recovery with a standard deviation of 1.4 mg.

The high recovery for the infrared method is somewhat misleading. The scope of the

method states, "the method is applicable to measurement of most light petroleum fuels,

although loss of about half of any gasoline present during the extraction manipulations

can be expected." Had the sewage been dosed with a gasoline as well as No. 2 fuel oil,

recovery would have been less than the 99 percent for the IR procedure and even lower than

stated for the other two.

A further discrepancy found by this laboratory for the IR procedure was a reversal of

peak profile in some instances at low levels of oil and grease effluent contamination.

Since the procedure uses a differential IR scanning technique, it was evident that the

unknown solvent extract lost something contained on the reference solvent cell which, in

this case, was FreonR 113. Close analysis of the solvent showed that it contained varying

minor quantities of low boiling contaminants. If care was not taken to use the same solvent in both reference cell and extract or if during the filtration of solvent extract

considerable solvent was lost, the scan reversal was observed. The reversal was only

observed in samples of low level oil and grease. At higher levels the effect was masked

by the stronger hydrocarbon absorbances. Some effluents have a tendency to form stable

emulsions with the extracting hydrocarbon, which extends the overall workup time and

increases evaporation losses during filtration of extract, thereby aggravating the solvent

contaminant effect.

The cited limitations made it desirable to develop a modified procedure. The IR method was selected as the base method since it was more amenable to low boiling hydrocarbons. The following goals were set:

1. Reduce overall time and manpower requirement.

2. Use smaller volumes of solvent to increase concentration of extracted

hydrocarbon in solvent.

3. Prevent loss of solvent to minimize light hydrocarbon loss and solvent

contaminant effect.

4. Be able to handle emulsion-prone samples with a minimum of handling.

The modified procedure developed has six steps. First, a one-liter sample is collected

in a wide mouth jar of 1250 cm^ capacity. Sodium acid sulfate is added at the time the

sample is taken to assure an acid pH.

Second, 30 cm^ of Freon^ 113 is added to the sample and the water/FreonR 113 is

agitated on a Red Devil paint mixer for 3 minutes.

Third, the solvent extract is allowed to settle to the bottom of the sample jar.

Fourth, a small sample of extract is removed by syringe equipped with a long needle.

Fifth, the syringe is connected to a filter assembly containing a MilliporeR teflon

filter and sample forced through directly into an IR cell.

Sixth, a differential IR scan is made over the rangfe of 3200 cm"^ to 2700 cm~i.

This procedure meets all the goals originally set.

Analysis time was reduced so that 50 samples can be run per eight-hour shift by a single technician, whereas the current method requires 2 persons to finish just 10 samples

in a like period. Severe emulsions can reduce the number below the 10 samples/day.

Smaller volumes of solvent require adequate mixing to assure complete extraction.

International Harvester describes a standard test for water tolerance in lubricants in

which oil and water are intimately mixed using a Red Devil paint shaker or its equivalent

260
for 5 minutes. It was found that 30 cm^ of Freon"^ 113 effectively extracted all the

hydrocarbons from a 1 liter sample of terminal effluent in a single extraction by agitating

with a paint shaker for 3 minutes. This gives a concentration 33.3% greater than in the

current procedure where the solvent extract is diluted to 100 cm^ before running the IR scan.

The 30 cm^ of Freon^ 113 are added directly to the sample container thus eliminating

the transfer of sample to separatory funnel and rinsing of sample jar with FreonR 113,

resulting in subsequent loss of solvent and light hydrocarbons.

After agitation, the Freon^^ 113 extract settles to the bottom of the sample jar and

the water layer acts as an effective barrier to any solvent/hydrocarbon loss.

The pressure filtration through the Teflon^ Millipore'^ filter acts as a coalescer and

not only dries the sample but breaks emulsions as well. In the most severe cases water

droplets may pass through the filter and a second filtration may be required.

Direct injection into an IR cell completes the sample handling. Since there is no solvent loss, all calculations are based on a 30 cm^ solvent extraction.

Standard curves are prepared at varying concentrations using standards which match

the type of contaminants expected from a given terminal. Standards containing gasoline

showed no difficulty from light hydrocarbon loss.

The infrared spectrograph used is a Hilger-Watts Infragraph H-1200, and a special

absorbance paper was designed so that ppm water can be read directly from the IR scan.

The modified procedure was checked against Storet 00560 for a series to terminal

effluents collected at the same time. This particular terminal did not handle gasoline,

and the problem of light hydrocarbons was not present. The results proved the effectiveness

of the modified procedure.

Work with gasoline storage tank bottoms brought out an additional advantage of the

modified procedure when large quantities of polar components are suspected. A 5 to 10 cm^

sample withdrawn with the syringe can be transferred to a vial, a large excess of silica

gel added, and the contents shaken thoroughly. A direct comparison of hydrocarbon content

before and after exposure to silica gel gives a reading of total hydrocarbon vs. non-polar

hydrocarbons

.

3. Conclusion

The modified procedure is now used by CITGO and samples have been handled on a sameday in and out analysis basis. It is felt that this procedure may offer the EPA an alternate method for determination of oil and grease in effluent water.

261

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

VARIABILITY OF TRACE METALS IN BED SEDIMENTS OF THE PO RIVER: IMPLICATIONS FOR SAMPLING

M. T. Ganzerl i-Valentini , V. Maxia, S. Meloni

Institute of Inorganic and General Chemistry

University of Pavia

Viale Taramelli 12, 27100 PAVIA, Italy

and

G. Queirazza and E. Smedile

ENEL Thermal and Nuclear Research Center

Environmental Laboratory of Trino Vercellese

13039 TRINO, Italy

1. Introduction

Since 1971 a stretch of the Po river (the largest Italian river) (fig. 1), nearby the

site where the fourth Italian nuclear power station is under construction, was submitted to

environmental analysis in order to achieve a thorough characterization of the rivers ecosystem

before plant operations started.

Special attention was devoted to the aquatic ecosystem controlling most of its components

(water, suspended material, periphyton, benthic organisms, bottom sediments, fish). This

investigation required a detailed sampling program with respect to the choice of the sampling

sites and to the sampling frequency.

The stretch under investigation is located in the middle course of the Po river; the

pollution load brought by effluents is very high, this area being downstream from the major

pollution sources (industrial, agricultural, and urban) of northern Italy.

This stretch may be distinguished into 2 zones: the first, upstream from the dam of a hydroelectric power station, characterized by a decreasing river current, and a second one,

downstream, with a swift river current. Despite these unfavorable conditions, the water

quality is generally satisfactory, thus indicating the efficacy of the self-purifying power

of the river.

This paper deals mainly with problems associated with the sampling and analysis of the

most significant components (water, suspended material and bottom sediments) of a riverine

ecosystem affected by different pollution sources. The investigated stretch (approx. 20 Km) covers eight sampling stations (fig. 1), six upstream and two downstream of the dam. In each station there are three sampling sites, nearby the right bank (A), in the middle of the

river (B) and nearby the left bank (C).

2. Experimental

Surface bottom sediment samples [2,4]^ were collected quarterly with a "Van Veen"

mechanical dredge from May 1973 to June 1974. An aliquot of the samples was freeze-dried

and used for neutron activation analysis and atomic absorption spectroscopy investigation

for elemental analysis. Another aliquot, oven-dried at 80°C, was analyzed for organic

nitrogen (after Kjeldahl) and carbon [1,2]. Grain size measurement was carried out by a

^Figures in brackets indicate the literature references at the end of this paper,

263
264
wet-sieving technique and the fraction below 2pni was submitted to x-ray powder diffraction

analysis to investigate the mineralogical composition. A 20-liter single sample of river

water was collected weekly over a one year period at one station and submitted to chemical

and physical analysis.

Water samples from the 21 sampling sites (collected at the water surface and near the

bottom to check any surface and vertical variations of the chemical composition) were analyzed

for the physical and chemical parameters according to APHA, FWPCA and AWWA methods [3].

The chelating capacity was measured with the method described by Kunkel and Manahan [4].

Suspended material was collected by means of a composite sampling device [5] and submitted

to gravimetric determination and chemical analysis.

Element analysis included the determination of iron, manganese, zinc, copper, nickel,

lead, cadmium, cobalt, chromium, mercury, cesium, selenium, and arsenic. Cs, Co, Cr, As, Se

and Hg were determined by neutron activation analysis at the Radiochemistry Laboratory of

the University of Pavia; Co, Cr and Cs content was evaluated by an instrumental method,

whereas As, Se and Hg required the use of radiochemical separations: they were carried out

either with a distillation method developed by Orvini, et al. [6] or by adsorption on inorganic adsorbers or by solvent extraction according to S. Meloni, et al. [7].

Fe, Mn, Cd, Pb, Cu, Ni and Hg (only in the water samples) were determined by atomic

absorption spectroscopy using flame and flameless techniques according to the nature of the

sample. Fe, Mn, Zn and Ni, in acidified (HNO3) water samples, were determined after preconcentration by conventional AAS. Pb, Cd and Cu in water samples were determined according to

Dolinsek and Stupar [8]. Hg determination was carried out with a cold vapor technique [9].

Sediment and suspended materials were mineralized with a mixture of HNO3-HCIO4 and HF before

AAS analysis.

3. Results

Water data reported in tables 1 and 2 show the ranges, average values, standard deviations and coefficients of variation of the measured parameters and of the elemental

concentrations with respect to time (table 1) and space (table 2). A comparison of the

coefficients of variation of each parameter or concentration in the two tables indicates

that the time variation is much greater than the space variation.

To obtain a better evaluation, on a statistical basis, of the influence of the time and

space variations on the measured parameters and concentrations, their average values were compared to a single result using the t^-test. The t^-values for data on table 1 show that

most of the parameters and concentrations have meaningful time variations for a 95 percent

probability (;t=2.01, 49 d.f.) except for BOD5, conductivity, alkalinity, chloride, sulfate,

detergents, phenols, cobalt and chromium. The results for detergents, phenols, chromium and

cobalt are very poor: their high variations are responsible for the fact that the t^-values

do not indicate any significant differences.

As for the space variations the data in table 2, relative to 21 sampling sites, show a limited variation (zinc and copper) or negligible variation for a 95 percent probability (t^= 2.086, 20 d.f.). The data from the grain size measurement are reported in fig. 2. The

grain sizes were divided into 3 groups: sand (>63ijm), silt (<63pm), sandy silt (mixed com- position). The clay mineral fraction (<2ijm) was not classified as this fraction was found

to be always below 2%.

According to the present classification the bottom sediment samples collected from

sampling sites T1(C), T2(A), T3(A), T6(A), T8(A,B,C), and T9(A,B,C) were considered sand;

the samples from sampling sites T1(B), T2(B,C), T3(B,C), T4(A,B,C), T5(A,B) and T6(B) were considered sandy silt; the samples from sampling sites T1(A), T5(C) and T6(C) were con- sidered silt. The data from fig. 2 indicates that the bottom sediments at all stations from

Tl to T6 are not homogeneous in respect to grain size, wereas at sampling stations T8 and T9

they are highly homogeneous and exclusively sand. The lack of homogeneity in the grain size

of the bottom sediments may be related to the hydrological regime [10]. The x-ray investigation carried out on the sediment fraction (<2pm) shows the presence of quartz, calcite and

the following clay minerals, listed according to their abundances: illite > kaolinite > chlorite = vermiculite > montmoril lonite = interlayered clays > quartz = calcite.

265
Table 1. Annual range, standard deviation, C.V., and average of

selected water parameters in the Po river at ENEL hydroelectric

power station.

Parameters Averages S.D. c.v. Annual range

3-1

Water discharge, m s 900 - — 4,300

Temperature, °C 13.5 6.6 49 3 25

PH 7.6 0.2 3 7 1 8.2

Conductivity, umhos cm~^

Dissolved oxygen, mg 0^

370 62 17 2fin 465

8.0 1.2 15 5. 2 10.1

Oxygen saturation, % 76 9 12 54 104

C 0 D, mg 0^ l'""

B 0 Dg, mg Og

Detergents, mg MBAS l"^

_1

Phenols, yg CgHgOH I

36 35 97 Q 237

3.9 2.7 69 1 2 6.2

0.01 0.02 200 <0. 005 0.07

1.5 1.7 113 <0.

1

4.6

Chelating capacity, mg Cu

Organic nitrogen, mg N

-1 Ammonia, mg N I

0.32 0.47 147 0. 1 3 2.80

1.0 0.5 50 0.4 3.1

0. 5 0.3 60 0. 2 1.3

Nitrite, mg N 0.04 0.01 25 0. 02 0.07

_i

Nitrate, mg N I 1.5 0.5 33 0 3 2.7

_i

Phosphate, mg P I _i

Total phosphorus, mg P I

0. 13 0.05 38 0. 03 0.29

0.22 0. 10 45 0 1

0

0.50

_i

Sulphate, mg S I _]

Chloride, mg CI I

15.5 7.0 45 6 28

11.7 3.4 29 6 3 18.2

Silica, mg Si l"^ 1.8 1.1 61 0. 2 4.0

_i

Total hardness, mg CaCQ,, I 173 27 16 126 250

-1 Total alkalinity, mg CaCOo I 119 17 14 90 164

-1 Total iron, mg Fe I 1 .39 1.95 140 0 20 9.85

_i

Total manganese, mg Mn I _i

Total zinc, yg Zn I

0.12 0.14 117 0. 02 0.77

55 33 60 22 190

Total copper, yg Cu l'^

Total nickel , yg Ni l'^

18 30 167 2 180

21 28 133 3 146

_i

Total chromium, yg Cr I 88 131 149 <1 5 474

Total lead, yg Pb 1"^ 9.9 13.9 140 1 .4 _ 82.0

_i

Total cadmium, yg Cd I

Total mercury, yg Hg I

^

Total selenium, yg Se l"^

0.66 1.03 156 0.07 5.10

<U. 1

<0.2

Total arsenic, yg As

Total cobalt, yg Co

1 .98 1.70 86 <1 5.63

4.80 4.12 86 <2 12.6

Total caesium yg Cs 3.31 1.87 56 1.9 9.0

266
Table 2. Space range, standard deviation, C.V., and average of

selected water parameters in 21 sampling sites.

Parameter Average S.D. C.V, Space range

3 -1 Water discharge, m s Temperature, °C

pH

Redox (E^), mV

928'

-1

-1

-1

Redox (E-7), mV

Conductivity, yS cm Dissolved oxygen, mg 0^ I

Oxygen saturation, %

C 0 D, mg 0^ l'^

-1 Detergents, mg MBAS I Chelating capacity, mg Cu I

Ammonia, mg N I

^

Nitrite, mg N l"^

Nitrate, mg N l"^

Phosphate, mg P I

^

Sulphate, mg S l'^

Chloride, mg CI I

^

Sil ica, mg Si 1'^

Total hardness, mg CaCO^ I

Total alkalinity, mg CaCO^ I' -1 Total iron; mg Fe I

Total manganese, mg Mn I

^

Total zinc, yg Zn I

^

Total copper, yg Cu I

^

Total nickel , yg Ni l'^

Total lead, yg Pb l"^

Total cadmium, yg Cd I

^

Total mercury, yg Hg I

^

Total chromium, yg Cr I

^

Total arsenic, yg As I

^

Total cobalt, yg Co I

^

Total caesium, yg Cs I

^

1

17.5 0.4 2 16.9 18.1

7.6 0.1 1 7.5 - 7.8

0.44 0.04 9 0.36 - 0.49

0.48 0.04 8 0.40 - 0.53

325 12 4 '315 - 345

6.3 0.4 6 5.5 - 6.8

65 3.9 6 59 - 71

7.9 0.9 11 6.9 - 9.4

0.040 0.005 13 0.030 - 0.050

0.21 0.14 66 0.10 - 0.50

0.30 0.02 7 0.27 - 0.34

0.12 0.01 8 0.10 - 0.14

1 .04 0.15 14 0.86 - 1 .36

0.13 0.02 15 0.09 - 0.14

11 .8 0.5 4 10.7 - 12.8

12.1 1.1 9 10.6 - 13.5

4.2 0.8 19 2.9 - 5.6

142 2.8 2 139 - 146

116 3.3 3 110 - 122

1 .59 0.74 46 0.76 - 3.02

0.190 0.076 35 0.100 - 0.330

68 30 44 40 - 140

18 10 56 11 - 44

48 12 25 35 70

8.4 4.1 49 2.9 17.2

0.23 0.13 57 0.13 0.50

<0.1

28.4 12.9 45 16.0 50.0

1.8 0.6 33 1.0 2.8

2.4 0.9 37 1 .0 4.1

<2

Single value

The contents of organic carbon and nitrogen and of the other 13 elements determined

the bottom sediments are summarized in table 3.

267
r~~] 0.5 - 0.063 mm

D.W.

(%)

100

OJ

100

0

100

0

100

0

100

oJ

100

0

100

OJ

100

2

Left

3

bank

< 0.063 mm

12 3 4

no

data

Middle of the river

B

CZl > 0.5mm

1 2 3

no

data

T9

T8

T6

T5

T4

T3

T2

Fig. 2 - Grain size measurement data (weight %): 1 sampling of May 197C ; 2 sampling of October 1973; 3 sampling of January 1974; 4 sampling

of June 1974. T1...T9 sampling stations.

A sampling site nearby the right river bank; B sampling site in the middle

of the river ; C sampling site nearby the left river bank.

268
Table 3. Summary of organic carbon and nitrogen, and of element

abundances in the three grain size groups of the bottom sediment.

SEDIMENT FRACTION

ELEMENT^ SAND SANDY SILT SILT

Range

Median or average+S.D.

Range

Median or average±S.D.

Range

Median or average±S.D.

Carbon, % dry weight U. 01 -0. 1

0

A f\l\ , A AO

0. 04±0. 02 A A*^ 1 /I A

0. 03-1 . 40 A T A

0. 1

0

A CA 1 AA

0. 50-1 . 90 1 yi 1 A /I1 .4±0.4

Nitrogen, % dry weight <U. 00 1 -0. 0 1 0 A AA T 0. 001 A AAl A AO^

0. 001 -0. 026 A AA /I 0. 004 A AAA A A^T/I 0. 008-0. 054 A AO^.A ATA

0. 0;:5±0. 0 1

0

Iron, mg/g 1 o on 1 "7 . /I

1 /±4 1 3-43 ^:5±9 3 1 -54 43+/

Manganese, mg/g 0. 1 -0. 4o 0. 34±0. 06 0. 25-1 . 1

3

A /I "7 0. 47 n CO 1 CO 0. bL- 1

.

be 0. y±o.

3

Zinc, 26-85 58±16 26-690 88 220-1070 585±248

Copper, 6-10 7±1 7-195 20 104-325 199+56

Lead, 9-27 16+4 13-160 26 70-450 202+110

Cadmium, 0.7-1.8 1.2±0.3 0.8-7.5 1.6 3.0-9.8 6.5+2

Nickel, 65-100 81 ±8 75-174 109±29 85-177 136±32

Cobalt, 6.1-10.9 8.6±1.4 8.0-21 .2 13±5 12.9-23.6 18±4

Arsenic, 0.2-3.4 0.9 0.1-7.9 2.7 0.1-13.6 1 .2

Selenium, <0.1 <0.1-0.9 0.5±0.2 0.22-1 .34 0.9±0.4

Mercury, <0.03 <0. 03-0. 46 0.08 <0. 03-2. 00 0.9

Chromium, 90-245 162±40 115-320 190+52 165-425 246±78

Caesium, 1.1-1.8 1 .5±0.2 1 .3-8.0 3.3±2.0 2.5-6.1 4.5±1 .1

yg/g except as noted.

The data are presented according to the three grain size groups and for each element

the concentration range was observed. The standard deviation of the average values are also

reported. The relatively low standard deviation for the element content in the sand type of

sediments indicates a small variability of the element content over a one year period and

from one sampling station to another: this implies a reduced capability of adsorption or desorption of the elements in the sand sediments.

The elements may be classified as major and minor elements. Major elements are: carbon,

nitrogen, iron and manganese, the latter are considered to be present as coatings of hydrous

oxides on the sediment grains. All the other elements are considered minor elements and are considered to be adsorbed or coprecipitated on the surface of the sediment particles.

The data (table 3) show an increasing concentration of the elements, arsenic excluded,

from the sand type sediment to the silt type sediment. The increase of the minor elements

may be ascribed to the increased specific surface area of the grains in the silt type sediment.

The rate of increase is not the same for all the minor elements. Zinc, copper, lead, cadmium

and mercury, show a higher increase than cobalt, nickel and cesium. This observation is

consistent with the suggestions advanced by Leland et al. [11], which divided the trace

elements in the bottom sediments of Lake Michigan into two classes: accumulating and non- accumulating. The accumulation effect is observed when the iron and organic carbon content

increases. Differences between accumulating and non-accumulating elements in the variation

of sediment contents were apparent (table 4). The data confirm that for selected sediment

samples with mixed grain size composition, the averages and their variability are uniform

With respect to sample numbers and sampling frequency.

269
Table 4. Averages and variability in concentrations (ug/g) of copper

and nickel for sediments samples upstream from the dam.

ELEMENT

N. SAMPLING N.

onl'lr Lto

AVERAGE ± S.D.

Copper 1 18 52 ± 85

Copper 4 72 64 ± 78

Nickel 1 18 103 ± 22

Nickel 4 72 in ±32

The element content of the sediments collected in sampling sites, where the fraction

<63ym was present, were normalized to 100% of this fraction. An index for each is thus

obtained and the indices have been compared for all the sampling periods. The results are shown in table 5. The last column in table 5 shows the average value of the indices and the

relative standard deviation. For most of the elements the coefficient of variation is very

low: this indicates that, notwithstanding the highly variable pollution load (table 1) and

the large station to station variability of the element content, the time variability is

limited. Only mercury and arsenic do not fit into this trend. Most of the mercury analyses

are reported with a high analytical error as the measured concentration was near the sensitivity limit of the method: this may give rise to the large variation of the indices. The

large coefficient of variation of arsenic may not be ascribed only to analytical error: a different uptake mechanism may occur for this element, but at the moment no valid suggestion

may be advanced.

Analyses of the suspended material (5-114 mg 1~^ in intermediate flow conditions) show

that the element content is higher or equal to the silt sediment content: this indicates

that the deposition of the suspended material is the major source of the trace element

enrichment in the bottom sediments. An analysis of the distribution of the considered

elements between the suspended and the dissolved materials (<0.45ijm) shows that the occurrence

of the elements in the solid phase varies from 4 to 90% according to the series Cs < Co < Cr < As < Ni < Zn < Pb < Mn < Cd < Cu < Hg < Fe.

4. Conclusions

The analytical data gathered in the course of the present investigation provide useful

information for planning programs of environmental control of river ecosystems lightly

polluted from the chemical point of view. Water analyses show a large time variability.

The station to station variability is limited so that the volume flowing in the interested

stretch may be considered homogeneous.

The sediment analyses show, upstream of the dam, a large station to station variability

mainly connected to the conspicuous variability of granulometric characteristics of the

bottom. The presence of the dam increases the deposition rate of the suspended material and

consequently the element contents of the bottom sediment. According to current profile in

the stretch, the rate of deposition may be different along the same section Tl . . .6(A,B,C)

thus giving rise to sediments at different element concentrations. Vice versa in the T8 and

T9 sampling stations, downstream of the dam, where the water current is swift and the deposition rate negligible, no differences in element contents were observed across the stations.

The occurrence of a correlation among the different types of sediments present in the investigated stretch was tested by means of the ratio-matching method of Anders [12]. The

results (fig. 3) confirm a good correlation among the sediment samples from sampling sites

having similar hydrologic conditions; on the other hand no correlations were observed among

samples from sampling sites having different hydrologic conditions.

270
Table 5. Element contents in sediments from the Po river

(normalized to 100% of the fraction <63 ym).

Element

SAMPLING PERIOD

Average±S.D.

(C.V.)

June, 1973 October, 1973 January, 1974 June, 1974

Carbon, % D.W. 1

.

94 1 .85 1

,

,82 1

.

,81 1 .86 ± 0.06

(3)

Nitrogen % D.W. 0. 053 0. 056 0. 040 0. 030 0.045 + 0.012

(27)

Iron, ma/a 46 57 55 54 53 ± 5 (9)

Manganese, mg/g 1

.

16 1 .12 1

.

,28 1

,

,30 1 .22 ± 0.09

(7)

Zinc, uq/q 595 619 651 745 653 ± 66

(10)

CoDDer, uq/q 195 268 233 196 223 ± 35

(16)

Lead, uq/q 149 207 185 204 186 ± 27

(14)

Cadmium, uq/q 8. 6 8,1 8.,1 9. 0 8.5 + 0.4

(5)

Ni ckel , ua/q 188 211 191 169 196+21

(11

)

Cobalt, uq/q 16 17 19 25 19 ± 4

(21

)

\'- ' 1 Arsenic, yg/g 7 3 5 + 3

(59)

Selenium, yg/g 0. 7 1.04 1

.

29 1

,

,52 1.14 ± 0.35

(31)

Mercury, pg/g 0. 24 1 .33 0. 91 2.,05 1.13 ± 0.76

(67)

Chromium, yg/g 266 231 194 399 273 ± 89

(33)

Caesium, yg/g 7. 3 4.2 4.,5 7,,4 5.9 + 1.7

(29)

In regards to the time variability, the normalized data (table 5) obtained for sediment

samples, collected upstream of the dam containing the granulometric fraction <63ym, show for

most of the elements a negligible variability.

Finally, the data presented herein suggest the following considerations: To obtain an estimate of average and range contents of elements in the river sediments, it is necessary

primarily to set up a current velocity investigation and/or granulometric analysis of the

sediments to map out the river sites where bottom sediments are to be collected.

In an area characterized by sediments with quite different granulometric compositions,

the evaluation of mean level and range of the element contents implies the choice of several

sampling sites to take into account the main hydrologic conditions and consequently different

granulometric compositions. In an area characterized by sediments with similar granulometric

composition a single site provides a sample representative of the area.

271
Q0.35(j0.61^#

/

/

0.19 ^

0.72 0.5^ / I L

I

T1

Legend :

^ 0 Sand

3 Sandy silt O Silt

I >^ I Main branch of

T8 '

I the current

I I

Fig. 3 - Correlation numbers (ratio-matching) for sediments

sampling sites.

272
Under the described conditions high sampling frequency is not required. To obtain an estimate of the mean content of elements in the river water the number of the sampling sites

is not relevant because each station may be considered representative of the rivers chemical

and physical characteristics. The pollution load is better evaluated if the sampling frequency is increased to reach a continuous monitoring of the water.

References

[I] McKenzie, L. R., Young, P. N. W., Analyst, 100, 620 (1975).

[2] Ellingroe, J. L., Wilson, J. E., Anal. Chem. , 36, 434 (1964).

[3] APHA, FWPCA, AWWA: Standard Methods for examination of water and wastewater, 13th ed.

[4] Kunkel, R., Manahan, S. E., Anal. Chem. 45, 1465 (1973).

[5] Queirazza, G., Smedile, E., Inquinamento 2, 3 (1973).

[6] Orvini, E., Gills, T. E., LaFleur, P. D., Anal. Chem. 46, 1294 (1974).

[7] Meloni, S., Caramella-Crespi , V., Ganzerl i-Val entini , M. T., Borroni, P., Radioghem.

Radioanal. Letters 25, 2, 117 (1976).

[8] Dolinsek, F., Stupar, J., Analyst 98, 841 (1973).

[9] Klemm, W. A., Fetter, N. R., Atomic Absorption Newsletter 11, 108 (1972).

[10] Battaglia, C, Calciati, A., Signorini, V., Energia Elettriaa Vol. Llll, 3, 1 (1976).

[II] Leland, H. V., Shukla, S. S., Shimp, N. F., Trace Metals and Metal-Organic Interactions

in Natural Waters, Ann Arbor Science, p. 89 (1973).

[12] Anders, 0. U., Anal. Chem. 44, 1930 (1972).

273

Part VI. APPLICATION OF LASER TECHNOLOGY TO ATMOSPHERIC MONITORING

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 19/7)

APPLICATION OF LASER TECHNOLOGY TO ATMOSPHERIC MONITORING^

A. Mooradian

Lincoln Laboratory

Massachusetts Institute of Technology

Lexington, Massachusetts 02173, USA

1 . Introduction

The rapid development of fixed frequency and tunable lasers has increased their use for in situ and remote detection of atmospheric contaminants. As laser systems become more

compact, efficient, and cost effective, environmental monitoring using lasers will become

wide spread and routine, without the need for highly skilled operators.

One of the major advantages of lasers for atmospheric monitoring is their ability to

detect contaminants remotely. The total amount of contaminant molecules can be determined

from the differential absorption of the laser beam over a fixed path with the return signal

coming from either a retroreflector or from topographic scatter. A more useful measurement

of the contaminant concentration can be made by using the backscattered signal as the laser

beam propagates through the atmosphere. The backscattered signal is due to Rayleigh,

Raman, or Mie scattering and is usually quite weak. Such laser radar systems have been

capable of ranges of several kilometers with range resolutions of a hundred or so meters.

Operation has presently been restricted to the use of dye lasers in the visible and CO2 TEA

lasers in the infrared. Dye laser systems rely on tuning to electronic transitions of

atoms or molecules in the ultraviolet and visible for absorption or resonance fluorescence

measurements. Many molecules, however, have their electronic transitions occuring in the vacuum ultraviolet, which limits the utility of this approach. The infrared signatures of

molecules are usually quite extensive and occur with high probability in atmospheric

windows. Figure 1 shows the layout of the Lincoln Laboratory/EPA mobile, long-path transmission measuring system which presently uses tunable diode lasers for multipol 1 utant

detection capability. Mobile, van-mounted laser radar systems are now in common usage

throughout the world.

^This work was supported by U.S. Department of the Air Force, and NSF/RANN.

277
Relay Mirror

Weather Dome

Electronics

Lens-Mirror

"Cats Eye

"

Retroref lector

Transmit Beam

Receive Beam

Storage

O

TIT

Figure 1. Schematic layout of long-path transmission apparatus for monitoring atmospheric

Contaminants using tunable lasers. Mobile van operated by E. D. Hinkley and P. T. Ku of

MIT Lincoln Laboratory under contract to EPA and NSF/RANN.

2. Discussion

The use of laser heterodyne radiometry has been rapidly developing as apassiye

technique for remote detection. A tunable laser is mixed with an incoming signal in a

nonlinear infrared detector to produce a radiofrequency difference frequency signal

(usually up to 1 GHz) that is detected with high resolution and sensitivity. Heterodyne

278
radiometry has the advantage of high detection sensitivity and eliminates the need to

transmit a high power laser beam which in some circumstances can be both hazardous and

illegal. In order to detect a spectral signature, a hot gas (smokestack) or a hot source

(sun) is needed.

Most measurements of atmospheric contaminants have been performed at or near the

surface of the earth. However, an increasing number of experiments are being carried out

at higher altitude in the troposphere using aircraft and in the stratosphere using balloons.

Some particularly important questions to be answered relate to the removal of the protective

ozone layer in the stratosphere by the photochemical catalysis of oxides of nitrogen and

of fluorocarbons, for example. A balloon-borne laser system has recently [1]^ detected

the variation of nitric oxide concentration between sunrise and sunset at altitudes near

28 kilometers, (see fig. 2). The National Aeronautics and Space Administration presently

has plans to place a remote laser detection system on the Space Shuttle to monitor atmospheric contaminants around the earth. Airborne and space-borne remote laser detection

systems have additional constraints for more compact and efficient lasers for long term,

reliable operation. Figure 3 shows two techniques which could monitor both troposphere

and stratospheric pollution using a ground-based laser system.

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MAY 22,1974 —

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Figure 2. Measured NO concentration as a function of time for balloon flight data of

reference [1].

^Figures in brackets indicate the literature references at the end of this paper.

279
Sun

Figure 3. Laser monitoring schemes for the atmosphere using heterodyne detection against

the sun as a black body source and using an active or a passive space satellite.

A rather extensive number of different types of tunable lasers are presently used for

atmospheric monitoring. In the visible region, dye lasers have been used primarily for

laser radar systems with flash lamp excited systems delivering the largest energy per

pulse. The recent development of the rare gas-fluoride lasers such as KrF, XeF, etc.,

may provide a very efficient and high energy pump source for dye laser systems.

Parametric oscillators [2] have become much more refined in their operational characteristics in recent years. The most versatile system uses a high power, high repetition rate

Nd:YAG laser to pump a LiNbOs crystal for tuning in the 1-5 ym region. A computer controlled, narrow-1 inewidth system can cover longer wavelengths by frequency down-converting

using a nonlinear crystal or possibly by Raman Stokes shifting in hydrogen or other gases.

In addition, it is possible to cover the visible wavelength region.

The most conceptually simple of all infrared tunable laser devices are semiconductor

diode lasers [3]. Figure 4 shows the wave length range over which devices with smaller,

but finer tuning capability can be fabricated by selection of lead salt alloy composition.

Most diode lasers operate best near liquid helium temperature, but recent progress [4] has

been made in devices which operate continuously above liquid nitrogen temperature. The

spectral output of a diode laser usually occurs in a number of modes each of whose frequency tunes continuously for about one cm"^ before a mode jump occurs. A comparison of

the relative resolution capabilities of a tunable diode laser and a high resolution

spectrometer is shown in figure 5, together with a Doppler limited absorption spectrum of

C2H4. The major advantage of tunable laser sources over such spectrometers using black

body radiation is the brightness of the source as much as the high resolution.

280
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281
spectrometer 0.5-Torr H

945.1 945.2 945.3 945.4 945.5

WAVENUMBER (cm'^)

Figure 5. Transmission of a high-resolution laboratory grating spectrometer taken using extremely high-resolution tunable diode laser. Also shown superimposed on the diode

laser scan is the Doppler-1 imited absorption lines of Cz^n. Data taken by E. D. Hinkli

282
A very important spectral region for the measurement of atmospheric contaminants is

between 2 and 4 ym where the fundamental hydrocarbon bands occur. A laser spectrometer

[5] has been developed which uses the difference-frequency between a continuous wave (cw)

argon-ion laser and a cw dye laser generated in the nonlinear crystal LiNbOs- An example

of the low pressure (Doppler-1 imited) spectrum and an atmospheric pressure broadened

spectrum of methane taken with this device is shown in figure 6. Spectra of this sort are quite necessary for modeling of atmospheric spectral signatures, particularly in the

presence of other contaminants and water vapor. While the difference-frequency spectrometer now used commercially available components, the LiNb03 crystal does not" transmit

beyond 5 pm. Wide wavelength coverage with sufficient power for spectroscopic applications

can be expected when suitable nonlinear crystals, which transmit in the visible and infrared

beyond 5 pm, are developed.

01 \ I I I I I I I I I I L 2948.6 8.4 8.2 8.0 7.8 7.6

FREQUENCY (cm"^)

Figure 6. Absorption of Methane taken using the cw dye-laser difference frequency spectrometer in the low pressure and high pressure cases. Spectral resolution is about

10 MHz. Data taken by A. S. Pine.

283
3. Conclusion

An alternate approach to a cost-effective and efficient tunable or quasi-tunable

infrared source is the use of the newly developed chalcopyrite nonlinear crystals such as CdGeAs2 and AgGaSe2 for frequency mixing of infrared molecular gas lasers. Figure 7 shows

the wavelength covered by the sum and difference frequency combination bands of a multi wave- length carbon monoxide and carbon dioxide laser. Line densities in these regions are more

than enough to coincide within a pressure broadened linewidth for most atmospheric con- taminant molecules. A significant improvement in the efficiency and average output power

for second harmonic generation of a CO2 laser has been achieved [6] using a 1 cm length of

CdGeAs2. Figure 8 shows the results of one experiment where the average second harmonic

output power increases linearly as the square of the input power, as it should theoretically,

without any sign of saturation due to crystal heating. Maximum average second harmonic

output power using a high repetition rate Q-switched CO2 laser of over one watt has been

demonstrated with peak and average power conversion efficiencies of 35 and 20 percent,

respectively, demonstrated in seperate experiments. Present crystals which are still

quite difficult to grow with high yield are capable of one watt average output power

levels over much of the sum and difference frequency bands. Use of these systems for

differential absorption measurements as well as laser radars is very attractive because of

the simplicity of frequency calibration, overall power efficiency, and the use of simple

molecular gas lasers.

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WAVELENGTH (p)

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MIXING OF CO AND CO^ LASERS

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Figure 7. Wavelengths covered by the sun and difference-frequency combination bands of a CO and CO2 laser.

284
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repetition rate Q-switched CO2 laser. From reference [6].

285
References

Patel, C. K. N., Burkhardt, E. G., and Lambert, C. A., Soienoe 174, 1173 (1974).

Burkhardt, E. G., Lambert, C. A., and Patel, C. K. N., Scienoe T88 , 1111 (1975).

Byer, R. , Tunable Lasers and Applications, in proceedings of an international

conference, Mooradian, A., Jaeger, T., and Stokseth, P., Eds., Springer-Verlag,

publ ishers.

Melngailis, I. and Mooradian, A., Lasev Applications in Optics and Spectroscopy

,

Jacobs, S., Sargent, M. , Scully, M., and Scott, J., Eds. (Addison-Wesley Company, 1975).

Groves, S. H., Nill, K. W., and Strauss, A. J., Appl. Phys. Lett. 25^, 331 (1974).

Walpole, J. N., Calawa, A. R., Harman, T. C, and Groves, S. H., Appl. Phys. Lett.

28, 552 (1976).

Pine, A. S., J. Opt. Soo. Am. 64, 1683 (1974).

Menyuk, N., Iseler, G. W., Mooradian, A., Appl. Phys. Lett, to be published, October,

1976.

286
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

LASER MONITORING TECHNIQUES FOR TRACE GASES

Win i am A'. McClenny

U.S. Environmental Protection Agency

Research Triangle Park, North Carolina 27711, USA

and

George M. Russwurm

Northrop Services Incorporated

Research Triangle Park, North Carolina 27711, USA

1. Introduction

Monitoring techniques based on laser sources have developed along lines that allow

utilization of their unique qualities. These qualities include high spectral radiance and

beam collimation. Three monitoring systems which use these qualities are discussed in

this paper: an opto-acoustic (OA) system, a long path monitoring system, and a laser

induced fluorescence system. The last two systems have been tested in field studies

during the Regional Air Pollution Study [1,2]^. Using an opto-acoustic system based on a CO2 laser, NH3, C2^k> Freon 11 and Freon 12 detection has been investigated under controlled

laboratory conditions.

Only in a few cases can the cost and sophistication of current laser-based monitoring

systems be justified for ambient trace gas monitoring. However, feasibility studies using

prototype systems have established the type and quality of data which can, at this point,

be obtained. Of particular interest as monitoring tools are the long path monitors that,

by their very nature, do not compromise the integrity of the sample being measured. This

feature is of particular importance in measuring reactive gas species such as ammonia and

hydrogen chloride. All three of the techniques discussed have low minimum detectable

limits for certain trace gases and they operate in real-time.

2. Optoacoustic Detection

The primary goal of recent opto-acoustic research at the EPA, Research Triangle Park,

has been to monitor NH3 in the ambient air. Max and Rosengren [3] have shown a linear OA

response to ammonia over the range 0.1 to 10 ppm using a resonant cell; they have projected

a detection limit of 0.1 ppb based on system response parameters. Fischer and Schnell [4]

also have indicated low detection levels for ammonia and have measured a surprisingly high

absorption coefficient for NH3 at 360 torr at the R(30) line in the 9.4 ym band of the CO2

laser [5]. The interest in NH3 detection has led to the measurement of NH3 absorption

coefficients by personnel at Lincoln Laboratory [6]. One of the measurements repeated

Fischer and Schnell 's work with the same result but also determined the ammonia absorption

coefficient at R(30) for atmospheric pressure and found a value of 75 cm'^atm"^. This

value was significantly higher than previously reported values at CO2 laser wavelengths.

^Figures in brackets indicate the literature references at the end of this paper.

287
e.g. 21.9 cm-iatm-i for R(8) in the 10.4 ytn band [7] and 36 cm-iatm-i for the R{18)

line in the 9 pm band of the laser [8]. Values for R(28) and a number of other

lines in the 9.4 um band had previously been measured at EPA [7]; the R(28) value was found

to be only 0.38 cm"iatm"^ and hence effectively zero with respect to NH3 absorption when

compared to R(30). With this previous work as a basis, an experimental OA system was designed for NH3 measurements. Main system components included a grating tuned CO2 laser;

a variable speed chopper; a 15 cm long, 0.95 cm diameter (inside) stainless steel OA cell;

an electret microphone (Model 5336 fabricated by Thermo Electron Corp.); a laser power

meter; a lock-in amplifier; and the necessary support equipment.

To obtain known concentrations of NH3, dry air was passed over a permeation tube and

then diluted to the desired concentration. The resulting sample was continuously passed

through the OA cell at a flow rate of 60 ml min"i. The cell was heated and a small amount

of humidified air was added to the sample prior to the cell inlet. Linearity of response

to NH3 was obtained over the range from 17 to 70 ppb, the lowest concentration used being

17 ppb. A background signal due to window (Irtran 2) absorption was equivalent to 51 ppb.

A noise equivalent concentration of 1.4 ppb was obtained using a 10 second time constant at

a chopping frequency of 300 Hz. Higher system sensitivity by a factor of 10 can be obtained

using a lower chopping frequency with a closed cell; however, desorption and adsorption of

NH3 from the cell walls makes repeatable measurements difficult.

The remaining problem with NH3 measurement is discrimination against interference. At

low concentration levels of NH3, absorption due to major atmospheric constituents such as H2O and CO2 results in OA signals comparable to those due to NH3. Since the OA response is

proportional to the product of absorption coefficient, a, and gas concentration, c, direct

comparison of ac values indicates the extent of interference for a single wavelength

determination. At R(30) the comparison of ac values and the resulting interference equivalent using the background window signal as a reference is given in table 1. Shumate

et al. [9] indicate that the ac values for H2O as given in table 1 have to be considered

with some caution since an interference due to ammonia was not entirely resolved. Since

variation of H2O and CO2 concentrations during a measurement sequence would ordinarily be

only a small fraction of their absolute concentrations, measurement at a second wavelength

would allow a maximum effective interference equivalent due to CO2 and H2O to be measured,

thereby reducing measurement uncertainty for NH3. Other interferences also exist for NH3

determination [10]. Interference problems of this type referred to in reference 10 have

been handled before by the use of several wavelengths along with a mathematical treatment

of data [10,11]. An alternative simpler approach to the interference problem is the use of a selective scrubber for NH3, one which will pass interferences and remove NH3

quantitatively.

Table 1

Interference equivalents of H2O and CO2

Gas Concentration c Interference equivalent (ppb)

H2O 5 torr^

10 torr^

15 torr^

1.40 X 10-6

1.65 X 10-6

1.93 X 10-6

.77 X 10-6

5.25 X 10-6

25.7

22.0

18.7

CO2

NH3

330 ppm

0.07 ppm

10.3

^Measurements by Shumate et al. [9] using OA cell.

288
A second type of experiment involving separation of gaseous compounds prior to detection has also been conducted using the opto-acoustic system as a detector. In a set of

feasibility tests a portable gas chromatograph (Model 510, Analytical Instrument Development, Inc.) was interfaced with the opto-acoustic system and used to measure sub-ppm

concentrations of Freon 11 and Freon 12. Cell volume was only 8 cm^, giving sufficient

resolution of the two eluted compounds to provide complete baseline separation when a sample loop of 5 cm^ was used. An unoptimized detection limit of 50 ppb was obtained using

the R(30) line; using optimum wavelengths available with the CO2 laser and limiting flow

noise through the system, an improvement of an order of magnitude in sensitivity is projected. This demonstration of feasibility shows the possibility of extending the GC-OA

approach into new areas of technique development for air pollution problems. The combination of gas chromatographic and infrared absorption methods may find wide and useful

appl ications.

3. Long Path Monitoring

Two current efforts are being directed at the use of long path monitors to obtain

unique measures of air quality. In one effort, measurements are being made around fixed

monitoring stations to determine typical differences between long line averages over distances of up to 0.5 km and point monitor readings. Documentation of such differences

provide a data base from which estimates of the accuracy of using point monitor data for

mathematical modeling of the atmosphere can be determined. Significant measurements of

this type have been made using a system based on a semiconductor diode laser and developed

at Lincoln Laboratory by Hinkley, Ku and associates. Field tests of this system in St.

Louis during the Regional Air Pollution Study (RAPS) consisted of area monitoring at sites

105 and 108 of the RAPS network of stationary monitors. The laser system is housed in a mobile van equipped with beam steering optics that can be rotated 270 degrees in the

horizontal plane and ± 10 degrees in the vertical plane to locate remotely placed retroreflectors.

Results of field tests for monitoring carbon monoxide have been given elsewhere

[1,12]. Analysis of the data for CO obtained during 1975 and 1976 field studies indicate

the following:

a. establishing zero and multipoint calibration is complicated by the existence of more than one wavelength in the output beam (multimoding)

;

b. active feedback control of the laser output frequency (or frequencies in the case

of multimoding) is required to fix the zero and calibration;

c. under controlled conditions monitoring of CO on a real time basis can be accom- plished over distances of up to 0.5 km (1.0 km total path);

d. data processing under current system constraints requires significant interpretation in order to insure accuracy to ± 10 percent.

In a second effort, measurement of NH3 is being attempted. Sample integrity of the

ammonia is insured since the NH3 is measured in-situ, i.e. in its natural state. Initial

attempts to monitor NH3 have been limited by the available power in state of the art diodes

in the 9-10 ym spectral regions. The current limit of detection is approximately 10 ppb of

NH3 over a total pathlength of 200 m, the pathlength being restricted by the available

laser power.

4. Laser Induced Fluorescence

The Aerospace Corporation under EPA sponsorship has developed a laser-induced

fluorescence monitor for NO2 [13]. This monitor has been used in field test comparisons

with a chemi 1 uminescence NOx monitor during the RAPS in St. Louis. Results show excellent

agreement between the two monitors during controlled tests although the fluorescence

monitor consistently reads slightly lower than the chemi luminescence monitor during ambient

289
air monitoring [2]. Other tests in smog chamber studies at the Environmental Research

Center in the Research Triangle Park, North Carolina have indicated the lack of interference of other nitrogen containing compounds; these tests suggest the use of such equipment to measure NOo in chamber studies [14].

References

[1] Ku, R. T. and Hinkley, E. D., Long Path Monitoring of Atmospheric Carbon Monoxide,

Report NSF/RANN/IT/GI-S7603, Lincoln Laboratory Interim Technical Report to the

National Science Foundation.

[2] Birnbaum, M. and Tucker, A. W., Field Test Comparison of Chem£liminescenoe and Laser

Fluoresoenae Monitors, Unpublished report by Aerospace Corporation for the Environmental Protection Agency, Research Triangle Park, NC (October 1974).

[3] Max, E. and Rosengren, L. G., Optics Communications, 1J_ 422 (1974).

[4] Schnell, W. and Fischer, G., Rapport de la Soaiete Swisse de Physique, 26_ 133 (1975).

[5] Schnell, W. and Fischer, G., Applied Optics, T4 2058 (1975).

[6] Hinkley, E. D. , Ku, R. T., Nill, K. W. and Butler, J. F., Applied Optics, 15 1653

(1976).

[7] Patty, R. R., Russwurm, G. M. , McClenny, W. A. and Morgan, D. R., Applied Optics, 13^ 2850 (1974).

[8] Allario, F. and Seals, R. K. , Jr., Applied Optics, 14 2229 (1975).

[9] Shumate, M. S., Mengies, R. T., Margolis, J. S. and Rosengren, L. G., Water Vapor

Absorption of Carbon Dioxide Laser Radiation, Jet Propulsion Laboratory, to be

published in Applied Optics.

[10] Kreutzer, L. B., Analytical Chemistry, 46 235a (1974).

[n] Morgan, D. R., Spectral Absorption Pattern Detection and Estimation Techniques Using

Linear Weights, Report R75ELS-024, General Electric Company, Electronics Laboratory,

Syracuse, New York (May 1975).

[12] Chaney, L. W. , McClenny, W. A. and Ku, R. T., Long Path Laser Monitoring of CO in the

St. Louis Area, Paper #75-56-6, 68th Annual Meeting of APCA, Boston, Massachusetts,

June 15-20, 1975.

[13] Birnbaum, M. and Tucker, A. W., BO-i Measuring System, EPA Report 650/2-74-059, Final

Contract Report for EPA Contract No. 68-02-1225, Aerospace Corporation (May, 1974).

[14] Unpublished results of smog chamber experiments, Environmental Sciences Research

Laboratory, Research Triangle Park, NC.

290
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

LONG-PATH MONITORING WITH TUNABLE LASERS^

E. D. Hinkley2 and R. T. Ku

Massachusetts Institute of Technology

Lincoln Laboratory

Lexington, Massachusetts, 02173, USA

1. Introduction

By using a tunable laser whose signal is reflected from a distant target, differential

absorption of the laser power can permit a quantitative determination to be made of the

integrated pollutant concentration over the path due to a particular gaseous species. Many

molecular pollutants, such as NO, NO2, SO2, CO, and O3 [1]^, have already been monitored in

the atmosphere using this technique, employing different types of tunable lasers in the

ultraviolet, visible, and infrared regions of the electromagnetic spectrum. Integratedpath measurements such as these are important for studying various computer models being

proposed for region-wide prediction of pollution levels, since their basic grid size is

usually around 1 km.

Traditionally, pollutant concentrations have been measured by point-sampling instrumentation. However, the limitations of these standard methods become obvious in cases where the average pollutant concentration over a large area must be determined. In this

paper, we describe a tunable laser system representing a development in the direction of a versatile and reliable monitor for such in situ ambient-air measurement. Moreover, with

eventual utilization of the new widely-tunable diode lasers [2], it is possible to monitor

several different pollutant gases simultaneously. A multi pollutant capability is extremely

useful since many pollutants interact with each other, and the time evolution of their

concentrations can be incorporated into the mathematical models, along with meterological

and topological data, for advance prediction of air pollution levels.

We have developed a tunable semiconductor diode laser system for monitoring pollutants

over long outdoor paths. The laser source is one of the Pb-salt types [3,4] which have

several useful properties for field applications, such as small size, ruggedness, and ease of wavelength tunability. By chemically tailoring various combinations of Pb-salt compounds

we can effectively cover the infrared wavelength range from 3 to 32 ym. Many important

atmospheric pollutants can be detected by lasers in this range. By using various PbS^.^Sex

lasers, which operate in the 4-6.5 ym range, we have monitored CO, H2O and NO over long

paths. Once a laser is constructed to operate nominally and in the wavelength region where

a particular pollutant has strong absorption lines, the laser can be tuned simply by

varying the injection current or laser temperature.

^This work was supported by the National Science Foundation (RANN) and the U. S. Environmental Protection Agency.

^Present address: Laser Analytics, Inc., Lexington, Massachusetts

^Figures in brackets indicate literature references at the end of this paper.

291
2. Discussion

The essential components of the laser optical system are shown in figure 1. The

diode laser is mounted in a closed-cycle cryogenic cooler, and its emission is collimated

by an Al-coated parabolic mirror M-1 , 12 cm in diameter. The beam is transmitted downrange to a remote retrorefl ector (hollow corner-cube) M-2 which reflects it back towards M-1,

and then refocuses it onto the infrared detector situated behind a calibration cell. In order to minimize the effects of atmospheric turbulence on system sensitivity, a derivative

spectroscopic technique is employed in which the laser is frequency-modulated at 10 kHz at

the pollutant gas absorption line of interest.

Figure 1. Long-path diode laser monitoring system.

292
This system was first used at our Laboratory's 300-meter test range in Bedford,

Massachusetts, where an experimental detection limit of five parts per billion of CO was established [5]. An identical system was then incorporated into a mobile van which has

since been utilized in St. Louis, Missouri, for atmospheric measurements of CO at various

sites during the summers of 1974, 1975, and 1976, in conjunction with the Regional Air

Pollution Study (RAPS) of the U. S. Environmental Protection Agency [5]. In addition, our mobile system has also been driven to Cambridge, Massachusetts for monitoring atmospheric

NO in the vicinity of a traffic rotary.

The sensitivity and accuracy of these measurements are discussed, and the long-path

measurements are compared with point sampling results in order to evaluate the potential

of the long-path laser monitor for providing more reliable and acceptable quantitative

measures for air quality.

3. Measurement Techniques

Tunable laser spectroscopic measurements in the laboratory are usually performed by

propagating the laser radiation through an absorption cell. The change in laser power

transmission during tuning can be used to obtain the absorption coefficients, line widths,

and line shapes of the spectral lines. The experimentally-determined absorption coefficients can then be used to measure an unknown pollutant concentration using the amount of

laser absorption in conjunction with Beer's Law.

Field measurements of ambient gases are similar to the laboratory procedures. The

amount of absorption over a long atmospheric path can be related to the average pollutant

concentration over that distance. In order to minimize atmospheric turbulence effects on laser beam propagation, a derivative spectroscopic technique can be employed [5]. Synchronous detection at a high a.c. modulation frequency, about the desired laser infrared

frequency, provides the derivative of the absorption signal. Atmospheric effects are reduced by ratioing the derivative with the direct transmission signal. System "zero" is

achieved by tuning the laser to line center (where the derivative/ratio signal should be

zero) or by placing a retroref lector near the transmitting optics (to simulate a signal

with effectively zero absorption).

Calibration is achieved by placing a known concentration of pollutant-N2 mixture in

the 10 cm cell. For example, if the monitored path outside is 610 meters, a calibration

gas of 1,000 ppm mixture produces the same signal as 164 ppb over the long path. Linearity

is confirmed by using several mixtures of different concentrations in the calibration

cell. Inaccuracies in the measurements which occur as a drift of the zero-ppm signal and

changes in linearity and repeatability of the calibration points, were mainly due to

variations in the laser frequency. By proper controls, we have been able to reduce these

effects to achieve an accuracy of ±5 percent of the nominal reading.

4. Monitoring Results

In order to evaluate the measurement technique, "zero," and calibration procedures,

comparative tests were made of pollutant variability using the long-path laser monitor and

an air bag sampler which was filled during a traverse of the laser path. Results will be

shown to support the validity of our measurement and calibration techniques.

The CO pollutant concentration was found to be quite dependent upon the location of

the monitored area. For example, results will be shown for a generally low-concentration

farm site in Illinois over which clouds of CO occasionally pass. In contrast, large

changes in concentration were noted for an inner city site in St. Louis at various hours

due largely to local traffic conditions. Significant spatial variations were also observed

by means of a conventional point sampling instrument moved along a 1 km path, indicating

the desirability for a long-path monitor for path-averaged pollutant measurements.

293
5. Conclusion

The long-path diode laser system has permitted unattended monitoring around the

clock, with calibration checks reduced to two or three times a day. Although these

results have demonstrated the feasibility and usefulness of long-path laser monitoring,

several improvements must be made in future systems in order to increase reliability and

provide legally-acceptable air quality measurements.

References

[1] Hinkley, E. D. , Ku, R. T. , and Kelley, P. L., Laser Monitoring of the Atmosphere,

Chapter 6, edited by E. D. Hinkley, Springer-Verlag, Heidelberg (1976).

[2] Hinkley, E. D., Ku, R. T., Nill, K. W., and Butler, J. F., Appl. Opt. 1^, 1653 (1976)

[3] Harman, T. C, J. Phys. Chem. Soc. Suppl. 32, 363 (1971 ).

[4] Calawa, A. R. , J. Lwninesoenoe 7_, 77 (1973).

[5] Ku, R. T., Hinkley, E. D., and Sample, J. 0., Appl. Opt. U, 854 (1975).

[6] Ku, R. T. and Hinkley, E. D., M.I.T., Lincoln Laboratory Interim Technical Report,

Long-Path Monitoring of Atmospheric CO — 1975 RAPS Study, St. Louis, Missouri (1976)

294
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

DEVELOPMENT OF A TWO FREQUENCY DOWNWARD LOOKING AIRBORNE LIDAR SYSTEM

J. A. Eckert, D. H. Bundy, J. L. Peacock

Remote Sensing Division

Environmental Monitoring and Support Laboratory

U.S. Environmental Protection Agency

Las Vegas, Nevada 89114, USA

1. Introduction

Extensive testing and operational experience gained with two existing airborne LIDAR

systems have demonstrated the utility of such devices for monitoring the height of elevated

inversion layers representing mixing depths over large geographical areas in relatively

short periods of time [1,2]^. During several field testing missions using a prototype

system, both point source and urban plume measurements were obtained suggesting even greater utility to this type of device. The two-wavelength downward looking LIDAR responds

to the following specific monitoring problems:

1. The determination of mixing layer height over relatively large geographical areas

in short time periods. This type of information is particularly useful in determining the

behavior of the mixing layer height during morning and evening transition periods.

2. The determination of point source plume dimensions referenced to a ground coordinate data base. The information can be used not only to characterize the plume behavior

but also to position sampling aircraft using in-situ techniques.

3. Obtaining dimensions and point source components of urban or other multi-source

plumes. The data are of principal interest to modelers but in some cases can also be of

interest in pinpointing emissions violations.

Although the three monitoring problems all utilize downward looking airborne LIDAR

systems, the monitoring requirements are substantially different for each and are differentiated in the following table:

Table 1

Monitoring requirements differentiated in matrix of three monitoring problems all

utilizing downward looking airborne LIDAR systems

Vertical Horizontal Particle Size Real Time

Resol ution Resol ution Discrimination Data DisDiav

Mixing layer height Moderate Low No No

10m 100m

Point source plume High High No Yes

dimensions 3m 3m

Urban plume characteristics Moderate Low Yes No

10m ^ 100m

^Figures in brackets indicate the literature references at the end of this paper.

295
296

Because of the relatively high capital costs ($120K) involved in constructing LIDAR

systems as well as the substantial commitments in personnel for system design, it is

desirable to construct a single general purpose system which will address itself to all

three problem types. The monitoring problems are being solved through the design and

construction of a two frequency downlooking airborne LIDAR system and the subsequent

technique development necessary for implementing the operational system.

2. System design/laser selection

In order to meet the various monitoring requirements, minimal system requirements

would include real time display capabilities, good horizontal and vertical resolution, and some ability to discriminate between distinctly different particle size distributions. In addition, certain operational constraints must be met for aircraft weight and power limitations, system reliability, and operator functions.

The system consists essentially of three components; a laser, a telescope receiver,

and a data handling and control system. The system can be installed in a small twin engine

aircraft (C-45 and larger) and will meet all air safety criteria. The system will be flown

at 10,000 feet (3,050 m) above ground, a value consistent with both eye safety requirements

for the casual observer and air traffic safety requirements over large urban areas.

Vertical resolution constraints are met by having a laser with a sufficiently short

pulse and a receiver and data handling subsystem capable of processing the pulses.

The resolution constraints are forced by the specifications of currently available

commercially built lasers. The laser procured for the system is a Nd:YAG laser transmitting

both the primary wavelength (1.06 pm) and the frequency doubled wavelength (0.53 ym). The

laser was designed specifically for airborne applications operating directly off aircraft

power. Pulse widths are 15 nsec for each wavelength and this parameter controls the maximum

vertical resolution for the system (3 m). Repetition rate for the laser is a maximum of 10

pulses per second which, coupled with the minimum ground speed for the supporting aircraft,

dictates the horizontal resolution. The use of the two widely spaced laser wavelengths

will yield some particle-size information, namely a qualitative differentiation between

markedly different particle size distributions [3].

3. System design/telescope

Telescope size is dictated by the port size in the bottom of the typical aircraft (0.4 m X 0.4 m). The two previous systems used Fresnel lens refracting telescopes which have

great weight benefits in non-imaging applications; however, because of the differences in

wavelength and the reduction of off axis light, a reflecting telescope has been incorporated

into the design. The device used a F/3 0.38 m Newtonian telescope. The two wavelengths

are separated through a dichroic beam splitter, filtered and imaged on the respective

photomultiplier tubes.

4. Systems design/electronics subsystem

Figure 1 is a block diagram of the electronics subsystem for the LIDAR device. The

four principle functions of the subsystem are: 1) conversion of the data into a digital

format; 2) recording of data; 3) provision of a real-time display of the data or subset of

the data; 4) provision for overall control of the system and the operator/device interface.

298
Output from the photomul ti pi ier tubes is first passed through log amplifiers because

of the wide dynamic range of the detector signals (40 DB). The amplifiers are incorporated

into the photomul tipl ier tube housings and yield minimum signal bandwidths of 50 MHZ.

Prior to each laser firing, background levels are monitored, digitized, and stored for

later processing. Photomultipl ier tube gating and range correction (l/R^) are performed

simultaneously with the detection of the returning LIDAR pulse through varying the potential

of four alternate dynodes as a function of time (range). Both range and photomul tipl ier

tube response characteristics are corrected by sequentially selecting a digital value for

dynode voltage from a Programmable Read Only Memory (PROM).

As the laser fires, a small amount of the output light pulse is optically coupled to

the detector to obtain instantaneous power. Signals are then collected, digitized and

stored for a period of 20 ysec, a value which allows detection of the ground return pulse

from an altitude of 10,000 feet (3,050 m). A buffer memory in the real-time processor now contains background values obtained prior to the laser firing, a value for instantaneous

power, and the LIDAR return plus background. A fast digital processor using bipolar

microprocessor technology subtracts the background and adjusts the data for variations in

laser output. The processor generates a 256-byte record for each frequency and each laser

firing. This record is operator selectable to extend over the entire 10,000-foot (3,050 m)

aircraft-to-ground path (40-foot (12 m) vertical resolution) or over the lower 2,500 feet

(762 m) (10 foot (3 m) vertical resolution). Operator options thus include looking over

the same vertical distance with two different frequencies to obtain particle size information or observing two different vertical scales by using the different frequencies.

Output from the real-time processor is next routed to a large (32K-byte) circulating

solid state memory which serves multiple functions including the interfacing of the bipolar

microprocessor system and an 8-bit NMOS microprocessor system which controls the data

output and control aspects of the overall system. The memory operates in a first in-last

out mode dumping onto a magnetic tape deck at the option of the operator. Contents of the

memory are displayed on a color CRT as 64 x 2 (frequencies) vertical traces yielding a real-time display of the last 64 laser firings. The two frequencies are assigned different

colors with eight levels of luminance. At the maximum repetition rate of the laser, the

display incorporates 6.4 seconds of data. The real-time display is described in figure 2.

The CRT display is continuously recorded on a video tape for immediate analysis of the data

upon mission completion. The video tape is multiplexed with a downward looking vidicon

used to obtain ground reference data.

The systems controller (see figure 1) formats the magnetic tape record of the data

with navigational and other reference data. The controller also performs some general

housekeeping functions of the device including warning the operator of malfunctioning

components or subsystems. Operator interface to the system is through a small CRT and

keyboard.

5. Summary

A two-frequency downward looking LIDAR system is now being constructed with the

following operational and physical parameters:

Physical

:

Laser - Q-Switched Nd:YAG

Pulse length: 15 nsec Output wavelength: 1.06 m or 0.53 ym

Energy per pulse: 500 mJ (at 1.06 urn) 200 mJ (at .53 ym)

Beam divergence: 0.25 mrad

Telescope - F/3-1 5-inch Newtonian with dichroic beam splitter

Detectors - 2-50 mm PM, S-20 and S-1 photocathodes

Size - 1.5 m^

Weight - 100 kg

Power requirements - 1.5 kw

299
Operational

:

Altitude - 10,000 feet (3,050 m) above ground level

Signal rate - 10 pulses per second

Vertical resolution - 3 m or 12 m

Real time display

Vertical resolution element - 13 m or 50 m Total traces - 128 (64 x 2 wavelengths)

Min. storage time - 6.4 seconds

Output - 9-track magnetic tape

Video tape of real-time display

When completed, the system will respond to a variety of monitoring needs involving

aerosol structure in the lower atmosphere. Specific applications include measuring mixing

layer heights and dimensions of point-source and urban plumes. The system is scheduled to

be completed in the fall of 1977.

References

[1] Eckert, J. A., McElroy, J. L., Bundy, D. H., Guagliardo, J. L., and Melfi, S. H.

,

Airborne LIDAR RAPS Studies, February 1974, EPA report EEPA-600/4-76-028 , June 1976.

[2] Eckert, J. A., McElroy, J. L., Bundy, D. H., Guagliardo, J. L., and Melfi, S. H.

,

Downlooking Airborne LIDAR Studies - August 1975, published in the proceedings of the

Intevnational Conference on Environmental Sensing and Assessment, EMSL-LV, Las Vegas,

NV, September 1975.

[3] McCormick, M. P., Laser Backacatter Measurements of the Lower Atmosphere, A Thesis

Presented to the Faculty of the Department of Physics, the College of William and Mary

in Virginia, 1967.

300
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

REMOTE ANALYSIS OF AEROSOLS BY DIFFERENTIAL SCATTER (DISC) LIDAR SYSTEMS

M. L. Wright

Stanford Research Institute

Menlo Park, California 94025, USA

and

J. B. Pollack and D. S. Colburn

NASA-Ames Research Center

Moffett Field, California 94035, USA

1. Introduction

A remote sensing system capable of determining the chemical composition of atmospheric

aerosols would be desirable for reducing the cost of long-term measurements, especially in

the stratosphere, and for avoiding some of the difficulties encountered in aerosol sampling

systems. A differential scatter (DISC) lidar system uses characteristic differences in the

infrared backscatter spectra of aerosols to identify the chemical composition of the

aerosol. Recent studies of backscatter spectra for stratospheric aerosols have shown that

substantial amplitude variations occur over relatively narrow wavelength ranges [1]^.

Figure 1 shows typical backscatter spectra for several different stratospheric aerosols.

This differential backscatter could be a useful mechanism for determining the composition

of stratospheric aerosols.

Backscattered signals received by an actual DISC lidar system are affected not only by

the differential aerosol backscatter but also by the gaseous attenuation of the atmosphere

and changes in the lidar system. The selection of lidar system parameters to provide

optimum performance for measurements on a specific aerosol must take into account all of

these factors. The use of the computer with the Modular Atmospheric Propagation Program

(MAPP) to perform these system optimizations is described for applications to stratospheric

aerosol measurements. Initial calculations indicate that a portion of the H2SO1+ concentration range of stratospheric aerosols can be measured by the DISC technique.

Multiple operating wavelengths will be necessary in order to discriminate between the

relative backscatter that is produced by the various constituents in a stratospheric aerosol. The optimum number of wavelengths and the optimum location for each of these wavelengths is dependent on the characteristics of the actual lidar system, the atmosphere

through which the optical signals must propagate, and the expected range of variation in

constituents in the stratospheric aerosol. The primary focus on the present work centers

on a ground-based CO2 lidar system. For this system, the optimum number of wavelengths and

their locations were determined for a variety of stratospheric aerosol models representing

a range of different constituents and different constituent concentrations.

Figures in brackets indicate literature references at the end of this paper.

301
1 r

• BASALT

Figure 1, Relative backscatter for several atmospheric aerosols

2. Objective

The first task in the analysis is to determine the atmospheric propagation characteristics for all the possible operating laser wavelengths for the system or systems desired.

Each of these lines is then evaluated for its low attenuation, freedom from interference by

gaseous constituents in the path, and relative system performance at that wavelength. This

evaluation results in a priority ranking for the laser lines, ranging from most to least

favorable for the specified application.

After selection of a priority ranking for laser lines, the next task is to select the

optimum number of wavelengths and their wavelength locations. This selection process is

treated as a pattern recognition problem because the system makes decisions among various

stratospheric aerosol models by choosing the model backscatter spectrum that best fits the

observed experimental data.

3. Results

To determine the best overall system performance, some criteria are necessary for

making comparisons of system performance with changes in the number or location of wavelengths. Unfortunately, a single performance criterion cannot be specified for operation

under all possible conditions and for all possible laser systems. Several goodness measures

were investigated for a variety of measurement scenarios. Different criteria gave slight

differences in the number of wavelengths and their locations; nevertheless the differences

among these criteria is shown in figure 2. This example is for a nonisotope CO2 laser

designed to discriminate between (NHtt)2S0tt, H2SO14 (75 percent), and obsidian. A fixed

experimental uncertainty (noise and other error mechanisms) of 40 percent was assumed for

this example. This figure shows that improved capability to discriminate between the

various materials changes very slowly after the number of wavelengths is increased beyond 3

to 6.

302
FIGURE 2 MEASURE OF GOODNESS vs NUMBER OF MEASUREMENT WAVENUMBERS

FOR NONISOTOPE CO2 LASER LINES. Fractional error = 0.4. Materials: HjSO^iyB), {m^)2S0^, obsidian.

Once the optimum number of wavelengths has been determined and the location of each of

these wavelengths has been specified, the next task is to indicate the level of system

performance that would be obtained in such a measurement. Several performance measures

were considered, and an example of the system performance that can be expected will be

presented.

DISC lidar systems are useful for various aerosol measurements in both the stratosphere

and troposphere. For example, the DISC technique could be useful for measuring the sulfuric

acid content of aerosols emitted by power plants, refineries, and automobile catalytic

converters

.

References

[1] Colburn, D. S. and Pollack, J. B., Infrared Backscatter Spectra for Differentiation of

Stratospheric Aerosol Composition, presented at the Seventh International Laser Radar

Conference, Stanford Research Institute, Menlo Park, California, November 4-7, 1975.

303

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977)

DIAL SYSTEMS FOR MONOSTATIC SENSING OF ATMOSPHERIC GASES

E. R. Murray, J. E. van der Laan, J. G. Hawley, R. D. Hake, Jr., and M. F. Williams

Stanford Research Institute

Menlo Park, California 94025, USA

1. Introduction

The differential absorption lidar (DIAL) technique has been established as a sensitive

technique for making range-resolved and integrated concentration measurements of gaseous

species [1,2]^. Range-resolved DIAL demonstrations have been performed using visible [3-5]

and ultraviolet [6,7] lasers. Extending DIAL capabilities to the infrared region of the

spectrum permits access to the characteristic infrared absorption lines of hundreds of

additional gaseous species with currently available high-energy discretely tunable gas

lasers.

Considerable effort has been devoted to the development of longpath infrared monitoring

systems using remotely positioned retroreflectors [8-12]. Several of these systems have

been assembled into fieldable configurations and have been used to obtain useful data in

the field. Demonstration of the first single-ended system using topographical reflections

was reported by Henningsen, Garbuny, and Byer [13]. This system, using a parametrical ly

tunable laser, was used for remote measurement of a sample of carbon monoxide [13].

Recently, a single-ended chemical laser system has been used for remote measurement of

hydrogen chloride, methane, and nitrous oxide as reported by Murray, van der Laan, and

Hawley [14]. The operation of an infrared DIAL system using aerosol backscatter was first

reported by Murray, Hake, van der Laan, and Hawley [15,16].

The objective of our program has been the development and demonstration of systems for

remote measurement of gases using discretely tunable high-energy gas lasers. Results

reported here were obtained with two infrared lidar systems: A lidar system based on a deuterium fluoride laser for remote measurement of integrated concentrations of HCl , CHi^,

and N2O using scattering from topographic targets, and a lidar system based on a CO2 laser

for measuring range-resolved concentration profiles of water vapor using scattered radiation

from naturally occurring aerosols. Performance predictions for both the DF and CO2 lidars

indicate that high-sensitivity, range-resolved measurements can be made of numerous gaseous

species at 10 km range with commercially available components.

2. Remote Measurement of HCl, CHt^, and N2O Using A DF Laser

A diagram of the single-ended DF laser system used to monitor HCl, CH^, and N2O is

shown in figure 1. This system used a topographic target to provide the backscattered

signal, and measured the integrated concentration over the path between the lidar and the

target. The DF laser beam was transmitted collinearly with the receiver axis and directed

through a sample chamber positioned 300 m away. The backscattered signal from the topographic target was collected by the receiving telescope and focused onto an infrared

Figures in brackets indicate the literature references at the end of this paper.

305
detector. The detector signal was amplified and displayed on a chart recorder. Different

concentrations of the gases being measured were injected into the sample chamber. The

concentrations were measured with both the lidar and an in-situ monitor, and the values were compared.

n

NEWTONIAN

TELESCOPE

TOPOGRAPHIC TARGET

REMOTELY

LOCATED

SAMPLE CHAMBER

DF LASER

FOCUSING cf:^

LENSES

IR DETECTOR

AMPLIFIER

TRIGGER

GATING

ELECTRONICS AND DISPLAY>-

FIGURE 1 EXPERIMENTAL APPARATUS

Experimental parameters are shown in table 1. The laser wavelengths that were used

and the corresponding absorption coefficients are shown in table 2. The absorption coefficient for the HCl was measured by Bair and Allario [17], and those for CH^ and N2O were measured by Spencer, Denault, and Takimoto [18]. The wavelengths were established by

Rao [19].

Table 1

Experimental parameters

DF Laser Transmitter

Energy 100 to 150 mJ/pulse

Pulsewidth 1.0 ys (FWHM)

Beam divergence 1.0 mrad (FWHM)

Typical PRF 1/6 Hz

Receiver

Telescope diameter 31.75 cm

Field of View 3.0 mrad (FWHM)

HgCdTe detector

D* (3.7 urn) 5(109)

Size 1 X 1 mm

Time constant 75 ns (to 1/e point)

306
Table 2

Laser wavelengths and absorption coefficients

Gas

DF Laser

Line

Wavelength

(ym)

Absorption Coefficient

(cm"i atm"i)

HCl P2^(3)^ 3.636239 5.64

CH4 P.iO) 3.715252 0.047

N2O P3(7) 3.890259 1.19

^Vibrational quantum number

'^Rotational quantum number

A summary of the HCl test for different concentrations is shown in figure 2. The HCl

concentrations were determined from the lidar data by calculating the transmission through

the sample chamber using the ratio of the backscattered to transmitted signals. The lidarmeasured HCl concentration is plotted as a function of the syringe-injected value. The

solid line represents perfect agreement between the lidar and the syringe values. The dots

are the experimentally determined data. The error bars shown represent the standard

deviation of 15 data points. Generally good agreement was found between the lidar and the

syringe value. This confirms that the lidar is functioning correctly and the absorption

coefficient used in the data reduction is accurate. The right vertical axis shows the

equivalent product of the concentration and the path length for the individual measurements.

The sensitivity of the system (the minimum detectable concentration) is defined as the

concentration that equals the standard deviation. For HCl, the sensitivity was determined

to be 0.05 ppm over a 1-km path, or 50 ppb over 1 km.

The summary of the CH4 data is shown in figure 3. Again, good agreement was obtained

between the lidar and the in-situ value, thereby verifying correct system operation and the

absorption coefficients used in the data reduction. For CHi^, the system sensitivity was found to be 6 ppm over 1 km.

307
2.5

_L

aiNE OF EXPECTED VALUES

MEASURED DATA

^ STANDARD DEVIATION -

\

\ \ L

60

50 < £

40 <

30

20 8

10

0 0.5 1.0 1.5 2.0 2.5

IN SITU-MEASURED CH4 CONCENTRATION — percent

FIGURE 3 SUMMARY OF REMOTEMEASUREMENT TESTS OF CH^ IN A

SAMPLE CHAMBER

A summary of the N^O data is shown in figure 4. The triangles represent data obtained

with a juniper tree of T-m diameter used as the back-scattering target; the circles represent data taken using a plywood board. The two targets were used to demonstrate system

operation on two different materials with different reflectivities. The foliage target was used because it provides a reflectivity typical of field operation. Both targets were

placed immediately behind the sample chamber. The lidar results obtained with both targets

agree well with the in-situ values. The system sensitivity for N2O was found to be 0.24 ppm/km

X

0 250 500 750 1000 1250 1500 SYRINGE-INJECTED NjO CONCENTRATION — ppm

FIGURE 4 SUMMARY OF REMOTEMEASUREMENT TESTS OF NjO IN A

SAMPLE CHAMBER

Calculations have been made of the performance attainable with a range-resolved DF

lidar system comprised of commercially available components. The signal-to-noise ratio

(SNR) at a given range provides an indication of the expected performance of a rangeresolved system. The backscattered signal from naturally occurring aerosols, assuming an attenuation coefficient that is uniform in range, is given by [20]:

Pr'^) = "t

^

2F ^180

308
where

Return signal, photons/s

= Transmitted energy, J

A = r

= Receiver area,

R

== Range, m

A

== Wavelength, m

e

== base of logarithm

h

== Planck's constant

3l80 '= Volume backscatter coefficient into a unit solid angle, m"^ steres"^

Ts

== Optical efficiency of the receiving system

a

== Atmospheric extinction coefficient.

The dominant noise mechanism in an infrared lidar system designed for maximum range is

usually detector noise. The expected SNR can be determined by calculating the signal from

eq. (1) and the noise from the detector characteristics. An SNR of 115 at a horizontal

range of 10 km with a laser pulsewidth of 100 ns can be obtained for the following

parameters

:

a = 0.0657 km"^

D* = 1 Oil cm HzVi

The backscatter coefficient is characteristic of a low-altitude haze, and the absorption coefficient is typical of sea-level attenuation. The conclusions are that highsensitivity range-resolved measurements are feasible at 10 km in range. Longer range or higher sensitivity can be obtained using multipulse integration.

A CO2 lidar system using backscatter from aerosols has been developed to provide

range-resolved measurement of the concentration of gaseous species. A diagram of this

system is given in figure 5. The laser beam is transmitted collinearly with the axis of

the receiving telescope. Scattered energy from naturally occurring aerosols is used to

provide the return signal, which is focused onto a mercury-cadmium-telluride detector. The

detector signal is amplified, filtered, digitized, and stored on magnetic tape for later

analysis. A real-time display of the return signal on the absorbed and nonabsorbed laser

lines is used to monitor system operation. The system parameters are shown in table 3. Results are presented here that were obtained with the 0.075-ys detector.

1 J/pulse

1.17 m^ (diameter = 1.22 m = 48 inches)

3.7 ym

0.5

8 X 10"^ m"i steres"!

3. CO2 Laser DIAL System for Range-Resolved Measurement of Gases

309
AEROSOL

BACKSCATTER

AEROSOL

BACKSCATTER

NEWTONIAN

TELESCOPE

REAL-TIME

DISPLAY

MAGNETIC

TAPE

TRIGGER

MINI- COMPUTER

HP 2115

16-CHANNEL A/D

HOUSEKEEPING

DATA

FOCUSING LENSES

A/D CONVERTER

10 BIT 4.8 MHz

I

LOW NOISE AMPLIFIER

I

2.5 MHz

FILTER

STORAGE

RING

FIGURE 5 THE INFRARED DIFFERENTIAL-ABSORPTION LIDAR SYSTEM FOR RANGE-RESOLVED

MEASUREMENT OF GASEOUS SPECIES

Table 3

DIAL System Parameters

CO? TEA Laser

Transmitted energy 1 J Lines R(12), R(18), R(20) on 10 pm band

Pulsewidth 100 ns (FWHM)

Beam divergence 1.8 mrad (to the 10 percent point)

Typical PRF 0.5 Hz

Receiver

Telescope diameter 31.75 cm

Field of view 3.3 mrad (to the 10 percent point)

Hg-Cd-Te detectors j D* 1.1(1010) cm^Hz"'

Time constant 0.075 \xs

Size 1 X 1 mm

310
The first target species for the CO2 laser lidar system was water vapor, which was used

because it is always present in the atmosphere and is therefore a convenient species with

which to optimize the system. The water-vapor absorption coefficients measured by Shumate

et at. [21] are shown in table 4.

Table 4

Water-vapor absorption coefficients

Line v (cm"M ct (10"'^ cm~^ atm"^)

R(12) 970.547 1.60

R(18) 974.622 0.935

R(20) 975.931 8.65

The measured water-vapor concentration profile is shown in figure 6. These results

represent a significant improvement over those reported earlier, [15,16] since the more recent measurements were taken with a faster detector to increase range resolution, and

because improved system alignment has increased the range by a factor of two.

atOQ.<

>

<5

0.25 0.50 0.75 1.00 1.25 1.50 RANGE — km

1.75 2.00

FIGURE 6 WATER VAPOR PROFILES OBTAINED

WITH IMPROVED SYSTEM ALIGNMENT, THE

0.075-Ate DETECTOR, AND A 120-m RANGE CELL

A range-resolved DIAL system can also be used to determine the integrated concentration

of species, using topographical reflections. Figure 7 is an example of a return signal on the P(14) line of the 10-ym band of CO2 with the lidar system pointed west toward the

coastal foothills near Menlo Park, California. A well defined topographical reflection

occurring at 10 km was obtained. In such a configuration, the range-resolved concentration

of a pollutant can be obtained to a range limited by the SNR. Simultaneously, the integrated concentration of the pollutant over a longer range between the lidar system and a suitable topographical target can be obtained. We foresee a wide applicability of such

combination range-resolved and integrated-concentration lidar systems for use in both source monitoring and ambient-air-quality monitoring.

311
0 2 4 6 8 10 12 RANGE — km

FIGURE 7 BACKSCATTERED SIGNAL INCLUDING

ATMOSPHERIC RETURN AND SCATTER FROM THE

COASTAL FOOTHILLS AT A RANGE OF 10km

In a prediction of the range-resolved performance of the CO2 lidar system, the following parameters were used:

Ut

== 15 J/pulse

A = r

= 1.17 m^ (diameter = 1.22 m = 48 in)

X

== 10.0 ym

Ts

== 0.5

618O '-- 1 .2 X 10"^ m"i ster"!

a

== 0.0927 km-i

D* == 2(1010) cm /~Tlz/W

The backscatter coefficient is characteristic of a low-altitude haze. The detector

characteristics are consistent with those of available detectors. The calculation of SNR

using eq. (1) yields an SNR of 50 at a range of 10 km for a single pulse. From this we conclude that range-resolved measurements are feasible at 10 km. The SNR is higher at

closer range and can be increased using multipulse integration.

Sensitivity of the CO2 lidar system to different gases has been calculated based on a system SNR of 200, which is equivalent to measuring the transmission through a range cell

to within 1 percent. The sensitivity values of 16 representative compounds are shown in

table 5. The absorption coefficients vary widely [21-26]. Those for carbon dioxide and

water vapor are relatively small, which is necessary to permit long-range transmission of

the beam. The absorption coefficient of many other gases is quite high, yielding a sensitivity of a few parts per billion in a kilometer.

312
Table 5

Calculated CO2 lidar system sensitivities

Species Absorption Coefficient Sensitivity

Name Formula (cm"i atm"M (ppb-km)

Ammonia NH3 120.0 0.42

Benzene 2.3 22.0

1 ,3 butadiene 3.45 15.0

Carbon dioxide CO2 1.8 (10-3) 28000.0

Ethylene C2H4 33.0 1.5

Freon 113 C2CI3F3 19.2 2.6

Freon 11 CCI3F 31 .0 1 .6

Freon 12 CCI2F2 92.0 0.55

Methanol CH3OH 19.4 2.6

Ozone O3 12.7 4.0

Perchloroethylene C2CI4 28.5 1.8

Sulfur dioxide SO2 6.73 7.5

Sulfur hexafluoride SFe 800.0 0.063

Trichloroethylene C2HCI3 14.0 3.6

Vinyl chloride C2H3CI 6.79 7.4

Water vapor H2O 8.36 (lO-^*) 60000.0

In conclusion, range-resolved multigas monitoring of these gases appears feasible at

10 km range with commercially available components.

E. K. Proctor and M. L. Wright made valuable contributions to the planning of the

experiments. W. B. Grant has previously reported his work in both UV and visible DIAL

systems, which established a firm foundation on which the infrared activities could build.

The work reported here was supported by the National Science Foundation/Research

Applied to National Needs program, and by the U.S. Geological Survey.

References

[1] Measures, R. M., Pilon, G., Opto-eleatronias, 4, p. 143 (1972).

[2] Byer, R. L., and Garbuny, M. , Appl. Opt., 12^, p. 1496 (1973).

[3] Schotland, R. M,, Proceedings of the Fourth Symposium on Remote Sensing of the

Environment, pp. 273-283, University of Michigan, Ann Arbor, Mich., (1966).

[4] Rothe, K. W. , Brinkmann, U., and Walther, H., Appl. Phys., 2_, p. 115 (1974); Appl.

Phys. 4, p. 181 (1974).

[5] Grant, W. B., Hake, R. D., Jr., Liston, E. M. , Robbins, R. C, and Proctor, E. K., Jr

Appl. Phys. Lett., 2A^, p. 550 (1974).

313
6] Grant, W. B., and Hake, R. D., Jr., J. Appl. Phys., 46, p. 3019 (1975).

7] Wade, W. R., Hoell, J. M., Jr., and Thompson, R. T., Jr., Conference abstracts^

Seventh International Laser Radar Conference, Stanford Research Institute, Menlo Park,

California, (1975).

8] Craig, S. E., Morgan, D. R. , Roberts, D. L., and Snowman, L. R., Technical Report

No. EPA-650/ 2-74-046-A, General Electric, Ordnance Systems, Pittsfield, Mass. (June

1974).

9] Rothe, K. W. , and Walther, H., paper presented at the Conference on the Applications

of Laser Spectroscopy, sponsored by the Optical Society of America, Anaheim, California

(March 1975).

Ku, R. T., Hinkley, E. D., and Sample, J. 0., Appl. Opt., U, p. 854 (1975).

Asai, K. and Igarashi, T., Opt. Quant. Electron., 7_, p. 21 1 (1975).

Menzies, R. T., and Shumate, M. S., paper presented at the International Conference on Environmental Sensing and Assessment, Las Vegas, Nevada (September 1975).

Henningsen, T., Garbuny, M. , and Byer, R. L., Appl. Rhys. Lett., 2A, p. 242 (1974).

Murray, E. R., van der Laan, J. E., and Hawley, J. G., to be published in Appl. Opt.

Murray, E. R., Hake, R. D., Jr., van der Laan, J. E., and Hawley, J. G., Conference

Abstracts, Seventh International Laser Radar Conference, Stanford Research Institute,

Menlo Park, Calif. (1975).

Murray, E. R. , Hake, R. D., Jr., van der Laan, J. E., and Hawley, J. G., Appl. Phys.

Lett., 28, p. 542 (1976).

Bair, C. H., and Allario, F., Conference Abstracts, Seventh International Laser Radar

Conference, Stanford Research Institute, Menlo Park, Calif. (November 1975).

Spencer, D. J., Denault, G. C, and Takimoto, H. H., Appl. Opt. U, p. 2855 (1974).

Rao, K. N., Ohio State University, private communication (1975).

Byer, R. L., and Garbuny, M., Appl. Opt., ]Z, p. 1496 (1973).

Shumate, M. S., Menzies, R. T., Margolis, J. S., and Rosengren, L. G., Proceedings of

the lEEE/OSA Conference on Laser Engineering and Applications, Washington, DC, IEEE,

N.Y. (1975). Also to be published in Appl. Opt.

Schnell , W. , and Fisher, G., Appl. Opt., 14-, p. 2058 (1975).

Patty, R. R., Russwurm, G. M. , McClenney, W. A., and Morgan, D. R. , Appl. Opt., 1_3, p. 2840 (1974).

Inaba, H., and Kobayashi , T., Optics Comm., 14_, p. 119 (1975).

McClenney, W. A., EPA, Research Triangle Park, NC, private communication (1975).

Kreuzer, L. B., Kenyon, N. D., and Patel , C. K. N., Science, Vn_, p. 347 (1972).

314
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

COHERENT ANTI -STOKES RAMAN SCATTERING IN GASES

J. J. Barrett

Materials Research Center

Allied Chemical Corporation

Morristown, New Jersey 07960, USA

1. Introduction

Recent experimental studies [1-4]^ of coherent anti-Stokes Raman scattering (CARS)

processes in gases are beginning to define the usefulness of this nonlinear spectroscopic

technique for quantitative gas analysis. The CARS process involves the generation of a coherent light beam at an anti-Stokes Raman frequency of the material under investigation.

This is accomplished by means of a four wave nonlinear mixing process whose efficiency is

proportioned to the square of the third order nonlinear susceptibility of the material.

The generation of a CARS signal in a gas is achieved by mixing two col linear laser beams at

the frequencies wp and ws to produce a CARS beam at the frequency aj/\ = 2ojp - ws- By tuning

the frequency difference cop - ws to be exactly equal to a Raman frequency shift for the

particular gas to be detected, a large increase in the magnitude of the generated CARS

signal over the nonresonant background is observed. This increase at resonance is typically

in the range of three to five orders of magnitude above the background. Since the CARS

process is dependent on the presence of molecular resonances, it is possible to use this

technique for the specific detection of a given molecular species. For example, the CARS

technique may be used to measure quantitatively trace amounts of a particular molecular

species in the presence of more abundant molecular species by tuning top - cos to a Raman

shift of the molecular species to be detected. The limiting factor with regard to detection sensitivity is the magnitude of the background signal which is produced by the non- resonant third order nonlinear susceptibility of the more abundant molecular species.

2. Experimental and Results

Two different CARS experiments are discussed. One of these experiments is the first

observation of a CARS signal which was generated by the use of low power continuous wave

(cw) lasers [2]. An argon ion laser provided the pump frequency cop = 19429.79 cm-^

(514.53 nm). The vibrational band of methane (CH^) gas at a Raman shift of 2916.7 cm"i was used to generate the cw CARS signal. The Stokes frequency cos = 16513.09 cm-^ (605.41

nm) was provided by a tunable frequency jet stream dye laser which was pumped by the 514.53

nm argon ion laser beam. The gas cell containing the CH^ gas was positioned in the dye

laser cavity at a common focus for the cop and cos laser beams. The co/\ CARS beam exited the

dye laser cavity through a special multilayer dielectric mirror which had high transmissivity at and high reflectivity at cop and coS- The CARS signal which was filtered

optically to remove any background due to the cop and cos beams was detected using a cooled

photomultiplier tube and photon counting electronics.

^Figures in brackets indicate literature references at the end of this paper.

315
For a power of 0.46W and an effective U5 power of 0.036W, the observed CARS signal was about 9000 counts/second. By correcting for mirror and filter transmission factors and

the quantum efficiency of the photomul ti pi ier tube, it was deduced that the true cw CARS

signal was approximately equal to 5.7 x 10^ photons/second. A theoretical calculation of

the CARS signal in methane was made for the conditions which were encountered in the experiment. Good agreement with the experimentally deduced CARS signal was obtained.

The second experiment describes the first obs.ervation of a CARS signal generated by a rotational Raman transition in a gas [4]. For this experiment, the J = 3 -> 5 rotational

transition in hydrogen gas at a Raman frequency shift of 1033.4 cm"^ was investigated. The

cap pump frequency of 18787.6 cm"^ (532.1 nm) was produced by a frequency doubled, acoustooptic-Q-switched, cw, krypton-arc-lamp-pump Nd:YAG laser and the beam at 17754.2 cm"^

(563.1 nm) was provided by a rhodamine 6G jet-stream dye laser pumped by the 532.1 nm radiation. The frequency doubled Nd:YAG laser produced pulses at a repetition rate of

about 4600 pulses per second and with a pulse energy of 0.076 mJ and a peak power of 175W.

For 250 torr of gas, the observed rotational CARS signal was 1.33 x 10*+ counts per

second from which the true rotational CARS signal was calculated to be about 1.68 x 10^

photons per second. The rotational CARS power which was calculated theoretically was in

good agreement with the experimental results.

3. Conclusion

The significance of the rotational CARS experiments is that they offer a way of improving the detection sensitivity of the CARS process. One way of improving the CARS detection

sensitivity is to utilize Raman transitions which have relatively large resonant third

order susceptibilities. The resonant third order susceptibility is directly proportional

to the differential Raman scattering cross-section and inversely proportional to the

spontaneous Raman linewidth. In general, the differential Raman scattering cross sections

are larger for rotational Raman transitions than for vibrational Raman transitions and the

rotational linewidths are smaller than the corresponding vibrational Raman linewidths.

Therefore, the resonant third order susceptibilities for rotational transitions are larger

than those for vibrational transitions and, since the generated CARS power is proportional

to the square of this nonlinear susceptibility, a substantial increase in CARS power will

be realized for experiments utilizing rotational rather than vibrational Raman transitions.

The CARS technique is well suited for applications in such areas as:

0 Air pollution measurement and monitoring

0 Combustion diagnostics on flames and plasmas

0 Kinetic investigation of gas phase reactions

0 High resolution spectroscopy (cw CARS techniques).

It is expected that the range of applications for the CARS technique will increase as the experimental research in this area expands.

References

[1] Regnier, P. and Taran, J. P. E., Laser Raman Gas Diagnostics, edited by M. Lapp and

C. M. Penny, p. 87 (Plenum Press, New York, 1975).

[2] Barrett, J. J. and Begley, R. F., Ap-pl. Physios Letters 2J_, 129 (1975).

[3] Nibler, J. W., McDonald, J. R., and Harvey, A. B., CARS Measurements of Vibrational

Temperatures in Eleatria Lisohargee, Optics Comm. (in press).

[4] Barrett, J. J., Generation of Coherent Anti-Stokes Raman Scattering by Means of Pure

Rotation and Rotation-Vibration Raman Transitions, Fifth. International Conference on Raman Spectroscopy, Freiburg, Germany, September 2-8, 1976.

316
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

HIGHLY SELECTIVE, QUANTITATIVE MEASUREMENT OF

ATMOSPHERIC POLLUTANTS USING CARBON MONOXIDE AND CARBON DIOXIDE LASERS

D. M. Sweger, S. M. Freund^, and J. C. Travis

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

Infrared gas lasers have many properties that make them suitable for applications in

analytical chemistry, particularly for detection of organic compounds in the gas phase.

Among those properties is a narrow bandwidth, which results in a high level of selectivity

in the vibrational transitions excited. A major difficulty in the analytical application

of gas lasers, however, is that they are not tunable in a continuous sense. Thus, in the

absence of any other tuning mechanism, one is restricted to exact coincidences between the

laser frequency and an absorption frequency in the molecule of interest. While exact

coincidences are few, near coincidences are much more probable, and the analytical usefulness of lasers can be increased manyfold if some technique can be found to utilize these near coincidences.

2. Objective

"Perturbation spectroscopy," or the use of electric (Stark effect) or magnetic (Zeeman

effect) fields to perturb energy levels and tune a near coincidence into exact coincidence

with the laser, offers such a technique. In addition to "tuning" the molecular absorption,

the same perturbation may be used to modulate the absorption and allow the use of available

ac detection methods. The purpose of this paper is to summarize the results of two

experiments applying perturbation spectroscopy to the quantitative determination of gases

at concentrations normally encountered in polluted environments [1,2]^.

3. Experimental and Results

In the first experiment. Stark spectroscopy techniques were applied to the detection

of ppm levels of vinyl chloride monomer (VCM) in air. Although VCM has made headlines

because of its carcinogenic properties, it has in the past received some attention among

laser researchers due to its use in passive Q-switching. VCM has several known near coincidences with CO2 laser frequencies in the 10 pm region, and by superimposing an appropriate static electric field, an electric field sweep, and a modulating field, it is

possible to Stark shift several vinyl chloride infrared transitions into exact coincidence

with the laser, sweep the transition across the laser, and to use phase-sensitive detection

of the absorbed signal. In addition, one near coincidence with a CO laser line in the 6 ym

region was found, and the two strongest absorptions, one from the CO2 laser and the one from the CO laser, were used in the experiment. Twelve calibrated samples of VCM in air

^Present address: Los Alamos Scientific Laboratory, P.O. Box 1663, Mail Stop 565,

Los Alamos, NM 87545

^Figures in brackets indicate the literature references at the end of this paper.

317
were prepared by the Air Pollution Analysis Section of the Analytical Chemistry Division,

NBS, and the absorption as a function of concentration was measured. Because of the sine wave modulation, the observed signal is the first derivative of the absorption line profile,

and the peak-to-peak intensity is the measured parameter. The data are normalized to one concentration and are a linear function of concentration from at least 0.1 to 1000 ppm.

The line extrapolates through the origin, indicating that only one point need be taken to

calibrate the apparatus. Improvements in the designs of the Stark cell and CO2 laser

should permit extension of measurements to the ppb range.

The second experiment investigated the quantitative detection of nitrogen dioxide in

part-per-mi 1 1 ion concentrations in nitrogen using magnetic field modulation of the molecular

absorption of 1616 cm"^ carbon monoxide laser radiation. The method relies on the near coincidence between the 615 6^5 transition of the V3 band in NO2 [3] and the P(ll)

transition in the 20 19 band of the CO laser and is an obvious extension of the recent

laser magnetic resonance spectroscopic investigation of this molecule in the 1600 cm"^

region of the infrared [4], and of similar detection schemes demonstrated for nitric oxide

[5,6].

Using NBS SRM 1629 NO2 permeation tubes, we adjusted the concentration of NO2 in N2 in

a flowing system to any value in the range 1-200 ppm by setting the N2 flow. The concentration range was limited at the higher concentrations by available flowmeters. The flowmeters were calibrated to maintain an overall system accuracy of about 5 percent. The pressure in

the cell was maintained at 27 torr (1 torr = 133.3 Pa) in order -to eliminate pressure

broadening effects while maximizing the signal. NO2 is a paramagnetic molecule, and a magnetic field of less than 500 gauss is sufficient to alter its energy levels such that

the infrared transition of interest is swept in and out of coincidence with the laser.

Consequently, a modulation in the absorption of the laser light is observed by a gold-doped

germanium detector. The detected ac signal is processed by conventional phase-sensitive

amplification and appears as a dc signal which is proportional to the modulated absorption.

The apparatus is found to have a linear response to the NO2 concentration over the two

orders of magnitude investigated. 1 ppm of NO2 in N2 are easily detected with a 1 second

time constant.

4. Conclusion

The principal advantage of these techniques is high selectivity. In addition to the

selectivity for absorption inherent at low pressures with a narrow-band laser, only those

molecules with the same electric or magnetic dipole moment will be shifted appropriately

into coincidence with the laser. Absorption by molecules that have no dipole moment, even though they may absorb strongly in the region of interest, will not interfere with the

measurement, since their absorption is not modulated. Investigation of fourteen chemicals

likely to be found in an industrial atmosphere (see table I) uncovered one possible interference (acrylonitrile) with vinyl chloride on the CO2 laser line used for the VCM measurements. Note should be made, however, that over half of these chemicals are strong absorbers

in the same spectral region as vinyl chloride, so that the number of interferences is

greatly diminished. Even when an interference is encountered, such a problem may be over- come by making a measurement on another laser line or at another electric field for which

there is no interference. One can further increase selectivity, at a sacrifice in sensitivity, by taking a voltage scan and looking at line shapes in order to detect the presence

of interferents

.

318
Table 1

Chemicals observed in stark cell using perturbation spectroscopy

and CO2 laser at fields less than 10000 V/cm

Chemical

Freon 11

Freon 12

Freon 113

Acetone

Acrylonitrile

Chloroform

Methanol

Methyl chloride

Methyl Fluoride

Tetrahydrofuran

Tol uene

Trichloroethylene

Vinyl acetate

Vinyl chloride

Signal on P(42), 10.8 ym

nothi ng

nothing

weak (<10% VCM)

at 250 V/cm

nothing

Strong

comparable

with VCM

nothing

nothing

nothing

nothing

nothing

nothing

nothing

nothing

strong

Other

R(4)-R(34), 9.6 ym band;

strongest on R(22)

Absorbs M to S (P14)-P(25),

9.6 ym band near zero field.

Absorbs W P(32)-P(42) 10.6 ym

band

No absorptions P branch, 10.6 ym

and R branch 9.6 ym

Many absorptions throughout P and R branches, 10.6 ym band,

with the strongest at P(28).

Nothing in P branch, 9.6 ym

band.

Various absorptions, some VS.

One of strongest P(26) 9.6 ym

band.

Various absorptions 9.6 ym band;

S on P(18), M on P(20), P(22),

and W on higher P branch lines.

Vinylidene chloride nothing

Absorptions P(8)-P(36)

10.6 ym band.

Additional strong absorptions

on P(46), P(36), P(30)-P(24),

P(20), P(16), P(2) and R{6),

10.6 ym band and M on P(38),

9.6 ym band.

S on R(24) 9.6 ym band.

319
While the sacrifice of sensitivity in favor of selectivity is not seen as a limiting

factor in many applications, there are cases where it may be. Some order of magnitude

calculations for the case of the vinyl chloride experiment indicate that at 0.1 ppm we are

4-6 orders of magnitude from a theoretical minimum detectable number of molecules. The

primary source of noise appears to be the amplitude instability of the lasers, which were

not designed for this type of application. One of the more promising recent developments

is the construction at NBS of a prototype waveguide CO2 laser. In addition to being compact

and easy to operate, the 20 cm long waveguide laser appears to be 3-4 orders of magnitude

more stable in amplitude than the 1.3 meter lasers used in these experiments. Such dramatic

decreases in noise leading to an increase in S/N coupled with improvements in cell design

should make perturbation spectroscopy a practical method for solving some difficult problems.

References

[1] Freund, S. M. and Sweger, D. M., Anal. Chem. 47, 930 (1975).

[2] Freund, S. M. , Sweger, D. M. , and Travis, J. C, Anal. Chem. 48, 1944 (1976).

[3] Lafferty, W. J., private communication.

[4] Freund, S. M. , Hougen, J. T., and Lafferty, W. J., Can. J. Phys. 53, 1929 (1975).

[5] Kaldor, A., Olson, W. B., and Maki , A. G. , Saienae ]76, 508 (1972).

[6] Bonczyk, P. A., Rev. Sai. Instrum. 46, 456 (1975).

320
Part VII. CHEMICAL CHARACTERIZATION OF AEROSOLS

I

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

CHEMICAL CHARACTERIZATION OF AEROSOLS: PROGRESS AND PROBLEMS

William E. Wilson

U.S. Environmental Protection Agency

Research Triangle Park, North Carolina 27711, USA

1. Introduction

Although substantial progress has been made in the chemical characterization of

aerosols during the last five years, many problems still remain. It was told years ago

that a major analytical problem was to determine the chemical compounds in aerosols as opposed to elemental analysis. This remains a key problem for environmental chemists

today. However, if a specific chemical species is of interest, it can usually be measured. It is useful, therefore, to consider not only what measurements are needed, but

the most appropriate technique in a variety of measurement situations. The variety of

situations in which aerosols need to be characterized as well as the types of measurements

that are needed are examined here. Some measurement techniques that should be developed to

better study aerosol formation, transport, and removal processes are discussed. This talk

will be limited to ambient air measurements and will not consider source measurements.

2, Discussion

Measurement situations in which aerosol characterization is needed cover a variety of

conditions: time resolutions from one week to less than one second; time intervals of a few seconds to years; data availability from real-time, continuous output to analysis days or months after the event. These varying data needs give rise to a wide variety of mea- surement needs. A number of measurement situations and associated time scales, shown in

table 1 are discussed. As new techniques and instruments are developed, it is useful to

consider each specific measurement situation.

Measurement situations .

Measurement situations

Compliance monitoring

Episode identification

Epidemiological measurements

(community and personal)

Laboratory chambers

(clinical exposure and smog

chamber)

Model development and evaluation

Aerial measurements (plumes)

Aerosol transport

Table 1

time scales associated with aerosols

Resol ution Interval Data output^

24 hours years R

1 hour days C

24 hours months R

1-15 minutes hours C

1 hour months R

1 second minutes C

3-6 hours months R

323

\
Table 1 (continued)

Source identification 1 hour days R

Ecological deposition 1 week years R

Deposition parameters <1 second hours R

= retrospective, results needed hours to days after measurements.

C = continuous, real-time data output needed.

Some basic measurements of aerosols and some specific effects or properties of

aerosols, given in table 2 are discussed. In considering the basic measurements, we are concerned with (1) both total and size-segregated samples, (2) the analysis of collected

samples and in-situ measurements, (3) minimal disturbance of the sample volume, and (4)

remote as well as point measurements. Some relatively new techniques for collecting

samples, including the dichotomous sampler and the streaker are described.

Of special concern at the present time is the analysis of sulfate compounds. For

sulfates both particle size and the particular ion associated with the sulfate are important. A number of laboratories have tried to develop thermal techniques for separating

sulfates in collected samples. These have all been inadequate due to a variety of reasons. Recently, a thermal technique using hot, dry air as a heating mechanism appears to be

successful, but only for separating H2SO1+ from other sulfates. In-situ thermal techniques

using a variety of detection devices also appear to have some value in separating H2SO1+

from other sulfates. A technique based on differences in hygroscopicity shows promise for

differentiating acid sulfates, W2^(iu, and NHttHSOi+, from (NH4)2S0i+.

The flame photometric detector, which is widely used for sensitive measurements of

gaseous sulfur compounds, has also been shown to give quantitative results for certain

sulfate particles. Changes in burner design, now being studied in several laboratories,

show promise of providing sensitive measurements of sulfates, perhaps with differentiation

of H2SO1+ from less volatile sulfates, and with sufficient time resolution to be applicable

to aircraft operations and aerosol deposition studies. The use of flame induced radiation

or ionization shows promise for other types of aerosol measurements.

Table 2

Basic measurements and specific effects or properties of aerosols

Basic measurements Specific effects or properties

Mass

Vol ume Number

Elemental composition

Valence state

Radical components

SO^', NO3, ml, POr= no;, SO3

Compound analysis

sulfates, nitrates, organics

Specific toxic components

Visibility reduction

Scattering properties

Absorption properties

Charge carrying capacity

Cloud condensation nuclei

Ice condensation nuclei

Hygroscopi ci ty

Volatility

Acidity

Mutagenic potential

Carcinogenic potential

324
3. Conclusion

Characterization of the organic fraction of the ambient aerosol presents several

problems. Most historical data gives the mass of the benzene soluble fraction. Recent

studies, however, show the existence of a substantial mass of more polar organic matter

that is not soluble in benzene. Studies with gas chromatography-mass spectroscopy and high

resolution mass spectroscopy have identified hundreds of organic compounds. These techniques provide more data than can be usefully handled except for very special and limited

studies. We, therefore, need techniques that fall somewhere in between the simple and

detailed techniques mentioned above. Also, more characterization studies are needed to

determine the composition of organic compounds in emissions from specific sources and in

rural/urban areas as a function of time. Techniques to analyze for elemental carbon,

organic carbon, and organic compound types, and plans for various systems to characterize

the organic fraction of ambient aerosols are discussed.

A number of non-aerosol measurement needs have been identified in attempts to study

the formation, transport, and removal of aerosol. These needs, which involve meteorological measurements, remote measurements, and measurements of gaseous species are described briefly.

325

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

DETECTION OF INDIVIDUAL SUBMICRON SULFATE PARTICLES

Yaacov Mamane and Rosa G. de Pena

Department of Meteorology

The Pennsylvania State University

University Park, Pennsylvania 16802, USA

1. Introduction

Significant quantities of sulfates exist as particulate matter in the atmosphere,

particularly in polluted air over densely populated areas and to a smaller degree in rural areas and mountains far from human influence [1]^ in Antarctica [2], and in the stratosphere

[3]. Recent data [4] at selected stations throughout the U. S. indicate that the concentration of sulfates (SO^) ranges from about 8 to 16 yg/m^ at urban sites, from 5 to 9 vg/m^

at non-urban sites, and about 2 pg/m^ in the mountains.

A number of investigators have been concerned with airborne sulfates, but very few

have dealt with individual particles. A recent critical review on the analysis of airborne

sulfate [5] states that the physical and chemical nature of airborne particulate sulfate

and the size distribution, are largely unknown. The inadequate amount of data on size

distribution for sulfate is limited to impactor data. But in order to collect sufficient

amounts of sulfate on every stage of the impactor for bulk analysis, many hours of sampling

are needed [6]. Also the size separations provided by the different stages of an impactor

are by no means clearly defined.

2. General Method

The method described in this paper, because of its high sensitivity can be used when- ever a high resolution in time is required (airborne samples, low concentration, eta...).

It is basically a modified spot test and it is based on a method suggested by Bigg et al.

[3]. King and Maher [8] applied this method for large hygroscopic particles in the size

range 0.5 to 200 yyg (0.8 ym < d < 5.8 pm if a density of 2 g/cm^ is assumed).

The purpose of the present work is to apply this method to lower sizes in a more quantitative way that has been done before.

The method consists of bringing a sulfate particle into contact with a very thin film

of barium chloride. In the presence of water vapor a reaction takes place. A persistent

spot (Liesegang type rings) of barium sulfate is formed and can be examined under the

electron microscope (EM). Under constant relative humidity (RH) and thickness of the

barium chloride film the ratio between the diameter of the spot and the particle diameter

is a constant. A "calibration curve" can be obtained for different sizes of particles, as

in figure 1, providing a method for both spotting and sizing sulfate particles. Under the

conditions of our experiment the size of the ammonium sulfate halo is about 1.5 times the

original particle. For sulfuric acid it is about twice as much. The halos formed by

sulfuric acid and ammonium sulfate are shown in figures 2 and 3.

^Figures in brackets indicate literature references at the end of this paper.

327
3.5

H2SO4 PARTICLE DIAMETER, wm

Figure 1. Calibration curve of halo-particle diameter relation for sulfuric acid particles.

328
Figure 2. Electron micrograph of sulfuric acid particles (a) before and (b) after

reaction with barium chloride.

329
I 9 B

S 1
The main steps of the technique consist of the following:

(a) Collect particles on electron microscope (EM) carbon coated grids (numbered and

lettered grids are the most convenient). Examine some representative fields under the EM

using the least intense beam and the smallest magnification.

(b) Deposit few milligrams of barium chloride on the sample in a vacuum (at about 10"^

Torr) bell jar from a heated tungsten filament. For submicron particles, 0.1 - 1.0 pm, a

o layer of about 300 ± 100 A give the best results.

(c) Expose the grid in a close chamber to a known relative humidity, usually 60 to 80

percent for an hour or so. Examine again the same fields of view seen before for reaction

spots

.

The above technique has been used to identify submicron sulfates generated in the

laboratory, including sulfuric acid, ammonium sulfate, and sodium sulfate. The particles

collected on a BaCl2 layer were exposed to a relative humidity of 70 and 80% respectively

to obtain a complete reaction. This study indicated that the vapor pressure (RH) needed

for the particle to react is lower than the equilibrium vapor pressure of a bulk saturated

solution as was observed by Junge (1963).

3. Results

The technique described gave positive results with particles as small as 0.04 pm

diameter (figure 4). This lower limit is only the result of the method of collection

(Casella impactor) and the grain of BaCl2. There is no practical limit to the upper size.

However, a thicker film has to be used for larger particles.

ilL

' ^^^^ " ^

Figure 4. Electron micrograph of the smallest halos observed (original particle was

(NHi+)2S0it) . The other particles are BaCl2.

331
The method is reproducible as can be seen in Table 1 where the results of three runs are shown.

Table 1

The relation between the halo diameter and that of the original particle

y = ax + b

run # a^ n

I 1 .53 (± 0.11 ) -0.05 (± 0.06) 172

II 1.66 (± 0.18) -0.08 (± 0.10) 85

III 1.66 (± 0.13) -0.03 (± 0.07) 215

X, particle diameter in ym.

y, halo diameter in ym.

n, number of particles.

a The 95 percent confidence intervals are given in parenthesis,

The structure of the reaction spot is different for different sulfate particles.

Figures 5 and 6 illustrate the spots obtained for H2SO1+ and (NHit)2 SO4.

Figure 5. A typical reaction of H2SO4 particle produced in the laboratory with a thin

layer of BaCl2.

332
Figure 6. A typical reaction of (NH^)2S04 particle produced in the laboratory with a thin layer of BaCl2.

The methods allow for distinguishing between sulfate and sulfite particles. In this

field our preliminary results indicate that BaSOs spots are destroyed in HCl vapor while

the BaSOi+ remain unchanged (figure 7).

References

[1] Junge, C. E., Aiv Chemistry and Radioactivity, Academic Press, New York, 382 (1963).

[2] Cadle, R. D., Fisher, W. H., Frank, E. R., and Lodge, J. P., Jr., Particles in the

Antarctic Atmosphere, J. Atmos. Soi., 25, 100-103, (1968).

[3] Bigg, E. K. , Stratospheric Particles, J. Atmos. Sai. 32, 910-917, (1975).

[4] Altshuller, A. P., Regional Transport and Transformation of Sulfur Dioxide to Sulfates

in the U. S., J. Air Poll. Control Assoc., 26, 318-324, (1976).

[5] Tanner, R. L. and Newman, L., The Analysis of Airborne Sulfate--A Critical Review,

J. Air Poll. Control Assoc. 26, 737-747, (1976).

[6] Kadowaki , S., Size Distribution of Atmospheric Total Aerosols, Sulfate Ammonium and

Nitrate Particulates in the Nagoya Area, Atmos. Env., 10, 39-43, (1976).

[7] Bigg, E. K. , Ono, A., and Williams, J. A., Chemical Tests for Individual Submicron

Aerosol Particles, Atmos. Env. 8, 1-13, (1974).

[8] King, W. D. and Maher, C. T., The Spatial Distribution of Salt Particles at Cloud

Levels in Central Queensland, Tellus 28, 11-23, (1976).

333

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

AN ANALYSIS OF URBAN PLUME PARTICULATES COLLECTED

ON ANDERSON 8-STAGE IMPACTOR STAGES

Philip A. Russell

Denver Research Institute

University of Denver

Denver, CO 80210, USA

1. Introduction

It is becoming increasingly apparent that human lungs selectively capture particles

from approximately 5.0-0.1 ym in diameter and effectively extract surface associated metals

and organic compounds. Even relatively inert materials such as quartz may be harmful if

deposited in the lungs. Thus interest in the respirable fraction of suspended particles

and their identification has become of increased concern.

2. Discussion

Cascade and virtual air impactors have been used extensively in particle size separation

for industrial and environmental sources. A combination of electron microscopy and energy

dispersive X-ray fluorescence spectrometry provides a powerful analytical tool for examining

impacted (and filtered) substrates. The electron beam of a scanning electron microscope

(SEM) may be used to examine an impaction spot or individual particle for morphology and

characteristic X-ray emission. The electron beam of a transmission electron microscope

(TEM) can be used to produce a selected area electron diffraction (SAED) pattern which can

be used to identify crystalline particles by chemical composition.

Urban plume particles collected on Anderson 8-stage cascade impactor substrates, LoVol

filters and paraffin coated mylar were examined using the techniques mentioned above.

Particles on Millipore and Nuclepore substrates from impactors and LoVol filters were examined in an SEM equipped with an energy dispersive X-ray spectrometer (EDS) after coating

with a thin layer of carbon. TEM-SAED investigations required the transfer of material

from collection substrates to carbon coated grids.

3. Conclusions

Examination of impactor spots on substrates of 8-stage cascade impactors demonstrated

that (1) sulfur (non mineral) is always found predominantly on the final impactor stage;

(2) lead and lead bromochloride were found in stages 5 and 6 or stage 7; and (3) the amount

of sulfur increased significantly during pollution episodes when air mass movement recirculated the urban plume back into the sampling area and was not correlated with lead

concentrations.

Elemental information from X-ray intensities of impact spots and quantitative estimates

of LoVol samples collected simultaneously at two different sampling sites is compared.

Total impact spot intensities for stages 3-7 and LoVol quantitative estimates had poor

correlations for lead, moderate for mineral elements (Si, Ca, K, Fe) and excellent (r = 0.90) for sulfur. Possible explanations for variance in correlation are (1) the wide range

of sulfur and low range of lead concentrations, and (2) the predominance of mineral particles

in the upper stages of the impactor where impact spots were not analyzed.

335
The variances of elemental compositions determined by simultaneous independent studies

at two sampling sites is similar for the different elements, suggesting that certain elements

(S, Si, Ca, K and Fe) were representative of a well-mixed plume while others (Pb) were associated with point sources near the sampling site.

Examination of individual particles impacted on various substrates of stages of cascade

impactors demonstrated that (1) there was little or no difference in particle sizes from

the outer edge of the substrate to the center; (2) particle sizes did decrease from stage 0

to stage 7 but variance, even for specific particle species, was large; (3) the measured

physical effective diameters of minerals and flyash were significantly different on all

stages; (4) mineral or mineral-like elements were present in all stages while lead, lead

bromochl oride, zinc, sulfur (non mineral) and carbon particles became more numerous and

sometimes dominant in the last impactor stages; and (5) sulfur was always associated with

auto emission particulates.

Comparisons of average diameters of mineral and flyash particles were made for different

sampling periods for an impactor stage where minerals and flyash were often present.

Flyash diameters determined by electron microscopy for four different dates were not

different at the 5% significance level where F = 1.195 for 3 and 34 degrees of freedom.

However, the average mineral particle diameters determined by electron microscopy were the same only when the significance level was 0.1% where F = 4.842 for 3 to degrees of

freedom; thus it is unlikely that the mineral species size populations collected during

different sampling periods are equivalent. There is apparently an unknown factor that

results in differential segregation of mineral particles from day-to-day sampling.

TEM-SAED was used to further analyze the particles collected on Stages 5 and 7 of one Anderson cascade impactor. The transferred material from the fifth stage of the Anderson

impactor was predominantly mineral and flyash with some lead-rich particles. Quartz

particles produced sharp SAED patterns, as did other minerals. None of the flyash or leadrich particles observed produced diffraction patterns. Particles observed on stage 7 were

very different from those observed on the stage 5 substrate. Most of the particles were

carbon, but some flyash was also present. Diffraction patterns were occasionally observed

for particles associated with flyash.

Sulfur-rich particles that were collected from the Los Angeles urban plume and examined

by TEM-SAED were observed to react strongly with the TEM copper grid when transferred in

xylene. No electron diffraction patterns were produced by any of these particles. The

particles were observed to be agglomerates of smaller particles less than 0.1 ym in diameter.

Fine particles of sulfur, sulfamic acid and ammonium sulfate produced in the laboratory and

transferred to copper TEM grids in xylene did not produce particles or grid corrosion like

the fine particles transferred from the environmental sample. It was concluded that the

seed material was probably carbon, and the surrounding material was a noncrystalline sulfur

compound.

336
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977)

SIZE DISCRIMINATION AND CHEMICAL COMPOSITION OF

AMBIENT AIRBORNE SULFATE PARTICLES BY DIFFUSION SAMPLING

Roger L. Tanner and William H. Marlow

Atmospheric Sciences Division

Department of Applied Science

Brookhaven National Laboratory

Upton, New York 11973, USA

1. Introduction

A method for sampling aerosols has been developed [1]^ by which particles below the

optical scattering region (<0.3 pm) can be separated into size-related categories by

diffusion in a battery of diffusion cells (collimated hole structures) of exceptional

length. The size-segregated particle fractions are efficiently collected on chemically

inert, phosphoric acid-treated quartz filters and the chemical composition of the sulfatecontaining particles are determined by state-of-the-art analytical techniques.

2. Theory

The "collimated hole structure" type of diffusion battery used in this work consists of

a series of cylindrical stainless steel blocks each containing oa. 14,000 parallel cylindrical holes. When the battery is operated under conditions where the fractional penetration, fc(, of aerosol particles of diffusion coefficient, D, passing through a cell length,

I, at a volume flow, g, (see eqs. 1 and 2 (Gorml ey-Kennedy equation) [2]), the fractional

penetration of an aerosol stream passed through a series of diffusion cells is the product

of fractional penetrations through each cell. From two or more simultaneously collected

ambient aerosol samples, one collected from untreated air and the other(s) after diffusion

processing, the chemical content of the smaller size fraction of the aerosol (removed

preferentially by diffusion to the cell walls) can be inferred by subtracting the concentrations measured with the diffusion processed sample from those with the ambient aerosol.

fa = 0.819 exp(-3.557a) + 0.097 exp(-22.3a) + 0.032 exp(-57a)

+ 0.027 exp(-123a) + 0.025 exp(-750a) (1)

where

a = nD£/g (2)

3. Experimental

The total particle contents from ambient and diffusion-processed air were collected on 47 mm circles of acid-treated quartz filter material and leached in pH 4 aqueous solution.

The leach solution was first titrated with standard base and the net acid determined from

Figures in brackets indicate literature references at the end of this paper.

337
the Gran titration curve [3]. Portions of the leach solution were then used to determine

the soluble sulfate concentration by a turbidimetric technique [4], ammonium by the indophenol colorimetric technique [5] and nitrate by reduction to nitrite, deri vatization and

colorimetry [6]. Sulfate determinations were supplemented by soluble sulfur determinations

by the flash volatil ization--flame photometric detection technique [7]. Precision of data

is ± 5-10 percent except ± 15 percent for acid data.

4. Results and Discussion

The results reported are from a nine-day, intensive, diffusion-sampling experiment

conducted at Glasgow, 111., a rural location 120 km N of St. Louis, Mo., during the period

of July 22-30, 1975, in coordination with the RAPS summer 1975 field program. Twelve-hour

samples were taken each day and night witn the Sinclair diffusion battery [2] sampling

ambient air (samples designated PQU), diffusion processed air with a 50 percent penetration

diameter (d5o%) of 0.035 ym (PQDBi), and diffusion processed air with dcno, = 0.13 ym

(PQDB2).

^°

Size distributions were also calculated from data simultaneously obtained using an 11-

port screen-type diffusion battery in conjunction with a condensation nuclei counter. The

size distributions were determined by a least-squares fit of 11 representative particle

sizes from 0.02 ym through 0.4 ym diameter. The calibration of this battery is that of

Sinclair, et al. [7]. Assuming the particles to be spherical, surface and volume distributions were computed.

Volume distributions thus calculated have been combined with the fractional penetration

curves to obtain distributions of the diffusion sampled aerosols collected as samples PQDBi

and PQDB2. Appropriate averaging of individual volume distributions yields reasonable

average volume distributions for each sampling period (7/26-7/30) which may be directly

compared with the chemical composition data.

The analytical data for sulfate (figure 1) in samples PQU and PQDBi are in good

agreement indicating little sulfate mass in the very small particles (<0.05 ym). However,

comparison of PQU and PQDB2 sulfate data indicate removal of 20-50 percent of the sulfate

mass in the diffusion battery, demonstrating clearly that for these rural ambient aerosol

samples, 1/5 to 1/2 of the sulfate mass is present in the suboptical size range (< 0.3 ym).

Comparison of the analytical data with the volume distribution data shows that most of the

suboptical mass can be accounted for by sulfate, if one makes reasonable assumptions

concerning the density of the small particles.

The analytical data for acid and ammonium during the sampling period have also been

compared with that for sulfate. Qualitatively different temporal patterns were observed

for acidity compared with sulfate. Sulfate episodes during the 7/22-23 and 7/26-27 periods were not accompanied by large acid concentrations whereas during the 7/29-30 period large

acid concentrations were present and showed diurnal variation. During daytime samples for

7/29 and 7/30 periods, the acid content was maximum (figure 2) and predominant in very

small (< 0.05 ym) particles; during the 7/29-30 night sample it was much reduced and

associated with larger particles. This contrasts with the diurnal behavior of ammonium

(figure 3) which was highest during the 7/29-30 night sample than on either 7/29 or 7/30

and was associated principally with optical -sized particles. Since the ambient sulfate

concentration remains nearly constant during the 7/29-30 period, there is substantial

evidence for photochemically generated sulfate on this occasion.

338
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Six-hour backward trajectories from the Glasgow, Illinois site have been determined

for this period by Meyers and Cederwall of our laboratory, and correlate well with both the

chemical composition and size distribution data. Trajectories from the north or west

result in lower sulfate levels and negligibly small acidity but with a significant fraction

of aerosol volume in the <0.1 ym range. Trajectories passing through urban and/or power

plant plumes for brief periods may result in higher sulfate concentrations which is not

necessarily acidic sulfate. Stagnant air masses such as the one passing through the

Glasgow site on 7/29-30 which passed through St. Louis, then over several major power

plants in the previous four days, may result in very high acid and sulfate levels.

References

[1] Marlow, W. H. and Tanner, R. L., A Diffusion Battery Method for Ambient Aerosol Size

Discrimination with Chemical Composition Determination, Anal. Chem. 48, in press

(1976).

[2] Sinclair, D., A Portable Diffusion Battery. Its Application to Measuring Aerosol Size

Characteristics, Am. Ind. Hyg. Assoa. J. 33_, 729 (1972).

[3] Askne, C, Brosset, C, and Perm, M. , Determination of the Proton-Donating Property of

Airborne Particles, Swedish Air and Water Pollution Research Laboratory, Gothenburg,

Sweden, IVL Report B 157, 1-20 (1973).

[4] Sulfate Method Vib via Turhidimetry, Technicon Industrial Systems, Tarrytown, NY

(1959).

[5] Bolleter, W. T. , Bushman, C. J., and Tidwell, P. W. , Spectrophotometric Determination

of Ammonia as Indophenol , Anal. Chem. 33^, 592 (1961 ).

[6] Mull in, J. B. and Riley, J. P., The Spectrophotometric Determination of Nitrate in

Natural Waters, with Particular Reference to Sea-Water, Anal. Chem. Acta. 12_, 464

(1955).

[7] Husar, J. D. , Husar, R. B., and Stubits, P. K. , Determination of Submicrogram Amounts

of Atmospheric Particulate Sulfur, Anal. Chem. 47, 2062 (1975).

342
NATIOMAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

THE IDENTIFICATION OF INDIVIDUAL MICROPARTICLES

WITH A NEW MICRO-RAMAN SPECTROMETER^

E. S. Etz and G. J. Rosasco

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

The ability to probe the molecular identity of individual microparticl es is of importance in a variety of areas. These include air and water pollution, corrosion, forensic

chemistry, pathology, and the study of terrestrial soils and lunar fines. To analyze such

specimens, it is usually necessary to work with particles less than 10 pm in linear dimensions and frequently detect as little as lO'^^ gram of a substance of interest. In the past

there did not exist a practical technique for performing molecular analyses; consequently,

the determination of the molecular composition of individual microparticles has been

neglected.

Laser-excited Raman spectroscopy applied to the chemical characterization of discrete,

small particles offers valuable information to the microanalyst. If the sample is Raman

active, the technique has the potential of furnishing not only the structural formula of

the molecular species contained in the particle, but in addition may also yield information

on the crystalline (or glassy) phase of the material under investigation. The Raman

spectrum will therefore, in many cases offer a unique "finger print" of the constituent

chemical species and their structural coordination for a broad range of inorganic and

organic materials.

2. Discussion

Earlier studies at NBS [1]^ demonstrated the feasibility of acquiring Raman spectra

from discrete, micrometer-sized particles. It was shown that these spectra could provide a basis for the chemical identification of small particles present in many forms of particulate matter. These investigations have led to the development [2] of a new laser Raman

spectrometer system for microanalytical applications. The design of the laser Raman microprobe is optimized for the routine spectroscopic analysis of single particles less than

10 ym in linear dimensions. The instrument has largely been constructed from commercially

available components. Its basic design is identical in principle to that of conventional

Raman spectrometers. It makes use of a gas laser as the source of excitation; it has beam

directing, pre-fi 1 tering and focusing optics and a separate optical system for collection

and transfer of the scattered radiation to a double monochromator employing photoelectric

detection and a digital photon counting system. The instrument incorporates a number of

unique mechanical and optical components which optimize the detection of the Raman signal

^Instrument development partially supported by the U. S. Air Force, Technical Applications

Center.

^Figures in brackets indicate the literature references at the end of this paper.

343
from a single particle of size 1 um, and smaller. The system is stable mechanically and

allows the positioning of a particle sample precisely (to less than 0.2 ym) at the focus of

the exciting laser beam and utilizes a highly efficient ellipsoidal mirror to collect the

scattered light. The system is interfaced to a minicomputer for experimental control and

for automated, optimized data acquisition.

The analytical capabilities of the new instrument are illustrated by representative

Raman spectra of individual microparticles of well -characterized laboratory source materials.

Detection and analytical characterization is demonstrated for several classes of inorganic

compounds, including oxides, carbonates, nitrates, sulfates and phosphates. Particle Raman

spectra were obtained for several selected organic materials and polymers, in every case

for single particles less than 10 ym in diameter.

A variety of applications are in progress at the present time. Of particular interest

is the spectroscopic analysis and identification of single particles in samples of airborne

particulates. The discussion will emphasize results on the characterization of respirablesize particles in urban dust samples and in fly ashes from power plants. Important in this

work has been the speciation of sulfur (as in sulfate) and nitrogen (as in nitrate or ammonium) bearing particulates. A major objective of our studies is to establish a ref- erence file of analytical -qual ity Raman spectra for the identification of single particles

in particulate samples from environmental sources.

For analysis, the particles of interest are mounted on the polished surface of a substrate which is chosen to minimize spectral interferences. Sapphire (a-Al203), lithium

fluoride, or highly reflecting metallic substrates can be used. Atmospheric aerosol can be

sampled for spectroscopic analysis on the collection surface of the Raman substrate when it

is inserted on the stages of any of the cascade-type impactor samplers now widely used for

the field collection of airborne particles in size-stratified samples. Any given particle

in the sample is observed in the spectrometer microscope (at 400X magnification) to achieve

precise positioning for measurement.

Routine spectroscopic measurements on particles of known compounds and on particles

isolated from environmental samples have employed the green line (514.5 nm) of the argon

ion laser for excitation of the Raman spectrum. For colored samples, or those contaminated

with absorbing surface films, the possibility always exists for the microparticle to absorb

the incident radiation. Appreciable absorption of the laser irradiation invariably leads

to heating of the sample. When this occurs, it can often be observed in the spectrum, as a temperature rise in the particle causes a shift in the Raman line(s) to lower frequency and

simultaneously brings about a broadening of the Raman band(s). In some cases, particle

modification or destruction can result from this heating. Selection of a different exciting

line {e.g. 647.1 nm) has been useful for some of the colored particles examined. In general, however, it is particularly important for successful analysis to judiciously

control the irradiance (power/area) of the exciting laser focused on the sample. Radiationsensitive materials must be measured at reduced irradiance levels and commensurately longer

measurement times. _Spectra are acquired at rates varying from 200 cm'Vmin (0.2 s integration time) to 20 cm'Vmin (2 s integration time) over the region from 50 to 3600 cm"^.

The positional stability of all mechanical and optical components of the instrument is such

that measurements can readily be performed over extended periods of time, without loss in

signal due to either beam or particle drift.

Specific examples are discussed that demonstrate the power of this new technique of

microanalysis. Raman spectra are shown for single, solid particles of size <3ym of the

various types of sulfates known to exist in atmospheric aerosol. In these cases, the

particle samples were prepared from laboratory source materials. The compounds studied

include sodium and ammonium sulfate, together with the bisulfate salts, and calcium sulfate,

each of which contributes to total particulate sulfate in air. The spectra of these

microparticles reproduce those obtained from bulk samples [e.g. single crystal or powder

samples) of the same source materials. They show that the various neutralized forms of

sulfuric acid can readily be characterized on the basis of their respective Raman spectra.

344
Reference spectra such as these have allowed us to identify small, single particles

isolated for analysis from bulk samples of environmental particulate samples. Representative of these successful measurements is the particle Raman spectrum, shown in figure 1, of

an "unknown" particle in a sample of urban air particulate dust. The particle analyzed is

supported by a sapphire substrate of optical quality. Included with the particle spectrum,

and shown as the lower trace, is the "background" spectrum arising from the weak Raman

scattering of the substrate material (a-Al203). The vertical bars placed below the recording trace indicate the Raman frequencies of the SO^" bands as observed on the spectrum of a small particle of a single crystal calcium-sulfate anhydrite. Spectroscopic characterization of a variety of sulfate minerals has shown all to be distinguishable on the basis of

their fundamental Raman bands. The 8 ym particle is therefore identified as calcium sulfate (anhydrite) based upon the close similarity of its spectrum with that of singlecrystal anhydrite.

These studies on microparticles have recently been extended to the Raman investigation

of liquid aerosols. Work in progress centers on the spectroscopic characterization of the

various types of sulfate in microdroplets of laboratory-produced sulfate aerosol. Included

are measurements on small single droplets of free sulfuric acid prepared from aqueous

sulfuric acid solutions of known initial concentration. The aim is to establish the limit

of detection for undi ssociated H2SQH and the equilibrium concentrations of the HSO;; and

SO^" ions in acid droplets of size 5 ym and below. These measurements also involve the

study of the formation of microparticles of NHt^HSOi+ and (NHttjaSO^ from microdroplets of

acid aerosol exposed to various trace concentrations (in the range from 1 to 100 ppm) of

ammonia vapor in air. Of interest is the estimation of the amounts of sulfate and bisulfate

present in the liquid NHt^HSO^/ (NH14 )2S0i4 system and the monitoring of any time dependent

changes in the relative concentrations of these species both in the liquid and solid phase

during the transformation from the microdroplet to the solid microparticle. The phenomena

governing the rates of formation of solid sulfate aerosol from liquid acid aerosol are also

being examined as a function of the sizes of the microdroplets under study. The Raman

spectroscopic characterization of these sulfate aerosol systems is unique in that observations are made of the molecular compositon of individual microscopic entities. The results

derived from these studies thus present an opportunity to better understand the peculiar

type of behavior associated with extremely small quantities of matter generally existing in

particulate forms with high surface-to-volume ratios.

The successful analysis of micrometer-sized samples has involved the development of

appropriate particle collection, handling and analysis techniques. These techniques include

the use of various aerosol sampling methods, overcoating of particles to preserve integrity,

procedures to remove surface contamination, and ways to mount, register and observe--on

suitable substrates--single particles for spectroscopic analysis.

The unique information obtained from the micro-Raman analysis of single particles is

briefly reviewed and compared to the data on the composition of such samples gained from

other microprobe techniques, such as electron probe and ion probe microanalysis.

References

[1] Rosasco, G. J., Etz, E. S., and Cassatt, W. l\.,Appl. Speatrosa. 29, 396 (1975).

[2] Rosasco, G. J., Etz, E. S., and Cassatt, W. A., Particle Analysis by Laser-Excited

Raman Spectroscopy, presented at 1976 Pittsburgh Conference on Analytical Chemistry

and Applied Spectroscopy, Cleveland, Ohio, Feb. 29 - March 5, 1976.

345
345
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

A COMPACT X-RAY FLUORESCENCE SULFUR ANALYZER^

L. S. Birks, J. V. Gilfrich and M. C. Peckerar^

Naval Research Laboratory

Washington, DC 20375, USA

1. Introduction

Measurement of the sulfur concentration in particulate effluent from emission sources

has become even more important recently in view of the potential necessity to use high

sulfur fuels for generating electrical power. The x-ray measurement of sulfur requires a helium path or, preferably, a vacuum path x-ray spectrometer. In addition, the presence of

intermediate and higher atomic number elements causes some difficulty because of line

interferences. Use of a high resolution crystal spectrometer minimizes this problem.

2. Discussion

The x-ray equipment used in the laboratory to perform the analyses of air pollution

particulate samples can be very sophisticated enabling the determination of as many as 20 or 25 elements in a sample every few minutes [1,2]^. Unfortunately such equipment requires

a relatively large capital investment and is quite bulky, making it inconvenient for on- site use. In response to the need for a field instrument, the Environmental Protection

Agency (EPA) initially requested the Naval Research Laboratory (NRL) to design and build a general, compact x-ray analyzer [3]. This crystal spectrometer instrument, which was delivered to the EPA laboratories in Research Triangle Park, NC, in February 1975, was limited to the measurement of atomic numbers above 23 (V) because it was an air-path

instrument.

A second-generation vacuum model of that air-path analyzer was suggested by NRL as a potential on-site device originally intended only for the measurement of total sulfur

concentration. After the initial design of the prototype had been conceived, a concurrent

project at NRL supported by EPA demonstrated that a high resolution single-crystal x-ray

spectrometer could determine whether the sulfur was present as sulfide or as sulfate. If

both forms were present, their proportions could be determined quantitatively [4]. The success of the valence work suggested that the sulfur analyzer should be redesigned to

incorporate this capability. Since the measurement of valence state required that the

spectrometer be adjustable (whereas the original concept had utilized a fixed crystal and

detector), a logical extension was to design the spectrometer to cover a large enough Bragg

angle range to measure elements other than sulfur. The prototype instrument is shown

schematically in figure 1.

^Supported by EPA under Interagency Agreement EPA-IAG-D4-0490.

^Present address: Advanced Technology Laboratories, Westinghouse Electric Corporation,

Post Office Box 1521, Baltimore, Maryland 21203.

^Figures in brackets indicate the literature references at the end of this paper.

347
Figure 1. Schematic Diagram of the Sulfur Analyzer.

The excitation source is a specially designed Pd transmission target x-ray tube which

requires only air-cooling at its rated power of 15 watts. Tube-target to sample distance

is less than two centimeters. The divergence allowed by the collimator is 0.07 degrees.

The crystal is freshly cleaved (200) NaCl for which we estimate the rocking curve breadth

(FWHM) to be less than 0.01 degrees. Thus the resolution is defined by the collimator and

is approximately 1 eV (.002 A) at SKa. The detector is a sealed proportional counter

having 50 m Be windows and a path-length of 4.7 cm filled with one atmosphere of Ne-C02;

detection efficiency is about 65 percent at SKa. The spectrometer is manually adjustable

over a 2e range of 90 to 150°, which corresponds to a wavelength span of 3.4 A to 5.4 A

with the NaCl crystal. Substitution of other crystals would permit the measurement of any

wavelength between about 2.0 and 25 A (although each crystal would only cover a small

portion of this range). The 50 pm Be window on the detector would not be very transparent

at wavelengths longer than about 8 A. The Pd transmission target tube was chosen because

of the favorable relation between the wavelength of the Pd L-lines and the sulfur K absorption edge; it would not be very efficient for many other elements.

References

[1] Wagman, J., Bennett, R. L. and Knapp, K. T., X-Ray Fluorescence Multi spectrometer for

Rapid Elemental Analysis of Particulate Pollutants, Environmental Protection Agency,

Report No. EPA-600/2-76-0S2, (March 1976).

[2] Goulding, F. S. and Jaklevic, J. M., X-Ray Fluorescence Spectrometer for Airborne

Particulate Monitoring, Environmental Protection Agency Report No. EPA-R2-73-182,

(April 1973).

348
Birks, L. S. and Gilfrich, J. V., Low Cost Compact X-Ray Fluorescence Analyzer for OnSite Measurements of Single Elements in Source Emissions, Environmental Protection

hgeucy Report No. EPA-600/4-75-002, (July 1975).

Gilfrich, J. V., Birks, L. S. and Peckerar, M. C, X-Ray Analysis of the Valence State

of Sulfur in Pollution Samples^ Final Report to the Environmental Protection Agency,

in preparation.

349

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

THE X-RAY IDENTIFICATION AND SEMI-QUANTIFICATION OF TOXIC LEAD COMPOUNDS

EMITTED INTO AIR BY SMELTING OPERATIONS

Peter F. Lott and Ronald L. Foster

Department of Chemistry

University of Missouri-Kansas City

Kansas City, Missouri 64110, USA

1. Introduction

Effects of lead and lead compound toxicity, which may produce conditions such as anemia,

nephritis, mental retardation, vision stenosis and muscular dystrophy, is well known

[1,2,3]^. Such toxicity comes about either through oral ingestion or by inhalation. Up to

50 percent of the particles 1 m or less that are inhaled are retained in the body, particles 2 ym or greater tend to collect on mucous membranes from which they are ingested.

The lower level for the appearance of mild systems of lead poisoning is observed with a blood level of 60-80 yg Pb/100 ml.

Current methods of analysis are usually limited determining the percentage of lead as the "element," and not the lead compounds. This prevents definite source correlations and

hazard evaluations, since the toxicity is usually a function of the compound involved. A

solution lies in the application of x-ray dif fractometry as the Bragg law reflection elucidation of crystal plane spacing provides unique identification of crystalline specimens.

The method is non-destructive and rapid. Restrictions for air particulate analysis are, the

relatively large sample size required to obtain a suitably thick path length specimen and

the 1 percent lower detection limit for compound characterization.

2. Discussion

Collection of the sample is accomplished by use of a "Hi-Vol" filtering unit. This

filtered dust is further concentrated by washing off the particulates with a 5 percent Duco

cement in acetone solution directed as a jet from a plastic squeeze bottle against the

filter. The suspended particles are washed into the cup of a stainless steel Buchner type

funnel (Schleicher and Schull 2.4 cm, #596 filter paper) mounted on a filter flask. After

completion of the washing, suction is continued until the sample is dry.

The concentrated sample is fastened with cellophane type over the opening of a Philips

diffraction sample holder, mounted and scanned at 1° 2e/min from 20° to about 50° 2e. Xray radiation is obtained from a Cu tube operated at 40kV, 25mA, and passed through a Ni

filter to select the Cu-Ka radiation. The pulse height selector was set on the 111 reflection plane of a lead metal film at a 2e angle of 31.33°.

Patterns were identified by use of the Fink Index [4], and Inorganic Index [4,5],

followed by comparison with the Powder Index File [6]. Additional identifications were made

by direct comparisons with the patterns of standard compounds (prepared in the sa>me manner

as the samples} of mineral or chemical specimens (fig. 9-12).

1 Figures in brackets indicate the literature references at the end of this paper.

351
Comparisons indicated the certain presence of PbS and PbSOi+. Additional possible

substances based on only one or two identifiable peaks were lead metal, PbO, and PbO-PbSOi+.

The problem of direct comparison was increased by shifts in peak location by as much as 0.4°

2e due to various causes, such as sample thickness and geometry for x-ray reflection as well

as inter-compound effects. This prevented discrimination where a few tenths of a degree 2e

separates the location of the major peaks of two compounds. A very broad peak, observed

from about 22° to 24° 2e, (fig. 1) was due to amorphous scattering from the filter paper

20 10

Figure 1. Schleicher and Schvell filter paper

background scatter pattern.

sample backing when the sample was less than "infinitely" thick. The diminuation of the

scatter peak height and the corresponding increase of compound peak heights were measured

for a series of samples of different thicknesses. A plot of the logarithm of the latter versus the scatter peak height produced a parallel series of lines that served to correct

peak heights to infinite thicknesses in thin samples. Consequently, the patterns could be

directly compared by peak height on a semi-quantitative basis for the relative abundance of

each compound.

35X
Further investigation of the earlier assigned [7] PbSOt^ peaks at 26.7° and 20.85° 26 were made in light of their appearance in the background samples from Fulton and Maryville,

MO with no supportive series of minor peaks. Quartz provided an alternative identification

for the major peaks at 26.66° and 20.85° 2e , and should be expected to be present, being a very ubiquitous compound. Additional minor peaks matched the pattern for CaCOs, nearly as common a background compound as quartz.

The quantitative aspect of the x-ray diffractometry technique was explored using the ore concentrate. The gravimetric analysis [8] was performed by dissolving samples in

concentrated HNO3, ^nd 70 percent HCIO4. This resulted in Pb determinations of 71.12 percent

and 71.03 percent respectively. By comparison, the measured peak heights in the diffraction

pattern predicted 86.17 percent PbS in the ore concentrate, giving a lead content of 74.62

percent, only 3.51 percent greater than the average of the chemical determinations. Statistical treatment of data gave the standard deviation 2.42, the 95 percent confidence limit

2.8, the 99 percent confidence limit 6.72, and the relative probably error 4.2 percent.

Thus, the error is within the expected range and acceptable as a quantitative method,

validating the sample preparation and mounting methods.

Further semi-quantitative comparisons between samples necessitated the separation of

the PbSOi+/quartz overlapped peaks. For binary mixtures, a ratio of the two analytical peaks

at 26.7° and 20.85° 2e, containing the contributions from the two compounds can be discriminated as to composition by plotting the variation of the ratio versus the weight

fraction of one compound [9,10].

To correct for differences in diffraction efficiency, a pure sample of each known

compound was prepared, and the peak heights of the major peak in the diffraction pattern (or

second peak when the primary peak overlapped the pattern) were compared against quartz, the

most efficient peak, and a ratio factor was calculated to equalize the height of the re- sponse to the weight fraction of a compound relative to the most efficient compound. No

attempt was made to correct for interelement effects, which appeared to be of secondary

significance.

3. Results

Most patterns were very similar, with peaks of highest intensity for PbS, PbSO^ and

quartz (fig. 2-6). The background comparisons from Fulton and Maryville, MO show the

presence of quartz, dolomite, and calcium carbonate (fig. 7,8). A typical smelter site

sample of air-borne particulates from Glover, MO (number 2224) (fig. 5) reveals a pattern

strikingly similar to the ore concentrate. Strong background peaks of dolomite, ZnS, quartz

and a slight CaCOs or chalcopyrite peak are observed at levels similar to the ore con- centrate pattern. The lack of significant PbSO[+ peaks rules out the blast furnace or sintering operations as possible sources, because both produce significant PbSO^. The

observed high level of PbS further discriminates against the blast furnace operation since

samples of this effluent contained no PbS.

During the period when this sample was collected, the plant was on strike, and sintering

operations ceased. Ore trucking operations took place on one sampling day. The similarity

with pattern 2224 reinforces the interpretation of the ore concentrate as the sample source.

The slight indication of PbSO^ is explainable as a residue from prior processing operations

that was stirred up in the dust of the plant yard by the truck traffic.

Conditions prevailing with the resumption of smelting operations are observable in a second typical pattern containing PbSO^. Sample 5117 was collected during a 24 hour period

of sintering, blast furnace, and ore trucking operations. The relative intensities of

quartz, PbSO^, and dolomite are among the highest found in this study. The ZnS is rather

353
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354
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Figure 3. Sintering plant stack cellar dust pattern.

355
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Figure 4. Ore concentrate pattern.

356
Figure 5. Typical air sample pattern, #2224.

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358
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359
Figure 8. Fulton, Mo. air sample background pattern.

360
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361
low and suggests that not all PbS came from

suggests significant windblown surface dust,

suggests a minor blast furnace contribution

of the PbS and PbSO^.

the trucking activities. The high background

The dolomite intensity along with possible PbO

with the sintering operation providing the bulk

Figure 10. Standard pattern for PbSOi,.

362
Most patterns can be interpreted by a trade-off of the compounds found associated with

either the ore concentrate or sintering operation. However, a few patterns were found which

strongly implicate a blast furnace origin. Sample 5329, collected at Herculaneum, MO, is an example. Due to adverse winds, the background quartz indication is relatively low, as are

the PbS, ZnS, and dolomite constituents or ore concentrate. Alternatively, the fall-out

3

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Figure 11. Standard pattern for PbO-PbSO

363
from the blast furnace operation is so great, that proportionally, the quartz background and ore concentrate contributions are insignificant. The pattern shows one of the best indications for the PbO-PbSO[+ compound, apart from the blast furnace standard pattern, as well

as the clearest, strongest indication of the 3 major peaks of ZnO. The strong similarity to

the blast furnace pattern implies it is the source. Unfortunately, no information is

available on plant operations during that sampling period. A sample taken only 6 days

later, number 5330, shows only the peaks attributable to background, with no indication of a smelting process compound. One month later, sample 5332 indicates a return to normal

activity, since the PbS and PbSOi+ compounds are once again present at normal levels.

ooooooooooo

Figure 12. Standard pattern for Galena (PbS).

364
Overall, the Herculaneum, MO samples are dissimilar to the Glover, MO samples. The

much lower levels of ore concentrate compounds in the Herculaneum patterns may indicate a different handling technique for the ore, or may be due to the fact that the sampling

station was located on the roof of a school building about 40 feet above ground level, while

the Glover sampling was conducted at ground level, in an open area near a country store.

Because only one sample from Herculaneum was taken during a period of dry weather, damp

surface conditions could have held down surface dusts. This is doubtful, since the quartz,

dolomite, etc. of surface dust background remain as high or higher in these samples compared

to that found in the Glover samples.

Since plant process residue samples were not available from the Herculaneum site, source determination is speculative unless the two plants are equivalent. Indications are,

however, that such is not the case.

The earliest Glover samples, 2227 to 2522, were taken during an extended period of

plant inactivity due to a strike. The lack of decline in the relative abundance of lead

compounds indicates that a significant reservoir exists in the surface dusts of the plant

area.

4. Conclusion

This study shows the feasibility of using x-ray diffractometry as a means of qualitatively and quantitatively analyzing air particulate samples for specific compounds,

identifying these compounds, and tracing them to suspected sources. Extension of this

technique can be made to suspended particulates in waste water discharge. The only significant drawback to the method is that it can be applied only to crystalline compounds. It

is a non-destructive method allowing samples to be stored, cataloged, re-run, or re-analyzed

by a second method for confirmation or additional information.

References

[1] Hall, S. K., Lead Pollution and Poisoning, Environ. Sai. Teahnol., 6(1) 30-5 (1972).

[2] Vints, L. A., Effects of Lead on the Visual Organs, Vestn Oftal'mol., (1) 74-5 (1975).

(English Abstract).

[3] Beattie, A. D., Moore, M. R., et at. , Role of Chronic Low Level Lead Exposure in the

Etiology of Mental Retardation, Lancet, 1(7907) 589-92 (1975).

[4] Fink Power Diffraction File Retrieval Index for Inorganic Compounds, 1972, ed. by

Leonard G. Berry, Swarthmore, Penn.: Joint Committee on Powder Diffraction Standards,

1972.

[5] Inorganic Index to the Powder Diffraction File, 1972, ed. by Leonard G. Berry, Swarthmore, Penn.: Joint Committee on Powder Diffraction Standards, 1972. (Incorporates the

Hanawalt Index).

[6] Powder Diffraction File, sets 1-15, ed. by Leonard G. Berry, Swarthmore, Penn.: Joint

Committee on Powder Diffraction Standards, 1967.

[7] Foster, R. L., Lott, P. F., The X-ray Identification of Toxic Lead Compounds Emitted

Into Air by Smelting Operations in Missouri, Trace Substances in Environmental HealthIX, University of Missouri 9th Annual Conference on Trace Substances in Environmental

Health, Columbia, Missouri.

365
[8] Furman, N. H., ed. The Elements, 6th ed. v. 1 of Standard Methods of Chemical Analysis,

Princeton, NJ: D. Van Nostrand Co., Inc., 1971.

[9] Azaroff, L. V. L., Elements of X-Ray Crystallography, New York: McGraw-Hill, 1968,

517-519.

[10] Kaelble, E. F., Handbook of X-rays for Diffraction, Emission, Absorption, and Microscopy, N€w York: McGraw-Hill, 1967, p. 12-1 to 12-12.

366
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

FLAMELESS ATOMIC ABSORPTION DETERMINATIONS OF CADMIUM, LEAD, AND MANGANESE

IN PARTICLE SIZE FRACTIONATED AEROSOLS

Mark E. Peden

Atmospheric Sciences Section

Illinois State Water Survey

Urbana, Illinois 61801 , USA

1. Introduction

Although the importance of particle size considerations in determining the potential

effects of aerosols is well documented [4,5]^, information on the chemical composition and

related size distributions of specific components is both sparse and inconclusive. In addition to detrimental health effects caused by direct inhalation of submicrometer toxic

aerosol particulates, particle size factors are of importance in assessing residence times

and subsequent transport distances. Residence times of airborne contaminants become the

major factor in determining the extent of possible deleterious effects including: 1)

reduction of visibility through haze formation, 2) cosmetic damage to surrounding structures, and 3) opportunities for atmospheric reactions between gaseous and aerosol pollutants

which have been shown to behave synergistically, thereby increasing their toxicity [13].

Coupled with the fact that existing industrial particle capture devices are least effective

in removing what are often the most toxic particles (those found in abundance in the submicrometer range) it becomes of paramount importance that both concentrations and particle

size distributions of aerosol components be accurately documented at the low levels in

which many exist.

For the purpose of this study, three aerosol constituents, Cd, Pb, and Mn were investigated. Cadmium and lead were chosen for investigation owing to their high toxicity and

abundance in the respirable size range below one micrometer, where particles deposit in the

pulmonary region of the respiratory tract. An extraction efficiency by the bloodstream of

60-80 percent of particles lodged in this region has been documented [4]. Although toxic

levels of airborne manganese are rarely found, even in heavily industrialized areas, it has

been shown by Johnstone and Coughanowr [10] to act as a catalyst in the oxidation of SO2 to

SO4 and warrants close monitoring as increased coal consumption continues.

A recent study by Campbell [2] points out that incineration of municipal solid wastes

may become the predominant source of lead emissions as leaded gasoline is phased out as well as providing a major fraction of cadmium emissions. As more thought is given to the

implementation of solid wastes as a possible energy source, accurate detailed emission data

for toxic metals from incineration facilities must be made available.

Flameless atomic absorption provides for a reasonably accurate, rapid analysis of a broad series of metals present in airborne particulates. The latest refinements in commercial graphite tube atomizers have supplied a means whereby chemical separation procedures

can be el iminated.

•^Figures in brackets indicated literature references at the end of the paper.

367
2. Experimental

The experimental design for the collection and analysis of particle size fractionated

aerosols was included as an integral portion of the overall scheme of Project METROMEX, an urban study based in the St. Louis metropolitan area during the summers of 1971-1975 to

quantitatively determine inadvertent effects of a major industrial region on the meteorology

and air quality of the surrounding area [3].

Andersen 8-staqe cascade impactors were operated at selected locations both upwind and

downwind from the area of concentrated industrial activity for periods of from 5 to 10

days. Impactors were run at the manufacturer's recommended flow rate of 28 min"^ with

Whatman 41 cellulose filters used as the deposition surface. Backup filters, also of

Whatman 41 paper, were changed daily throughout the sampling period to prevent alteration

of the flow rate by the accumulation of particulate matter. Filters weve removed after

collection and transferred to the laboratory where a chemical digestion was performed prior

to atomic absorption analysis. Dissolutions were performed in 100 milliliter Teflon

beakers under a laminar flow fume hood to minimize possible contamination from both the

digestion vessel and surrounding laboratory air.

A combination of 1 milliliter each of HF, HNO3, and H2S0[+ was added sequentially to

solubilize all particulate matter and to create a silica free solution by volatil izating

SiF^. Hydrogen peroxide (H2O2) was added as needed to air in the complete digestion of

organic matter present. The resultant solution was topped to 25 milliliters with deionized

water and stored in new acid-rinsed polyethylene bottles prior to analysis. The volume of

reagents was kept at a minimum to avoid the introduction of trace metal contamination into

the samples. The final normality of the dissolved particles was 0.64 N HN03-1.44 N H2SO4.

Analysis was performed using an Instrumentation Laboratory Model 455 (IL 455) carbon

tube atomizer interfaced with an IL Model 151 single beam spectrophotometer incorporating

simultaneous background correction via a deuterium hollow cathode lamp. Instrumental

response was measured on a Linear Instruments Corporation strip chart recorder. Peak

height and area modes available on the IL 151 were not utilized due to transient electronic

signals present within the laboratory causing false peaks to appear on the digital display.

A constant voltage transformer (CVT) is recommended to alleviate this problem. A slit

height reducer inserted into the entrance port of the monochromator was used to minimize

radiation effects from the tube at elevated temperatures. Manufacturers supplied pyrolytically-coated graphite tubes exhibiting poor reproducibility, apparently due to an uneven coating with hairline cracks resulting in inconsistent atomization efficiency. The use of

uncoated graphite solved this problem and yielded an average of 5 percent precision for all

determinations

.

Sample volumes of 10 pi were dispensed with Eppendorf microliter pipets with disposable

acid rinsed polyethylene tips. The closed cell design of the IL 455 is effective in maintaining an oxygen free environment thereby greatly increasing the tube life. However, this

creates an additional problem in that the evolution of copious SO3 fumes, during the drypyrolyze cycle, seriously coats the quartz end windows resulting in erratic absorbance

values. Additionally, the venting mechanism engineered into the atomizer, as shown in

figure 1, does not provide for effective removal of SO3. To alleviate these problems,

three modifications were incorporated into the normal atomizer operation: 1) existing

vents were closed and an L-shaped aluminum tube was installed into the top of the atomizer

cell with a vinyl tube extending upwards into the laboratory exhaust duct to effectively

remove all fumes, 2) polypropylene tubes were installed in the purge gas entrance ports and

directed in front of the end windows to minimize the fogging effect and resultant attenuation of the incident light intensity, and 3) an argon purge rate of 20 Standard Cubic Feet

Hour ^ (SCFH) instead of the recommended flow of 10 SCFH was used to insure a more rapid

removal of SO3 fumes.

368
Instrumental parameters shown in table 1 are the optimal settings for the three elements

Cd, Pb, and Mn employing the equipment described. A 100-second dry-pyrolze program consisting of a gradual temperature increase to 600°C sequentially evaporates the solvent, vaporizes

the acidic components, and ashes any remaining organic matter. The same pre-atomization

program was found to be suitable for all three elements under investigation. Atomization

temperatures of 2100°C were used for Cd and Pb determinations, and a temperature of 2700°C

was necessary for complete Mn removal. The experimental calibration curves of absorbance

versus weight in grams shown in figure 2 represent the interel emental sensitivity differences common to flameless atomic absorption and also illustrate the effect of high anion

concentrations on absorbance values, specifically for manganese. As seen from the sensitivity curves, absorbance values for Cd and Pb suffer no attenuation of intensity whether

in a dilute nitric acid matrix or in a relatively concentrated 0.64 N HNO3-I.44 N H2S0it

matrix. Conversely, manganese exhibits a 59 percent reduction in sensitivity in a nitricsulfuric acid solution largely due to the presence of high anion concentrations. Similar

reductions in manganese sensitivities have been reported by Barnard and Fishman [1] and

Segar and Gonzalez [16] in high salt matrices containing appreciable amounts of sulfate.

The dependence of matrix composition on absorbance values stresses the importance of

careful matrix matching between samples, standards, and blanks when analyzing environmental

samples. The addition of a relatively large amount of a specified compound, in this case

sulfate, can enhance an analysis by 1) converting the different valence states of an element

369
present in a sample to a single compound thereby reducing asymmetric and multiple peaks and

creating a single peak which appears at the same temperature in successive atomization

cycles and 2) in the case of cadmium, decreasing the normal volatility such that a higher

pyrolysis temperature is attainable which results in a more complete removal of matrix

components prior to atomization [7].

Table 1

Instrumental Parameters

Cd Pb Hn

Wavelength, nm: Bandpass, nm: Photomultiplier:

P, M. voltage:

Elemental lamp current, milliamps

Continuum lamp current, milliamps

Sensitivity^, grams {lO"^^):

228.8 217.0 279.5

0.5 1.0 0.3

R446 R446 R372

800 800 900

3 7 3 18 7 25

0.3 5.4 5.9

^The amount of analyte causing an absorption of .0044 absorbance units.

Figure 2. CALIBRATION CURVES

0 2 4 6

WEIGHT (grams 10"^°)

370
3. Results

Results of the three metal determinations at various sites were plotted as concentration in air (ng,m"3) versus particle size (ym). The Lee and Goranson [12] calibration,

which takes into account fluctuations in flow rates, was used to determine the effective

cutoff diameter for each stage. The map of the St. Louis metropolitan area shown in figure

3 includes the locations of sampling sites and industrial facilities known to be potential

emission sources of Cd and Mn compounds. Airborne Pb is assumed to be entirely due to

motor vehicle exhausts as no major lead processing plants are present within the sampling

area. As shown on the map, the concentrated areas of industrial activity are located in

the Alton-Wood River and East St. Louis-Granite City areas.

Figure 3. MAP OF ST. LOUIS AREA WITH MAJOR

INDUSTRIAL FACILITIES

Pere Marquette

371
CADMIUM: Cadmium is known to be a naturally occurring constituent of all zinc ores

and to remain with the zinc ore throughout refining and separation processes (U.S. Environmental Protection Agency,) [18]. For this reason it is assumed that both cadmium and zinc

processing facilities will be potential cadmium sources. Estimates of cadmium emissions on

a nationwide basis [18] attribute 76 percent to metallurgical processing involving cadmium

or zinc, 12 percent to the consumption of coal in power plants and coke ovens, and 11 percent to the incineration and disposal of metal wastes.

The particle size distribution spectra with associated mass median diameters (MMD)

shown in figure 4 reveal average MMD's of between 1-2 ym. The illustrated mean spectra were obtained from two to three sampling periods all taken during the summer months. Alton

and Wood River samplers were operated without backup filters. While the general shape of

the spectra are valid, the MMD values are appreciably shifted to larger values since

particles smaller than 0,5 micrometers were not captured.

Figure k. Cd HISTOGRAMS AT SELECTED SITES WITH ASSOCIATED

MASS MEDIAN DIAMETERS (MMD)

1 I I I I I 1 1 {

I I I I I I 1

1

1 r Pere Marquette

0.6

0.4

0.2

0.6

0.4h

0.2

Collinsville

0.95

0

0.1

1.0

0.8

0.6

0.4

0.2

0

T I I I I 1 1

1

1

1—I—I 'I I 1 1

1

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KMOX

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0.95

Centrevi lie

1.53

1.0 10 30 0.1 1.0 10 30

PARTICLE DIAMETER, pm

The largest average concentration of cadmium occurred at Centreville (which is downwind

of the zinc smelter located in Sauget, northwest of Centreville) and is the probable source

of high cadmium concentrations. The second highest average occurred at Wood River which is

in close proximity to both coal burning steel industries and power plants. The distribution

illustrated for Pere Marquette State Park (PMQ), the highest elevation in the area, is

characteristic of a nonaffected upwind site. Twin peaks present at PMQ, Alton, and the

KMOX radio transmitter were also observed in St. Louis by Lee et at. [12] in the National

Air Surveillance Network (NASN) study.

372
LEAD: Lead distributions shown in figure 5 illustrate the importance of backup

filters in obtaining reli-able MMD's and total average concentrations when the bulk of the

material is present in the submicrometer range. Samplers of Alton and Wood River operated

without backup filters show a grossly over-estimated MMD and a lower than average normal

concentration. The narrow range of MMD between 0.54-0.66 micrometers is consistent with a common emission source for lead aerosols which in this case is motor vehicle exhaust.

Estimates of lead emissions attributable to automobile exhaust range from 90-98 percent on

a nationwide basis (National Academy of Science,) [14] and as there are no major lead

processing industries in the sampling area, it is assumed that airborne lead is entirely

due to motor vehicle traffic. The spectrum shown for Pere Marquette is again characteristic

of an upwind nonaffected site yielding the lowest total concentration, approximately six

times less than the other three stations reporting complete data. The Centreville, KMOX

and Collinsville histograms all show the typical spectra obtained downwind of urban areas where motor vehicle lead is the dominant contributor.

Figure 5- Pb HISTOGRAMS AT SELECTED SITES WITH ASSOCIATED

MASS MEDIAN DIAMETERS (MMD)

120

100

80

60

40

20

0

80

60

40

1 III 1 1 1

1

1

1 1 1 1 1 1 1 1

1 1 Pere Marquette

MMD 0.66

L " • * 1 • . . ,

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140

120

100

80

60

40

20

1

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0.55

50

40

20

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120

100

80

60

40

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0

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0.54

. • • • <

•••*•••

F^ 340avI

Centreville

0.55

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PARTICLE DIAMETER, pm

373
MANGANESE: Manganese distributions pictured in figure 6 exhibit different particle

spectra from either cadmium or lead, being much broader with less prominent highs and

lows. These broadened spectra are consistent with the findings of Lee et al. [2] in the

NASN study and the findings of von Lehmden [20] on a study of coal fly ash.

Figure 6 Mn HISTOGRAMS AT SELECTED SITES WITH ASSOCIATED

MASS MEDIAN DIAMETERS (MMD)

CDc

en

o

10

8

6

4

2

0

10

8

6

4

2

0

10

8

6

4

2

0

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1

1

1 1 I I I I I I Pere Marquette

MMD 3.58

Wood River

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1 ~ Collinsville

1

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.

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12

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• ••••••

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I Centrevi lie

MMD 4.28

1.0 10 30

0

0.1

Li

1.0 10 • 30

PARTICLF DIAMETER, ym

Manganese is used widely in the steel manufacturing industry as an agent in nullifying

the harmful effects of sulfur (National Academy of Science,) [15] and accounts for 80

percent of the nationwide anthropogenic emissions (U. S. Environmental Protection Agency,

[19]. Other sources of lesser importance include cement manufacturing industries and

facilities engaged in the manufacturing of dry cell batteries. Although Struempler [17]

attributes the presence of aerosol manganese in western Nebraska to airborne dust particles,

in cities such as St. Louis, it is generally assumed that soil contributions are exceeded

by industrial sources [19]. The major anthropogenic source of manganese compounds in the

research area is the steel industry, concentrated in the Alton-Wood River and East St.

Louis areas.

Of the six distributions shown in figure 6, five show fairly uniform profiles both in

average concentrations and overall shape of spectra. The large peak occurring between 1-2

micrometers in the Alton area is in close proximity to the second largest blast furnace in

the area and is the suspected source of that maximum. Heindryckx [8] found a similar peak

at the same particle diameter near a ferromanganese plant in the industrialized region of

Belgium. The uniform, relatively flat profile obtained at the remaining locations is

attributable to the background urban manganese aerosol obtained at various sites up and

374
downwind of industrial facilities. Once again Pere Marquette is a reference site for a nonaffected location.

4. Discussion

The preceding histograms for the three metals Cd, Pb, and Mn illustrate that a wide

range of both concentrations and shapes of particle size distributions is obtained for

metals which naturally occur at low levels, which can be affected by localized emission

sources. For this reason, it is crucial to accurately assess the methodology involved as

it pertains to both precision of measurements and accuracy in determining size distributions.

Recent work by Dzubay et al. [6], Rao [21], and Hu [9] points out that the material

used as an impaction surface has an important bearing on the resultant size distributions

obtained. Teflon and aluminum foil surfaces have been shown to suffer from particle bounce

which results in a lowered capture of larger particles on early stages and a subsequent

buildup on later stages and the backup filter. The net effect is a shift in the deduced

MMD values to a smaller particle size. If the particle bounce phenomenon does occur, the

percentage of error in the resultant size distribution will be greater if the bulk of

particles present are in the upper size categories and, conversely, lower if they naturally

occur in the lower size ranges, less than 5.0 micrometers. Additionally, an increase in

pump flow rate will enhance particle bounce resulting in even larger errors. Recommendations to alleviate this problem include: 1) coating of impaction surfaces with a thin

layer of high vacuum silicone grease (Dzubay, et al.) [6] (Rao) [21], or 2) utilizing glass

fiber filters as suggested by Hu [9]. The application of silicone grease to surfaces

analyzed for trace metals is not recommended due to the introduction of contaminants in the

coating process and also the problems of incompatibility with the analytical method,

specifically an acid dissolution followed by atomic absorption analysis. Consequently, for

studies of this nature, glass fiber or cellulose filters with a low trace metal content

should be employed while operating samplers at a low flow rate to minimize particle bounce

effects

.

An example of possible shifting of MMD values can be seen when comparing data from the

METROMEX study to average MMD values for the St. Louis area obtained in the NASN study (Lee

et al,) [12]. Cadmium and lead MMD values obtained in the St. Louis NASN study yielded

average values of 1.54 and 0.70 micrometers, respectively. Averages from METROMEX for

three summers revealed values of 1.34 and 0.63 micrometers, remarkably close to the NASN

values. Manganese values, on the other hand, averaged 2.30 micrometers in the NASN study

and 4.12 in this study. This indicates a possible downward shift in the manganese spectra

of the NASN study, which is attributable to the use of aluminum foils as impaction surfaces

and a flow rate of 154 1 min"^ instead of 28 1 min-^ (Lee and Goranson) [12]. A particle

bounce phenomenon could explain the differences for the manganese results.

5. Conclusion

The overall precision obtainable in atmospheric sampling of this type is best illustrated as in figure 7 by plotting the results of two adjacent samplers operating simultaneously

for an equal duration of time and comparing the values for different elements. In so doing, it becomes apparent that reproducibilities will vary corresponding to three factors:

1) the greater the concentration of an element naturally present, the lower the standard

deviation of replicate determinations is likely to be, 2) analyses made by flame atomic

absorption will have greater precision than non-flame techniques due to the inherent

principles involved in each method, and 3) elements with known high volatilities may

exhibit losses during the acid dissolution phase if excessive splattering occurs upon

reagent addition. Applying these factors to figure 7, the lowest standard deviations are obtained for the elements calcium, potassium, and zinc, all determined by flame atomic

adsorption. Calcium, present at the highest concentration, clearly shows the strongest

correlation between adjacent samplers. The lower correlations shown for lead, manganese,

and cadmium are attributable to: 1) low concentrations involved which result in minor

contaminants contributing a large relative error, and 2) inherent lower precision obtainable

375
with flameless atomic absorption. These plots emphasize the meticulous care that must be

taken during all aspects of sampling, processing, and analysis to minimize the introduction

of contaminants from both reagents and the laboratory environment. Provided these parameters are satisfied, direct flameless atomic absorption determinations of Andersen cascade

impactor samples are achievable after an acid dissolution of cellulose filters. The

precision of replicate atomic absorption determinations averages ±5 percent with the

precision of the entire methodology largely element dependent.

Figure 7- COMPARISON OF ADJACENT SAMPLERS AT PERE MARQUETTE

1.0

10 0.1

PARTICLE DIAMETER, ym

I am grateful to F. F. McGurk for her help in completing many of the analyses. This

work was performed under the general direction of R. G. Semonin and D. F. Gatz whose

careful review of the manuscript was appreciated. The research was supported by the U. S. Energy Research and Development Administration, Contract No. AT(11-1 )-1199,

376
References

[I] Barnard, W. M. and Fishman, M. J., Evaluation of the use of the heated graphite atomizer

for the routine determination of trace metals in water. Atomic Absorption Newsletter,

12^(5), 118-124 (1973).

[2] Campbell, W. J., Metals in the wastes we burn? Envir. Soi. and Teohnol. 10(5)

,

436-439 (1976).

[3] Changnon, S. A., Huff, F. A., and Semonin, R. G. , METROMEX: An investigation of

inadvertent weather modification. Bulletin American Meteorological Society, 52(10)

,

958-967 (1971).

[4] Davison, R. L., Natusch, D. F. S., Wallace, J. R., and Evans, C. A., Jr., Trace elements

in fly ash. Dependence of concentration on particle size. Envir. Soi. and Teohnol.

8(13), 1107-1113 (1974).

[5] Dulka, J. J. and Risby, T. H., Ultratrace metals in some environmental and biological

systems. Anal. Chem. , 48(8), 640A-653A (1976).

[6] Dzubay, T. G. , Mines, L. E., and Stevens, R. K. , Particle bounce errors in cascade

impactors. Atmospheric Environment, 1_0, 229-234 (1976).

[7] Ediger, R. D., Atomic absorption analysis with the graphite furnace using matrix

modification. Atomic Absorption Newsletter, 14(5), 127-130 (1975).

[8] Heindryckx, R., Comparison of the mass-size functions of the elements in the aerosols

of the Gent industrial district with data from other areas. Some physico-chemical

implications. Atmospheric Environment, 1_0, 65-71 (1976).

[9] Hu, J. N. H., An improved impactor for aerosol studies--modified Anderson sampler.

Environ. Soi. and Teohnol. 5_(3), 251-253 (1971 ).

[10] Johnstone, H. F. and Coughanowr, D. R. , Absorption of sulfur dioxide from air.

Industrial and Engineering Chemistry, 50(8 ) , 1169-1172 (1953).

[II] Lee, R, .E. and Goranson, S., National air surveillance cascade impactor network.

I. Size distribution measurements of suspended particulate matter in air. Envir. Soi.

and Teohnol. 6(12), 1019-1024 (1972).

[12] Lee, R. E., Goranson, S. S., Enrione, R. E., and Morgan, G. B., National air surveillance cascade impactor network. II. Size distribution measurements of trace metal

components. Envir. Soi. and Teohnol. 6_(12), 1025-1030 (1972).

[13] Lee, R. E. and von Lehmden, D. J., Trace metal pollution in the environment. J. of the

Air Pollution Control Assoc., 23(10), 853-857, (1973).

[14] National Academy of Science, Lead; Airborne Lead in Perspective, 330, (National Academy

of Sciences Printing Office, Washington, DC, 1972).

[15] National Academy of Sciences, Manganese, 191, (National Academy of Sciences Printing

Office, Washington, DC, 1973).

[16] Segar, D. A. and Gonzalez, J. G., Evaluation of atomic absorption with a heated

graphite atomizer for the direct determination of trace transition metals in sea water. Anal. Chim. Acta b8, 7-14 (1972).

[17] Struempler, A. W., Trace element composition in atmospheric particulates during 1973

and the summer of 1974 at Chadron, Neb., Envir. Soi. and Teohnol. 9^(13), 1164-1167

(1975).

377
[18] U. S. Environmental Protection Agency, Scientific and Technical Assessment Report on Cadmium. (Office of Research and Development, Washington, DC, 1975).

[19] U. S. Environmental Protection Agency, Scientific and Technical Assessment Report on Manganese. (Office of Research and Development, Washington, DC 1975).

[20] von Lehmden, D. J., Manganese in fly ash. U. S. Environmental Protection Agency,

Research Triangle Park, NC, unpublished data, 1973.

[21] Rao, A. K. , An experimental study of inertial impactors. Ph.D. Thesis, Dept. of

Mechanical Engineering, University of Minnesota (1975).

378
Part VIII. AIR POLLUTION MEASUREMENT

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

AMBIENT AIR QUALITY MONITORING

George B. Morgan

Environmental Monitoring and Support Laboratory

U. S. Environmental Protection Agency

Las Vegas, Nevada 89114, USA

1. Introduction

The monitoring of ambient air quality is of paramount importance for determining

ambient levels of pollutants so that they can be related to adverse effects on man and his

environment. The monitoring of air quality is also necessary to establish a quantitative

relationship between air quality and pollutant sources to determine the efficacy of control

measures, and to determine compliance with standards.

2. Reasons for Monitoring - Discussion

Air quality monitoring is defined as the systematic collection of physical, chemical,

biological, and related data pertaining to ambient air quality, pollution sources, meteorological parameters, and other factors that influence, or are influenced by ambient air

quality.

This systematic approach is very complex. Without a systematic approach based on stated objectives and guidelines, proper ambient air quality assessment cannot be accomplished. Failure to recognize and to take into account the complexities associated with

ambient air quality has led to the present situation where we cannot document the relationship between sources and exposure or between exposure and effects.

Major questions which must be considered in air quality monitoring system are as

fol lows

:

1. what are the objectives of the air monitoring network?

2. what is the area for which measurements are required?

3. what is the proper mix and location of fixed stations, moveable stations,

airborne stations, and what is the role of modeling in achieving the objectives?

4. what level or degree of errors are acceptable?

5. what is the importance of exposure monitoring as related to the pollutants

that are air oriented or to those that occur in other media including the food

chain?

6. what related meteorological data must be collected with air quality data?

7. what is the importance of sample averaging times to the network design?

8. what are the effects of physical and chemical transformations on the sampling

location and network design, for example, for monitoring ozone or sulfates?

9. what quality assurance program is necessary to assure that data are representative and legally and scientifically defensible?

381
Once an air monitoring network has been properly designed, it can furnish data to be

used for one or more of the following uses:

1. to establish or revise standards;

2. to demonstrate that adequate progress is being made toward \

attainment of the standards;

3. to demonstrate that compliance with standards is maintained;

4. to furnish information during high pollution episodes or accidental discharges

and provide guidance on choice of subsequent actions;

5. to define air pollution problems for periodic determination of priorities

for resource allocations, and to develop control programs.

Present air monitoring must be re-designed to provide an effective capability to

detect and quantify ambient levels of toxic or non-regulated pollutants which may pose a threat to human health and welfare. In order to accomplish this, a priority list of toxic

pollutants must be assembled. For those pollutants which transcend the media, an air

monitoring program must be developed in conjunction with other appropriate monitoring

programs so that total exposure to important receptors may be qua'ntified.

Pollutant priorities for monitoring and control must result from demonstrated effects,

the probability that projected benefits will be commensurate with resources expended, and

last but not least, from public concern. The following factors should be considered when

establishing pollutant priorities:

1. Severity of known or suspected effects on human health, including neurotoxic,

mutagenic, teratogenic and carcinogenic effects.

2. Severity of effects on soil, plants, animals, and structures.

3. Persistence of the pollutant in the environment, and accumulation in man or his food chain.

4. Conversion into more toxic substance {e.g.^ SO2 to sulfuric acid).

5. Ubiquity and environmental levels which can be estimated from an emissions inventory.

6. Size and type of human population exposed.

7. Availability of adequate control technology.

8. Availability of adequate methods for measuring the pollutant in the environment.

9. Legal mandates.

3. Types of Monitoring

Air monitoring activities may be divided into the following categories: (a) permanent

fixed-site (trend) monitoring; (b) ambient source-linked monitoring; (c) exposure monitoring;

and, (d) biological monitoring.

A. Permanent fixed-site (trend) monitoring

Permanent fixed-site (trend) monitoring is necessary to judge the attainment and

maintenance of the present Ambient Air Quality Standards through the State Implementation

Plans (SIP's). Included in the SIP's are air quality maintenance, land use planning,

transportation controls, prevention of significant deterioration, episode prediction and

control , etc.

Monitoring of trends at permanent sites involves the measurement of pollutants and

their effects over extended periods of time. These data are primarily for the evaluation

of conditions over time whether at the source, in industrial areas, urban areas, rural areas or geophysical baseline areas.

382
B. Ambient source- 1 inked monitoring

Ambient source-linked monitoring involves relating ambient air quality to sources

through modeling, considering other pertinent supporting data such as meteorology, demography,

and topography.

Computer models are becoming extensively used to provide a mathematical relationship

between air emission sources and resulting air quality. These models are normally validated

on the basis of air quality measurements for a limited number of fixed and mobile monitoring

stations and time periods and can then be used to extrapolate or predict the variations of

pollutant concentrations at locations and times which are not measured directly. Once

models are validated they provide a basic tool for assessing the effectiveness of abatement

strategies for immediate or long-term problems. Also they are the only method for evaluating

the impact of proposed new sources.

Much of research monitoring falls into the ambient-source linked category. Projects

that typical ly< require significant research monitoring support include studies of the

movement, distribution, fate, pathways and effects of a specific pollutant entering a given

environmental medium and assessment of the effectiveness of experimental control systems or procedures.

C. Exposure monitoring

Exposure monitoring should give a true picture of the impact of air pollution control

on reduction of exposures and adverse effects on human health and welfare. An exposure

monitoring system which can provide such information is the preferred way of reporting

progress toward cleaning the air and thus carrying out the intent of the Clean Air Act.

Exposure monitoring involves measurement of pollutant concentration at locations where

exposure may occur. The primary requirements for such systems are:

1. Identification of critical receptors at risk and the pollutants which

produce the adverse effects.

2. Development of siting requirements and numbers of sites including mobile

and remote measurement systems based on the time and variability of

pollutant concentrations and the relevant receptor population.

3. Integration of networks for estimating receptor exposure with networks

for other purposes, e.g., standards attainment and maintenance.

D. Biological monitoring

Biological monitoring can be an important part of an ambient air monitoring program.

For many pollutants the major pathway from source to receptor is through the air. The

monitoring of tissues and biological fluids collected from receptor plants, wildlife,

domestic animals and humans can indicate levels, patterns and trends of atmospheric pollutants or their metabolites. Incidences of pollution can often be detected by unusual

changes or mortality in animal populations caused by pollutants such as DDT, mercury,

cadmium, lead, fluorides, and arsenic. Valuable information on lead, cadmium, mercury and

arsenic exposure may be furnished by the analysis of selected human tissues or fluids such

as hair, teeth, fingernails and blood.

4. Components of an Ambient Air Quality Monitoring Network

To provide valid data on pollutant concentrations, an ambient air quality monitoring

network must have the following essential components: central laboratory facility, manual

sampling network, automatic monitoring network, and support facilities.

The central laboratory facility is required for any air monitoring network. No matter

how sophisticated the facilities are in the field, a central laboratory is necessary.

383
The manual network is the most efficient first step in establishing a total network.

This system can provide basic data upon which a comprehensive network can be designed. The

manual network will provide 24-hour integrated measurements of total suspended particulates,

S025 and NO2. A most important feature of the manual network is that valid data can be

rapidly obtained with relatively simple and inexpensive field sampling equipment.

The automatic network will provide continuous 'tn-s-itw measurements of pollutants.

This is really the only feasible way to get peak and diurnal concentrations of pollutants.

In the long run, the automatic network is the most accurate and economical means for

measuring the usual spectrum of pollutants of concern. This network will require some major types of support equipment. A fully equipped mobile laboratory is required for

calibration of field stations, for quality control functions, for pollutant profile studies,

and for interrelating monitoring systems. Meteorological support equipment is needed at

all automatic stations.

An automatic network for multi pollutant monitoring represents an extensive investment

and merits special consideration regarding site location, station design, instrument

selection, instrument calibration, and data acquisition and handling.

Valid pollutant concentration measurements cannot be made without adequate instrumentation, thus the selection of instruments for individual pollutants must be given due attention.

Instruments should meet certain guaranteed performance specifications for accuracy, sensitivity, zero and span drift, freedom from interferences, response time, maintenance requirements, etc. Fortunately, considerable information and expertise is available based on previous instrument evaluation programs. (The U.S. EPA equivalency document, 40CFR53,

February 1975, is one such source.) Such information may be used to provide guidelines on instrument performance to be expected for a given pollutant and for performance specifications to be included in procurement contracts.

An automatic station providing continuous measurements of several air pollutants

generates a copious amount of data. The acquisition, handling, storage, retrieval and

utilization of such data requires a large investment in data systems and manpower. Automatic data acquisition systems are necessary for handling such large amounts of data.

5. Quality Control

A quality control program involves taking all of the necessary steps to assure that

monitoring data and supporting information upon which decisions are based are legally and

scientifically defensible. A quality control system which utilizes reference methods is

necessary if data generated by one network or one laboratory at a given time are to be

comparable to similar data produced elsewhere at another time. It is only through such a program that the accuracy and precision of the data are known.

It is necessary that all operational phases of a monitoring network system be considered

in a quality control program; for example sampling, sample handling and storage, sample

preparation, sample analysis, instrument performance, data calculations, data validation,

data reporting, and data evaluation. In addition, any such quality control program must be

applied in field operations for selection of sampling site, verification that the sampling

site is adequately representative of the area, size of sample collected, sampling rate, and

frequency oi^ sampling. All of these parameters must be specified so that resulting data

fulfill the goals and objectives of the monitoring network system.

Guidelines and operational manuals for implementing and for operating a routine

quality control program must be available for the following areas: laboratory construction,

laboratory operation, supplies and equipment, personnel, training, data acquisition and

analysis, interlaboratory calibration, intralaboratory quality control, and report

preparation.

384
6, Conclusion

Many of the responses to environmental monitoring needs have resulted in less than

adequate data, have not been cost effective, and in certain instances have resulted in

implementation of costly programs which provided questionable benefits. We must make

maximum use of new concepts and methodologies as they become available. Such concepts as integrated monitoring systems, new optimization techniques and state-of-the-art measurement

devices, such as those employing remote sensing techniques, are becoming operational in the sense of being available for testing and application, and failure to use them to their

fullest capabilities will result in a loss of the opportunity to develop rational environmental assessment tools.

The ability to assess ambient air quality depends heavily on the availability and

applicability of appropriate sensors. Until recently, most pollutant sensors capable of

providing quantitative information were of the in-situ or contact type. Such sensors are restricted to measurement of a parameter at a single point in space or, when mounted on a mobile platform, at sequential points as a function of time. Because of the difficulty of

relating a point in space remote from the sensor to sensor data, great care must be taken

in selecting the site for the sensor.

As new devices become available, they should be incorporated into operational monitoring

systems. There is no doubt of the ever increasing importance of remote sensing for EPA's

monitoring programs. Yet these techniques will not replace contact monitors but rather

will augment and improve monitoring methodology. As newer techniques and hardware become

more available and enhance our ability to monitor our environment, we will be faced with

the question of "what is the most cost-effective combination of fixed, mobile contact and

remote sensors for a specific monitoring problem?" Another area where advances are yet to come is in the development of monitoring methods for assessing exposure-dose relationships.

In the past, environmental monitoring has been carried out in response to an already

existing hazardous condition. Future monitoring systems must be able to detect potential

problems and monitor the appropriate parameters before they reach crisis proportion. Some

possibilities which might be explored are the use of biological exposure indicators as trend monitors to predict changes, and the development of personal exposure meters, such as biochemical measurements which integrate the total exposure of an individual to a pollutant

or class of pollutants. Another example is the fluorescent film technique for ozone

exposure. When we achieve accurate, valid and broadly applied exposure monitoring, we then

shall have made a major step toward achieving the ability to truly and rationally evaluate

the management of our air resources.

385

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

APPLICATIONS OF REMOTE MONITORING TECHNIQUES IN AIR ENFORCEMENT PROGRAMS

Francis J. Biros

Technical Support Branch

Division of Stationary Source Enforcement

Environmental Protection Agency

401 M Street, SW

Washington, DC 20460, USA

1. Introduction

The Clean Air Act, as amended, June 1974, (42 U.S.C. 1857 et. seq.) authorizes the

development of effective and practical processes, methods and prototype devices for the

control of air pollution. This authority is granted to EPA to facilitate the achievement

of the purposes of the Act which include the protection and enhancement of the quality of

the nation's air resources so as to promote the public health and welfare and the productive

capacity of its population. "Processes, methods and devices" have been developed by EPA

and private industry to inter alia measure atmospheric emissions of pollutants (criteria

and non-criteria) from stationary sources as well as to measure ambient concentrations of

such pollutants. These pollutant measuring methods have been based on many principles

ranging from manual to automatic, extractive to in~situ, and remote to proximate. The

purpose of this discussion is to evaluate the utility of remote monitoring techniques

(exclusive of visible emissions observations by trained observers) in stationary source enforcement programs based on a consideration of the possible program applications and

their scope. In this process, advantages and disadvantages of remote monitoring technology

will be defined and suggestions will be presented relating to possible future activities in

the development and application of these techniques.

Major elements of a control agency's program designed to improve environmental quality

include the establishment of appropriate standards, identification and inventory of those

sources to which the standards apply, notification of affected sources, conduct of surveillance activities and, finally, administrative or judicial enforcement of standards, if

necessary, to ensure compliance.

2. Discussion

Generally, the objectives of stationary source air enforcement monitoring are to

locate affected sources; determine their compliance status; where necessary, develop

compliance schedules; monitor increments in compliance schedules; and monitor to ensure

final compliance. A special objective associated with case development monitoring is the

establishment of evidence for administrative or judicial proceedings. Most of these objectives can be achieved only by use of data obtained in field surveillance procedures

employing pollutant emission measurement techniques such as remote monitoring.

Remote techniques may be used therefore, in monitoring activities directly related to

enforcement of Federal and state/local agency regulations including:

(a) Determination of stationary source compliance status, i.e., whether a source (presently or previously on a compliance schedule) is complying with emission

1 imitations

;

(b) Case development activities, i.e., collection of data specifically to support

administrative or judicial actions; and

387
(c) Enforcement surveillance activities, i.e., screening studies to evaluate unknown

status of sources.

There are many enforcement related activities in which remote monitoring techniques

may prove to be valuable; these include, but are not limited to, the following:

(a) Evaluation of emission requirements for major sources when developing or revising

regulations

;

(b) Verification of the adequacy of control strategies to meet NAAQS;

(c) Development of representative emission factors; and

(d) Development and validation of long and short-term air quality modeling procedures.

Control agency enforcement monitoring activities potentially encompass literally hundreds

of thousands of sources. Thus the need for accurate, precise, cost-effective monitoring

methods such as remote techniques is apparent.

For example, enforcement activities under §110 of the Clean Air Act involve approximately 200,000 stationary source facilities. To date, emphasis has been placed on approximately 22,000 major sources which represent 85 percent of total stationary source pollution.

Under §111, standards of performance for new stationary sources. Federal standards (some

delegated to certain states) have been promulgated for 24 source categories. To date,

approximately 350 sources have been monitored and it can be expected that at least 1,500 sources per year will come under the ambit of these regulations. Finally, §112 provides

for emission standards for hazardous air pollutants. Under promulgated rules, approximately

800 fixed sources and 3,300/year transitory sources require enforcement monitoring on a routine basis.

Remote monitoring techniques offer a number of operational and functional advantages

which are of interest to air enforcement and regulatory programs.

Cost-Effectiveness - Although the initial capital costs are higher for remote instruments than for other types of monitors, the operational costs are less because of the

mobility of the instruments which allows coverage of more sources and areas in a shorter

period of time than manual test equipment. Remote monitors are also less manpower intensive

inasmuch as some may be operated by a single individual in the field, whereas manual

instruments may require a team of three to five engineers.

Unannounced and Non-interference Monitoring - Remote Monitoring techniques provide a most effective tool for compliance monitoring, even at night with active systems, without

entry into the premises of the source. In addition, remote monitoring interferes with

normal plant operations to a lesser degree than monitoring with manual methods.

Rapid Response - In emergency episodes involving environmental pollutants, the highly

mobile and flexible remote monitors can be used to assess the document the extent of the

emergency more rapidly than stationary iwsitu monitors. Enforcement countermeasures can,

therefore, be instituted more rapidly.

A number of disadvantages to the use of remote monitors can be identified. These

include:

• Inability to Measure Mass Emission Rates - Most regulations are written in the form of mass emission limitations. Therefore, documentation of violation requires determination of mass emissions rates for a particular facility. Most remote monitors will

provide measurements in relative concentration terms. Conversion to mass emission

rates requires a second measurement, in-situ or remote, using instrumentation such as

a laser Doppler velocimeter.

388
• High Initial Costs - Remote monitoring instruments are generally more costly than

the extractive or in-situ system. Similarly, active remote systems are more expensive

than passive systems. It can be assumed, however, that cost of instrumentation would

be reduced as more are produced and used in the field.

• Limited Application Under Certain Conditions - Adverse weather conditions such as fog,

heavy rain, or extremely high particulate content in the atmosphere can affect the

measurement capability of remote monitoring instruments.

0 Complicated Calibration Procedures - Remote techniques are more difficult to calibrate

than extractive or in-situ devices because of the atmospheric background influence.

Large calibration cells to simulate long atmospheric paths or test ranges with calibrated stack emission generators may be required.

3. Conclusion

Because of their significant advantages as well as the general acceptance by the

scientific community of the validity and adequacy of the technical principles underlying

remote monitoring instruments, however, the enforcement and regulation development use and

application of remote monitoring can be expected to increase in the future. More remote

instruments will need to be made operational and provided to field enforcement personnel

for compliance monitoring purposes. In addition, successful use of these techniques in an enforcement case will be an essential initial step to administrative and judicial acceptance

of the remote instrument technique as an enforcement monitoring tool.

389

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg , Md. (Issued November 1977).

INDIVIDUAL AIR POLLUTION MONITORS

S. C. Morris

Brookhaven National Laboratory

Upton, New York 11973, USA

and

M. Granger Morgan

Carnegie Mellon University

Pittsburgh, Pennsylvania 15213, USA

1. Introduction

In the field of community air pollution, emphasis has been placed on general measures

of air quality based on fixed sampling stations. Traditionally, epidemiological studies

have used data from one or several fixed stations as an estimate of the exposure received

by a neighborhood or by an entire city.

The dearth of appropriate data makes estimation of the error introduced by using

ambient air quality as a surrogate for population exposure difficult. Rough calculations

place it between a factor of two and a factor of seven. As a further complication, the

magnitude and even the direction of the error varies by pollutant and is not likely to be

consistent from one city to another. As the averaging time for exposure decreases, the

value of fixed monitor data as a surrogate for population exposure is likely to decrease.

Nonetheless, studies using fixed station surrogates have demonstrated a correlation

between air pollutants and health effects sufficient to form the basis for a public policy

decision to begin air pollution controls.

2. Discussion

There is little concensus among epidemiologists, however, on the specific quantitative

relationship between air pollution exposure and health effects. Consider the experimental

difficulties: air pollution varies with time and place, people move around, the population

receives not a single exposure but a range of exposures at different concentration-time

histories. In addition, individual susceptability varies with age, health, previous

exposure history and genetic factors.

The weakest link in attempts to determine exposure-response relationships for air

pollution is accurate, quantitative estimation of population exposure. An approach to

improving this situation is the use of individual air pollution monitors.

In the work place environment, Exposure to air pollutants is regulated in terms of

individual doses received by workers. Because of this different legal and regulatory

environment there has been considerable emphasis on developing individual monitors for use

in the occupational field. Both the National Institute for Occupational Safety and Health

and the Bureau of Mines have successful programs of research support in instrument development. A large number of commercial firms market individual monitoring instruments for

occupational applications. Few of the instruments that have been developed under these

programs are directly applicable to use in ambient air. Difficulties involve such factors

as sensitivity, dynamic range, and running time. With the exception of a modest and

391
sporadic program run by the Environmental Protection Agency, no program of Federal support

currently exists for developing individual air pollution monitoring instruments for ambient

air. The current absence of a significant market for such instruments inhibits their

development by private firms.

Some informal efforts have been made to use available individual monitors developed

for the work place to measure public exposures and a major study using a Bureau of Mines

type instrument has been initiated by a group at the Harvard School of Public Health with

support from the National Institute of Environmental Health Sciences [1]^.

In July of 1975 the Biomedical and Environmental Assessment Group at Brookhaven

National Laboratory convened a workshop of health effects and instrumentation specialists

to consider the role of individual air pollution monitors in air pollution health effects

studies, and to develop an assessment of research needs in this field. Two early conclusions of the workshop group were 1) "the importance of population exposure estimates in air

pollution epidemiology makes it imperative that future epidemiological studies include

exposure estimates more representative of what people actually breathe," and 2) "the use of

individual air pollution monitors is a necessary factor in the design or performance of

definitive studies of the health effects of air pollution" [2].

3. Conclusion

The Brookhaven workshop produced a first order ranking, by promise, of a number of

candidate instrumentation technologies. For each candidate instrumentation technology, a first order estimate of the research needs was developed. It seems clear that a number of

acceptable prototype devices could be produced within three years. The uncertainties about

the ultimate performance of the various candidate technologies are still sufficiently

large, however, to preclude an immediate focusing on one or a few approaches.

Work supported by the U. S. Energy Research and Development Administration, Division

of Biomedical and Environmental Research.

References

[1] Speizer, F., An Epidemiologiaal Approaah to Health Effects of Air Pollutants, Proceedings of the Fourth Symposium on Statistics and the Environment, National Academy of

Sciences, Washington, DC, 1976, in press.

[2] Morgan, M. G., Morris, S. C, Individual Air Pollution Monitors: An Assessment of

National Research Needs, Brookhaven National Laboratory, BNL 50482, Upton, NY, 1976.

Figures in brackets indicate the literature references at the end of this paper.

392
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1975, Gai thersburg , Md. (Issued November 1977).

INTERCALIBRATION OF NITRIC OXIDE/NITROGEN DIOXIDE/OZONE MONITORS

D. H. Stedman and R. B. Harvey

Department of Atmospheric and Oceanic Science

The University of Michigan

Ann Arbor, Michigan 48104, USA

1. Introduction

In the process of a measurement program we have tested the photostationary state

relationship:

J(N02) [NO2] = ksENO] [O3] (1)

where J(N02) is the rate of photolysis of NO2 and is the known rate of reaction between

NO and O3. These tests have been carried out successfully in urban polluted environments

and in rural air masses. The success of these tests indicates that the above relationship

can be used to non-invasi vely test air monitoring data as the measurement takes place. A

number of new techniques developed are described below.

2. Discussion

A. Optimized J(N02) detector

A schematic diagram of the J(N02) detector is shown in figure 1. A solution of the error equations gave operating points; initial [NO2] = 26 ppm, flow time = 0.7 second. An

automated switching valve for zeroing is included. Figure 2 shows a comparison between the

ROOF TOP LABORATORY

CAPILLARY ORIFICE

EPPLEV UVRADIOMETER

3-WAV TEFLON

SOLENOID VALVE

.27 cm X Im QUARTZ TUBE

I NO-NO, j CHEMILUMINESCENT

I ANALYZER I

Kz CfZ O7 FILTER

N02 SOURCE

DRYING AGENT

Figure 1. Schematic diagram of J(N02) detector.

393
0 0.2 0.4

J (NOjl |min-<)

90-

0.6

Figure 2. Comparison between the measured J(N02) and

an absolutely calibrated uv photometer.

measured J(N02) and an absolutely calibrated uv photometer. The solid curve is the

calculated response characteristics based on absolute photometry.

B. Mobile NO/NO2 detector

We have constructed in a mobile unit an NO/NO chemiluminescent monitor capable of

measuring accurately on scales as sensitive as 1 ppm full scale with a ten second time

response. This detector is the one whose sensitivity and accuracy were to be tested using

the photostationary state equation (eq. 1) and other methods.

C. Flow independent ozone calibration

Figure 3 shows schematically a method for measuring the ozone content of a photochemical ozone source by means of its stoichiometric reaction with NO. Strictly this

method intercal ibrates NO and O3 detectors such that any systematic errors are equal and of

the same sign. Incidentally, it also gives a calibration of the NO converter for pure NO2

systems. Ozone is also sometimes calibrated by photometry over a 2 m path.

394
NO CAL. lANK

O3

SOURCE

f(oJ

F(NO)

no/no^

DETECTOR

REACTION

VOLUME

VENT

Gas Phase Titration Apparatus

Figure 3. Gas phase titration apparatus

D. Rapid response permeation tube calibrator

We also calibrate the NO detector using

calibration has been much impi^oved by a rapid

using a pressure technique. Figure 4 shows a traces taken in 100 minutes and in 10 minutes

NO2 permeation wafers. The success of this

in-situ calibration of the permeation rate

schematic of the method and figure 5 shows

of the flow calibration. Notice that apart

from increased noise the 10 minute calibration is satisfactory at a permeation rate as low

as 25 ng/min.

CONSTANT TEMPERATURE ENCLOSURE

STANDARD OUT

GAS FLOW MEASUREMENT

FLOW

0 DUMMY

TUBE

TEFLON WAFER

Permeation Tube Calibration 8, Flow Dilution System

Figure 4. Permeation tube calibration & flow dilution system

395
Figure 5. Traces taken in 100 minutes and 10 minutes of the flow calibration.

The overall result of the above techniques is already redundant calibration. Table 1 shows the species independently calibrated.

Table 1. Calibration methods for NO/NO2/O3.

Permeation tube NO

Standard tank NO

Flow independent calibrator O3, NO

Photometry O3

We thus have five measured independent parameters to fix three variables. This

should be enough, but instrument malfunction in the field can cause any of these data to be

in error. Further, the above calibrations are invasive in that their use ties up the

instrument away from its measurement role. Thus we used our detectors as calibrated above

to test eq. (1). Under all conditions of reasonable fetch of the impinging air mass the

equation was found to hold within the limits of data measurement. Table 2 lists reasons when departures have been observed due to improper fetch.

Table 2. Departures from the photostationary state will be observed.

a) When the impinging air is in a region of heterogeneous J. i.e., the detector is in

patchy shade or within •^^^ s of flow time from a heavily shaded area.

b) When a source of NO (road, heater vent etc.) is within 60 s of air flow.

A

c) If an inlet system residence time is greater than '^1 s.

d) If a detector has a response time long compared to typical fluctuations (<60 s in a clean area). Thus, for a properly sited monitoring station in an open area, the equation

can always be used. Note that at night either [NO] or [O3] must be zero, as is observed.

396
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464 Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

A REACTIVE GAS GENERATOR

Wing Tsang and James A. Walker

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

1. Introduction

In an earlier paper [1]^ we have described the construction and operation of a reactive gas generator. In particular, we have demonstrated its utility in the continuous

and accurate generation of low levels of formaldehyde, acetaldehyde, and acrolein. As

mentioned in the earlier report, this is actually a general purpose instrument with capability of generating a wide variety of thermally stable reactive gases. Possible uses include calibration of analytical instruments, the evaluation of analytical methodology

and the carrying out of toxicity investigations. We now validate this claim by using the

reactor to generate sulfur dioxide, hydrogen cyanide and hydrogen chloride continuously

and at levels that are of interest in pollution and occupational health contexts.

The reactive nature of these gases is well known. This renders unsatisfactory the

usual static methods [2] for sample preparation. Obviously, a dynamic method where the

required samples can be prepared immediately prior to use can be expected to circumvent

some of these problems. This has been the basis of practically all present day approaches

to this problem and is best exemplified by the use of sulfur dioxide permeation tubes for

calibration purposes. A complete discussion of this and other related methods can be

found in a recent text [2]. Our instrument represents a fusion of two of the methods

mentioned in the text [2]. It involves the generation of a dilute concentration of a selected large organic molecule in an inert medium through the diffusion cell technique

and then the complete pyrolysis of this molecule to produce the reactive gas of interest.

The "parent" molecule of choice is one that undergoes pyrolytic decomposition exalusively

via the reaction:

parent molecule hydrocarbon + reactive compound.

Thus, knowledge of the concentration of the parent molecule gives the concentration for the

reactive gas. Furthermore, from the stochiometry of the reaction one can deduce the quantity

reactive compound by the amount of hydrocarbon present. Calibration of the latter is

straightforward. The presence of this internal standard is an added and extremely attractive feature. Finally, we note that this method has infinite dynamic range. In contrast, the concentration of static samples is always fixed.

2. Experimental

Front and top views (with instrument open) of the reactive gas generator can be found

in figures 1 and 2. Operation of the instrument involves flowing inert gas (N2, He', eta.)

at a pressure of about 1.5 atm and flow rate of 20-200 cm^/min past the diffusion cell

(where the parent molecule diffuses into the stream), through a buffer cell (to remove downstream pressure fluctuations) and into the pyrolyzer where the decomposition reaction

is carried out. The newly formed reactive gas is now ready for use.

^Figures in brackets indicate the literature references at the end of this paper.

397
Figure 1. Front view reactive gas generator.

398
Figure 2. Top view (with instrument open) reactive gas generator.

399
The relationship between the concentration [C] of reactive gases generated and the physical

parameters of the system is

c

= I:

1" ^P^^

where D = diffusion coefficient, A = diffusion tube cross-section, L = diffusion tube

length, P = pressure in diffusion cell, Q = flow rate of carrier gas and = partial

pressure of diffusing vapor. The reactive gas concentration can be changed by

suitable adjustments on the physical parameters of the system. As a practical matter

these are the flow rate, diffusion tube area and temperature. The latter arises from the

exponential dependence of the vapor pressure on temperature and since we usually operate

in the range P >> P^ this is directly reflected in the concentration. In addition there

is also a -x. 3/2 th power dependence of the diffusion coefficient on temperature. Overall

this means that temperature is probably the most important variable with respect to the

proper operation of the system. The diffusion cell temperature is thus controlled to

better than ± .1 K. The working temperature range of the instrument is between ambient

and 200°C. For most of the substances that we have tested this means a dynamic range of

about two orders of magnitude. Note that since the flow rate and temperature can be

externally set, reactive gas concentration can be "dialed." It should be noted that since

the mass thru-put (ijg/min) is independent of flow-rate for most applications, the temperature is a more useful variable.

The compounds of choice for the present application are those which decompose unimolecularly into molecular fragments and which do not have significant side reactions.

The avoidance of surface or chain induced decomposition processes is of prime importance.

These processes are frequently i rreproduci bl e and thus completely unsuitable for the

present purposes. This is the reason for the use of the gold reactor. An excellent

source for possible "parent" molecules is the review by Benson and O'Neal [3]. A more

thorough discussion of the factors to be considered in the choice of compounds can be

found in an earlier paper [4]. The unimolecular nature of these reactions dictate that

the extent of conversion is dependent only on the reaction time (t), temperature (T) and

the thermal stability of the appropriate compound. The relation is

In C./C^ = t A exp (-E/RT) (2)

where A and E are Arrhenius parameters for unimolecular decomposition reaction [3] and

characteristic of the compound of interest and C-j and Cf are the initial and final con- centrations. In the present context interest is focussed in the region of high conversions or where C^-/Cf is greater than 50. Thus, C is very close to the concentration of

reactive gas. Under these conditions the concentr''ation of products is relatively insensitive to changes in reaction variables. Thus these variables need not be strictly

controlled and the operational procedure to locate the minimum necessary temperature is to

increase the pyrolysis temperature until the product yield reaches a maximum and/or when

the parent molecule disappears.

400
3. Results

The experimental results will be presented in terms of the particular reactive

molecule that is generated;

A) HCN: The parent compound for hydrogen cyanide generation is ethyl cyanoformate

.

The decomposition reaction is

C2H5OCOCN ^ C2H4 + HCN + CO2

Gas chromatographic analysis with a Poropak P-S^ column and flame ionization detection

yielded over the entire range (a factor of 30) an ethylene to hydrogen cyanide area ratio

of 6.29 + .09. Although the constancy of the area ratio is suggestive, the lack of any

literature values on the relative sensitivity of flame ionization detections of hydrogen

cyanide to hydrocarbons prevents the use of this number to establish the stochiometry of

the reaction. Accordingly, absolute determinations of HCN concentration have been carried

out by collecting HCN in NaOH solution and measuring CN" concentration using a specific

ion electrode. This is compared with the concentration of ethylene as determined by gas

chromatography. Over the entire range one to one production of ethylene and HCN is

achieved thus confirming the postulated stochiometry. Maximum thru-put (100 percent

conversion) in terms of HCN output/min as a function of cell temperature (30-95°C and

8.8 psig) obeys the following relationship.

Logio[yg HCN/min] = -2316 ± 29 [ ^ ] + 8.24 ± .09 (3)

This covers a thru-put range of 4-100 ug/min and the standards deviation or "settabi 1 i ty" over this range is 4 percent. The use of the internal standard will improve the accuracy

to ± 1 . 5 percent. For flow rates of 20-200 cm^/min (He) the temperature range of the

pyrolyzer is 600-680°C. Continuous operation of the generator for 168 hours indicate that

the maximum concentration variation is less than 3 percent.

^Certain commercial materials and equipment are identified in this paper in order to specify adequately the experimental procedure.- In no case does such identification imply

recommendation or endorsement by the National Bureau of Standards, nor does it imply that

the material or equipment is necessarily the best available for the purpose.

401
B) $02 : The parent compound for sulfur dioxide generation is trimethyl ene sulfone.

The decomposition reaction is

(CH2)3S02 cyclo-CjH^ + SOj

propyl ene

In an earlier report Cornell and Tsang [5J, using an evaporative method [2] have demonstrated the utility of trimethylene sulfone as a source for SO2. In particular, they show

that in the range covered (10-100 ppm and 20-40 cm^/min, flow rate) equivalent amounts of

C3 hydrocarbons and sulfur dioxide are produced. The present results will demonstrate

that this compound is compatible with the new generator. Indeed, it is shown that the use of the diffusion technique offers a considerable increase in flexibility so that the range

covered can easily be extended.

All of the present results have been obtained with a diffusion cell head containing a column with a 1/4 in. diameter. This is in contrast to the 1/8 in. diameter columns used

for the other compounds. Gas chromatography with a Poropak T column and helium ionization

detection is used for analysis. Because of an interfering water peak, which eluted on the tail of the SO2 peak, the Poropak T column was preceeded by a methyl silicone column.

Quantitation of the experimental results is based on bottled samples of propylene (206 ppm,

measured) and sulfur dioxide (1000 ppm, stated). It is assumed that in the range covered

the detector is linear. Over the entire thru-put range (a factor of 100) the ratio of

hydrocarbon to SO2 yield is 1.024 ± .04. Together with the earlier results this is a satisfactory demonstration of the postulated stochiometry. The larger than usual un- certainty is actually an artifact that arose from the existence of a small water impurity

which impinged on the tail of the sulfur dioxide peak. This is especially important at

low thru-put. Thus there is an actual drift in the measured concentration ratio ranging

from .97 at thru-put of 100 yg/min to 1.09 at the 1 ug/min level. It is suspected that

the former number is more likely to be the correct one and that had it been possible to correct for the water peaks a lower uncertainty limit would have been obtained. We have

also attempted to measure sulfur dioxide concentration using a sulfur dioxide specific ion

electrode following the prescription given by Orion Research. Unfortunately, the results

showed wide scatter (± 50 percent) and have not been used. Maximum thru-put (100 percent

conversion) in terms of SO2 output/min as a function of temperature obeys the following

least squares relationship.

LogiQEygS02/min] = -3145 ±41 E y ] + 9.16 ± .1 [4)

The standard deviation is ± 5 percent. These data cover a thru-put range of 1 to 100 ug/min

and extend over the temperature range of 70-170°C. The generator is operated at 1.5 atm.

Over a period of 168 hours of continuous operation the variation in concentration is less

than 3 percent. For flow rates of 20-200 cm^/min the pyrolyzer temperature should range

from 600-660°C.

402
C) HC1 : The parent compound for HCl generation is cyclohexyl chloride. The decomposition reaction is

CeH^iCl ^ CeHio + HCl

In the temperature range where these pyrolytic studies are carried out the conversion to

ethylene and butadiene is less than 10 percent. Verification of the postulated stochiometry

has been carried out using gas chromatography with a Porapak P-S column and flame ionization detection for the hydrocarbon and a CI" specific ion electrode for the quantitation

of HCl yields. The ratio of cyclohexene (including the small quantity converted to ethylene and butadiene) to HCl is (1.007 ± .03) to 1 and covers a concentration range of a factor of 25. Maximum thru-put in terms of HCl output per minute as a function of cell

temperature follows the least squares relationship.

LogioLug HCl/min] = -2239 ± 32 [ y ] + 7.81 ± .09 (5)

The generator pressure is at 10 psig and the temperatures 30-90°C. In this temperature

range the thru-put covers from 2 to 50 ug/niin. The standard deviation is 4 percent. With

flow rates in the 20-200 cm^/min (He) range the pyrolyzer temperature must be set between

580-650°C. Continuous generation over a period of 168 hours show concentration variation

of less than 3 percent.

This work is supported in part by the Office of Air and Water Measurement and the

Center for Fire Research of the National Bureau of Standards.

References

[1] Tsang, W. and Walker, J. A., Anal. Chem. , in press.

[2] Nelson, G. 0., Controlled Test Atmospheres, Principles and Techniques

(Ann Arbor Science Publishers, Ann Arbor, Michigan, 1971).

[3] Benson, S. W. , and O'Neal, H. E., Kinetic Data on Gas Phase Unimolecular

Reactions, Nat. Stand. Ref. Data Series, Nat. Bur. of Stds. US, 2]_,

545 pages (Feb. 1970).

[4] Tsang, W. , Journal of Research of the National Bureau of Standards,

Vol. 78A, 157 (1974).

[5] Cornell, D., and Tsang, W. , Anal. Chem., 46,933, 1974.

403

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

SEMICONDUCTOR GAS SENSOR EQUATIONS FOR PREDICTING PERFORMANCE CHARACTERISTICS

S. M. Toy

Interscience Laboratory

Palo Alto, California 94086, USA

1. Introduction

Three semiconductor gas sensor equations have been derived so far to characterize and

predict the Taguchi, TGS, type gas sensor performance characteristics [1 ,2,3,4, 5]^

.

2, Experimental and Results

The first equation relates the gas sensor resistance to gas concentration and is given

in the form

R = R.C" (1)

where

R is the semiconductor resistance in K ohm,

R| is a constant, K ohm

L is gas concentration in parts per million (ppm)

n is the straight line slope of a log-log plot.

The equation parameters found for CO, hydrogen, methanol, and CO in 100 percent relative humidity (100 RH) are listed in Table 1 and are valid under the test conditions

investigated and where a linear relationship is found (see figure 1).

Table 1

TGS semiconductor sensor equation parameters

R = R.C"

Gas sample Ri (K ohm) n eq n exp

CO dry 182.4 -0 98 -0 98

CO T00% RH 561 .0 -0 98 -0 955

Hydrogen 164.2 -0 98 -0 98

Methanol 141 .4 -0 98 -0 98

Concentration, C (ppm)

20 to 200

10 to 200

50 to 100

20 to 100

Figures in brackets indicate literature references at the end of this paper.

405
genus S91 «osi\i3s sv9 aoj'iv/(oo2) iv 'oiiva iN3aan3

Figure 1. Current ratio, Al(200)/Al vs dry CO concentration.

A comparison between the semiconductor equation values (R eq.) and the experimental

test data (R exp.) are listed in Table 2. For CO in 100 percent RH air (low emission air),

there is good agreement between results. The experimental resistance, R, was determined by

an approximate expression provided by the vendor as Vm = 0.7 R adj t R where Vm is the

measured voltage reading taken across a variable resistance, R adj, adjusted to an appropriate value {i.e., 300 ohm) and R is the calculated semiconductor sensor's resistance. An

alternate means to measure R was to measure the sensor's DC current and voltage.

406
Table 2

Comparison between semiconductor sensor equation values and experimental val ues for CO in 100% rh in J- Ui the range lu to zuu ppm

concentration (ppm) K eq (K ohm) K exp ohm) D / D r\e~t K/K?nn eq r^/Kp-OO exp

10 CO n

00. U da c Db . D 17 C

1 / . b

1 P Q 1 c> . y 15 iv . b OQ Q OO . O 10 7 1 R 7 ID./

22 07 O cl .i. OQ 0 Q Q O . O 1 1 Q 1 1 . y 30 on c\ D . 1 Q Q

42 14.3 15.0 4.6 0 . 1 45 13.4 15.0 4.2 5.7

54 11.2 12.4 3.6 5.0

60 10.1 8.4 3.6 3.4

200 3.1 2.5 1.0 1.0

Standard gas mixtures were prepared in 19.9 liter glass bottles (distilled water

bottles). Sensors were inserted into bottles. A few flow tests were run at 1 SCFH

(standard cubic feet per hour).

By a reiteration process, the R values were obtainable with an n = -0.98 and Ri = 561

which allows one to study the various gas effects on this semiconductor gas sensor in terms

of one common equation given as

i= x

R = ^

Ri (la)

i=l

where Rj + R2...Rx ai^e the constants found for the individual gases investigated under the

test conditions reported.

This general equation therefore allows one to predict the semiconductor sensor's

performance in both single or mixed gases by examining the equation parameters with a suitable computer program. This program will provide a better technical basis for selecting,

evaluating and specifying these type gas sensors for many safety applications.

The second equation relates gas sensor resistance to gas inlet temperature and is

found to be

^ = -R2 C 2n (dv/dT) (2)

where

dR/dT is the change in sensor's resistance, dR, with a change in gas inlet temperature,

dT,

Ri is a constant K ohms for the ith gas,

C is the gas concentration in ppm, and

dV/dT=a is the gas inlet temperature coefficient in volts per degree.

It has its origin by differentiating with respect to temperature T, an approximate

experimental equation relating the gas sensor's resistance to voltage [1,2].

By substituting the required CO gas sensor's parameters for humid (100 percent RH)

air, the equation reduces to the following expression:

407
R = -(561)2C "1-96 (.16 X 10"3) (T2 Ti) (2a)

where

R is

a=dV/dT is

T2 is

the gas sensor's resistance in K ohms,

0.16 X 10"^ volts per degree (average value), and

the change in gas inlet temperature from a selected reference gas inlet

temperature .

Next, assume

AT = 24°C = (T2 Tj) (2b)

then

AR = 50.35 (24)0-1-96

= -1206.5

Now

log C* = [log (R/Ri) v -0.98] without gas inlet temperature compensation. (2c)

So

log C* = log [(R + AR)/Ri i 0.98].

To obtain C*, the concentration, ppm, with the gas inlet temperature effect incl uded solve

for C*.

The gas inlet temperature error introduced to the sensor's readings as predicted by

this equation is in good agreement with the experimental test data. See figure 2. It also

is in agreement with the reports in the literature that the gas inlet temperature affect is

small at the high CO concentration ranges [i.e., 200 ppm CO).

By plotting the predicted CO concentration error in ppm versus normal gas sensor concentration reading in ppm, one observes that the ppm error remains constant at 2.5 ppm

beyond about 15 ppm and a peak error occurs at 4 ppm at about 5 ppm. See figure 3 and

The results provide an explanation for the reported negligible gas inlet temperature

error reported at the higher CO concentration ranges, i.e.^ 200 ppm. For example, at 1000

ppm the gas inlet temperature error is 2.5/1000 or 0.25 percent error.

However, at the lower CO concentration i.e.^ 10 ppm, the percent error is 28 percent.

See figure 4 and Table 4.

Table 3.

408
10 20 30 40

CO METER READING. MV

50

gure 2. Percent gas inlet temperature error vs CO concentration.

409
1

(li-3i)=aofr3=l7 UOd lAJdri

'3 'N0liVUiN33N03 03 Nl QB13IQBHd

Figure 3. Gas inlet temperature error effect on TGS sensor CO reading in ppm.

410
Figure 4. Percent gas inlet temperature vs CO concentration.

411
Table 3

Calculated gas inlet temperature effects on TGS type sensor reading:

Humid CO (100% RH and AT = 24°C

aR = _1 ?nfi t; r"l • 95 (R + AR)

C ( nnm

i

In UiIUI IN U 1 INI K ohm Log C* L ippm;

c? uO*-T . H -1 ?

1 /I n 0

. <1 D 1 4

i; 1 1 S ft /I

. 4

n c n Q 1

1 u Rft 7 - 110.^ ^ ? 4b,. b 1 . 1 1 1 ^ . o

Or? . 3 - 0 . y / 0 o 00 . b 1 . (lb 1 / . o "I.JO 18 /I "7 .4/ 1 . 51 Oc . 0

1 3 . U -u . o/ 14 .1 1 . 63 . D

- U . OD 11 .5 1 . 72 Oc . D 60 10.1 -0.36 9 .73 1 . 796 62.6

70 8.7 -0.29 8 .41 1 . 86 72.4

80 7.6 -0.22 7 .38 1 . 92 83.2

90 6.8 -0.178 6 .6 1 . 97 93.3

100 6.2 -0.145 6 .0 2. 01 102.3

200 3.1 -0.037 3 .05 2. 31 203.7

300 2.1 -0.016 2,.08 2. 48 302.0

^log C* = [log (R + aR)/561 v (-0.98)]

Table 4

Calculated gas inlet temperature error effects on TGS type sensor readings

in ppm and percent error

C (ppm) aC(C* - C) (ppm) Percent error

2 2,,1 105,,0 5 4,,1 82,.0 10 2,,8 28,.0 15 2,.8 18,,7

30 2,.3 7,,7

40 2..6 6,,5

50 2.,5 5,,0

60 2,,6 4,,3

70 2..4 3,,4

80 3..2 4,,0

90 3,,3 3,,7

100 2,.3 2,.3 200 3.,7 1

,

,8

300 2..0 1

.

,0

The third equation relates the gas sensor heater voltage to the sensor resistance and

is expressed as

V = RgR" (3)

where

R = semiconductor resistance, K ohms,

V = applied voltage across semiconductor sensor, volt (equivalent to heater voltage).

412
R = individual sensor constant,

e

n

= the straight line slope on a log-log plot.

Three individual semiconductor sensor's resistance vs. voltage were tested in humidi

fied air and the test data revealed the above mentioned relationship. The individual sensor constants were determined and n was found to be - 0.15. See figure 5 for details.

rrr

ci

II GC

03

cc

03 CC

II

I r

CO

o

iM I I I I—

r

CO

O

II II CC

03 CC

OO OS O CO

in

in

ai

CCo

CO

CO

un r-^ CM CO

CO

^

^ =tt -tt ^

X • O <]

I I I I I I I L I I I I I I L

o

<

a

LU

o iZ

2 5

CC

LU

CJ

<

o »—

»— CO

CO

UJ

CC

CC

o

CO

LU

CO

SnOA 'A '39VnOA a3iV3H

Figure 5. Heater voltage vs. sensor resistance in humidified air

413
3. Conclusion

In summary, the results indicate that the three equations derived can provide a satisfactory means for developing criteria for testing, recommending standards and providing direction for improving semiconductor, TGS, type gas sensors to be used in portable

gas detectors. They can meet NIOSH present toxic threshold limit values and have potential

to reach lower limits.

The new generation of TGS solid state gas sensors indicates potential for providing

better low cost portable gas detectors for use by both compliance officers and industrial

hygienist to meet NIOSH requirements.

References

[1] N. Taguahi Gas Detecting Deviae^ U, S. Patent 3,695,848 (Filed on April 7, 1970

Ser. No. 26, 228, Kobe, Japan).

[2] Newly Developed Figaro Gas Sensors No. 711 and No. 812, Figaro Report, Figaro Engineering, Inc., Toyonnaka City, Asaka, Japan.

[3] Parker, C. D., Strong, R. B., Evaluation of Portable Direct-Reading Carbon Monoxide

Meters, HEW Publication No. (NIOSH) 75-106, Cincinnati, Ohio, September 1974.

[4] Toy, S. M., i4 Semiconductor Gas Equation for Taguchi Type Gas Sensor, TGS, Technical

Report for Gas Tech., Inc. Mountain View, California, August 1975.

[5] Toy, S. V[. , An Expression Related Gas Sensor's Resistance Relationship To Gas Inlet

Temperature, Technical Report of Gas Tech,, Inc., Mountain View, California, September

3, 1975.

414
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

MONITORING NON-METHANE HYDROCARBONS IN THE ATMOSPHERE BY PHOTOIONIZATIOM

J. N. Driscoll

HNU Systems, Inc.

383 Elliot Street

Newton, Massachusetts 02164, USA

A new continuous analyzer has been developed which employs the principle of photoionization for detection. The sensor consists of a sealed ultra-violet source adjacent to an ionization chamber. The instrument has a sensitivity of 2 ppm full scale, a 90 percent

response time of less than 3 seconds, is independent of sample flow rate, and has a repeatability of better than ±1 percent. Both zero and span drift were <1 percent over a twoweek period. The photoionization technique is a carbon counter in the same manner as flame

ionization. Relative sensitivities for the unsaturated hydrocarbons are surprisingly

similar for both techniques. A major difference, however, is the lack of response of the

photoionization technique to methane. This effect allows the direct measurement (by

photoionization) of non-methane hydrocarbons in the atmosphere without the requirement for

a chromatograph. As a result, the instrumentation is considerably less complex than a gas chromatography/fl ame ionization detector (GC/FID) and the reading is continuous rather

than every five minutes. The photoionization monitor was compared to a GC/FID (Bendix

8201) and the preliminary data are shown in figure 1. The agreement between the two techniques is quite good with a correlation coefficient (r^) of 0.93 and a regression equation

equal to PI = 0.059 + 1.36 GC/FID. Some preliminary data obtained over a two-month period

in the Newton, Massachusetts, area indicated an average non-methane hydrocarbon value of

0.19 ppm with excursion of 1 ppm when the wind was blowing from the highway. Some typical

data are shown in figure 2.

415
f Ol

0) <0 N 0>

416
E

417

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

A STUDY OF VERTICAL DIFFUSION IN THE ATMOSPHERE

USING AIRBORNE GAS-CHROMATOGRAPHY AND NUMERICAL MODELLING

R. S. Crabbe

National Aeronautical Establishment

Ottawa, Canada

1. Introduction

Air pollution studies have become a practical matter since passage in 1967 of the

U.S. Federal Clean Air Act, e.g. the meteorology program of the EPA [6]^. Many of the

familiar pollutant sources are located near the ground and emit contaminants more or less

continuously throughout the daylight hours. In these cases, the mean crosswind distribution of diffusing material in the plume has been observed to be Gaussian at mesoscale

distances [8]. The mean vertical concentration distribution is less accessible to the

ground observer and measurements are scarce. In many cases it is assumed to be Gaussian

as well (the so-called Gaussian plume model).

The adoption of a Gaussian profile for the vertical concentration distribution is,

however, suspect and has recently been invalidated by the studies of Lamb, Chen and

Seinfeld [7]. The problem is that the vertical eddy diffusivity is not constant with

height but rather increases owing to the characteristic scaling of the vertical turbulence

scales with distance above ground. Lamb and his co-workers have demonstrated that gradienttransfer theory, which models this height behavior, gives a prediction of the mean concentration field downwind of a steady source in the atmospheric boundary layer which is in

much closer agreement with their detailed Lagrangian prediction than the Gaussian plume

model. It therefore becomes an attractive method of predicting vertical diffusion in the

atmosphere over mesoscale distances.

In this paper, the predictions of this hypothesis are compared to measurements in a tracer-gas plume of an aircraft-mounted Gas Chromatograph (G.C.) incorporating a short

pre-column or adsorber as described in Elias [4]. Crosswind sampling was performed to measure the mean crosswind-integrated concentration profiles which are predicted by the

two-dimensional di ffusion-advection equation of gradient-transfer theory. Good agreement

is demonstrated between measurement and theory. On the other hand, the Gaussian plume

model fails to predict the data, thus supporting the conclusions of Lamb and his coin gradient-transfer theory, the upward flux of material down the mean crosswindintegrated concentration gradient, 3x/3z, is equal to -K(z)3x/8z where K(z) is the vertical

eddy diffusivity. The conservation of a passive scalar contaminant is then expressed by:

workers.

2. Gradient-Transfer Calculations

8x/8t + U(z)9x/3z 1^ [K(z)3x/3Z]

3x/3Z 0 at z = 0, zi

x(o,z) = Q6(z - zsRc)/U(zsRc) (1)

Figures in brackets indicate the literature references at the end of this paper.

419
where U(z) is the mean wind speed and Q is the strength of the source located at a height

ZSRC- X is measured downwind and z vertically. Unidirectional wind with height is assumed

here, appropriate to convective daytime conditions. Equation 1 is valid for vapors and

for particulates whose terminal velocity is less than '\^0.03w2^, where w is the fluctuating

vertical wind speed [2,3], if turbulent deposition is neglected, z-j denotes the height of

the inversion base.

The profiles of vertical eddy diffusivity and mean wind speed in eq. 1 are modelled by:

Zq^z^zh K(z) = (u^Zi/15)tanh(15kz/Zi){1.35(z/zN)"+a/^[l(z/z^)"]}

Zj^^z^z. : K(z) = K(z^) exp [-a(z-Z|^) (z . - Zj^)]

z^^$Zv<2zj^/3 : kU(z)/u^ - l(|VLl dz

'

z>2z /3 • kU(z)/u = rz° dz ^^dz'

1^ In these expressions, u^ is the friction velocity, =(-uw)q, u being the wind-speed fluctuation

along x and 'o' denoting conditions at "ground level". ^Z|\j, <z-j, is the height above

ground where the vertical potential -temperature flux, w0, goes through zero, a and (j) are empirical functions of the atmospheric stability parameter, z/L, given in Businger et at.

[1] where L is the Monin-Obukhov length. a(>0) is such as to preserve continuity of 9K/3z

at zi^. k. = 0.35, is Von Karman's constant, n, = 0.15, is an empirical constant and Zq is

the surface roughness length, f is the Coriolis parameter, g is gravity, and 8T/3y is the

lateral ambient temperature gradient. Eqs. 2 to 4 apply to a convecti vely-unstable mixing

layer capped by an inversion lid at z-j and containing a region from z^ to z-j where we is

increasingly negative. Their derivation is given in Crabbe [2].

3. Experimental Procedure

The three tracer-gas experiments described in this report were flown in the fall of

1975 during midday periods when approximately stationary meteorological conditions existed.

Gaseous sulfur hexafluoride (SFg) was released from a height of 1.5 m at the upwind end of

the test range (fig. 1 ) at a rate of from 1-3 gs"i depending upon the mean wind speed and

distance to the sampling station(s). The range consists of open fields and scattered wood

lots with an assumed value of 0.3 m for Zq. The elevation varies from 3 to 400 ft MSL in

the interior to between 2 and 300 ft in the river valleys. Table 1 summarizes the

experiments

.

420
421
Table 1

Sampling schedule in tracer-gas experiments

Sampling Altitude No.

Date Stn AGL Passes Meteorological Conditions

Clear variable scattered, 25 m wind from 260° mag. at 4.0 ms-^.

Estimated values of L and u^,

-15m and .45 ms"^

.

Stable layer from 360 m to base

of inversion at 790 m (g/fT)

9T/9y = -(3.7 X 10-3 s-i)

Scattered variable broken, 25-m

wind from 015° mag. at 2.2 ms'^.

Estimated values of L and u*,

-7 m and .29 ms'^.

Cloud based at 720 m, stable

layer above. (g/fT) 3T/3y - 0.

Clear, 25-m wind from 315° mag.

at 6.6 ms-i

.

Computed values of L and u^,

-520 m and .59 ms"^, using T-33

turbulence data.

Stable layer from 900 m to base

of inversion at 1400 m. (g/fT)

8T/3y = -(0.0030 + 2.6 x 10-6z s-i)

Clear variable scattered, 33 m wind from 310° mag. at 3.0 ms"^.

Computed values of L and u^,

-30 m and .32 ms"^, using T-33

turbulence data.

Unstable from ground to base of

inversion at 700 m. -(g/f)

3T/9y = 4.5 X 10-3s-i

(1) 7.10.,75 30 Km 30 m 2

150 m 4

530 m 5

(2) 17.10.,75 30 Km 350 m 5

540 m 5

740 m 5

(3) 5.11

.

,75 30 Km 90 m 2

550 m 4

1250 m 4

100 Km 1280 m 2

(4) 15.12,, /b 30 Km 90 m 2

290 m 2

510 m 2

540 m 2 610 m 2

730 m 2 100 Km 280 m 1

The NAE Twin-Otter sampling aircraft flew 18-km tracks at the 30-km station and 60-km

tracks at the 100-km station centered on the mean wind direction. The number of crosswind

sampling passes listed in table 1 was calculated by the method of Crabbe [2] to yield x to

within about 15 percent. In exp. 2, the source failed as sampling began so the timedependent form of eq. 1 was used to predict the .measurements. In exp. 3, turbulencemeasuring flights were flown over the test range in the NAE-instrumented T-33 aircraft.

From these data, values of K(z) = 0.41 a^/e, where ow is the standard deviation of w and e is the dissipation rate of turbulent kinetic energy [9], were calculated for comparison to

the prediction of eq. 2. Tabulated values of u,^, L and Zf^ were also calculated from these

data.

422
In the other two experiments, L was estimated according to the stability-category

method of Pasquill [8] and was then calculated from eq. 4 using the measured 25-m wind

speed. Zf^, in these cases, was approximated by the height where the potential -temperature

gradient, 3h/3z, changed sign from negative to positive in the Twin-Otter-measured temperature profile, which also gave the values of z-j in all cases. The lateral temperature

gradient appearing in eq. 4 was approximated by a polynomial fit to values of 3T/3y

measured by the Twin-Otter aircraft during its crosswind sampling flights.

The profiles of temperature, wind speed and, in the case of exp. 3, eddy diffusivity,

which were measured during the three experiments are plotted in figures 2 to 7. The

modelling of both the K(z) and U(z) profiles, eqs. 2-4, is seen to be adequate, especially

since the Maniwaki upper-wind soundings were not made during the experiments but rather in

early morning and evening.

x: K

u

+J

+JO

a,X

w

H

M-l0

>-l

<D P

(Cu

<ue

-p

Iu

•HP

nS -P

•H

in o ino

(IDV-WM) spnt^T^TV

423
S-l 0) +J-po

uo

u

•H

-P IT) 03 -P

U)

U-i 1 o 0 CN

CNl H

0)

J-l dJ

0) -P > -Po

0)

c

iH

-p EH H

+JrH 0)

nJ !h 1

(1) -P -P fC 0) S-i

>-l 0) u

cn

e

•HQ -P X

Ehg

-H

rHO0

+J

(0

^1Im

(0

in

LnI

424
0)

S-l ;3 -P

ra

s-l CDe

-P

(T3 H

-PC

(D -Poc

tou

-p

-p

COw

(UCn

fO

0)

O > o

rH

0) I O

:3 •=}• P CN

^1

0) -p

•p

0)

o

u

c

•H

u

tn -HQX

LDO

CMO

inI

CM CN

ino

425
426
427
428
4. Comparison of Theory to Measurement

Calculated values of x(x>z) from eq. 1 are compared to airborne G.C. measurements in

figures 8 to 10. For exp. 3, both the prediction using the modelled eddy diffusivity, eq. 2 and that using the polynomial fit to the T-33 values of K(z) are plotted. For the latter,

the inversion base was placed at the height where K = 0, which was slightly greater than

the preferred value of z-\ based on the measured temperature profile (fig. 4). Also shown

are the predictions of the Gaussian plume model in exps. 1 and 3. Those denoted "groundbased observation" were calculated from the expression x

= i^2/tt (Q/Uoz) exp (-z2/2a|)

using the 10-m wind speed with 02 taken from the Pasquill-Gifford graph [5J. Those

denoted as "fitted" used a value of calculated from the above expression using the

measured surface value of x and the vertically-averaged wind speed (6 and 11 ms"',

respectively, in exps. 1 and 3).

429
CM

I _1

rr( U

'n

4J

<Un

»*-« jj•H

M

*-] "n

UJ

r-t

i-J p

(11 n -r-l v*

+-'1 1 i_i M j 1 n, n3 M

<D >i OJ -p

M-l 4-> iH CO -H

r* S M-l 'H _^J

'U o,

1 M-l

1 i ii 1 r-*

>-i fO u

0) xi •H •H I CO o

1 :3 u

03 <

3.

LD

(IDV-WH) 3pn:^T:nv

430
431
1 1—1 0) 1 >

13 U o 3 C OJ H to 3 03 -P (0 0 X!

OJ q; S-i O

u e Cn to o 1 13 C

(U u E 0) O

x: 0 to -H

-p M rd 4-) 4-1 XI m

CnC c ^ • •H •H

U5 .-H 3 3 1 to >i OJ >i <U e E e e

(-1 i-H U M >^ M

0 -H 0 -H o m o

0) 4-1 0) 4-1 m o • £1 0 0 ro o^ in LD P +J u 4-) II II . Cu Cu 4-1 4J P D

S-l rd 0) >i <U

4-1 4-J 4-1 4-) rH m rd in -H •H 4-) 4-1 C > c > 4-4 (d rd

rd -H O 13 13 • u m u

-P 3 Cu • •

1 4-4 1 4-1 U • -P 4-1 4-1 4-1 c • • C -H C -H o o

<D 13 (U 13 •H

•H 1 •H 1 CO 1 1 13 >l 13 >i

n} 13 rd 13 3 u u

i-i 13 O 0) < <

I

(IDV-WX) ^pn::^T::^xv

432
Overall, it is evident that the present gradient-transfer model yields a prediction

of the G.C. data very much superior to that of the Gaussian plume model, even when fitted

values of and vertically-averaged mean-wind speeds are used. Since neither would, in

general, be accessible to the ground observer, the apparent success of the fitted Gaussian

profile is misleading. The success of the gradient-transfer hypothesis is a result of its

incorporating the height dependence of K(z) which is lacking in the Gaussian plume model.

In this context, the success of both the A/C-measured and theoretical K-profiles in

predicting the G.C. data suggest the present diffusion model is adequate for mesoscale

dispersion.

5. Conclusion

A study of vertical diffusion in the atmosphere using airborne G.C. and numerical

modelling has been described. In the tracer-gas experiments reported here, the prediction

of gradient transfer theory are superior to those of the Gaussian plume model, in agreement

with the conclusion of Lamb, Chen and Seinfeld [7]. The overall agreement suggests that

quite economical computer predictions are possible for vertical diffusion over mesoscale

distances by using a simple but physically plausible modification to surface-layer similarity values of K(z) to account for the presence of an overlying stable layer. For example,

a typical calculation out to 200 km with the present model requires about 30 sees on the

IBM 360.

References

[1] Businger, J. A., et at. Flux Profile Relationships in the Atmospheric Surface Layer,

J. Aim. Sci., m, #2, (March 1971).

[2] Crabbe, R. S., Some Environmental Measurements of the Vertical Spread of Pollutants

from Low-level Sources, Natl. Research Council of Canada, LTR-UA-28, (April 1975),

and Examination of Gradient-transfer Theory for Vertical Diffusion over Mesoscale

Distances Using Instrumented Aircraft, Natl. Res. Council of Canada, LTR-UA-37,

(August 1976).

[3] Csanady, G. T., Diffusion of Heavy Particles in the Atmosphere, J. Atm. Sci., 20,

(1963). ~

[4] Elias, L., et at. On-site Measurement of Atmospheric Tracer Gases, Geophysioal Research

Letters, 2_, #1, (January 1976).

[5] Gifford, F. A., Use of Routine Meteorological Observations for Estimating Atmospheric

Dispersion, Nuclear Safety, 2, #4, 47-51, (June 1961).

[6] Hosier, C. R. , The meteorology Program of the Environmental Protection Agency, Bull.

Am. Meteor. Soc. , 56, #12, (December 1975).

[7] Lamb, R. G., Chen and Seinfeld, Numerico-empi rical Analyses of Atmospheric Diffusion

Theories, J. Atm. Sci., 32_, (1975).

[8] Pasquill, F., Atmospheric Diffusion, 2nd edition, (1974), (John Wiley & Sons) and

Atmospheric Diffusion, (1962) (Van Nostrand, N.Y.).

[9] Hanna, S. R., A Method of Estimating Vertical Eddy Transport in the Planetary Boundary

Layer Using Characteristics of the Vertical Velocity Spectrum, J. Atmos. Sci.,

25, 1026-1033, (November 1968).

433

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

IN-SITU QUANTITATION OF BACKGROUND HALOFLUOROCARBON LEVELS

L. Elias

National Aeronautical Establishment

Ottawa, Canada

1. Introduction

The technique described in this paper, originally developed for use with electrophil ic

tracer gases in atmospheric dispersion studies [1]^, has been adapted to the measurement of

halofluorocarbon levels in ambient air. One advantage of the in-situ determinations

obtained is that the method avoids the risk of the sample loss associated with other

storage and retrieval procedures and, more significantly, allows for on-the-spot checking

of interesting or unusual results that may arise. An integral part of the method is the

calibrations which are performed in the field during the course of the analyses.

2. Apparatus and Materials

A single column GC equipped with two 8-port gas sampling valves and an Ni-63 electron

capture detector is employed, shown schematically in figure 1. A metered volume of sample

air enters the GC through a 6 ft. x 1/16 in. o.d. stainless steel inlet tube and is drawn

through a short precolumn, or adsorber, located outside the oven. Flow rate through the

adsorber circuit is throttled to 60 cm^/min on the exit side of the air pump. The subsequent valving sequence allows for purging the adsorber with N2 , isolating and heating the

adsorber, and transferring the released vapors to the column via the N2(I) carrier stream.

The total time involved in an analysis is generally less than 10 minutes.

The adsorber used in this study is depicted in figure 2. It is a 3*2 in long x 1/4 in

o.d. Pyrex tube vertically mounted between two heavy-walled steel arms attached to the GC oven. Swagelok fittings welded on to the steel arms as shown permit ready changing of the

adsorber, which is connected by means of Vespel ferrules. An aluminum heating block,

grooved to accommodate the precolumn, and a similar cooling block are moved transversely on

a guide rail to heat and cool the adsorber, respectively, to 200°C and 0°C.

.

For use with SFg and CF2CI2 the adsorber was packed with 60/80 mesh charcoal, while

for CF2Br2, CFCI3 and CCI1+ Chromosorb 102 was suitable. For the work to date various

columns have proven adequate. Molecular Sieve 5A for SFg, Porapak Q for CF2CI2, Carbowax

400/Porasil C for the others. The columns were 1/4 in o.d. by about 3 ft. in length and

operated at 80°C.

^Figures in brackets indicate the literature references at the end of this paper.

435

The GC system was calibrated in two ways, depending on whether the calibration standard

was stored as a compressed gas or at normal pressure. When the standard was a compressed

gas, an auxiliary 6-port valve and sample loop installed in the N2(I) carrier line permitted

the injection of a known volume of the standard to enter the column, either via the adsorber

or bypassing the adsorber [1]. In the case of a calibrating mixture at ordinary pressure,

injections were made with a gas-tight syringe through a septum installed in the air inlet

line. For this purpose, the air drawn through the inlet during the calibration was filtered

through a charcoal scrubber to provide a clean air reference.

3. Preparation of Calibration Standards

Standard mixtures of 1 ppb (v/v) of the gaseous compounds in nitrogen were prepared in

Fisher Lecture-Spheres by a two-stage dilution procedure. In this procedure, a 6-port valve

fitted with a sample loop is used to transfer a known volume of the pure compound into the

first bottle by means of a N2 stream under about 10 psig pressure; the bottle (also of

known volume) is then pressurized to several hundred psig with N2 and subjected to a heat

lamp for 1 hour or more to promote mixing. A measured volume of the stock mixture (of the

order of 100 ppm in concentration) is similarly transferred to a second Lecture-Sphere,

which is then pressurized to about 1500 psig and also heated. Cross-checks between standards of differing concentrations prepared in this manner yielded analyses within 5 to 10

percent of the expected ratios in the cases of SFg, CF2CI2 and CF2Br2. Although mixtures

of SFg and CF2CI2 appeared to be stable with time, the integrity of no mixture was relied

upon one month after its preparation.

Standard mixtures of a few ppb of CFCl 3 and CCI1+, as well as CF2Br2 (all liquids at

20°C) were prepared by an alternative two-stage dilution procedure. The vessels in this case were 1 liter Pyrex volumetric flasks fitted with a septum and containing a quantity of

glass boiling beads to create turbulent mixing when shaken. The flasks were made by

cutting the necks just above the volume mark and sealing a short length of 1/4 in o.d. tube

onto each. A threaded sleeve, made from one-half of a 1/4 in Swagelok union was slipped

over the tube, the latter flared, and a septum held in place against it by the Swagelok

nut. The flasks were flushed with N2 by removing the septum and inserting a 1/15 in stainless steel purge line. The first stage dilution consisted of injecting 1 yl of the liquid

halocarbon into the N2-filled flask, shaking the flask to obtain thorough mixing, then

injecting an aliquot of the mixture by means of a 100 pi gas-tight syringe into the second

flask, again followed by mixing. The precision limits of the standards so prepared

appeared to be within the reproducibility of the analyses attained by syringe injections of

the standards, i.e., about 10 percent. The agreement between syringe samples of CF2Br2

standards prepared in the Lecture-Spheres and in the glass flasks was again within these

precision limits, corroborating the procedures employed. Standards prepared in the glass

flasks were kept no longer than two days.

4. Laboratory Testing

A simple internal check on establishing the overall cleanliness of the GC system and a prerequisite to successful air sampling was the test of "collecting" a few hundred cm^ of

N2(I) carrier. Such a test normally resulted in a completely flat baseline. On one occasion, however, the persistence of residual peaks was traced to a leaky GC valve and the

consequent diffusion of laboratory air into the adsorber.

The efficacy of the adsorber for use with a particular hal of 1 uorocarbon was tested by

comparing the peak areas derived from standard samples injected directly into the column

with those obtained from collection on the precolumn. It was also important to determine

the maximum volume of air which could be passed through the precolumn before a collected

vapor began to elute. This volume was determined by first collecting a standard sample on

the adsorber and then purging with purified air via the inlet probe for increasing times

until the analyzed peak was reduced in size appreciably. The adsorber packings mentioned

allowed a sample volume well in excess of 1000 cm^ to be processed. It is estimated that

the minimum detectable concentration for the above compounds is well below 1 part per

trillion.

437
5. Field Measurements

In addition to the SFg and CF2Br2 plume dispersion study reported on at this Symposium

[2], some initial results have been obtained on levels of CF2CI2, CFCI3 and CCI4 in the

Ottawa-Hull area, a 1

i ght-to-moderately industrialized region with a population of less

than 1/2 million. The results are summarized in table 1.

Table 1

Background levels near Ottawa

Compound Concentration, ppt Relative location

SFe 0.2 - 0.4 Above 1500 ft.

CF2Br2 < 1 Upwind, downwind

CF2CI2 150 ± 8 Upwind

CFCI3 85 Upwind, 10 miles

110 Downwind, 5 miles

104 Downwind, 13 miles

88 Downwind, 24 miles

CCli^ 122 ± 28 Upwind, downwind

The few measurements of CF2CI2 were made outside the laboratory in early spring of

this year under light NW winds.

The CFCI3 and CCI4 determinations were made in late summer with the GC mounted in the

laboratory van. Air sampling was carried out downwind of the capital region to a distance

of 50 miles or more and upwind to 10 miles of the outskirts. A total of 50 samples were analyzed over a period of 3 days; in one series, CF2Br2 was released at a rate of 7 Ib/h to serve as a tracer for the city plume. Winds were generally SW at 5 to 10 knots. In the case of CFCI3 a distinct trend was observable: within about 10 miles of the outskirts,

readings were as much as 25 percent larger downwind than those observed upwind, and

remained slightly higher to distances as far as 25 miles. The CCI1+ data, on the other

hand, showed no such trend, for the most part fluctuating randomly within about 10 percent

of the mean, but occasionally varying much more.

It may be possible from such data to estimate the contribution to the total halofluorocarbon burden from a particular locale. Work is continuing along these lines.

References

[1] Elias, L., McCooeye, M. , and Gardner, G., On-Site Measurement of Atmospheric Tracer

Gases, Geophysical Research Letters, 3_, (1), 17-20, January 1976.

[2] Crabbe, R. S., A Study of Vertical Diffusion in the Atmosphere Using Airborne GasChromatograph and Numerical Modeling, Presented at 8th Materials Research Symposium,

Gaithersburg, Maryland, (September 1976).

438
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

ORIGIN AND RESIDENCE TIMES OF ATMOSPHERIC POLLUTANTS: APPLICATION OF i^C

L. A. Currie and R. B. Murphy

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1, Introduction

As man's activities yield continually increasing rates of production of atmospheric

pollutants, it becomes imperative for us to improve our knowledge concerning their recycling

by nature. Two of the critical parameters in this process are: (a) residence times (or

the inverse, removal rates); and (b) the relative contributions of natural and anthropogenic

sources, both to current pollutant burdens and to regional pollution episodes. Residence

times are of concern because they are indicative of the time required to compensate for a transient increment in pollutant output. They relate also to the distributional breadth of

locally emitted pollutants. Exchange between the northern and southern hemispheres, for

example, must be taken into account if residence times are on the order of one year or more [26]^.

The relative production rates from man's activities as opposed to natural processes

provide basic input for the evaluation of the various potential control strategies. When

combined with data on transport, atmospheric reactions and natural sinks, such source data

permit one to effectively construct the overall cycle for a given chemical pollutant.

Unique information concerning the above parameters can sometimes be obtained through

isotopic measurements. Following a brief look of some pertinent applications of isotope

ratios and molecular tracers, we shall address ourselves to the problem of carbonaceous

pollutants. Experiments to discriminate among sources of such species, via i'+C/^^q ratio

measurements, will be discussed in the final section of the paper.

2. The Role of Tracers and Isotopes

Budgets of contaminating species may be estimated by compiling data for all known

natural and anthropogenic sources. The assumption of steady-state may be tested via a suitable record of measured concentrations along with a tabulation of all known removal

processes, including transport. The residence time may then be calculated from the steady

state concentration and the production rate [12]. The principal weakness of such an approach, of course, is the possible existence of unknown sources and sinks, which results

in spurious estimates for residence times and production rates. The search for additional

sinks to explain the relatively constant atmospheric concentration of carbon monoxide led

to the so called "CO sink anomaly", as new sources were instead discovered [20].

Molecular tracers, along with stable and radioactive isotopes, can often provide

critical information to supplement uncertain budget estimates which derive from production

inventories. Work in our laboratory has taken this latter route: the determination of

^Figures in brackets indicate the literature references at the end of this paper.

439
atmospheric transport parameters [15] was the goal of our measurements of ^^Ar [24]; the

elucidation of the relative contributions of man and nature to atmospheric hydrocarbons is

the goal of our present investigation [8].

The utility of molecular tracers lies chiefly in the quantitation of transport, uptake

and exchange, while isotopic measurements can provide data concerning pollutant sources. A

number of molecular species not normally occurring in nature and with relatively long

residence times in the environment (sulfur hexafl uoride, chlorofl uoromethanes , ^^CDt^) have

been successfully employed as tracers [7a]. Isotope ratios in the light elements (C,0,N)

can be useful both for geophysical source characterization and for the investigation of

sinks for pollutants involving (chemical) exchange.

Some recent work involving stable isotopes includes: (1) ^^N and ^^N for the identification of sources of atmospheric nitrogen compounds [18]; (2) gp^j 365 for the tracing

of atmospheric sulfur [19]; and (3) ^^C/^^C and ^^O/^^O for the assignment of sources of

carbon monoxide, as a function of both location and season [28]. The last study indicated

five major sources of carbon monoxide, all characterized by distinct isotopic compositions.

The application of radiocarbon (^^C) to the resolution of the relative magnitude of

the fossil fuel contribution to the carbon dioxide balance was first advanced by Suess [29].

The "Suess Effect, "which is visible as a perturbation in recent radiocarbon dates, has been

utilized by a number of investigators to assess the projected magnitude of the "Greenhouse

Effect" on the Earth's climate [4,9].

3. Carbonaceous Pollutants

Aside from carbon dioxide, the principal species of concern include CO, CHi+, gaseous

and particulate hydrocarbons, and the halocarbons (chlorofluorocarbons and carbon tetrachloride, in particular). Significant questions remain as to the nature of the sources and

sinks for all of these contaminants. Carbon monoxide, for example, has been assigned

residence times ranging from 0.1 year [30] based upon radiocarbon measurements [16] to 2.7

years from atmospheric budget considerations [22]. Similarly, the presumed major cycle for

carbon monoxide in the troposphere has changed at least three times since 1969. The

anthropogenic CO contribution is of some concern, as the annual production rate has increased by more than a factor of two between 1966 and 1974 [27]. Though this (anthropogenic) CO

had been believed to be the principal component, a recent compilation suggests that natural sources account for 90 percent of the total production [20]. Tropospheric methane, which

arises largely from natural processes, is of special interest because its oxidation is

currently believed to be the major source of CO, thereby linking the carbon and hydrogen

cycles in the atmosphere [10].

Sources and sinks for halocarbons and hydrocarbons continue to be evaluated in light

of the potential destruction of stratospheric ozone by the former [23], and the production

of urban and rural photochemical oxidants by the latter. As with CO the halocarbons were originally believed to be primarily anthropogenic, but recent assessments have suggested

the existence of very significant natural sources of carbon tetrachloride [1] and methyl

chloride [11]. Consequently, the fluorocarbon contribution to the total atmospheric

halocarbon balance may be as little as 25 percent [7].

On a worldwide scale, naturally-emitted "reactive" hydrocarbons exceed those produced

by man by more than a factor of six [20]. The abundance of these species together with

their large photochemical reaction rates with hydroxyl radicals [31] and the recurrence of

rural pollution episodes continue to raise questions regarding the relative importance of

vehicular us botanical emissions [21,17]. Progress in identifying sources contributing to

the insoluble organic fraction of atmospheric particulates has been made through the

application of high vacuum pyrolysis--gas chromatography [13].

Measurement of the ratio i^^C/^^C in selected samples of various atmospheric hydrocarbon

species should permit us to deduce the fractions in each case due to natural sources. The success of such an approach depends upon the assumption that anthropogenic carbon is

principally derived from fossil fuels, and can therefore be considered "dead" in comparison

with natural carbon, which arises primarily from recent biological activity. Previous

440
measurements of radiocarbon ratios have been carried out for atmospheric methane by Libby

[13a], Bishop [5], and Bainbridge [3], all cited in [10]. Tropospheric radiocarbon has

also been measured in CO by MacKay [16] and in particulates by Clayton [6] and Lodge [14].

The necessity for collecting large amounts of carbon added to the difficulty of such

measurements, and led to the possibility of non-representative sampling. Such problems may

be overcome with the use of our present system.

4. Collection and Measurement of Radiocarbon in Atmospheric Hydrocarbons

The many problems of sampling and counting discussed above are now avoided in the lowlevel radiocarbon measurement system at the National Bureau of Standards, which is unique

in several respects. First, we utilize very small gas proportional counters, which hold as little as 15 ml of fill gas, and require 10 mg of carbon or less. Figure 1 illustrates a typical small counter, constructed of high-purity quartz, with its associated high purity

copper shield. The counter background is currently about 0.15 count per minute (cpm), and its

dead volume is minimized by the use of a reentrant seal at the end to support the center wire.

The second distinctive feature of our system is the ability to discriminate not only

on the basis of pulse energy (pulse height analysis) but also by means of the pulse shape.

This permits us to distinguish between different classes of particles because of the

dependence of the relationship between pulse height and track length (pulse shape) on the

type of event. Pulse shape is assessed by sampling each counter event during the first 10

nanoseconds; integration and differentiation then yields a signal whose amplitude is inversely proportional to the rise time.

We have the capability of displaying two dimensional spectra from counting experiments,

with the pulse height defined on the x-axis and the pulse shape parameter on the y-axis.

Two such spectra are shown in figure 2, where the pulses corresponding to shortrange events in the counter lie in a narrow band at the 45-degree diagonal between the two

axes. Longer range discharges will generally lie below the diagonal with respect to the x- axis. Events above the 45 degree line may for the most part be ascribed to electrical

noise. Such noise is a serious problem, particularly in very small counters; it may arise

as a result of electrical field distortion at the ends of the counter wall. Pulse shape

discrimination is therefore extremely beneficial in such minicounter systems.

An additional advantage to the use of pulse shape spectroscopy lies in the ability to

separate contributions from certain contaminating radionuclides, such as or radon. These

nuclides often occur with the sample, the chemical reagents or apparatus or even in the

construction materials of the counter.

Regarding the choice of counting gas, we have found that while carbon dioxide may be

used in the minicounter its pulse shape characteristics are relatively poor, and it exhibits considerable sensitivity to trace chemical impurities. Performance appears to be

optimal when methane or methane-noble gas mixtures are used. The current approach is

therefore to reduce the CO2 formed from combustion to CHit, after purification. For this

purpose, we apply the procedure of Anand and Lai [2] with some minor variations.

The feasibility of measuring carbonaceous pollutants has been reviewed by one of

us [8] recently, where it was concluded that as little as 10 milligrams of carbon would be

adequate in our system for source discrimination. It was shown that all species of interest except the halocarbons could be collected in a reasonable sampling period with transportable apparatus, without having to rely upon air liquefaction plants or similar facilities.

This conclusion is based on typical concentrations in polluted air of 2 mg/m^ for the total

nonmethane hydrocarbons, 0.1 mg/m^ for total particulates, 20 mg/m^ for carbon monoxide, and

8 X 10"^ mg/m^ for carbon tetrachloride (the most abundant halocarbon).

441
Figure 1. Photograph of the small quartz counter (15 ml volume) and associated shield.

The shield, along with the inner wall of the counter, is constructed of OFHC copper.

442
Figure 2. Background Spectra: Pulse Shape vs Pulse Height. Fig. 2a shows a high gain

spectrum (most pulses at amplifier saturation, wi th short range events due to a small

amount of lying along the diagonal (dashed line).

443
Figure 2. Background Spectra: Pulse Shape vs Pulse Height. Fig. 2b, obtained with

15 ml counter at relatively low gain, shows isolated noise pulses lying above the

diagonal

.

444
For the collection of gaseous species of interest, we utilize a large stainless steel

trap which holds about 3 kilograms of NaX zeolite, grade 13A ("molecular sieve"); this trap

may be cooled to the temperature of dry ice (-78° C) conveniently in the field. Preceding

the NaX zeolite trap are similar ones containing CaA, NaA, and KA zeolites, respecti vely--al

1

similarly cooled. The entire system is evacuated to a. a. 1 x 10-^ torr and baked out at

200-250° C before use. The selectivity of the molecular sieves for hydrocarbons, CO, and

CHit over oxygen and nitrogen is such that enrichment factors up to 10^ to 10^ are projected.

A noncontaminating stainless steel bellows pump, electrically powered, is utilized to

draw air through the zeolite traps. The maximum flow rate of the system is 0.155 m^/minute,

thus enabling collection from 100-200 m^ of air in a reasonable amount of time. The collected

organic pollutants are desorbed from the zeolite by carefully controlled heating in a vacuum.

In a sense the sieve functions as a chromatographic column, and several fractions are removed

from the vacuum system during the course of the programmed heating cycle. Following GC/MS

identification of those species which are present, preparative gas chromatography is employed

to provide sufficient quantities of separated components for combustion and conversion to

counting gas.

The collection of atmospheric particulate matter will also take place; this is

especially valuable for the higher molecular weight hydrocarbons. In a preliminary measurement of a typical urban particulate sample we obtained an upper limit of 20 percent natural

(contemporary) carbon, in approximate agreement with the work of Clayton, et al. [6].

Also under investigation is the possibility of the collecting intermediate molecular

weight (Ci^-Ce) hydrocarbons from the atmosphere by means of rainwater. With a total organic

carbon concentration of rougly 12 milligrams/liter, little sample is required for a minicounter fill. For the study of individual species perhaps 10-20 liters would be desired.

The organic compounds of interest are removed simply by flushing the rainwater with ultrapure helium [25], followed by trapping with liquid nitrogen. The species of interest

are then further separated gas chromatographical ly and converted to counting gas as described above.

Preliminary data concerning the relative utility of the various methods of sampling

have been obtained from an experiment conducted during a pollution alert in Auaust 1976 at

the NBS atmospheric monitoring station in Gaithersburg, Maryland. We are currently com- mencing comparative studies in urban areas, represented by downtown Washington, DC, and

rural areas in West Virginia and Pennsylvania.

Thanks are due W. F. Libby and B. Weinstock for helpful discussions, and G. Ritter for

programming assistance in the preparation of figure 2. Partial support by the Office of

Air and Water Measurement of the National Bureau of Standards is gratefully acknowledged.

References

[1] Altshuller, A. P., Average Tropospheric Concentration of Carbon Tetrachloride Based on Industrial Production, Usage, and Emissions, Environ. Sai. and Tech. 596 (1976).

[2] Anand, J. S. and Lai, D., Synthesis of Methane from Water for Tritium Measurement,

Nature, 201, 775 (1964).

[3] Bainbridge, A. E., Suess, H. E., and Friedman, I., Isotopic Composition of Atmospheric

Hydrogen and Methane, Nature 192, 648 (1961).

[4] Baxter, M. S. and Walton, A., A Theoretical Approach to the Suess Effect, Proc. Roy.

Soc. (London) A318 , 213 (1970).

445
5] Bishop, K. F., Dalafield, H. I., Eggleton, A. E. J., Peabody, C. 0., and Taylor,

B. T., The Tritium Content of Atmospheric Methane, Proo. Sym. Tritium Phys. Biol. Sai.,

Vienna, Austria, May 1961, 1, 55 (1962).

6] Clayton, G. D. , Arnold, J. R. , and Patty, F. A., Determination of Sources of Particulate Atmospheric Carbon, Science, 1 22 , 151 (1955).

7] Covert, D. A., Charlson, R. J., Rasmussen, R. , and Harrison, H., Atmospheric Chemistry

and Air Quality, Review of Geophysics and Space Physics, 1_3, 765 (1975).

7a] Cowan, G. A., Ott, D. G., Turkevich, A., Machta, L., Ferber, G. J., and Daly, N. R.

,

Heavy Methanes as Atmospheric Tracers, Science 191 , 1048 (1976).

8] Currie, L. A., Noakes, J., and Breiter, D., Measurement of Small Radiocarbon Samples:

Power of Alternative Methods for Tracing Atmospheric Hydrocarbons

,

r. Berger and H. Suess,

Edit., 9th Intevnatl. Radiocarbon Conf. Univ. of Calif., Los Angeles and San Diego, June 1976

9] Dugas, D., Increase of Exchangeable Carbon in the Earth's Reservoirs from Combustion

of Fossil Fuels, RAND-P-3990 (1968).

10] Ehhalt, D. H. , The Atmospheric Cycle of Methane, Tellus 26, 58 (1974).

11] Grimsrud, E. P., and Rasmussen, R. A., The Analysis of Fluorocarbons in the Troposphere

by Gas Chromatography-Mass Spectrometry, College of Engineering, Research Division,

Washington State Univ., Pullman, WA 99163 (1975).

12] Junge, C. E., Residence Time and Variability of Tropospheric Trace Gases, Tellus 26_, 4

(1974).

13] Kunen, S. M. , Burke, M. F., Bandurskii, E. L., and Nagy, B., Preliminary Investigations

of the Pyrolysis Products of Insoluble Polymer-Like Components of Atmospheric Particulates. Atmos. Environ. 1_0, 913 (1976).

|13a] Libby, W. F., personal communication.

14] Lodge, J. P., Jr., Bien, G. S., and Suess, H. E., The Carbon-14 Content of Urban

Airborne Particulate Matter, Intl. J. Air Poll. , 2, 309 (1960).

15] Machta, L., Argon-37 as a Measure of Atmospheric Vertical Mixing, Noble Gases,

R. E. Stanley and A. A. Moghissi, Ed., ERDA TIC: CONF-730915 (1973).

^16] MacKay, C, Pandow, M., and Wolfgang, R., On the Chemistry of Natural Radiocarbon,

J. of Geophysical Research, 68, 3929 (1963).

17] Maugh, T. H., II. Air Pollution: Where Do Hydrocarbons Come From? Science, 189 , 277 (1975).

18] Moore, H., Isotope Measurement of Atmospheric Nitrogen Compounds, Tellus, 26_, 169

(1974).

19] Nielsen, H., Isotopic Composition of the Major Contributors to Atmospheric Sulfur,

Tellus, 26, 213 (1974).

^20] Rasmussen, K. H., Taheri , M., and Kabel , R. L., Global Emissions and Natural Processes

for Removal of Gaseous Pollutants, Wat., Air and Soil Poll. 4^, 33 (1975).

|21] Rasmussen, R. A., What Do the Hydrocarbons from Trees Contribute to Air Pollution?

J. of the Air Pollution Control Assn. 22_, 537 (1972).

'2.2'] Robinson, E., and Robbins, R. C, Sources, Abundance, and Rate of Gaseous Atmospheric

Pollutants. Final Report, PR-6755, Stanford Research Institute (1968).

446
[23] Rowland, F. S. and Molina, M. J., Chlorofl uoromethanes in the Environment, Reviews of

Geophysics and Space Physics, 1_3, 1 (1975).

[24] Rutherford, W. M. , Evans, J., and Currie, L. A., Isotopic Enrichment and Pulse Shape

Discrimination for Measurement of Atmospheric Argon-37, Anal. Chem. , 48, 507 (1976).

[25] Saunders, R. A., Blachly, C. H., Kovacina, T. A., Lamontagne, R. A., Swinnerton, J. W.

,

and Saalfeld, F. E., Identification of Volatile Organic Contaminants in Washington, DC

Municipal Water, Water Res. 1143 (1975).

[26] Schmidt, L)., Molecular Hydrogen in the Atmosphere, Tellus 26, 78 (1974).

[27] Seiler, W. , The Cycle of Atmospheric CO, Tellus 26, 116 (1974).

[28] Stevens, C. M., Krout, L., Walling, D., Venters, A., Engelkemier, A., and Ross, L. E.,

The Isotopic Composition of Atmospheric Carbon Monoxide, Earth and Planetary Science

Letters 16, 147 (1972).

[29] Suess, H. E., Radiocarbon Concentration in Modern Wood, Science 1 22 , 415 (1955).

[30] Weinstock, B., Carbon Monoxide: Residence Time in the Atmosphere, Science 166 , 224

(1969).

[31] Winer, A. M., Lloyd, A. C, Darnall, K. R., and Pitts, J. N., Jr., Relative Rate

Constants for the Reaction of the Hydroxyl Radical with Selected Ketones, Chloroethenes, and Monoterpene Hydrocarbons, J. Phys. Chem. 80^, 1635 (1976).

447

Part IX. CHEMICAL CHARACTERIZATION OF INORGANIC AND ORGANOMETALLIC CONSTITUENTS

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

CHEMICAL CHARACTERIZATION OF INORGANIC AND ORGANOMETALLIC CONSTITUENTS

Robert S. Braman

Department of Chemistry

University of South Florida

Tampa, Florida 33620, USA

1. Nature of the Analytical Problem

The field of environmental microanalytics is not without its challenges. The first

and perhaps the most important one is to define the objectives and nature of the task

facing an investigator. Typical objectives of analytical studies might be: to develop a system for monitoring a specific pollutant source, perhaps for several components; to

monitor at locations far removed from immediate pollution sources; to analyze for pollutants

at remote locations; to study chemical reactions of specific pollutants in the environment;

and to study in the laboratory the effects of selected pollutants on selected biological

systems

.

When going beyond these general objectives one is faced with: identifying the specific

chemical compound or compounds for which analytical data is sought; determining the concentration and range of concentrations at which they are present in samples; and determining

the needed accuracy and precision. Designed into the analytical plan may be factors such

as desired analysis frequency, synoptic survey considerations, diurnal, seasonal, and

weather effects and perhaps the impact of anthropogenic sources.

In a reasonably large number of circumstances, the identity and concentration of

specific chemical forms of elements has been well known for a long time and excellent

methods of analysis are available. This is true of such common ions as nitrate, nitrite,

chloride, sodium, etc. Characteristically, such ions are either present in comparatively

high concentration in samples or their chemistry does not permit more than one form under

environmental conditions. In the latter case total element analyses are sufficient.

This situation is generally not the case for most of the transition metals and metalloids

although excellent methods are available for these too in higher trace concentrations.

In many circumstances one may have only meager data on total element concentration and

by methods which could be totally unreliable because of circumstances of sample acquisition.

It is not uncommon that an investigator has nothing to go on other than pure speculation.

This individual then finds himself defining the problem in the process of investigating it.

It appears to this writer that the great majority of environmental analysis problems should

be of the individual component type for the present.

A clear distinction exists between monitoring methods and investigative methods.

Monitoring implies a continuous operation, the data from which is used to assess some environmental impact. Monitoring is expensive and places severe strain on the reliability

of individuals and equipment. Thus, the implementation of monitoring for a specific component is a serious matter. The most reliable monitoring methods are the less complex to use

and thus minimize operator error. Many of the newer, more complex and often slower methods

for various forms of the chemical elements may perhaps be considered for monitoring. It

must first be justified that selective analysis produces data which can be more reliably

compared to environmental effects than easier techniques for total elemental composition

before their use in monitoring is justified.

451
For the most part then, most of us in the environmental speciation field are dealing

with investigative work with little immediate concern for monitoring. We are concerned

with the other problem areas, pollution studies near sources, remote location analyses,

chemical transformation studies, and controlled laboratory experimental studies.

A wide range of sample types and concentrations are encountered in environmental

studies. Each sample type (air, water, soil-sediment, biota) requires a different sample

modification step in analysis and each has its own concentration range.

Whatever the analytical problem, we are generally faced with the necessity of obtaining

good analytical precision in the analysis from 1 ng to 1 microgram of analyte per sample.

Air particulate analytes may range from 1 pg to 100 micrograms/m^ . The portioning of 4-

10 ng/m-^ of arsenic into As(III), As(V) and the methyl arseni c compounds is illustrative of

the problem which can arise when speciation is a goal.

Modification of the acquired sample size is about the only factor which can be changed

to meet the need for improved concentration limits of detection. Remote sampling for

analysis, for example at the polar regions, presents the maximum need for low limits of

detection (LD) in air analysis. Many cubic meters of air must be sampled in order to

obtain a sufficient sample for analysis of particulate trace metals.

Water samples are often similar. Non polluted samples often require parts-per-tri 1 1 ion

(ppt) concentration limits of detection. Mercury in open ocean sea water is present at

concentrations on the order of 10 ppt. The speciation of that amount of mercury into Hg°,

HgCl2, CHsHgCl and CHsHgCHs forms has yet to be solved.

Fortunately biota are inclined to preconcentrate metals, somewhat selectively, and so their analysis is less challenging. Parts-per-mi 1 1 ion (ppm) concentrations are more common. The major problem is sample preparation so as to obtain essentially quantitative removal of

all analytes sought. Homogenizing and extraction are the most used techniques.

Sediments and soils, are generally similar to the biotic concentrations. Nevertheless,

the chemical forms are often non-volatile, non-soluble and non-extractable without altering

the chemistry of the analyte sought. Much more work on analysis of these solids is needed.

2. Sample Processing for Analysis

Sample processing for- analysis is in two parts, acquisition and modification. The

object is to be able to present to the detector in a form suitable to the measurement, the

analyte or analytes extracted from the sample. The analyte must be present in the active

volume of the detector in a concentration or sample size above the limit of detection. The

ultimate concentration limit of detection is achieved when the entire analyte is present in

the active volume of the detector. Many analysis methods include a preconcentration step

simply to achieve this purpose.

Direct analysis without modification of the sample is the case for some analytical

methods. Long path absorption spectrophotometry is a notable example. Atmospheric ozone,

hydrocarbons, nitrogen oxides and sulfur dioxide have been measured down to ambient concen- trations with this approach.

Direct analysis without preconcentration is used i-n the analysis of sulfur compounds

in air after gas chromatographic separation. Here the limit of detection of the detector

is sufficient to meet the limit of detection required by the sample concentration.

Direct spectrophotometry can be applied to analysis of solutions after conversion of

the analyte to a form more recognizable from the matrix, i.e., to a colored complex.

Determinations of silica, phosphate ion, nitrite ion, nitrate ion and certain metal ions

have been done thereby to parts-per-bi 1 1 ion (ppb) concentrations in natural waters.

452
Nearly all other sample processing involves preconcentrati on techniques often combined

with a phase transfer such as from a gaseous form in air to an absorbed state on a filter

or in a scrubbing solution. Frequently these sample modification steps offer opportunities

for greatly improving both the specificity and limits of detection of an analysis system.

Filters such as used in collecting air particulates exhibit a very high degree of

preconcentration with a minimum of complexity. Scrubbing solutions for air analysis are probably next in popularity and offer opportunities for use of specific chemical reactions

to achieve specificity. Nevertheless, a further preconcentration of the scrubbing solution

may be needed to reach detectable concentrations of analytes.

In air analysis active surface sampling tubes or tapes offer excellent preconcentration

and selectivity possibilities. If solution chemistry is contemplated, solution volumes

may be generally kept small and reagent contamination may be minimized. This approach has

been recently used for the determination of mercury forms and the methyl arsi nes in air by

techniques developed in the laboratory. Sulfur also shows considerable promise.

Cryogenic sampling has been largely used in organic analysis and it could be useful

for collecting inorganic or organometal 1 ic compounds. It is not very selective and samples

require separation.

Separation techniques are almost always necessary for purposes of eliminating interferences in all speciation type analyses. Gas or liquid chromatography is most often used

and many commercial models are available that are more or less complex. It should be

noted that chromatography does not usually preconcentrate samples, it only separates

components, and in fact, it actually decreases the sample concentration presented to the

detector. Consequently, preconcentration is usually a necessary step prior to and separate

from the actual separation.

Separation by volatilization out of a large sample volume is widely used as a preconcentration method. Hydride formation by analyte reaction with a strong reducing agent

such as sodium borohydride in the analysis of arsenic is a typical example. The hydride

may be cold trapped into a very small volume thus effecting a large preconcentration

ratio. A growing number of elements may be preconcentrated by hydride evolution and

includes: As, Bi , Sb, Ge, Sn , Se, Te, and some compounds of Si and Pb. Organometal 1 i

c

hydrides have also been produced for some of these elements.

Preconcentration by solvent extraction and by co-precipitation are classical methods

which also continue to be used and improved.

3. Detectors and Detection Systems

The salient feature of any analysis system is its detector. Each detector has the

characteristics: selectivity, fundamental lower limits of detection, dynamic range of

detection and active volume. The active volume is defined as the volume in which the

measurement is made during detection of the analyte. The fundamental lower limit of

detection is the amount of material in that volume which gives a discernible signal above

the background electronic noise detected.

Detectors are always reported in the literature associated with sample processing and

it is sometimes difficult to determine the above mentioned characteristics of a detector

from the publication. There is often a confusion between the detection concentration

limit of a method and the detection fundamental limit of the detector. For example, a limit of detection of 1 ng per sample gives a concentration limit of detection of only

0.1 ppm if 10 microliters is the maximum sample size. Of course, if needed, preconcentration

may improve the concentration limit of detection.

It is in the area of combination of separation, sample preconcentration, and detection

that new methods for environmental analysis are being developed. Some of the more used or readily available techniques have been selected and will be treated in some detail in

following sections.

453
4. Detection Systems-Solid Surface Analyses

A. Electron spectroscopy

Electron spectroscopy is as yet the only technique available for the direct examination

of solid surfaces for the chemical form of trace metals present. Identification of chemical

forms depends upon the number of compounds present, their concentration and the chemical

shift available. The detection of seven different forms of sulfur in air particulate by

ESCA [l,2]i is a good demonstration of a probably favorable case. Czuha and Riggs [3] in an excellent study of their ESCA approach to trace metal detection demonstrated a limit of

detection of 10 ng for silver on an acrylic acid grafted to a polyethylene surface. Since

they found that some 90% of the silver had penetrated to beyond ESCA analysis depth, the

potential limit of detection must be approximately 1 ng.

Specificity of ESCA is only moderately good and a complex matrix probably would require

some pretreatment. Removal of heavy loads of organic or inorganic materials may also be

needed to avoid "burying" the trace materials sought.

B. X-Ray fluorescence spectroscopy

This method is more sensitive than ESCA and is used more for quantitative analysis.

Quantitative multielement trace element analyses are easily achieved but the method cannot

be used for detection of chemical forms. Sample modification is needed for this and would

involve deposition of a particular separated analyte onto a surface for analysis. Limits

of detection depend upon the element; examples are, 0.02 ng(Zn, U), 5 microgram(Al ) [4,5].

5. Detection Systems-Solution Measurements

A. UV-vis absorption

Absorption spectroscopy is deserving of substantially more consideration in application

to environmental analysis. Based upon the absorption of ions or complex compounds, the

approach holds excellent promise for speciation uses. There are several appealing features

of spectrophotometry. Literally thousands of compounds have been investigated for one application or another and a large background of literature exists from which to select

specific complexing agents. A good current review listing a large number has been presented

by Boltz and Mellon [6].

Limits of detection are often considered poor for spectrophotometry at least in com- parison with some other instrumental methods. Nevertheless, it is easily demonstrated that

the methods may be applied to ppb concentrations of analytes.

Table 1 of Beer's Law calculations gives the sample weight and concentration which are needed for the molar absorptivities listed, using a cell path of 1 or 10 cm, for which As = 0.005. Performance with preconcentration is also given.

This method of analysis is related to the .high performance liquid chromatography

(HPLC) methods in that UV absorption detectors are used in the latter method. A major

disadvantage is that spectrophotometric methods usually are applied to analysis of one component at a time. If 10 different components must be measured, 10 different methods

would probably be needed. The technique has been automated extensively.

^Figures in brackets indicate the literature references at the end of this paper.

454
Table 1

Beer's law calculations

no preconcentration

(10 ml volume)

analyte preconcentrated from

1 liter to 10 ml

e = 10^ e = IQS £ = 10"^ e = 105

500 ng

(0.05 ppm)

50 ng

( 5 ppb)

1 cm

cell

500 ng

(0.5 ppb)

50 ng

(0.05 ppb)

50 ng

( 50 ppb)

5 ng

(0.5 ppb)

10 cm

cell

50 ng

(0.05 ppb)

5 ng

(0.005 ppb)

B. High performance liquid chromatography

Ultraviolet absorption detectors are popular for trace HPLC work. Although largely

applicable to UV absorbing organic complexes of metal ions, inorganic complexes can probably

also be detected with good sensitivity. A great variety of inorganic separations have been

reported in a recent review by Walton [7]. An approach to improving limits of detection is

the use of highly absorbing (or fluorescing) derivatives [8].

For molar absorptivity = 14,000 the predicted limit of detection is on the order of

10 ng per sample [9] probably typical of the ultimate for the HPLC techniques.

Largely used in organic analysis this technique has also been applied to the analysis

of metal ions down to the ppb range. The need for separations in procedures is considerable

to avoid interferences. The method is potentially useful for speciation analyses since

specific compounds are detected. Perhaps a typical example of detection limits is the

determination of lead and cadmium by Hefley and Jaselskis [10] who report a limit of

detection of 2.24 ng/ml or 2 x lO'^ M Cd.

Ion selective electrodes have the theoretical advantage that measurements may be made

on a sample without disturbing its composition. An electrode is specific for a selected

ion. There are many practical limitations.

Concentration limits of detection are resonably good. Many electrodes studied have

been used down to 10"^ to 10"^ M analyte concentrations and thus are satisfactory for

direct measurements on aqueous samples in the ppm to ppb range [11]. Preconcentration by

ion-exchange chromatography in HPLC prior to use of electrodes can be used to reach limits

of detection and to effect necessary separations. An example is the separation of nitrate

and nitrite ions by HPLC followed by detection using a nitrate selective liquid ion exchange

membrane electrode [12]. Note that both ions were detected by the same "selective"

electrode. The active volume of the detector was 50 microliters and the limit of detection

was 0.1 to 0.3 ng for the nitrate and nitrite ions respectively.

The active volume of an ion selective electrode is not easy to define unless used in some fixed cell holder as in the previously described case [12]. From the active volume

and concentration limit of detection one can estimate the sample size limit of detection.

If we assume a 0.1 ml active volume with analyte at 10"^M for cupric ion for example, then

this 0.1 ml sample will contain 0.06 ng, clearly a trace element sample size.

A resonably large number of ions may be sensed by electrodes already developed including:

K+, Na+, Mg2+, Ca2+, Cu^+ , CI", F" , Br", CN", I" and NO3 with more or less good selectivity.

C. Fluorescence spectroscopy

D. Ion selective electrodes

455
Copper ion selective electrodes have received considerable attention. Jasinski,

Trachtenberg and Andrychuk [13] have demonstrated that "uncompl exed" copper on ocean water

may be directly determined at approximately 1 ppb concentrations. They noted that measurements inshore indicated that complexing agents were binding some of the copper. Andrew [14]

in an elegant piece of work demonstrated that fathead minnows and daphnia magna responded

to the toxicity of "uncompl exed" copper indicated by a copper selective electrode.

E. Anodic strippng voltammetry and differential pulse polarography

A number of electrochemical methods may be applied to environmental analyses. The more sensitive ones are listed in table 2, taken in part from reference [15].

Table 2

Electrochemical methods applied to environmental analyses

Method LP (reversible systems) LP (irreversible systems)

Classical dc 5 x 10"^ M 5 x 10-^ M

Normal pulse 5 x 10"^ M 5 x 10"^ M

PPP 8 X 10-9 M 10-7 M

Rotating disc + Hydrodynamical ly Modulated

Pise Electrodes 5 x 10"^ M

ASV methods have variable sensitivity and have been applied to concentrations as low

as 0.005 ppb for some metals [5]. Nevertheless, the theoretical ability to selectively

operate on an ion via potential control has not been well established in practice for

environmental samples.

6. Petection Systems-Measurements in Vapor State

Nearly all of the detectors in this group must be used with a separation system and

one which eventually presents the analyte to the detector in vapor form. An exception

might be the direct analysis of solutions in plasmas capable of vaporizing the solvent.

Even in this case the analyte is in vapor form during detection.

These detectors have little capability for differentiating between one chemical form

or another of an element. Nevertheless, owing to their considerable sensitivity and with

separations, they have been widely used in environmental work.

A. Flame ionization and electron capture detectors

These classical GC detectors are comparatively non-specific. Volatile organic com- plexes should be detectable but such applications have been few. The main environmental

analysis use of the ECD has been the determination of methylmercury type compounds in

biological samples. Limits of detection range from 10"^ to lO-^^g -jn small active volumes

for good cases.

A recent application of the FIP in combination with HPLC exhibited a limit of detection

of 3 to 4 ng per sample [16]. Although this value was for organic compounds, the organic

complexes of metals should be similarly sensed.

456
B. Mass spectrometry

GC-MS combinations are in wide use and need no introduction. An interesting and

potentially useful combination is HPLC-MS. Lafferty et al. [17] have adapted a MS inlet

system for directly handling the solvent stream from a HPLC. Approximately 1% of the

effluent is analyzed by the MS. The limit of detection for organic compounds was found to

be near 0.5 ng per sample. Thus only 5 picograms of sample was detected in the MS.

Improvements would appear to be possible. Separation and analysis of metal complexes

would appear to be feasible even though not yet reported.

A variety of metal chelates have been determined by chemical ionization MS with

limits of detection near lO'^^g [5].

C. Atomic absorption spectrometry

The best lower limits of detection of this technique are obtained with the so-called

flameless modification. Analyte metals are atomized by thermal means usually in a graphite

tube furnace or high temperature metal atomizer. Detection limits are generally in the

10"^^ to 10"i2 g/sample range with the flameless methods. Concentration limits of detection

are generally in the ppb range. Although used mainly for total element analyses, the

technique may be used in separation systems.

Major limitations are lifetime of the high temperature furnace and difficulties in

atomization of elements which have tendencies to form stable oxides.

D. Emission methods

Methods in this group are similar with differences due to the method of producing

electrical discharge or plasma. All are approximately equivalent in the type of specificity

obtained, atomic line or diatomic band emission spectra are observed. These detectors

have the advantage of providing for readily verifiable positive signals, i.e. emission

lines of the analyte.

Inductively coupled plasma sources have excellent stability and multielement detection

capability. Limits of detection are in the ppb range [18].

Direct current discharges in helium carrier gas have been used to determine inorganic

and organometal 1 i c As, Ge, and Sn compounds after separation of hydrides or methyl hydrides

in a U-trap [19]. Limits of detection are near 1 ng per sample providing a 0.01 ppb

concentration limit of detection for 100 ml samples. The method is under study for use in

detection of Pb, Bi , Se and Te. D.C. discharges have also been used in the speciation of

mercury in air [20].

A microwave stimulated plasma used with a GC system has been applied to the analysis

of arsenic and methylarsenic compounds after reduction to the arsines [21]. Limits of

detection are near 0.02 ng per sample with concentration limit of detection in the ppb

range.

Atomic fluorescence methods have limits of detection near 0.1 ng per sample.

7. Conclusions

The great variety of detectors available for analyzing ng amounts of analyte provides

a choice of combination methods for environmental analyses. It appears as if future

effort is needed largely in developing selective chemistry for separations or preconcentration.

Methods have already been developed for the methyl forms of those elements which are biomethylated in the environment. Success here is attributable to separation chemistry.

457
The next problem to attack is separation and/or determination of the oxidation states

of transition metals of interest. This will likely be done with some combination of

specific complexation followed by HPLC separation and elemental detection.

More difficult tasks will be detection of labile metal ion complexes and the analysis

of sediments.

References

1] Craig, N. L., Harker, A. B., and Novokov, T., Atmos. Environ., 8, 15 (1974).

2] Novakov, T., Joint Confevenae on Sensing Environmental Pollutants (Proc), 2nd conf .

,

197, 15A (1973).

3] Czuha, M., Jr., and Riggs, W. M. , Anal. Chem. 47, 1836 (1975).

4] Elder, J. F., Perry, S. K. , and Brady, F. P., Environ. Sai. Teohnol., 9_, 1039 (1975).

5] Dulka, J. J. and Risby, T. H., Anal. Chem. 48, 640A (1976).

6] Boltz, D. F. and Mellon, M. G., Anal. Chem. 48, 216 (1976).

7] Walton, H. F. , Anal. Chem. 48, 52R (1976).

8] Jupille, T. H. , American Laboratory (5), 85 (1976).

9] Borch, R. F. , Anal. Chem. 47, 2437 (1975).

10

11

12

13

14

15

16

17

18

19

20

21

Hefley, A. J. and Jaselkis, B., Anal. Chem. 46, 2036 (1974).

Buck, P. P., Anal. Chem. 48, 23R (1976).

Schultz, F. A., and Mathis, I. E., Anal. Chem. 46, 2253 (1974).

Jasinski, P., Trachtenburg and Andrychuk, D., Anal. Chem. 46^, 364 (1974).

Andrew, R. W. , Proceedings of Workshop on Toxicity to Biota of Metal Forms in Natural

Waters, Great Lakes Research Board, Ch. 6, (1975).

Miller, B. and Bruckenstein , S. Anal. Chem. 46, 2026 (1974).

Szakasits, J. J. and Robinson, R. E., Anal. Chem. 46, 1648 (1974).

McLafferty, F. W. , Knutti , R. , Venkataraghavan , R. , Arpino, P. J. and Dawkqns, B. G.

,

Anal. Chem. 47, 1503 (1975).

Fassel , V. A. and Kniseley, R. N., Anal. Chem. 46^, lllOA (1974).

Braman, R. S. and Foreback, C. C. , Science, 182, 1247 (1973).

Braman, R. S. and Johnson, D. L. , An. Env. Sci. Technol., 8, 996 (1974).

Talmi, Y. and Bostick, Anal. Chem. 47, 2145 (1975).

458
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

ANALYTICAL TECHNIQUES FOR THE STUDY OF THE DISTRIBUTION AND SPECIATION

OF HEAVY METALS IN AQUATIC SYSTEMS

H. J. Tobschall , N. Laskowski^ and K. Kritsotakis

Department, of Geosciences

University of Mainz

Saarstrasse 21, D 6500 Mainz

Federal Republic of Germany

1. Introduction

The awareness of the hazards deriving from elevated concentrations of heavy metals in

aquatic systems has increased the activity in the development of trace analytical techniques.

However, knowledge of the total concentration of a trace metal in a particular aquatic

compartment is not sufficient to permit an accurate interpretation of both its biological

effects and geochemical reactions.

The chemical behavior of a metal in the aquatic environment depends on its forms,

those in solution, and those present in colloidal and particulate phases. For example,

the toxicity of copper to some marine organisms is controlled by the formation of copper

organic complexes [1]^. Speciation influences the participation of an element in geochemical processes such as precipitation-dissolution and adsorption-desorption. Obviously, an understanding of these processes is essential to determining pathways by which heavy

metals are transported through the aquatic media. Additionally, only by characterizing

trace metal species and the reactions by which they are transformed, can we hope to

understand the changes of biological and geochemical processes which are initiated by

man's activity. The kind of data needed includes the type and number of natural and

synthetic organic compounds, their chemical stability and their capacity to react with

metals. Furthermore, we have to improve our understanding of interfacial phenomena and

apply our knowledge of the competitive equilibria in aqueous solutions to interfacial

regions, (particularly to the sediment-water interfaces) if eventually we are able to

quantify the processes and mechanisms whereby heavy metals are released, transported and

accumulated in both natural and polluted aquatic systems.

The objective of this paper is to consider a series of selected analytical tools

which might be capable of providing data closing the information gap outlined above. The

analytical techniques are illustrated by discussing our study on the distribution of Ni

,

Cu, Zn, Ag, Cd, and Hg in sediments and waters of a highly polluted cut-off channel of the

Rhine River near Mainz [5,6].

2. Discussion

Recent work to identify chemical species of metals has centered around two basic

concepts. One is to elaborate techniques which can distinguish different chemical forms

present in a water sample; the other is to develop chemical models of the aquatic environment based on the general chemistry of the relevant elements.

^Present address: Department Geochemistry, University of Cape Town, Rondebosch, Cape,

South Africa.

^Figures in brackets indicate the literature references at the end of this paper.

459
Techniques of the first concept lead to chemical speciation which is operationally

defined. They include analytical measurements following various types of physical or chemical separation such as filtration, centrifugation, dialysis, chromatography, and

solvent extraction. Furthermore, measurements of the response of a particular species to

various chemical perturbations such as oxidation of dissolved organic constituents and pH

shifts are applied.

At present, anodic stripping voltammetry (ASV) has received considerable attention

from water chemists because of its great sensitivity, precision and resolution. Additionally, it offers new dimensions with respect to the determination of metal species in water

since some forms {e.g. certain organic complexes) are not reducible at the mercury electrode

whereas other forms are. Most known organic complex formers in natural waters are weak

acid salts. Thus it is probable that metal -organic interactions occur under neutral or alkaline {i.e. under environmental) conditions but under strong acid conditions the metals

exist as free hydrated species. The difference in peak current under environmental conditions and under experimental acid conditions may be interpreted as representative of the

amount of metal ions present in "nonlabile" organic complexes of unknown nature.

Studies on the proportion of heavy metals present in ionic forms have been performed

by coupling an ion exchange technique with dialysis [2]. A major advantage of this

procedure is a reduction in adsorption and contamination problems. We are using this

technique to obtain information on the percentage of ionic forms of Cd, Cu, Pb, Zn, and Fe

in natural waters.

A very promising technique for determining the total concentrations of heavy metals

in waters has been published by Kinrade and Van Loon [4]. Using two chelating agents,

ammoniumpyrrol idindithiocarbamate (APDC) and diethylammoniumdiethyldithiocarbamate (DDDC)

the metals Cd, Co, Cu, Fe, Pb, Ni , Ag, and Zn can be extracted simultaneously.

References

[1] Davey, E. W., Morgan, M. J., and Erickson, S. J., A Biological Measurement of the

Copper Complexation Capacity of Seawater, Lirmol. Oaeanogr. 1_8, 993-997 (1973).

[2] Hart, B. T., Determination of the Chemical Forms of Selected Heavy Metals in Watviral

Waters and Wastewaters, Progress Rep. 1, A.W.R.C. Research Project 74/50, Caulfield

Institute of Technology (1976).

[3] James, R. 0. and Healy, T. W. , Adsorption of Hydrolyzable Metal Ions at the OxideWater Interface, J. Colloid and Interface Science 40, 42-81 (1972).

[4] Kinrade, J. D. and Van Loon, J. C, Solvent Extraction for Use With Flame Atomic

Absorption Spectrometry, Analy. Chem. 46, 1894-1898 (1974).

[5] Laskowski, N., Die Gehalte der Elemente Ni, Cu, Zn, Rh, Sr, Y, Zr, Eh, Ag, Cd imd Eg

in Komgrossenfraktionen der Sinkstoffe und Sedimente des Ginsheimer Attrheines . - Ein Beitrag zur Geochemie einea Fluviatilen Gewassers mit Intensiver Urban-Indus trielter

Belastung, Diploma thesis. Department of Geosciences, University of Mainz, 130

unpublished (1975).

[6] Laskowski, N., Kost, Th., Pommerenke, D., Schafer, A., and Tobschall, H. J., Abundance

and Distribution of Some Heavy Metals in Recent Sediments of a Highly Polluted LimnicFluviatile Ecosystem near Mainz, West Germany, Nriagu, J. 0. (Ed.), Environmental

Biogeoohemistry 2_, 587-595, Ann Arbor Science Publishers (1976).

[7] O'Connor, T. P. and Kester, D. R. , Adsorption of Copper and Cobalt from Fresh and

Marine Systems, Geochim. Cosmochim. Acta 39, 1531-1543 (1975).

460
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

INORGANIC SPECIATION OF COPPER IN ESTUARINE ENVIRONMENTS!

David C. Burrell and Menq-Lein Lee

Institute of Marine Science

University of Alaska

Fairbanks, Alaska 99701, USA

1. Introduction

This report is primarily concerned with some initial work on the nature of inorganic

complexes of copper present in seawater and also on the partition of this element between

suspended sediment and water under estuarine conditions. The latter work relates to

Alaskan fjord-estuaries which offer ideal environments for the study of the nature and

behavior of heavy metals under predominantly inorganic marine conditions. Anthropogenic

contamination is absent, natural dissolved and particulate organic contents are very low at

most times of the year, and very large amounts of glacially derived, silicate particulate

sediment accompany the fresh water inflow during the summer months.

2, Discussion

It is necessary first to briefly consider the role of organic complexation in marine

waters since there has been a good deal of speculation on this topic in recent years.

Interest here has, in fact, centered on copper, probably because this has been the most

comprehensively studied transition element and also because copper forms high stability

complexes with a number of organic ligands. Various field and laboratory investigations

have suggested that upward of 50% of the total copper in unimpacted seawater may be present

in this form. Identification has largely been attempted via separation and analysis of

"organic fractions" defined by various solvent extraction systems, by differnece between

oxidized and untreated sample aliquots, or by indirect, bioassay procedures. No one copper

organic complex has been identified to date, however. It is believed that the various

seawater equilibrium models incorporating organic ligands which have been published to date

are also largely unrealistic. Total dissolved organic carbon contents are frequently over

estimated, for example. But the major errors are introduced both because of the assumptions

inherent in attempting to project ideal conditions to the natural environment, and through

the choice of exotic organic ligands. The latter is a consequence of the general paucity

of thermodynamic data for naturally occurring organic compounds in saline solution. A

complexometric titration of Alaskan fjord water has given a "complexation capacity" for

copper of 2 X 10"^ M. This would approximate to a dissolved organic carbon content in the

range 3 x 10"^ mg C/1 ; which is undetectable by conventional techniques. This isolated

experiment is probably unrepresentative and does not per se preclude complexation; however,

we consider [1]^ that the current evidence for a major role for organically complexed

metals in "average" seawater is unconvincing.

^Contribution no. 292 from the Institute of Marine Science, University of Alaska, supported

in part by U.S. Energy Research and Development Adminstration Contract No. AT(45-1 )-2229.

^Figures in brackets indicate the literature references at the end of this paper.

451

i
There is considerable controversy at the present time regarding sorpti on-desorpti on reactions of heavy metals at the fresh-marine junction. This cannot be considered in any

detail here, but it is instructive to consider the definition of the "particulate" and

"soluble" fractions. The generally used convention calls for partition using a 0.4 ym

membrane filter; an operational convenience without much scientific basis. It was initially

considered that this would be a reasonable working definition for use in these fjords since

particle floes in excess of 1 mm are produced when the salinity exceeds 4 to 5 ppt. A

marked correlation between suspended sediment load and "soluble" trace metal concentrations

has long been noted, however, and we have found [2] this relationship to hold when the

particulate material is fractionated into a series of size divisions down to 0.1 pm. It is

likely that the filtering action regenerates some fine grained, primary-sized silicate

material which is subsequently analyzed as part of the soluble fraction. There is also

increasing evidence that some stabilized colloidal size material may not be flocculated

following injection into the higher ionic strength medium, so that a wide size spectrum of

particulate metal species may coexist in seawater. We have no evidence for the release of

sorbed copper from suspended sediment following mixing with seawater but, at the same time,

it would seem an almost impossible task to define a meaningful soluble fraction.

As a generalization, it might be expected that the fraction of free metal ion should

increase passing from fresh to marine water because of a decrease in effective complex

formation constants with increase in the ionic strength. In fact, for many metals, including copper, the free ion concentration (as measured polarographically, for example)

decreases in seawater as a direct consequence of complex ion formation with the major

anions. The following ligands might be expected to be important: 0H~, C1-, C0|, (and

possibly, SO4 for some metals). The major inorganic carbon anion in seawater is HCO3, but

no unequivocal bicarbonato complex with the common heavy metals have yet been identified.

Since the carbonate activity exceeds all the trace metals in solution, this distribution is

unlikely to be limiting, however.

The fact of inorganic complexation in seawater has long been appreciated but very few

individual associations have been directly identified. The nature and abundance of many

sets of inorganic metal complexes have been calculated most commonly via thermodynamic

equilibrium models in the same fashion as noted above for the organo-metal 1 ic species. The same caveats apply. Table 1 is a compilation from the recent literature (in order of

publication) of suggested inorganic copper species computed for matrices approximating

seawater.

Table 1

Equilibrium copper species computed for seawater

(% total metal in solution; literature data)[l]

J 2 3 4 5

Cu2+ _ _ 3 14 _

CUCO3 n 22 93 49 2

Cu(C03)2- _ - 4 - -

CuCl+ - 6 - 10 97

CuCl? - 2 - - -

Cu0HCl° - 65 - - -

CuOH"' - 4 - 22

Cu(0H)2 83 - - - -

462
It may be seen that this modeling approach has not lead to a consensus regarding the

predominating species in seawater. The primary reasons for this are an absolute lack of

stability constant data for many of the complexes of interest, and differing approaches for

computing the activity coefficients needed to relate thermodynamic constants to the saline

medi um.

It would appear that there is an urgent need for the direct qualitative and quantitative identification of the major inorganic forms of the heavy metals existing in seawater.

We are currently conducting such a program to obtain this speciation information for copper,

and can give here preliminary data for chloro and hydroxo species. These data have been

determined from pH and pCl titrations, following the oxidation peak shifts via anodic

stripping voltammetry. The relevant Nernst relationship for a ligand L and peak height

potential Ep is:

Cu2+ + xL ^ Cu L2-X

X

AEp = In (3x[L]^)

The experiments have been conducted in perchlorate solution to match the ionic strength

of seawater and the NaCl used (0.7 M) has been purified most carefully to remove traces of

other halogen ions. Employing this ionic medium convention, [L] represents the concentration

of ligand not complexed with copper. Previous workers in this field have reported operational difficulties due to over-lapping of the copper and mercury stripping signatures; we

have effected excellent separation using thin-film, glassy carbon electrodes under closely

controlled analytical conditions. Non-linear titration curves (AEp vs pCl or pOH) confirm

the formation, under these conditions, of a series of hydrolysis and higher chloro species.

Previous work on zinc by Bradford [3] determined that these latter complexes formed insufficiently rapidly at the electrode surface to be observed. This does not appear to be the - case with copper.

Table 2 lists our initial values for the relevant formation constants:

Table 2

Uncorrected stability constants for copper complexes (I = 0.7)

log gi log 52 "log

OH 6.4 15.0

CI 3.2 6.4 8.9

It must be emphasized that these data have been obtained from uncorrected projections

of titration curve tangents and, at this stage, are order-of-magni tude estimates only and

subject to revision [4].

Fc^ a system of i controlling ligands, the fraction of copper present as any one species Cu L-j is given by:

^ix (h)'

1 + ZE3i^(L.)><

463
Using the Bi values cited above for chloro and hydroxo species, together with literature data (log 3i, 62 ^ 10.0) for carbonato complexes, it is possible to calculate the

proportion of species present in seawater of pOH, pCl and PCO3 equal to 6, 0.26 and 3.6

respectively. Thus, table 3 provides a representative estimate.

Table 3

Approximate % fraction of inorganic copper species calculated for seawater

(pH 8; pCl 0.26; pCOj 3.6)

Major (%) Minor (% x 10*^)

CuCl+ 10.0

CuCl^- 98.8 CuOH+ 3.0

CuClo 1.0 CuCQO 1.6

Cu(0H)° 0.14 Cu(C03)2" 0.06

Cu2+ 0.01

It may be seen that some 99% of the total dissolved inorganic copper is present as

CuCltt" and that this order of magnitude predominance will not be greatly affected by

refinements of the stability constant data. These calculations have not, however, taken

account of potential mixed ligand complexes (notably OHCl ), and further experimental work

is required in this area.

The importance of copper chloro complexation in seawater has not generally been

appreciated (see table 1). In the absence of definitive formation constant data, carbonato

complexation seems to have been intuitively favored. A re-evaluation of the sorption

characteristics of this metal would be of considerable interest (cf. the behavior of HgCl^ ) Carbonato complexation may be supposed to predomimate in natural fresh waters. Table 4

illustrates a computation for waters having [CO3] of 2 x 10"^ M at pH 7:

Table 4

Approximate % fraction of inorganic copper species calculated for freshwater

([CO3] = 2 X 10"^ [OH] = 10'^)

Species %

CUCO3 51 5

Cu(0H)2 43 0

Cu2+ 4 3

CuOH+ 1 1

Cu(C03)2- 0 2

Fresh waters have quite variable carbonate ion contents, and the effect of this on the

pontential free copper ion concentration should be noted.

464
References

Burrell , D. C. , A review of the chemical speciation of copper in seawater, Mar. Soi.

Comrmn. , (in press, 1976).

Burrell, D. C. , Trace metal associations in fjord-estuarine environments. Unpublished

report to U.S. Energy Research and Development Adminstration, Institute of Marine

Science, University of Alaska (1975).

Bradford, W. L. , The determination of a stability constant for the aqueous complex

Zn(0H)2 using anodic stripping voltammetry, Lirmol. Oceanogr. 18:757-762 (1973).

Lee, M-L and Burrell, D. C, The chloro and hydroxo speciation of copper in a saline

medium, MS in preparation.

465

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

USE OF ION-SPECIFIC ELECTRODES IN STUDYING

HEAVY METAL TRANSFORMATION IN AQUATIC ECOSYSTEM

S. Ramamoorthy and D. J. Kushner

Department of Biology

University of Ottawa

Ottawa, Ontario, Canada

T. Introduction

The mobility of trace metals in fresh surface waters and their availability for

interconversions such as methylation into toxic forms depends on competitive physicochemical reactions with various compartments of the ecosystem. The following chemical

mechanisms partition trace metals in natural waters [1]^.

(1) Solution as ionic species and ionic associations.

(2) Complexing or chelating with dissolved organic molecules.

(3) Adsorption on sediments.

(4) Precipitation on solids.

(5) Incorporation into biological materials.

(6) Incorporation into crystal structures of mineral grains.

The compartment comprising metal ions complexed with dissolved organic molecules No. 2,

is especially important in determining the biological interactions of these metals, including

their toxicity. Organic-bound Hg compounds such as methylmercury are several orders of

magnitude more neurotoxic than inorganic Hg compounds. However, the rate of methylmercury

production depends on the concentration of free Hg^"*" in the ecosystem [2,3]. Lead alkyl

compounds are much more poisonous than free Pb^"*", and biological methylation of lead was recently shown to occur in certain natural conditions [4]. The increased toxicity of these

organometal 1 ic compounds may be due to their lipid solubility and hence transport across

cell membranes. In contrast, Cu^^ and Cd2+ are detoxified when these ions become chelated

[5-8]. Though all effects of complex formation on the biological activity of toxic metals

are not understood, the above considerations show that it is very important to determine

the chemical state of the toxic trace metals in surface waters. This may be more specifically

illustrated by considering the possible fates of Hg2+ ions in water.

2. Discussion

The forms in which metal ions are present in natural waters depends on pH, E^, presence

of chelators and other factors. The pH of natural waters is usually around 7, and Hg2+ and

Cu2+ ions are likely to be present in hydrolyzed forms, Hg(0H)2 and Cu(0H)2, if chelators

are not present. However, in the presence of chelators there will be competition between

the OH groups and the chelators for the heavy metal ion. The stability constants of Hg2+

-organochelators, for example, are several orders of magnitude higher than those of the

Hg^''"-hydroxy complexes; hence, Hg2+ will preferentially bind to chelators instead of being

^Figures in brackets indicate the literature references at the end of this paper.

467
hydrolyzed. Moreover, the pH-Eh relationship for the distribution of various charged forms

of mercury, HgO, Hg"*" and Hg2+ will be determined by the amount of Hg2+ bound to chelators.

The equation.

850 + 30 log [^^] (1

)

where E = potential in mV necessary for oxidation of Hg° to Hg2+ and k= the binding constant

representing the strength of binding between Hg2+ and ligand, shows that the higher the

value of k, the lower will be the value of E at which other forms are converted to a form

of Hg2+ able to combine with the ligand. The biological availability of Hg2+ for methylation

and other reactions within the biota is determined by the magnitude of the k factor.

If the organic ligands present in natural waters regulate the availability of the

trace metals to the biota, knowledge of the abundance and metal binding strengths of such

ligands may be essential in understanding the biological and toxicological effects of such

metals. The complexing capacity of natural waters has been measured by determining the

extent to which trace metals are complexed and held in bound forms. Several methods have

been used to measure this capacity [9-14].

Mercury entering natural waters is largely taken up by bottom sediments, and this

explains the low levels of mercury in water compared to the relatively high amounts in bed

sediments of the same ecosystem. The mechanisms for release of mercury from sediments are not well known, although it is clear that sediment types play an important role in making

mercury available for microbial production of methyl mercury. For example, mercury bound to

sulphides in sediment is not available for bacterial transformation unless preceded by an oxidation step [15,16], whereas organic-bound mercury and mercury bound on mineral grains

are readily available for bacterial methylation [17]. Jernelov [18], and Langley [19}

demonstrated that the rate of methylation in sediments does not correlate with the total

mercury content.

The correlation of heavy metal sorption-desorption characteristics of sediments with

respect to variables such as pH, time, sediment type (grain size, specific surface area,

cation exchange capacity, and organic matter) and natural/synthetic leachates, is important

in assessing the role of sediment compartment (No. 3) in regulating the release of these

metal ions into natural waters for further transformations.

Electrodes specific for anumber of different metallic cations have been developed in

the last few years. We have found that these provided rapid, convenient, and sensitive

ways of measuring very small amounts of free toxic metal ions. The ions so far studied

(Hg^+, Pb^"*", Cu^^, and Cd^"*") are all important pollutants in Canadian waters.

These solid state electrodes can detect low levels of metal ions with the following

limits of detection: Hg2+=lpg/l, Pb2+=20yg/l, Cu2+=2yg/l and Cd^+^lOyg/l; calibration plots

for these cations showed a perfect Nernstian response. In an uncomplexed medium, the

optimum pH for measurement of [Hg2+]f^ is 2-6, since Hg2+ undergoes hydrolysis at alkaline

pH's. In contrast to Hg2+ ion, the other cations hydrolyze only at pH values above 8.0 in an uncomplexed medium.

The specific-ion electrodes used were previously shown to give good Nernstian responses

to their respective cations in highly complexed media, show greater sensitivity, and are capable of detecting very low levels of M2+ ions in strongly complexed media, due to efficient

buffering of these cations [20]. Electrodes can be calibrated directly in terms of concen- tration, provided the total ionic strengths of the metal ion solutions used for calibration

and the test solutions are roughly similar. When the total ionic strength is below, lO'^M

(which is usually the case with metal ions in natural fresh waters) the difference in total

ionic strength between standards and test solution can be as large as fivefold without

resulting in serious errors.

468
Lower limit of detection for the ion-specific electrodes may be, in some cases, higher

than the levels of heavy metals found in natural environments. The metal binding constant

calculated under equilibrium conditions varies only with the activity of the metal ion.

Activity of such metal is equal to their concentration below 10" (the activity coefficient

of each metal ion is unity below lO'^M). Therefore, the calculated constants and hence

metal-speciation are applicable to concentrations below lO'^M without any correction.

Moreover, natural waters have a constant ionic background {10"^M) despite the trace levels

of heavy metal ions, thus making the extrapolation of data to trace levels valid.

The aquatic ecosystems studied ranged from simple two component systems such as river

sediment and water to multi-component such as river water containing dissolved micro- and

macrosolutes (of different size fractions), and particulate matter. Studies were also

carried out on heavy metal speciation in natural waters sustaining algal growth.

A. Mercury sorption and desorption characteristics of some Ottawa River sediments

Bed sediments of the Ottawa River downstream of the Gatineau River confluence are predominantly sandy, with variable organic contents, chiefly wood chips. Mercury sorption

by these sands was studied at constant temperature using a mercuric-ion specific electrode,

and varying added [Hg2+] and pH. Sorption rates are highest for organic-rich sands, but

variation in particle size is apparently not sufficient to reveal sorption trends related

to this parameter. Sorption data were fitted to a linear form of the Langmuir equation,

from which sorption maxima and mercury bonding coefficients were derived. The maxima do

not vary between samples, whereas the bonding coefficient relates most closely to organic

content. Mercury sorption was little affected by pH.

Desorption rates are lowrless than 1% Hg was leached from sediment after agitation in

distilled water for 70 hours, and a similar amount in fulvic acid solution. The mercurysediment bonding is evidently much stronger than that between fulvic acid and mercury,

irrespective of organic content of the sediment. Above studies have been extended to Pb,

Cd and Cu with variety of fresh sediments. Desorption of heavy metals in the presence of

CI" and NTA and metal displacement order were also studied.

B. Heavy metal binding components of river water

Ion-specific electrodes were used to measure the heavy metal binding capacity of river

waters near Ottawa. Binding capacity was measured in unfiltered water and in water passed

through filters retaining particles (0.45 ym) and macromolecules of molecular weight (MW)

45,000, 16,000 and 1,400. In the most studied water samples, almost all the Hg2+-binding

ability passed through the smallest filter. Filters of different pore sizes retained

substantial fractions of the binding ability towards other heavy metal ions. Binding

strengths and conditional binding constants were calculated for each metal ion and low MW

components of the Ottawa River water.

Binding in Ottawa River water was not due to HCO3 or CO3" ions; in the Rideau Canal,

and probably in other bodies of water, such ions caused a substantial amount of binding.

After complete ashing of Ottawa River water and reconsti tution with deionized water almost

all the metal binding ability was lost; thus, an organic compound(s) is responsible for

binding.

The binding pattern towards different metal ions of fulvic acid isolated from soil was different from that of unfiltered or filtered Ottawa River water. Fulvic acid is not the

sole binding component of this water. These experiments suggest a way of assessing the

importance of fulvic acid and other humic substances in heavy metal binding by natural

waters

.

469
C. Heavy metal binding by algae growing in natural waters

Algae can secrete many extracellular substances, including polypeptides, polysaccharides

and low molecular weight compounds. Many of these have the ability to bind heavy metal

(HM) cations. In addition, the external layers of algae might be, and in some cases have

been shown to be, important heavy metal binding sites. Ion-specific electrode techniques

have been applied to laboratory cultures of blue-green algae and also to natural algal

blooms in lakes and rivers. In the summer of 1975 Leamy Lake near Hull, Quebec showed an important bloom of blue-green algae, mainly Aphanizomenon flos-aquae and Anabaena spivoides,

which persisted eight weeks. Samples were taken at two week intervals until the bloom

disappeared. Heavy metal binding was determined in the lake water with algae suspended in

it and in fractions obtained after filtration through a 0.45ym filter as well as through

ultrafilters of different pore sizes, down to those retaining substances of molecular

weight greater than 500. The different suspensions and solutions were assayed for ability

to bind Hg2+, Pb2+, Cu2+, and Cd2+ ions. Chemical analyses for total organic and inorganic

carbon, CI", phosphate and other ions were carried out on the water samples.

A similar procedure was followed with samples taken above, inand below a thick bloom

of the filamentous green algal species, Ulothrix aequalis located in the Rideau River just

above the Rideau Falls by which this river enters the Ottawa River.

The bloom of blue-green algae caused very high metal binding, approximately one hundred

times that of water entering the lake. In contrast, the green algal bloom from the Rideau

River seemed to contribute little to metal binding by these waters.

Attempts were made to correlate the heavy metal binding in terms of the species composition of each bloom and the chemical composition of the water. It is evident from the

results thus far obtained that the kinds of algae causing a bloom can make a great difference

in the metal-binding potential of each bloom.

References

[1] Gibbs, R. J., Science, 180, 71-73 (1973).

[2] D'ltri, F. M., The Environment Mercury Problem, (CRC press, Ohio, 1972).

[3] Bisogni, J. J., Jr. and Lawrence, A. W. , Tech Beport No. 63 (Cornell Univ., Ithaca,

NY, 1973).

[4] Wong, P. T. S., Chau, Y. K. and Luxon, P. L., Nature 253, 263-264 (1975).

[5] Stiff, M. J., Wat. Res. 5, 585-599 (1971).

[6] Water Pollut. Res. Dept. Environ. London, England, Her Majesty's stationer office,

p. 36-41.

[7] Fleischer, M., Sarofim, A. F., Fassett, D. W., Hammond, P., Shacklette, H. T.,

Nisket, I. C. I., and Epstein, S., Environ. Health Perspect. 253-323 (May, 1974).

[8] Friberg, L, Piscator, M. , Nordberg, G. , and Kjellstrom, T. , Cadmium in the Environment,

2nd Ed. (CRC Press, Chemical Rubber Co. Ohio, 1974).

[9] Allen, H. E., Matson, W. R. , and Mancy, K. H., J. Water. Pollut. Control Fed., 42,

573-581 (1970).

[10] Kunkel , R. , and Manahan, S. E., Anal. Chem. 45, 1465-1468 (1973).

[11] Manahan, S. E., and Jones, D. R. , Anal. Lett. 6, 745-753 (1973).

[12] Davey, E. W. , Morgan, W. M. J., and Erickson, S. J., Limnol. Oceanogr. 18^, 993-997

(1973).

470
[13] Chau, Y. K. , and Lum-shue-chan , J. Wat. Res. 8, 383-388 (1974).

[14] Chau, Y. K. , Gachter, R., and Lum-shue-chan, K. , J. Fish. Res. Bd. Can. 31_, 1515-1519

(1974).

[15] Jernelov, A., Conversion of mercury compounds. Chemical Fallout, pp. 69-73 (Charles C. Thomas, Springfield, 111., 1969).

[16] Gillespie, D. C, and Scott, D. P., J. Fish. Res. Board. Can. 28, pp. 1807-1808 (1971 ).

[17] Wood, J. M. , Environmental Pollution by Mercury, Advances in Environmental Science and

Technology, Volume 2, pp. 39-56 (R. L. Metcalf and J. N. Pitts, Eds., Wiley-Interscience,

New York, 1971).

[18] Jernelov, A., Address to the Conference on Mercury in the Environment, Ann Arbor, Mich

(1972).

[19] Langley, D. G., Mercury Methylation, Am. Chem. Soo. I62nd Nat. Meeting, Div. of Water,

Air and Waste Chem., 11, pp. 184-186 (1971).

[20] Orion lonalyzer Instruction Manuals for Specific-Ion Electrodes, 1974, IM 94-53/4701.

1968, IM 94-29/869. 1 968, • IM 94-48/071 . 1972, IM 94-82/276.

471

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

ELECTROCHEMICAL STUDIES OF THE METHYLMERCURY CATION

Richard A. Durst

Analytical Chemistry Division

National Bureau of Standards

F. E. Brinckman and Kenneth L. Jewett

Inorganic Materials Division

National Bureau of Standards

John E. Doody, F.S.C.i

Christian Brothers College

Memphis, Tennessee

1. Introduction

Even before the discovery of the high toxicity and the environmental impact of methylmercury, organomercury compounds had been the subject of numerous electrochemical

studies. [l-7]2. Aside from the general agreement [8,9] that the reduction process occurs

in two one-electron steps producing first the organomercury radical and second, metallic

mercury plus the reduced organic radical, there has been little agreement on other aspects

of the reduction mechanism or the observed electrochemical phenomena. Much of the disagreement is due to the sensitivity of the reduction processes to subtle changes in pH,

ionic strength, depolarizer concentration, anion effects, etc., which lead to such electrochemical irregularities as prewaves, peak "splitting", and unexplained "reduction" peaks

during the anodic scan.

Our studies of the electrochemistry of methylmercury were undertaken for two purposes:

to gain a better understanding of the mechanisms of methylmercury redox processes and to use this information to develop an electrochemical procedure for the selective determination of methylmercury compounds. At this point in time, our preliminary data have

resulted in partial success toward both of these objectives. We have gained new insights

into the complexity of the mechanisms involved and have also demonstrated the feasibility

of using the first reduction step as the basis for the determination of methylmercury

ions.

2. Experimental 2

The cyclic voltammetry was performed using a PAR 170 Electrochemistry System with

both glassy carbon and hanging mercury drop electrodes. The pulse polarography was performed using a PAR 174 Polarographic Analyzer with the dropping mercury electrode. All

1 NBS Guest Worker, 1976-1977, NSF Faculty Research Participant.

2 Figures in brackets indicate the literature references at the end of this paper.

3

I In order to specify the procedure adequately, it has been necessary to identify commercial

' materials and equipment. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the material or equipment is necessarily the best available for the purpose.

473

I

I
supporting electrolytes were purified by continuous control led-potential electrolysis

using ESA 2014P Reagent Cleaning Systems. The pH of the samples was monitored with a combination pH electrode mounted in the voltammetric cell and with digital readout on a Radiometer PHM64 Research pH meter. A view of the voltammetric instrumentation is shown

in figure 1

.

Figure 1. View of the electrochemical instrumentation.

Solutions of Inorganic ions were prepared from analytical reagents obtained com- mercially. Methylmercury chloride and dimethylmercury were also commercial materials

checked for purity by infrared and nuclear magnetic resonance spectrometry prior to use. Both methylmercury nitrate [10] and methylmercury perchlorate [11] were synthesized by

literature methods. Prior to preparation of their solutions, the solid materials were

analyzed for residual by-product contaminations {e.g. , Ag"*" or Br") and found to be free of

such impurities. All methylmercury salt solutions were checked for proton-containing

impurities by NMR before dilutions [12]; in general all methylmercury reagents were estimated to be >98 percent pure.

Preparation of the organomercurials required the use of a grease-free high-vacuum

line and a recirculating N2 drybox. Methylmercurials were weighed in the drybox prior to

dissolution in Pyrex bottles fitted with Teflon caps previously washed with dilute HNO3.

Care was taken to maintain these ca. 10"^ M stock solutions in 0.01 M supporting electrolyte under N2 and away from fluorescent lights [13]. For each voltammetric study, a fresh

aliquot of the stock solution was delivered directly into the PAR electrode vessel contain

ing 50 ml of the supporting electrolyte under N2.

Initially, studies were performed using the glassy carbon electrode (GCE). These

studies gave us our first indication of some of the complexity that was to follow. In figure 2 is shown a voltammogram (two 20 mV/s cycles scanned from +0.8 to -1.8 V vs. SCE)

of an approximately 20 ppm solution of methylmercury chloride (MeHgCl) in 0.01 M KNO3.

The first cycle shows an irreversible reduction of MeHg'*' to the radical MeHg Tdrawn-out

peak at about -0.85 V) followed by the second reduction step to mercury metal at about

-1.55 V. The reverse scan of both cycles shows no significant oxidation process until

potentials more anodic than +0.1 V vs. SCE are applied. The mercury metal is stripped

474
475
(oxidized) from the glassy carbon as shown by the doublet peaks at about +0.25 V and

+0.45 V vs. SCE. During the second cathodic cycle, a new peak appears at +0.05 V, cor- responding to the reduction of mercuric ions produced during the previous anodic scan. Interestingly, the reduction peak of MeHg"*" shifts anodically to about -0.6 V and has the

appearance of a more reversible reduction. It appears from this shift that the MeHg"^ is more easily reduced at the mercury-plated glassy carbon electrode than on glassy carbon

itself. There is no change in the second reduction step.

Another interesting phenomenon was observed (fig. 3) when th^ GCE was rotated at

E VS. SCE

Figure 3. Cyclic voltammogram obtained with the

rotating glassy carbon electrode.

675 rpm and the potential scanned at 50 mV/s from +0.6 V to gradually increasing negative

potentials (0.1 V steps from -0.4 V to -1.6 V). Up to scan number 7 (-1.0 V), very little

reaction occurs. At #7, a slight mercury oxidation peak occurs at +0.1 V indicating a small amount of MeHg"*" was reduced to the metal during the cathodic scan. At scans #8 and

above, a new reduction process occurs in the region more negative than -0.5 V, but it only

appears during the anodic scan! As expected, the mercury oxidation peaks increase as the

cathodic scans increase in negative terminal values thereby producing more of the reduction

product (mercury). The anomalous reduction process occurring during the anodic scan is

apparently produced by the reduction of some adsorbed depolarizer. It was not possible,

however, to elucidate the nature of the species from the available data.

476
These studies and subsequent ones on a mercury-plated GCE, showed that some very

interesting phenomena were occurring during the anodic scan, which were dependent upon pH, scan rate, methylmercury concentration, surfactants, etc., and these effects were only

observable by cyclic voltammetry on a mercury electrode. Consequently, the remaining

studies described below were performed on a hanging mercury drop electrode (HMDE).

Of the hundreds of vol tammograms run on the HMDE under a wide variety of conditions,

several particularly interesting ones have been selected to illustrate the most significant results and the sensitivity of the electrochemical reactions to changes in the

experimental conditions.

In one series of experiments, solutions of MeHgNOs in 0.01 M NaClO^ were run at

several scan rates (50, 100, 200, 500, 2000 mV/s), pH from 2.1 to 11.2, and cyclic potential

scan from +0.1 to -1.7 V vs. SCE (except where hydrogen ion reduction interfered). The pH was adjusted by the addition of HNO3 purified by sub-boiling distillation or GAP highpurity NaOH. Since the solutions were not buffered (in order to avoid interactions,

e.g., complexation, adsorption, etc., with buffer anions), the vol tammograms in the neutral

region may be subject to significant pH variations in the vicinity of the electrode

surface during redox processes involving hydrogen ions. Future studies will examine the

effect of buffering.

In general, one type of voltammogram was observed at pH values lower than about 4,

another type at pH greater than 6, and very interesting but poorly reproducible effects in

the intermediate pH region.

In the pH <4 region, vol tammograms of the type shown in figure 4 were observed. Both

reduction peaks were observed [oa. -0.5 V and -1.3 V vs. SCE) during the cathodic scan. A

prewave (sometimes a doublet) was usually observed before the first reduction peak. The

size of the prewave was time dependent and is probably caused by slow adsorption of the

cation. During the reverse scan (anodic), a reduction "hump" was sometimes observed in

the region between -0.5 and -0.8 V and may be related to the production of molecular

hydrogen during the cathodic scan. At higher scan rates, a small oxidation peak occurs at

oa. -0.45 V, corresponding to the expected oxidation of MeHg* to the cation, MeHg"*".

In the neutral-to-basic range (pH 6-12), the most significant difference is the

appearance of a very pronounced reduction peak at about -1.2 V during the anodic scan

(fig. 5, 50 mV/s scan). This "inverse" peak is very dependent on the methylmercury

concentration, scan rate (decreasing with increasing scan rate as shown in fig. 5),

surfactants (disappears upon addition of Triton X-100), and only appears when the second

reduction step has occurred. The height of this peak is poorly reproducible even under

virtually identical experimental conditions, which further complicates its interpretation.

The only other differences between the basic and acidic cyclic vol tammograms are the

disappearance of the "hump" and a shift in the potential of the first reduction peak to more negative values as the pH is increased. This shift is consistent with the formation

of hydroxy 1 complexes with the methylmercury cation.

One other experimental parameter which has an enormous effect on the cyclic voltammograms is the methylmercury concentration. Above 10"^ M^, there appears to be much more

interaction between the reactants, products and electrode surface which produces con- siderable "fine structure" in the form of peak doublets and higher-order multiplets,

especially at potentials more negative than -1.0 V vs. SCE.

In the intermediate pH range, there is a considerable amount of peak formation,

disappearance, shifting, doubling, and blending which defy a unified description. The

only peak which shows reasonable stability at all pH values and most other operating

conditions is the first reduction peak. However, even this peak shows a shift to more

positive potentials as the concentration of methylmercury is increased.

477
T

Figure 4. Cyclic vol tammogram in acidic medium on the hanging mercury drop electrode.

478
Figure 5. Variations in cyclic vol tammograms caused by changes in scan rate.

Finally, to summarize the cyclic vol tammetry results, it appears that the first reduction step is reversible on a mercury electrode and suitable for the determination of methyl mercury. The second reduction peak is "usually" larger and sharper (less tailing) than the first reduction peak indicating some adsorption character along with perhaps catalytic or other regeneration of the electroactive species. The "inverse" peak observed during the anodic scan is highly dependent on kinetic factors and appears to be an electrode surface phenomenon involving the formation of a new electroactive species or a desorption

process. Some possible mechanisms are proposed in the next section.

3. Reaction Mechanisms

As indicated above, although the literature on this subject still contains conflicti

statements concerning reversibility, prewaves, and adsorption effects, it is generally

agreed that the reduction mechanism involves two one-electron reductions479
CHsHg^ + e" 'CHsHg- (1)

CHjHg- + e" —^CH^ + Hg° (2)

At high scan rates, the first reduction process approaches reversibility as indicated by

the development of the corresponding anodic peak. At slow scans, the peak disappears

suggesting a slow chemical reaction of the methylmercury radical. Several possibilities

exist for this following chemical step:

2 CHjHg ^(CH3Hg)2 .(CH3)2Hg + Hg° (3)

CHsHg. + nHg° ^CH,{Hg)- ^^^-^^^^^^{CH,)2Hq^^^ (4)

These steps may involve catalysis by or chemisorption onto the mercury electrode.

The second reduction in acidic solution is likely to be the generally -accepted

reduction to methane and mercury, reaction [2] above. This reaction effectively removes

the intermediate products from further activity, and thus the "inverse" peak is not seen

in acidic solutions except at higher methylmercury concentrations where the H"*" con- centration at the electrode surface is reduced. In basic solution, the following sidereaction may be postulated:

CHsHg. + e^;—^[CHsHg-] —^3Ha^(CH3Hg)2 (5)

and the reduction of this dimer, or its disproportionation product, dimethylmercury , may

be the species reduced during the anodic scan. This latter possibility was tested by

comparing the reduction of dimethylmercury to that of methylmercury. As can be seen in

figure 6, the dimethylmercury reduction produces a very drawn-out peak at aa. -1.1 V vs. SCE. When methylmercury chloride is added to this solution, the usual reduction peaks are superimposed on the dimethylmercury vol tammogram. Although there is a distinct difference

of about 100 mV between the two peak potentials (at aa. -1.1 and -1.2\/ vs. SCE) which would

indicate that the "inverse" peak is not due to dimethylmercury reduction, the overall illdefined nature of these peaks and the possibility of shifts caused by adsorption cannot allow

us to rule out the dimethylmercury reduction mechanism.

In summary, the overall mechanisms postulated for the observed electrochemical

reactions of the methylmercury cation are shown in figure 7. This scheme is based on cyclic voltammetric studies alone. Further work is planned by other techniques to help

elucidate the mechanisms.

4. Quantitative Analysis

Based on the foregoing observations, it was decided that the first reduction step

provided the best electrochemical reaction for the voltammetric determination of methylmercury. Using differential pulse polarography, preliminary measurements indicate that

this technique will be applicable to ppb levels of methylmercury and above. It is un- likely, based on our present data, that this technique will provide precise data below the

ppb level. Studies are in progress to improve both the sensitivity and precision of the

technique, and to determine methylmercury in the presence of other organomercurials and a number of interferences, including metal ions and complexing agents.

This work was supported in part by the Environmental Protection Agency, Office of

Energy, Minerals and Industry.

480
(CHglsHg in KNO3/KCI

SAME SOLUTION + CHsHg CI

50 mV/s

HMDE

•E VS. SCE

Figure 6. Comparison of dimethylmercury and methylmercury

cation voltammograms.

431
CHgHg*

CHoHg

OXIDATION -e 1

e- 1ST REDUCTION

r

CHgHg'

e' 2ND REDUCTION

(CHgHgjj CHgHgCHoHg

Hg% {CH3)2 Hg

^

(CHgHgjg CH4+ Hg'

e e' "INVERSE" REDUCTION

T t

CHgHg. + CH'g CHgHg. + CHgHg

Figure 7. Proposed mechanisms for the observed electrochemical behavior

of the methylmercury cation.

482
References

[I] Kraus, C. A., J. Amer. Chem. Soc, 35, 1732 (1913).

[2] Benesch, R. and Benesch, R. I., J. Amer. Chem. Soc, 73, 3391 (1951 ).

[3] Benesch, R. and Benesch, R. E., J. Phys. Chem., 56, 648 (1952).

[4] O'Donnell, M. L., Schwarzkopf, A., and Kreke, C. W., J. Pharm. Sai., 52, 659 (1963).

[5] Hush, N. S., and Oldham, K. B., J. Eleatroanal. Chem. 6, 34 (1963).

[6] Toropova, V. F., Saikina, M. K. , and Khakimov, M. G., Zh. Obshch. Khim., V_, 47

(1967).

[7] Jensen, F. R., and Richborn, B., Eleotrophilia Substitution of Organomerourials

,

McGraw-Hill, New York, pp. 137-142 (1972).

[8] Fleet, B. and Jee, R. D., J. Eleatroanal. Chem., 25, 397 (1970).

[9] Heaton, R. C. and Laitinen, H. A., Anal, chem., 46, 547 (1974).

[10] Johns, I. B., Peterson, W. D., and Hixon, R. M., J. Amer. Chem. Soc, 52, 2820 (1930).

[II] Goggin, P. L. and Woodward, L. A., Trans. Faraday Soc, 58, 1495 (1962).

[12] Hatton, J. V., Schneider, W. G., and Silbrand, W., J. Chem. Phys., 39, 1330 (1963).

[13] Jewett, K. L., Brinckman, F. E., and Bel lama, J. M., ACS Symp. Ser. 18, Marine

Chemistry in the Coastal Environment (T. Church, Ed.) pp. 304-318 (1975).

483

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

AN ELEMENT-SPECIFIC TECHNIQUE FOR THE ANALYSES

OF ORGANOMETALLIC COMPOUNDS

Y. K. Chau and P. T. S. Wong

Canada Centre for Inland Waters

Burlington, Ontario

1. Introduction

Biclogical methylation of elements to their methyl derivatives has been documented

for several decades. Its environmental significance has only recently been the subject of

increasing concern since the discovery of mercury methylation in sediments. Biological

transformation of several elements has been reported [1-6]^. In many cases the compounds

are transformed into volatile forms. Here we describe a technique, primarily developed to

study the biological transformation of elements at their environmental concentration

levels. This technique utilizes the features of the combination of gas chromatography and

atomic absorption spectrometry (AAS) to provide the capability of separation and specificity for the analyses of low boiling organometall ics in gaseous and liquid forms.

2. Instrumentation

A MicroTek Gas Chromatograph 220 and a Perkin Elmer Atomic Absorption Spectrophotometer 403 were used to build the system. Any GC instruments with temperature programming

capability and AAS with background correction accessory can be used. The coupling of

these two instruments was made by a transfer line of a stainless steel tubing, 2 mm

o.d., connected to the GC column outlet at one ena, and to the silica furnace tube of the

AAS at the other end. For alkyl derivatives of mercury, a Teflon transfer line of similar

size was used to reduce the possibility of decomposition and adsorption of the mercurials

to the stainless steel tubing. The transfer line was wrapped with heating tapes. In all

the analyses, the background corrector was used, and an integrator was used to measure

peak areas.

3. The Sample Trap

The gaseous sample was collected in a sample trap made of a glass U-tube, 6 mm dia.,

26 cm long, packed with 3 percent OV-1 on Chromosorb W (80-100 mesh), and immersed in a dry ice-methanol bath at aa. -70 °C. The sample was drawn through the trap and metered by

a peristaltic pump at 130-150 ml/min. The trap was connected to a 4-way valve installed

between the carrier gas inlet and the injection port of the GC. After warming up the trap

to ca. 80-90 °C in a hot water bath, the sample was swept to the GC column by diverting

the carrier gas in the 4-way valve. For samples in liquid forms (organometals absorbed in

solvents), they can be directly injected into the GC column through the injection port.

4. The AA Furnace Tube

The furnace tube was made of silica tubing, 7 mm i.d., open at both ends. Two types

of furnace design were used. Type A: The furnace tube was 4 cm long. The GC effluent

was introduced to the center of the furnace tube through a side arm. Hydrogen was added

at the same point, the burning of which improved the atomization of the elements. The

furnace tube was wrapped with asbestos and Chromel wire, and heated electrically to na. 980-1000 °C regulated by a variable transformer (fig. 1).

I Figures in brackets indicate the literature references at the end of this paper.

485
Ca. 20V a.c.

4cm.

x±kj\

7 mm.

8 cm.

H

FROM G.C

SILICA FURNACE A

Figure 1. Silica furnace type A.

486
Type B: For certain elements notably As and Se whose absorption lines (194 nm and

196 nm respectively) are in the far UV region (where organic solvents and hydrocarbons

absorb), a pre-combustion section made of silica tubing (3 mm o.d., 10 cm long with a side

arm for air supply) attached to the furnace, was found necessary to "burn off" the interfering organics. Both sections of the furnace were heated to aa. 980-1000 °C (fig. 2).

Both types of furnace were mounted on top of the AA burner and aligned to the light path.

SILICA FURNACE 'b"

Figure 2. Silica furnace type B.

487
5. Operation Parameters

The following is a listing of instrument parameters for the analyses of a number of

alkyl metallic compounds. The GC column used was glass, 6 mm dia., 1.8 m long, packed

with 3 percent OV-1 on Chromosorb W, 80-100 mesh, unless otherwise specified. Gases

supply: N2 40 psi; H2 20 psi; Air 30 psi. Sensitivity on the AAS was set at 0.25 A Full

Scale (4X expansion)

.

Pb alkyls (Me^Pb, MejEtPb, Me2Et2Pb, MeEtgPb, Et^Pb) [7]:

GC: carrier gas N2 70 ml/min, temperature programs, initial 50 °C for 2 min,

15 °C/min until 150 °C, injection port temp. 150 °C, transfer line 150 °C.

AAS: 217 nm line, lamp current 8 mA, spectral band width 0.7 nm, furnace type

A, H2 135 ml/min.

Se alkyls (Me2Se, Me2Se2) [8]:

GC: N2 70 ml/min, temperature programs, initial 40 °C for 2 min, 15 °C/min until

120 °C, injection port 225 °C, transfer line 120 °C AAS: 196 nm line, lamp

current 15 mA, spectral band width 2 nm, furnace B, H2 120 ml/min, air 130 ml/min.

As alkyl arsines (MeAsH2, MejAsH, MejAs):

GC: column 10 percent OV-1 on Chromosorb W, carrier gas N2 30 ml/min, temperatures,

oven 25 °C, injection port 25 °C, transfer line 100 °C. AAS: 193.7 nm line,

lamp current 14 mA, spectral band width 0.7 nm, furnace B, H2 120 ml/min, air

130 ml/min.

Hg alkyls (MeHgCl , EtHgCl):

GC: column 5 percent DEGS on Chromosorb W, carrier gas N2 80 ml/min, temperatures,

oven 145 °C, injection port 150 °C, transfer line. Teflon, 150 °C. AAS:

253.6 nm line, lamp current 15 mA, spectral band width 0.7 nm, furnace A, H2

260 ml/min, mixed with air at 90 ml/min.

Cd alkyl (MeCd):

GC: N2 70 ml/min, temperatures, oven 70 °C , injection port 80 °C, transfer line

80 °C. AAS: 228.8 nm line, lamp current 8 mA, spectral band width 0,7 nm,

furnace A, H2 135 ml/min.

6. Standardization

Most of the alkyl compounds in this study were obtained from Alfa Chemicals (Beverly,

Mass.). The mixed alkyls of lead were provided by Ethyl Corp, (Ferndale, Mich.). Methylarsine and dimethylarsi ne were prepared according to Braman et al. [9j, The method was calibrated by injecting a known amount of a standard (about 10 ng as the element) to the

GC through the injection port or through the sample trap, and measuring the peak area.

7, Results and Discussion

The retention times established with the standard compounds were used for the identification of the compounds. As an atomic absorption spectrophotometer was used as the

detector, the response was related to the element. Different alkyl compounds of the same element gave the same absorption response.

The hydrogen introduced to the furnace tube was to generate a small burning jet which

was found to improve the sensitivity. Since the conventional flame was not used in the

atomization, the baseline was stable and higher scale expansion could still be used if

desired. With a 4X expansion, the detection was about 0.1 ng of the element. Figure 3

shows the recorder tracings of several alkyl compounds.

488
80

80-

Me2Cd

(10 ng)

CO

£ 40

CO

J L 2

min.

80 -

CO

o

00 40 -

Me Hg CI

20 ng Hg

Et Hg CI

20 ng Hg

J I L

2 4

min.

60-

coi 40

QCO

20-

V)

<

cn <

CO

_csi <j

CM

<03

03

J L2 4

min.

Figure 3. Recorder tracings of several alkyl metal compounds.

489
This technique has been applied to the studies of methylation of lead [5] and selenium

[6] in the environment.

References

[1] Wood, J. M., Scienae 183, 1049 (1974).

[2] Braman, R. S. and Foreback, C. C, Soienae J82, 1247 (1973).

[3] Huey, C. W. , Brinckman, F. E., Grim, S., and Iverson, W. P., Proo. Int. Congress on Transport of Persistent Chemicals in Aquatic Ecosystem, Q. N. Laltam, Ed, (NRC,

Canada, 1974) pp. 11.73 to 11-78.

[4] Huey, C. W. , Brinckman, F. E., Iverson, W, P., and Grim, S., Abstract-Program,

Int. Conf. Heavy Metals in the Environment, Toronto, 1975, C-214.

[5] Wong, P. T. S., Chau, Y. K., and Luxon, P. L., Nature (London) 253, 263 (1975).

[6] Chau, Y. K. , Wong, P. T. S., Silverberg, B. A., Luxon, P. L., and Bengert, G. A.,

Science 192, 1130 (1976).

[7] Chau, Y. K., Wong, P. T. S., and Goulden, P. D., Anal. Chim. Acta 85, 421 (1976).

[8] Chau, Y. K. , Wong, P. T. S., and Goulden, P. D., Anal. Chem. 47, 2279 (1975).

[9] Braman, R. S., Johnson, D. L., and Foreback, C. C, First NSF Trace Contaminants

Conf. Oak Ridge, 359 (1973).

490
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

CHROMATOGRAPHY - ATOMIC SPECTROSCOPY COMBINATIONS.

APPLICATIONS TO METAL SPECIES IDENTIFICATION AND DETERMINATION

Douglas A. Segar^ and Adrianna Y. Cantillo^

1. Introduction

Determination of the concentration of a trace metal in an environmental sample is

often a difficult task. The identification of the chemical species of the metal in such a sample is much more difficult, so difficult that such analyses have rarely been performed.

Nevertheless, the chemical form of an element is critically important in determining the

properties of the element in an ecosystem. For example, methylmercury is more toxic and

fat soluble than inorganic mercury compounds, whereas the cupric ion is more toxic to algae

when it is not chelated.

Most analytical techniques that are capable of identifying a metal species, particularly

metal -organic compounds, require a sample with a high concentration of the species in a simple matrix, because of their lack of sensitivity and specificity. Within the last several

years, relatively simple and inexpensive analytical systems have been introduced which interface chromatographic separations with the high sensitivity of atomic spectroscopy detectors.

The simplest of this new family of chromatography - atomic spectroscopy techniques is

the combination of gas-liquid chromatography and flame or flameless atomic absorption spectroscopy. The availability of this simple technique has enabled many laboratories to determine, simply and routinely, in environmental samples the concentrations of volatile

organometal 1 ics , such as the alkyl compounds of lead, selenium, arsenic, and cadmium. In only a short period, the data obtained have dramatically improved our knowledge of the occurrence and importance of alkylated metals in the environment.

Several other chromatographic-atomic spectroscopy combinations have been reported in

the literature. The most promising of these is perhaps the combination of a high-pressure

liquid chromatograph with a flameless atomic absorption spectrophotometer. The principle

advantage of this combination compared to the gas chromatography systems is its potential

for analysis of the nonvolatile metal -organic compounds. Very little is known about the

occurrence, transformations, and effects of these compounds in the environment despite

their much greater abundance than volatile metal species.

2. Discussion

The flameless atomic absorption high-pressure liquid chromatograph can be used in two

modes. In one mode, the eluant flow through the chromatographic column is continuous and

the flameless atomic absorption detector samples a fraction of the eluant stream every

several minutes. In a second mode, the flow of the high-pressure liquid chromatograph is

either stopped between injections to the flameless atomizer or flows at a rate such that

virtually all of the column effluent is passed into the atomizer. The first mode is useful

where it is desired to save a portion of the column effluent fractions for further characterization of the eluted species. The second mode is used when the quantity of material

separated is limited.

^National Oceanic and Atmospheric Administration, National Ocean Survey/Office of Marine

Technology, Engineering Development Laboratory, 6001 Executive Boulevard,

Rockville, Maryland 20852, USA.

^National Oceanic and Atmospheric Administration, Atlantic Oceanography and Meteorological

Laboratories, 15 Rickenbaeker Causeway, Miami, Florida 33149, USA.

491
Preliminary investigations of the copper compounds in coastal sea waters have been

carried out using gel filtration on molecular exclusion gels (Sephadex) and microporous glass

beads. Several different fractions of the metals are eluted from the columns. However,

adsorption (particularly with the Sephadex) and reactions apparently caused by ionic strength,

composition, and pH changes during passage through the column have made interpretation of the

data difficult. It has not been possible to obtain trace metal and organic-free sea water

for use as an eluant. Elution has, therefore, been carried out using dilute acid solutions

and high molecular weight complexes which proceed down the column faster than the ionic

salts, experiencing a different physicochemical environment. As the complexes pass ahead of

the ionic form with which they are in equilibrium, they will dissociate. The net effect of

the separation, if adsorption does not occur, is that nondissociable excluded metal -organic

compounds pass through the column with the void volume or the volume characteristic of their

molecular weight. Excluded dissociable metal-organic compounds cause the peak at the salt

volume to be broadened and shifted forward (see fig. 1). The degree of broadening and shift

is a complex function of the stability constant of the complex, its rate of dissociation, the

stoichiometry, and the characteristics of the column including the flow rate. In general,

the preliminary studies have shown that both dissociable and nondissociable compounds of

copper are present in the sea water samples (New York Bight) which had been filtered and

acidified to a pH of about 1. An aqueous extract of a marine sediment sample from the same area showed predominantly nondissociable excluded compounds. It should be emphasized that

the compounds that are eluted in the column void volume need not necessarily be metal -organic

but could equally be colloidal and inorganic in nature.

VOID

VOLUME

SALT

VOLUME

METAL

TOTALLY EXCLUDED

CONCENTRATION IN ELUANT

NONDISSOCIABLE COMPOUNDS

PARTIALLY EXCLUDED

""^1 \ NONDISSOCIABLE COMPOUNDS

EXCLUDED

DISSOCIABLE

COMPOUNDS

INORGANIC

SALTS

ELUTION VOLUME

Figure 1. Metal complex separations from sea water by microporous glass bead

molecular exclusion chromatography.

492
Successive additions of 40 and 200 ppb of ionic copper to the sea water sample led to

successive shifts of the broad dissociable complex peak towards the salt volume. However,

the bulk of the added copper was still eluted ahead of the salt indicating that the excess complexing capacity of this water sample was high.

3. Conclusion

The potential applications of the flameless atomic absorption high-pressure liquid

chromatograph are diverse. Many column solid phase materials and eluants, sample types, and

separation conditions are possible. However, the applications of molecular exclusion chromatography appear to be possibly the most exciting. Several different experiments are possible

which offer the promise of quantitative characterization of the stability constants, kinetics

of dissociation of metal complexes (with naturally-occurring organics) and the complexation

capacity of natural waters. This information is vital to the understanding of trace metal

toxicity and biological uptake in natural waters. One of the possible experiments can be

carried out as follows. The natural water sample is passed continuously through a column of

molecular exclusion support (microporous glass beads) until the metal concentration in the

effluent is equal to the concentration at the input. A spike of the water sample with

additions of either metal or a chelating agent is then passed onto the column and elution is

continued with the unspiked natural water sample. The position and magnitude of the peak of

higher or lower metal concentrations in the effluent may then be related to the complexation

processes occurring in the natural water sample. This approach is similar to the method of

stability constant determination for metal organic complexes proposed by Hummel and Dreyer^.

The flameless atomic absorption high-pressure liquid chromatograph will permit such experiments to be carried out in natural waters with concentrations of metals and organic com- plexing agents within the natural range. More important, however, is the ability to investigate the response of organic matter to metal additions (and vioe versa) in natural water

samples without being first required to separate and identify the organic compounds involved.

^Hummel and Dreyer, Bioahim. Biophys. Acta. v. 63, p. 530, 1962.

493

NATIOMAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

CHANGES IN THE CHEMICAL SPECIATION OF ARSENIC

FOLLOWING INGESTION BY MAN

Eric A. Crecelius

Battel le-Northwest

Sequim, Washington 98382, USA

1. Introduction

Of the chemical forms of arsenic to which man is normally exposed, trivalent arsenicals

are the more toxic. Little information is available on the changes in the chemical forms

of arsenic that occur within the body. However, reviews and summaries on the biochemistry

of arsenic in man indicate the following: 1) arsenic which enters the blood stream is

excreted mainly in the urine; 2) arsenic has a biological half-life of 30-60 hours; and 3)

arsenic is excreted in urine in several forms, including arsenite (As"'"^), arsenate (As"*"^),

methylarsonic acid (MAA), dimethyl arsinic acid (DMAA), and other organically bound arsenic

compounds. Other information on the behavior of arsenic in the human body that is either

contradictory or unsupported includes such suggestions as: 1) As^^ accumulates in the

body; 2) As+2 is oxidized to As+^ in the body and then excreted; and 3) As+3 and/or As''"^ are methylated in the body.

Because As+3 is much more toxic than As"*"^, MAA and DMAA, processes that convert As+^

to other forms may be part of the body's normal protective response of detoxification. The

purpose of this study was to determine in a semiquantitative manner the chemical species

and excretion rates in urine following ingestion of known arsenic species. The results were expected to provide insight into the possible arsenic reactions and their rate within

the human body.

2. Experimental

Three different chemical forms of arsenic were ingested: 1) As+^-rich wine; 2) As"*"^ -rich drinking water; and crab meat that contained an unidentified organo-arsenic compound.

For several days after the ingestion of the arsenic-containing material, urine samples were analyzed for As+3, As"*"^, MAA and DMAA. The species of arsenic were selectively reduced to

volatile arsenic compounds and then detected using an emission spectrometer equipped with a helium plasma excitation source [1]^.

3. Results

In the As+3-rich wine ingestion experiments within 5-10 hours after ingestion, the

urinary levels of As+3, As+^, MAA and DMAA had each increased by about a factor of five.

The levels of As"'"^ and As+^ rapidly decreased and were near normal 20 hours after ingestion. However, the MAA and DMAA levels remained elevated, reaching the maximum levels about

Figures in brackets indicate the 1 iterature_ references at the end of this paper.

495
40 hours after ingestion, then gradually approached normal levels 85 hours after ingestion.

Approximately 80 percent of the ingested arsenic was excreted in the urine within 61 hours.

The major species of arsenic excreted was DMAA, which accounted for about 50 percent of the

63 Mg of arsenic ingested. Arsenite and As+'^ each accounted for 8 percent and MAA for

14 percent.

Several urine samples were analyzed for organically bound arsenic (non-reducible

arsenic) by first digesting with hot acids and then analyzing for As+^. This procedure

indicated that organically bound arsenic accounted for an insignificant amount of the

arsenic in these samples.

In the As"'"^-rich water ingestion experiment, the level of urinary As"*"^ remained at the

normal level of 1 to 2 ppb; however, As+^ did show a marked increase during the first 8

hours after ingestion. The greatest arsenic excretion occurred 10 to 30 hours after

ingestion as the DMAA form.

Both the As+2 and As"*"^ ingestion experiments indicate that inorganic arsenic can be

excreted from the body, but the majority is methylated in the body and excreted as DMAA.

In the crab ingestion experiment, 340 grams wet weight of Dungeness canned crab was

eaten. During the following three days, no elevated level of As"*"^, As+^, MAA or DMAA was detected in urine. However, when urine samples (collected 1020 hours after ingestion) were treated with hot 2 N NaOH, high levels of DMAA were detected (200-300 ppb). The presence of

high concentrations of DMAA only after NaOH treatment suggests that the arsenic is in an organic compound that cannot be broken down to inorganic arsenic, MAA or DMAA in the human

body. Arsenic in crab muscle is apparently unavailable to humans because of the chemical

form. The small amount of data available indicates that other marine shellfish and fish

contain this same arsenic compound which is not broken down by cooking, mild acids or human

di gestion

.

Children living near the Tacoma, Washington copper smelter have been shown to often

have high urinary and blood arsenic levels. The chemical species of arsenic in urine

samples from these children showed a pattern of elevated levels of both As+3 and DMAA

indicating ingestion and/or inhalation of As+3 and excretion of DMAA.

References

[1] Braman, R. S. and Forelock, C. C, Science 182 1247 (1973).

496
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

THE DETERMINATION OF LEAD IN AQUEOUS SOLUTIONS BY THE DELVES CUP TECHNIQUE

AND FLAMELESS ATOMIC ABSORPTION SPECTROMETRY

Haleem J. Issaq

NCI Frederick Cancer Research Center

Frederick, Maryland 21701, USA

1. Introduction

The use of the Delves Cup Technique for the determination of lead in blood by atomic

absorption spectrometry has been previously reported [1].-^ The method was elaborated by

Fernandez and Kahn [2], and modified by other investigators [3,4,5].

Although the Delves Cup technique represents a reliable and rapid microsampling method

for the determination of lead in blood by atomic absorption spectrometry, it failed to give

satisfactory results for the determination of lead in aqueous solutions [1,4,5] and in urine

[4]. The reasons given for this failure are varied and sometimes contradictory. Delves [1]

showed that the lead absorption signal in aqueous solutions is less than that in whole

blood. He attributed this to the occlusion of the analyte in a matrix that may be more or

less volatile than the analyte itself. Another explanation was given by Olson and Jatlow

[4], who attributed the loss of signal in aqueous solutions to the penetration of the aqueous

standards into the cup surface, which leads to broad absorption peaks. Another explanation

[5] suggested that the lack of signal in aqueous solutions is due to the capillary migration

of the solution over the edge of the cup, thus leading to low and imprecise signals. This

explanation has been accepted by other workers in the field [6,7].

The purpose of this paper is to offer an experimentally based explanation of the

decreased lead absorption signal when aqueous solutions containing lead are analyzed.

2. Experimental

Apparatus: A Perkin-Elmer Model 403 atomic absorption spectrophotometer with a deuterium

background corrector, a strip chart recorder and a lead hollow cathode lamp (Westinghouse)

was used. The Perkin-Elmer Delves Microsampling System and nickel cups were used without

any modifications. The 283.3 nm line was employed for the detection and measurement of the

Pb signal

.

Reagents: All reagents, unless otherwise stated, were of analytical grade. Deionized water

was used in all sample preparations. The stock lead solution (1000 ppm certified atomic

absorption standard) and activated charcoal were obtained from Fisher Scientific. Eppendorf

microliter pipets with disposable plastic tips were used for sample handling.

Frocedure: The bottoms of the cups were covered with activated charcoal, then introduced

into the flame until no signal was observed. Following this conditioning, 10 pi of 0.4 mg/ml

lead aqueous solution were pipetted into the cups which were then dried at 140°C on a hot

plate. The cups were removed and allowed to cool to room temperature after which 20 yl of

hydrogen peroxide were added. The cups were re-dried and samples were then analyzed and the

signals recorded. Care was exerted in handling the cups so that no charcoal was spilled.

The usual procedure for lead determination in blood was then followed [2].

^Figures in brackets indicate the literature references at the end of this paper.

497
3. Results and Discussions

A comparison of lead absorption signals, with and without activated charcoal in the

cups, is given in figure 1. The results show that the signals from cups containing charcoal

is higher than that in cups without charcoal (CWC). Furthermore, the signal in CWC is

broader and less uniform than that in the charcoaled cups. It has been suggested [4] that

the broad peak in the CWC case is due to penetration of the aqueous standard into the cup

surface. It is a known fact that charcoal surfaces are highly absorbent, yet the signal in

the charcoaled cups is of narrow peak width and more intense than that in CWC. This suggests

that penetration of the sample into the cup surface may not account for the decreased

sensitivity. Berthel et al. [5], in contrast, argued that decreased signals occur as a result of capillary creepage of the sample from the cup. Since water has a surface tension

of 71.97 dynes/cm at 25°C [8], it is difficult to conceive that water would creep up the

cup. In addition, when blood samples are analyzed for lead, hydrogen peroxide is added to

the dried blood in the cup, a froth is generated which fills the cup to the rim, and a considerable residue is left on the walls of the cup after drying. It is thus clear, from

the observation reported here, that Pb losses due to creeping or penetration phenomena do

not account for diminished Pb signals when aqueous solutions are analyzed.

Figure 1. Comparison of aqueous lead signals (4 ng) without charcoal (a)

and with charcoal (b)

.

498
The lead signal in blood samples is higher than an equivalent concentration in aqueous

solutions clearly because of a more efficient mechanism of generating free lead atoms. It

is our belief that the carbon left in the cup, after incomplete oxidation with hydrogen

peroxide (this is clearly indicated from the smoke peak that precedes the signal peak),

offers a more favorable reducing atmosphere for the generation of lead atoms in the flame.

Figure 1 supports this hypothesis, where the lead signal in a charcoaled cup is more intense

than in the CWC case. It had been presumed [4] that coating a cup with albumin prevents the

penetration of the solution into the cup. Albumin (a good source of carbon), affords the

same vital characteristics as blood and charcoal, a favorable reducing atmosphere in the

flame. It was shown [2] that the use of dilute albumin bovine solution (2 percent W/V) as the diluents for lead standards produced no change in sensitivity when the graphite furnace

was used. This is understandable since the graphite tube itself offers a very favorable

reducing atmosphere for lead ions.

It is suggested here that if charcoal is employed, the signal of lead in aqueous

solutions is equivalent to that in blood having the same lead concentrations. This is shown

in figure 2.

10.0-

E

o

CO

5.0-

Time (sec.)

I—

I

10 sec.

Figure 2. Comparison of lead signals (4 ng) in aqueous solutions added

to charcoal (a) and to blood (b).

499
The graphite tube atomizer can be successfully used for the analysis of lead in aqueous

solutions, blood and urine. However, each sample should be treated individually, i.e., dry,

char and atomize; while with the Delves Cup, 20 samples can be treated with hydrogen peroxide

at the same time, then atomized individually. While the Delves technique is faster, the

tube is more reproducible and more sensitive.

The procedure for the analysis of clinical or biological samples by the tube is as follows: 20 pi of hydrogen peroxide are pipetted into the tube followed by 10 pi of the

sample to be analyzed, heated for 40 s at 70°C, charred for 40 s at 400°C, then atomized for

5 s at 2100"C. A caution is offered here, the drying temperature should be below 110°C to

revent sputtering of the sample, also to prevent the H2O2 from drying too fast. Sputtering

eads to irreproducible results, fast drying prevents complete oxidation of the sample.

Addition of the sample to the hydrogen peroxide is preferred to adding the H2O2 to the

sample, because the blood (for example) is pipetted into a pool of H2O2 which oxidizes it

all; while, if H2O2 is added to the blood, the bottom of the blood droplet is facing the

graphite and might not digest completely. When analyzing for lead in aqueous solutions, the

hydrogen peroxide is not needed. However, hydrogen peroxide or nitric acid 2 v/v percent

should be added to the solution to prevent the adsorption of lead to the containers surface.

[10]

References

[1] Delves, H. T., Analyst, 95, 431 (1970).

[2] Fernandez, F. J., and Kahn, H. L., At. Absorption Newsletter, 10, 1 (1971).

[3] Ediger, R. D., and Coleman, R. L., At. Absorption Newsletter, 11, 33 (1972).

[4] Olson, E. D., and Jatlow, P. I., Clin. Chem. , 18, 1312 (1972).

[5] Barthel, W. F., Smreck, A. L., Angel, G. P., Liddle, J. A., Landrigan, P. J., Gehlbach,

S. H., and Chisolm, J. J., JAOAC, 56, 1252 (1973).

[6] Ediger, R. D., Perkin Elmer Corp., Norwalk, CO., Private Communication (1974).

[7] Beaty, R., Perkin Elmer Corp., Gaithersburg, MD, Private Communication, (1974).

[8] Handbook of Chemistry and Physios, 50th Edition, 1969-70, pp. 5-30.

[9] Fernandez, F. J., Atomic Absorption Application Study No. 512, Perkin Elmer Corp.

Norwalk, CO.

[10] Issaq, H. J., and Zielinski, W. L., Jr., Anal. Chem., 46, 1328 (1974).

500
Part X. THE STATUS OF REFERENCE MATERIALS FOR ENVIRONMENTAL MEASUREMENT

iceedings of the 8th IMR Symposium

d September 20-24, 1976, Ga i thersburg , Md. (Issued November 1977).

THE STATUS OF REFERENCE MATERIALS FOR ENVIRONMENTAL ANALYSIS

John K. Taylor

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

The growth of modern analytical chemistry has generated a parallel demand for well

characterized reference materials for the evaluation of analytical data and for further

development of measurement procedures. The emergence of instrumental techniques, often

comparative in nature, hence completely dependent on calibration materials, has further

accentuated this need. In the environmental area, regulatory measures are requiring trace

analysis of air, water, and process and waste materials for exotic substances at concentration levels that would have sounded fantastic only a few years ago. Because of quality

assurance requirements for these measurements, their traceability to national standards is

fast becoming a legal requirement.

The present situation was anticipated, in part, as early as 1966 when the NBS program

for development of Standard Reference Materials was initiated. Progress has been slow

partly because of the level of funding available, but largely because of the need to solve

problems concerned with the accurate measurement of low concentrations of reactive or

labile materials and stabilizing them for long-term storage as required for Standard

Reference Materials.

The ideal SRM would duplicate in all respects the samples routinely analyzed, both

with respect to form and composition. Unfortunately, this is rarely achieved. Both air

and water samples are complex in nature and consist of dynamic systems which are entirely

unsuitable as reference materials. Accordingly, the best that can be achieved is to

simulate the analytical problems, as far as practical, within the accuracy and stability

requirements for reference materials. Stabilizers may need to be added in certain cases,

while freeze-drying and/or radiation sterilization may be required in some situations.

The fuel oils, coals, and fly-ash SRM's are exceptions to the above described situations. However, the materials supplied as SRM's may differ in detail from those undergoing

analysis at any particular time. Furthermore, the SRM provides no insight into the sampling

operation which may impose major problems. Accordingly, the results bbtained using SRM's

need to be interpreted by analytical chemists versed in environmental measurements.

The National Bureau of Standards now offers 63 SRM's which are either directly or

indirectly applicable to environmental analysis. Some of these have been specifically

developed for evaluating measurements of ambient or emission levels mandated by air quality

standards. However, most of the SRM's are more general in nature, hence applicable to a variety of analytical situations.

2. General Considerations

3. NBS SRM Program

503
The enactment of the Occupational Safety and Health Act created additional needs for

Standard Reference Materials. While some of the contaminants are the same as those specified in the air quality standards, with only minor differences in the levels of interest,

many substances peculiar to occupational exposure are encountered for the first time. The

analytical requirements include both space monitoring and time-weighted-average exposures

of workers, measured at the breathing zone. Clinical measurements of blood, sera, and

urine are also required. Accordingly, an entirely new breed of SRM's is needed, in

addition to extensions of existing ones.

Table 1 lists the analyzed gases which are currently available as SRM's. These are binary mixtures, certified to one relative percent and stable for a period of 6 months to one year. In the case of the nitric oxide mixtures, the certified composition is further

restricted to tank pressures in excess of 2.8 kPa (400 psig).

Table 1

Analyzed gas mixtures

SRM No. Type Nominal Values

1 ^ n /I ^ 1504a Oxygen in nitrogen O2 5 1.5 ppm

1 bU/ Oxygen in nitrogen U2 5 c,\ c. ppm

1 end 1 boy Oxygen in nitrogen A OA fiC Mi-\1 0/ U2 » rlO 1 . /o

1 c c o

1 bbo Methane-ai r LHi^ 5 1 ppm

1 bby Methane-ai r LHt^ , ID ppm

1 bbO Methane-propane-ai r LHi+ , 4 ppm; C3H8, 1 ppm

1 561 Sulfur dioxide-nitrogen CA ^OA nwKBVS SO2 » 480 ppm

1 652 Sulfur dioxide-nitrogen CA ACA SO2 , 950 ppm

1663 Sulfur dioxide-nitrogen SO2, 1400 ppm

1664 Sulfur dioxide-nitrogen SO2, 2500 ppm

1665 Propane in air C3H8, 2.8 ppm

1666 Propane in air CsHg, 9.5 ppm

1667 Propane in air C3H8, 48 ppm

1668 Propane in air C3H8, 95 ppm

1669 Propane in air C3H8, 475 ppm

1673 Carbon dioxide in nitrogen CO2 J 0.95 Mol . /o 1574 Carbon dioxide in nitrogen TOUT 0/ CO2 , 7.2 Mol . %

1575 Carbon dioxide in nitrogen CO2 , 14.2 Mol . %

1 <^ 77 lb// Laroon monoxiae in mirogen uu 5 y . / H ppm

1678 Carbon monoxide in nitrogen CO, 47.1 ppm

1679 Carbon monoxide in nitrogen CO, 94.7 ppm

1680 Carbon monoxide in nitrogen CO, 484 ppm

1581 Carbon monoxide in nitrogen CO, 957 ppm

1683 Nitric oxide in nitrogen NO, 50 ppm

1684 Nitric oxide in nitrogen NO, 100 ppm

1685 Nitric oxide in nitrogen NO, 250 ppm

1686 Nitric oxide in nitrogen NO, 500 ppm

1687 Nitric oxide in nitrogen NO, 1000 ppm

2511 Carbon monoxide in air CO, 1 ppm

2512 Carbon monoxide in air CO, 10 ppm

2513 Carbon monoxide in air CO, 18 ppm

2614 Carbon monoxide in air CO, 45 ppm

2619 Carbon dioxide in nitrogen CO2, 0.5 Mol. %

2620 Carbon dioxide in nitrogen CO2 , 1.0 Mol . %

2621 Carbon dioxide in nitrogen CO2, 1.5 Mol . %

2622 Carbon dioxide in nitrogen CO2, 2.0 Mol . %

2623 Carbon dioxide in nitrogen CO2, 2.5 Mol . %

2624 Carbon dioxide in nitrogen CO2, 3.0 Mol . %

2625 Carbon dioxide in nitrogen CO2, 3.5 Mol . %

2626 Carbon dioxide in nitrogen CO2, 4.0 Mol . %

504
standard Reference Materials for ambient-level measurements of SO2 and NO2 are issued

as permeation tubes and listed in table 2. The permeation rates for SO2 are certified over

the temperature range of 20 to 30°C while those for NO2 are only at 25°C. Permeation tubes

can provide reliable test mixtures but their high temperature coefficients (approximately

10 percent per degree centigrade) require accurate temperature control. Generated gas

concentrations are also directly dependent on the flow-rate of the diluent gas. Accordingly,

the accuracy of the generated test gas in the final analysis will depend on the calibration

of the thermometer and flow meter used and in the care with which these measurements are

made.

Table 2

Permeation tubes

SRM No.

1625

1626

1627

1629

SO2 Tube (10 cm)

SO2 Tube (5 cm)

SO2 Tube (2 cm)

NO2 Device

Nominal Permeation

Rate per Minute (25°C)

2.8 yg

1.4 yg

0.56 yg

(0.5 to 1.5

Individual rates between limits shown.

It has not been feasible, up to the present time, to provide low concentrations of

reactive substances such as sulfur dioxide and nitrogen dioxide as compressed gases, due to

stability problems. The use of specially treated aluminum cylinders now appears to be a promising remedy, hence this approach is presently being investigated. Gas mixtures would

certainly be preferred by many of the present users of permeation tubes. However, the

convenience, simplicity, and flexibility of concentrations that can be produced by permeation

tubes suggests that they will continue to find considerable useage as calibration devices

for the forseeable future.

A group of SRM's classified as analyzed liquids is listed in table 3. There are four

fuel oils certified for their sulfur content and another in which a number of trace elements

are certified. Reference fuels, consisting of gasoline containing certified concentrations

of lead are also available. In an entirely different vein, two samples of water certified

for their mercury concentrations at the ng/ml and yg/ml levels are also offered.

Table 3

Analyzed liquids

SRM No. Type Nominal Values

1621 Residual fuel oil S— 1 .05 wt %

1622 Residual fuel oil S—2.14 wt %

1623 Residual fuel oil S--0.268 wt %

1624 Distillate fuel oil S--0.211 wt %

1634 Residual fuel oil Trace elements

1636 Reference Fuel Pb— 12,21 ,28 and 773 y 12 vials, 3 of each

1637 Reference Fuel Pb--12,20, and 28 yg/g

12 vials, 4 of each

1638 Reference Fuel Pb-773 yg/g

12 vials

1641 Water Hg--1.49 yg/ml

1642 Water Hg— 1.18 ng/ml

1643 Trace Metals in Water 19 trace elements

505
A variety of solid materials of environmental interest have also been developed and

certified. Table 4 contains a listing of those SRM's presently available and includes

coal and fly ash certified for sulfur and trace elements. SRM 1571 Orchard Leaves is not

strictly an environmental material but it simulates such and hence has found considerable

use in methodology studies. Likewise SRM 1577 Bovine Liver has peripheral interest

because trace elements are certified in a biological matrix. A sample of powdered leadbased paint, SRM 1579, is of interest in connection with the Pica problem.

Table 4

Sol id materials

SRM No. Type Elements Certified

1571 Orchard Leaves Lead, Mercury and

17 others

1577 Bovine Liver Lead, Mercury and

10 others

1579 Powdered Lead-Based Paint Lead, 11 .87 wt %

1631 Coal , Sul fur in Sulfur, Ash

1632 Coal, Trace Elements in Lead, Mercury and

12 others

1633 Coal Fly Ash, Trace Elements in Lead, Mercury and

10 others

1645 River Sediment Matrix elements, trace

elements, nutrients

1648 Urban Particulate Matter Matrix elements, trace

elements, organic

consti tuents

4350 River Sediment, environmental

radioactivity

10 radionuclides

A series of SRM's developed for use with OSHA-related standards is given in table 5. The filter samples were developed to simulate the amount of material collected during an 8-hour work period using the personal sampler concept. The urine samples are freeze-dried

materials which can be reconstituted to give samples containing normal and elevated concentrations of fluoride and also of mercury.

Table 5

Work-place atmosphere analysis SRM's

SRM No. Type Certified for

2661 Liquids on charcoal Benzene

2662 Liquids on charcoal m- Xylene

2663 Liquids on charcoal p-dioxane

2664 Liquids on charcoal ethylene di chloride

2665 Liquids on charcoal chloroform

2666 Liquids on charcoal trichloro-ethylene

2667 Liquids on charcoal carbon tetrachloride

2671 Freeze-dried urine certified Hg

for mercury

2672 Freeze-dried urine certified F for fluoride

2675 Beryllium on filter media Be

2676 Metals on filter media Cd, Pb, Mn, Zn

2677 Quartz on filter media Si02
The foregoing tables have listed SRM's presently available. Additional standards are under development or the feasibility of their preparation and certification is under

investigation. A special publication may be obtained from the Office of Standard Reference

Materials, National Bureau of Standards, Washington, DC 20234, which lists the SRM's

currently available, their cost, and ordering information [1]^.

4. Use of SRM's

The role of SRM's in a measurement system, both general and specific uses of SRM's,

and selected fields in which they have made significant contributions are discussed in a recent NBS publication [2].

The NBS SRM's were designed to serve as primary standards, rather than working standards or for day-to-day calibration. Their best use is in conjunction with the evaluation

of methodology or in the development of new measurement techniques. Commercial suppliers

could use them to check their own measurement routines and thus provide a means of traceability of working standards to NBS.

No matter what the application is, SRM's should never be used until the analytical

system in which they are employed has been demonstrated to be in a state of quality control.

Under such circumstances a limited number of measurements using SRM's can evaluate the

compatibility of analytical measurements from a given laboratory with those generated

el sewhere.

References

[1] Catalog of NBS Standard Reference Materials, NBS Special Publication 260, U.S.

Government Printing Office, Washington, DC 20402.

[2] Cal i , J. P., et al. , The Role of Standard Reference Materials in Measurement Systems,

NBS Monograph 148, National Bureau of Standards, Washington, DC 20234, (January 1975).

^Figures in brackets indicate the literature references at the end of this paper.

507

j

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977)

REFERENCE TYPE SAMPLES FOR WATER/WASTE ANALYSES IN EPA

John A. Winter

U.S. Environmental Protection Agency

Cincinnati, Ohio 45268, USA

1. Introduction

The quality assurance program of the U.S. Environmental Protection Agency is focussed

in three major laboratories of the Office of Research and Development. These

Environmental Monitoring and Support Laboratories (EMSL), are located at Cincinnati, Ohio,

Las Vegas, Nevada, and Research Triangle Park, North Carolina, and are responsible for

water and waste, radiation, and air analyses, respectively.

EMSL-Cincinnati ' s Quality Assurance Program for water and waste analyses has four

functions: 1) To provide necessary manuals and guidelines on sampling, sample preservation,

analytical methodology and quality control, 2) to provide samples for the within-laboratory

quality control efforts, 3) to validate EPA's analytical methods through formal studies

and 4) to evaluate the performance of EPA and state laboratories and certify them as required by law. Of these four functions, the latter three require use of reference-type

samples to accomplish their objectives.

As shown in table 1, EPA's use of reference- type samples in direct support of its

Quality Assurance Program distinguishes these samples from NBS' use of standard reference

materials to support the basic measurement system. This paper will describe the design and

development of EPA's reference-type samples.

Table 1

Use-comparison of reference- type samples in NBS and EPA

Certification

Interlab Q.C.

Reference Methods Intralab Q.C.

Standard Reference Materials Method validation studies

Basic units or measure Selected analytical methods

National Bureau of Standards U. S. Environmental Protection Agency

2. Sample Design

Because routine samples are received in a fully-diluted form, it would be ideal to

provide reference samples as natural water samples which the analyst could test directly

without dilution or special treatment. However, as shown in table 2, requirements for

reference-type samples are difficult to satisfy with natural or full-volume samples.

509
Table 2

Sample requirements

Homogeneous replicate series (precision)

Exact known concentrations for multiple

test parameters (accuracy)

Separate measure of bias and interference

Use in a variety of waters

Evaporation, leakage control and stability

Preparation, storage and shipment

EMSL-Cincinnati concluded that whenever feasible, these needs could be best met by

samples prepared as liquid concentrates using the purest-available chemicals, then sealing

and preserving them in all-glass ampuls. When diluted to volume with distilled and natural

water by the analyst, the samples contain exact concentrations of the desired constituents.

The advantages of this sample form in meeting EPA's objectives will be discussed in the

following sections.

A. Precision

Preaision, the most widely-used characteristic of analytical performance is meaningful

only when other conditions are held constant or randomized. By preparation of a sample

concentrate from pure, uniform chemicals and solvents, by continuous mixing of solutions

and by preparation of samples as a single batch in a single day, we have good assurance of

replicate sample homogeneity which is necessary to measure between-analyst error.

B. Accuracy

Aoouraay, another important characteristic, is measureable only when chemicals and

solutes can be obtained with the high levels of purity required to prepare replicate

samples having known true values for each desired property.

With the rapid increase in use of instrumental and automated analyses, accuracy has

become even more important because the mechanical and electronic character of these methods

achieves repeatability and reproducibility which are greatly improved over manual methods

yet with no sense of true values. Consequently, their accuracy has the most potential for

error.

To measure accuracy, exact amounts of constituents are weighed, dissolved and brought

to volume with ultrapure water or other solvent to form the sample concentrate. Multiple

parameters are present in each concentrate to simulate natural samples. Later, when the

analyst dilutes the sample concentrate to volume according to instructions, parameter

levels are obtained which are established as the true values. Prior to release of samples,

these true values are verified by repeated analyses over time. If not verified, the

samples are discarded and the problem solved before remaking. The true values are never adjusted to the analyzed values. This concept is a key factor in EPA's sample design

because it permits the establishment of values independent of bias and interference. True

values and accuracy would be difficult or impossible to measure with natural or full volume

samples

.

C. Bias and interference

It is necessary to distinguish the inherent bias in the method from the positive or negative interferences in water samples. Measurement of method bias requires analysis in

ultrapure water, of samples with exactly known values, whereas testing for interferences

510
requires analyses in a range of natural waters. These varied test water conditions can only be satisfied, practically, through addition of an increment to distilled and natural

waters

.

D. Variety of test waters

Evaluation of methods, techniques, instruments or analysts requires testing with

different waters. Use of the spike technique is the most practical approach. Each laboratory selects a natural water for test under his own conditions. In an i nterl aboratory

study, each analyst selects his own natural water for spiking and the method is evaluated

in as many water conditions as there are analysts, far exceeding the types of water practical to prepare as full volume samples.

E. Evaporation, leakage and stability

Use of all-glass ampuls avoids evaporation and leakage which are common to screw-cap

or friction-stopper containers. Further, after filling and sealing, many sample concentrates can be preserved by steam sterilization, without loss or leakage. Finally, with no problem of contamination from paper, rubber, metal or plastic liners or caps the all-glass

ampuls can be used with acid preservation or organic solvents.

F. Ease of preparation, storage and shipment

Sample concentrates in volumes of 5-50 ml are easily prepared using small, fast and

relatively inexpensive, filling, sealing and labeling equipment. Ampuls are light, easily

handled and stored. For example, a 20 ml ampul requires only about 1/16 of the space of a full-volume, one liter sample. Further, storage and shipping expenses, two other cost

factors that have been accelerating very rapidly, are reduced drastically.

3. Constituents in Samples

The parameters prepared in the reference- type samples relate directly to EPA's responsibilities for analyses under the current water laws.

A. P.L. 92-500 The 1972 FWPCA Amendments

Seotion 304 NPDES System limits discharge of some 71 pollutant parameters including:

metals, solids, general organics, nitrogen, phosphorus, halogens, oil and grease, phenols,

radioactivity, algicides, surfactants, chlorinated organics, and indicator bacteria.

Section 207 Toxic Substances cites 65 pollutants as serious toxicants for which limits

are to be set for waste discharges. These include many specific organic compounds from

industry.

Seotion 311 permits or regulates discharge of oil and hazardous substances in U.S.

navigable and coastal waters.

B. P.L. 92-532 marine protection, research and sanctuaries act of 1972

P.L. 92-532 marine protection, research and sanctuaries act of 1972 prevents or regulates dumping materials which would adversely affect human health, welfare, or marine

environment. These materials include: radioactive, chemical and biological warfare

compounds, persistent inert floating or suspended material, metals, organohal ides and oils,

organosi 1 icones , cyanides, fluoride, chlorine, titanium dioxide wastes, petrochemical and

other organics, biocides, oxygen-consuming materials and the toxic substances/hazardous

materials listed in Sections 307 and 311 of P:L. 92-500.

511
C. P.L. 93-523 safe drinking water act

The interim regulations set maximum permissible levels for seven metals, turbidity,

nitrate-nitrogen, chlorinated hydrocarbon pesticides, herbicides and coliform bacteria.

Based on program priorities, reference-type samples have been prepared for metals,

demand, nutrient, mineral and physical parameters, and chlorophyll. Samples are in preparation for chlorinated hydrocarbon pesticides, polychlorobiphenyls, herbicides, bottom

sediment, sewage sludge, suspended solids, cyanide and phenols.

4. Other Considerations in Preparation of Reference- type Samples

The chemical compounds used must consider:

1. The form in whiah the parcaneter is found as a pollutant. For example, cyanide might

be present as free cyanide, ferrocyanide, organic cyanide and cyanate.

2. The form must be analyzable by the test method. For example, cyanide can be measured

as total cyanide, cyanide amenable to chlorination, or cyanide measured by Roberts-Jackson

method.

3. The form must be soluble and stable at the levels tested so as to be practical for

preparation and under conditions of use.

4. The form must be available in a pure form for calculation of true values.

Water, acetone, methanol, hexane and other organics are used as solvents for these

samples. Generally, water is the solvent for inorganics and the organic solvents for

specific organics. Obviously, the choice of solvent is based on the solubility of the chemical compounds but since samples are prepared as concentrates, the compound must be soluble

enough for preparation at 100-500 times the final concentration in the dilute samples.

The solvent also must not interfere with the method of analysis. This is particularly

critical for specific organics which are separated and analyzed by gas chromatography.

Here an organic solvent must not elute at the same rate as the solute or its peak will

overlap and prevent a valid measure.

The levels and number of samples respond to:

1. Measure of the range of concentrations normally tested by the method. For example, if

the method is set up for 0.1-10 mg/1, samples are prepared in this range.

2. Verification of the minimum detectable level reported for a method.

3. Applicability of the method to high concentrations found in specific wastes.

4. Applicability of method to limits set by discharge permits or water supply limits.

5. The number of concentrations necessary to fit the program need. The number may range

from a single concentration for quality control to paired samples at the three or four

levels necessary to establish equations of the line for measures of precision and accuracy.

5. Quality Control Practices in Preparation

The chemical compounds used are selected from the purest available materials that are practical. For instance, if the purest aluminum is available only as a solid bar, it would

be impractical for weighing small amounts and pure aluminum wire might be substituted. For

other elements, a primary standard or analytical reagent grade chemical is chosen based on the availability and solubility of the salt or oxide.

512
The chemicals are dissolved in ultrapure water, water/acid solution or chromatographygrade organic solvents. The ultra-pure water is prepared by passage of distilled water

through a recirculating purification unit composed of a prefilter, activated carbon, mixedbed resin and final filter. Only redistilled reagent grade acids are used.

To prevent false assumptions or calculation errors, the calculations and preparation

plans are worked out independently by two people and checked by the laboratory chief. A

print-out analytical balance is used to weigh chemicals. The paper tape print-out of

weighings is placed directly in a laboratory notebook as a true record and to avoid transposition of numbers.

The preparation of a sample concentrate from stock solutions is critical because a number of volumetric measurements by pipet and by flask must be made as exactly as possible.

A flow-chart of the preparation plan is drawn up and copies given to team members to prevent mix-ups in the series of dilutions. One person on the team designated as the observer,

is responsible for monitoring measurements and verifying that pipets and volumetric flasks

are the proper sizes. Most importantly, the observer must verify that the measured volume

of each stock solution is correct, is added in proper sequence and is placed in the proper

make-up flask. Since a typical sample contains a number of chemical constituents, the

sequence of addition and use of sufficient volumes of dilution water are critical, to

prevent precipitation or other changes. Ultrapure water is equilibrated at 20°C overnight

to assure accurate measure of solution volumes. A concentrate is made up in separate

volumes in four, six, or ten liter volumetric flasks then combined in a single large volume.

The prepared sample concentrate is continuously mixed as it is pumped through the

filling and sealing machine via a Teflon line and glass syringe assembly into cleaned

borosilicate glass ampuls. After the ampuls are filled, sealed and labelled, analyses are performed over a 90 day period to verify the stability and homogeneity of the series.

Since any laboratory can exert systematic error, the prepared sample series is sent to

at least two referee laboratories for analyses as unknowns. Multiple methods of analyses

are used if available, but analyses must be made on the fully-diluted samples and must be

performed in part by EPA's methods of analyses so that EMSL is assured the true values are obtainable. Data must agree within the expected limits. Differences must be resolved

before the samples are considered ready for use.

6. Summary

In EPA, the Quality Assurance Program for water and waste analyses requires referencetype samples for method selection, method validation, intralaboratory quality control,

performance evaluation and certification functions.

The samples are prepared as concentrates in sealed glass ampuls using water or an organic solvent. Aliquots are added to distilled and natural waters by the analyst and the

recovery of the spike determined. Use of true values permits the measure of accuracy, bias

and interference. The samples are used as knowns or unknowns and incorporated in intralaboratory or interlaboratory evaluations as needed. The organic and inorganic chemical,

biological and microbiological parameters respond to EPA's needs under the three water

laws

.

513

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

THE PREPARATION AND ANALYSIS OF A TRACE ELEMENTS

IN WATER STANDARD REFERENCE MATERIAL

J. R. Moody, H. L. Rook, P. J. Paulsen, T. C. Rains,

I. L. Barnes and M. S. Epstein

Analytical Chemistry Division

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

The determination of trace metal ions in natural waters is a difficult procedure which

is complicated by more than just the low elemental concentrations being sought. The subject

of valid sampling and noncontaminating storage of samples will not be examined here although

their collective influence on an analysis can be easily appreciated. Because of its high

sensitivity and high sample throughput it should not be surprising that most water chemists

use atomic absorption spectrometry (AAS) or one of its variants such as graphite furnace

atomic absorption spectrometry (6FAAS).

Regardless of the method used, most analytical procedures are relative; that is, the

signal developed must be compared to or calibrated by the signal developed by a standard

under the same conditions. Unfortunately, experience has shown that a pure aqueous standard

cannot compensate for interferences or changes in sensitivity caused by the analyte matrix.

Indeed, the procedure of standard addition of an aqueous standard to a sample aliquot is

seldom satisfactory. These problems are referred to in general as the matrix effect.

What the water chemist needs is an artificial water reference material containing all

of the trace elements of interest as well as the major matrix ions found in natural waters.

By the calibration of chemical procedures and instrumentation with such a reference material,

much of the uncertainty in these procedures is removed. Thus, although data from any given

laboratory will not become any more precise, they will become more accurate. Meaningful

comparison of interlaboratory data is a function of the accuracy of the data being compared.

Any improvements in the accuracy of the data base will assist the water scientist in the

better understanding of trace metal chemistry in water systems.

Proposed SRM 1643 represents the best standard of this type which can be made at this

time. It contains 19 trace elements of importance at levels approximating those found in

natural fresh water estuaries [1]^. In addition it contains gold (stabilizing agent) [2]

as well as the major matrix cations of Na, K, Ca, and Mg. Table 1 lists those elements

present in proposed SRM 1643 together with their target concentrations and corresponding

natural water levels as determined by polling available Department of Interior data [1].

While the proposed SRM cannot be a perfect match to all natural water samples, it does

represent the best possible approximation to a natural water sample that has tDeen filtered

and acidified.

^Figures in brackets indicate the literature references at the end of this paper.

515
1

Table 1

Proposed composition of standard reference materials 1643

Concentration, ng/g Concentration, ng/g

Natural Proposed Natural Proposed

Element Water SRM 1643 Element Water SRM 1543

Au 10 Mo 53 105

Hq 1 .

1

Mn 29 30

Aq 2.3 3.5 Ni 13 50

Al 76 80 Pb 21 25

As 70 75 Sr 215 190

Ba 40 40 VV 39

Be 0.12 20 Zn 60 65

Cd 9 8 Se 12

Co 15 20 Na 19^ 10^

Cr 11 16 K 2^ 2^

Cu 13 15 Ca

27a 27a

Fe 52 75 Mg

^Concentration, yg/g. — Not determined.

2. Stability Studies

Two of the most important concerns in the preparation of an SRM are those of analysis

and stability. Although it is obvious that an unstable standard would be useless, proving

the stability of a material is not easy. A preliminary stability study was carried out

with radioactive tracers to determine possible losses to container walls or interelement

effects. For this study a preliminary test solution was preparea by carefully diluting

known amounts of ten selected metals (As, Be, Cd, Cr, Cu, Hg, Mn, Pb, Se, and Zn.)

All of these elements were at or below the yg/g concentration level. The solution was stabilized with 0.5M HNO3 and 10 ng/g of gold (to stabilize mercury). All storage containers

were thoroughly cleaned in dilute nitric and dilute hydrochloric acids. Five radioactive

tracers were added to one liter of the stock solution. The tracer concentrations were low

enough so that elemental concentrations in the stock solution were not affected. After a number of analyses over a period of 255 days, no losses were detected with the possible

exception of cadmium.

However the tracer studies yielded no information of potential blank problems either

from the reagents or from the containers. Fortunately, a concurrent study of a number of

different container materials shed some light on potential blank problems as well as suggested a reasonable procedure for cleaning a large number of containers [3]. To provide

additional information on stability and potential blank problems as well as to determine

potential analytical problems, the trial sample of a multiple element standard was analyzed

twice over a 17 week interval. The analytical determinations of this trial sample were performed by neutron activation analysis (NAA), by isotope dilution-spark source mass spectrometry (ID-SSMS), and by AAS. The repeat analyses showed no significant increase or loss in

concentration for any element over this time interval.

516
3. Preparation

Concentrated solutions of each element were prepared by dissolving known amounts of

spectrographically pure metal (carbonates or other salts used for some elements). By

accurate dilution of these standard solutions, a test solution containing 17 trace elements

plus mercury, gold, and the four matrix elements Na, K, Ca, and Mg was made. In certain

instances, most notably for Be, it was necessary to elevate the concentration over the

normal value to assure a reasonable chance for analysis by two independent methods. Analysis

of this sample by NAA and AAS indicated no potential problems at these concentration levels.

The polyethylene containers for SRM 1643 were carefully cleaned with dilute acid and

pure water. A single, 55 gallon polyethylene drum and a polyethylene stirring paddle were

cleaned in a similar manner. To prepare SRM 1643, we carefully added weighed amounts of

pure water and pure HNO3 [4] to the 55 gallon drum with stirring. Three master solutions,

which together contained all 24 elements were carefully prepared by weight dilution of the

original concentrated standard solutions. Aliquots of these three dilute master solutions were then added to the water and HNO3 in the 55 gallon drum with constant stirring.

The resulting solution was stirred for several days and then to insure mixing vertically

throughout the drum, aliquots were removed from a spigot at the bottom and poured into the

top of the drum. Finally, after the mixing was judged to be complete, the solution was transferred into 230 clean one liter polyethylene bottles which were serially numbered.

All of the dissolutions, dilutions, and other manipulations were carried out in a Class 100

clean laboratory using techniques designed to avoid contamination of the samples. Selected

samples were taken for certification analyses and long range stability studies.

4. Analysis of Proposed SRM 1643

Three techniques, (NAA, ID-SSMS, and AAS and related methods), are being used for most

of the analytical work on proposed SRM 1643. Not all elements will be analyzed by each

method but no less than two independently determined values will be obtained for each

element. It is beyond the scope of this paper to present the analytical methods of each

technique; instead comments will be reserved for a review of the analytical program.

To date, the only element for which no analytical results have been obtained is Fe.

For all other elements the analysis program is in various stages of completion. For some elements this program is essentially complete while for others the program is only partially

completed. For example, in table 2, preliminary results are presented for Cu, Pb, Mo, and

Mn. Note that two mass spectrometric values were obtained for Pb, one by isotope dilution

SSMS and the other by isotope dilution thermal emission mass spectrometry. No isotope

dilution values were obtained for Mn.

Table 2

Preliminary analytical results (ng/ml)

Element

Approximate

Concentration IDMS GFAES GFAAS NAA Polarography

Cu 15 16.4^ 16 14.2 16.6

Mo 105 110 110 100

Mn 30 28 27.5 30.0

Pb 25 20.3^ 19.6 21

20.9

^IDMS by thermal emission mass spectrometry, others by SSMS. — Not determined.

517
In addition, no NAA results have been obtained for Pb whereas results have been

obtained for Cu, Mo, and Mn. Nearly every element is being analyzed by graphite furnace

AAS and seven elements have been analyzed by the graphite furnace AES. Furthermore,

results have been obtained by polarography and a few preliminary results have been obtained

by the plasma emission spectrometer. In analyzing the preliminary data tabulated in table

2, it is necessary to recall the relative merits of each method for each element.

A complete statistical review of the data has not yet been attempted since the analytical program is incomplete. However, the inter-method agreement for data presented in

table 2 is believed to be within error limits of the respective methods. With the exception

of Pb and Ba, good agreement has been obtained with respect to the approximate (theoretical)

concentrations. For Pb the results are low by 20 percent but appear to be stable. For

Ba, a serious discrepancy exists between the theoretical value and the analytical results

obtained thus 'far by three methods. By contrast, mercury may be slowly gaining in concentration due to migration of mercury vapor in the room air through the polyethylene bottle

and into the solution.

Thus, in summary, for most of the elements attempted, the analytical program will

probably be sufficient to lead to the certification of 18 elements. For the moment the

problem with Ba is unresolved and Hg is also in doubt though for different reasons.

References

[1] Kopp, J. F. and Kroner, R. C, Trace Metals in Waters of the United States, A Five

Year Summary of Trace Metals in Rivers and Lakes of the United States, Report of the

U.S. Dept. of Interior (Oct. 1, 1962 - Sept. 30, 1967).

[2] Moody, J. R., Paulsen, P. J., Rains, T. C, and Rook, H. L., The Preparation and

Certification of Trace Mercury in Water Standard Reference Materials, in Proc. of 7th

IMR Symposium, Accuracy in Trace Analysis, NBS Special Publ . 422, (P. D. LaFleur,

Ed.) U.S. Government Printing Office, Washington, DC 20402, pp. 267-273.

[3] Moody, J. R. , and Lindstrom, R. M. , Unpublished data. Publication in Progress.

[4] Kuehner, E. C. , Alvarez, R. , Paulsen, P. J., and Murphy, T. J., Production and

Analysis of Special High-Purity Acids Purified by Sub-Boiling Distillation,

Anal. Chem., 44, 2050-2056 (1972).

518
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

THE STANDARD FINEPARTICLE

Brian H. Kaye

Institute for Fi neparticl es Research

Laurentian University

Sudbury, Ontario

1 . Introduction

The characterization of fineparticles is a topic of concern for many environmental

engineers in problem areas such as smoke abatement-monitoring, pesticide application,

industrial health hazards from inhaled dust and evaluation of suspended debris and other

particles in water systems. In many of the theoretical discussions of the various procedures

used to characterize fineparticles, in which dense smooth spheres are used as hypothetical

fineparticles moving through the characterization equipment, it appears as if the characterization data generated by the instrument can be interpreted in terms of fineparticle

magnitude parameters from physical theory without recourse to calibration procedure. In practice, however, the working scientist does not have access to all the relevant physical

properties of the fineparticles to be characterized and it is necessary to calibrate the

equipment using reference material.

There are two main problems associated with the organization of a system to provide

standard fineparticles for calibration procedures. The first problem is one of storing and

handling fineparticles. By definition a fineparticle system is one in which surface forces

compete with macroscopic forces to determine the behavior of the system. When a fineparticle

system is stored the surface activity tends to change either through agglomeration of particles, anealing of surface defects or the absorption of gases and/or moisture onto the sur- face of the system. The other problem which arises from the handling of powders is that

segregation by size can occur in the handling process. In the next section physical problems

associated with the organization of so-called fineparticle banks for the calibration of

powder systems is discussed.

The second difficulty involved in the provision of fine particles for calibration

purposes arises from a semantic confusion in the definition of the behavior of many fineparticle systems. The art of fineparticle characterization has evolved rapidly over the

last thirty years with scientists from many formal disciplines contributing to the development of the various characterization instruments described in the technical literature. One

of the results of this multidiscipl inary development of the subject is proliferation and

confusion of terminology. One of the great needs of the subject of Fineparticle Science is

the adoption of clearly structured unambiguous terminology [1]^. Closely associated with

this problem are two other major sources of confusion in fineparticle characterization

studies. These are: I

1. The failure to specify information needed in a characterization study,

2. An inadequate understanding of the limitations of the interpretative hypotheses used to

transform raw data obtained from a characterization study into fineparticle descriptor

parameters

.

This latter problem is often obscured by the fact that data transformations in a fineparticle characterization instrument are carried out internally using dedicated electronics and

descriptor parameters and statistics displayed in converted form without warning of the

various assumptions implicitly incorporated into the data transformation procedures. If a

^Figures in brackets indicate the literature references at the end of this paper.

519
"standard" fineparticle used to calibrate a fineparticle characterization instrument functions differently in the sensitive zone of the instrument, as compared to the operative

system f ineparticl es to be calibrated, then unsuspected implicit data transformation procedures in the characterization study can lead to hopeless confusion in the use of the descriptor parameters to discuss operational problems. It is not possible to discuss in depth the

many problems of this kind which arise in fineparticle science, we use the language of set

theory and the symbolism of Venn diagrams to illustrate the problems of choosing appropriate

fineparticle reference systems.

2. Ideal and Operative Fineparticle Reference Material

When discussing the provision of standard fi neparticl es from a bank of reference

material, it is useful to differentiate between two types of reference material. We will

define them in this communication as ideal reference material and operative reference material. An ideal reference material is usually composed of dense smooth spherical particles,

the characteristics of which can be measured directly using different characterization

procedures and employing different physical measurement technology. Thus, a smooth dense

glass sphere is an ideal reference material. A glass bead can be passed through the hole of

a sieve, or it can be sedimented in a viscous fluid to obtain a settling velocity. The

calculated magnitude from the settling velocity can be directly correlated to the magnitude

observed through the microscope and the magnitude of the opening in the sieve used in the

experiment. As will be discussed in the next section, the problem with ideal standards is

that they can give problems in interpreting data for fi neparticl es measured in an operative

environment. (Note that in this communication, when we refer to an operative environment

for a fineparticle, we are discussing the system of interest to the engineer who has requested

characterization data. Thus, smoke particles in the atmosphere are in an operative environment and when they are sampled and placed under the microscope they are functioning in a characterization environment.) Some of the first attempts to provide ideal standards utilized glass beads. However, glass bead standards suffer from the problems of having bubbles

in the bead structure and individual beads often depart from complete sphericity when

examined closely. Alternatively, attempts were made to use spherical metal powders such as bronze and tin manufactured by an atomization process. Again, such powders tended to have

doublets in them produced by fusion at a point of contact during the atomization process and

again were not completely spherical. Such standard powders were made available in one of

the first attempts to provide a reference bank of material on a commercial basis by Stanford

Research Institute in the early 1960's [2]. This type of standard is still being made

available by the two commercial companies operating fineparticle reference material banks

[3,4], Many of the uses of glass bead standards for the calibration of measurement instrumentation have been replaced by the use of latex spheres. These were originally available

from the Dow Chemical Company but now are available from Dow Diagnostics and some of the

companies involved in selling fineparticle characterization instrumentation [5,6,7,8].

The other type of reference system which has been used is the so-called operative

reference system which attempts to develop non-spherical particle standards by means of

comparative testing utilizing so-called round robin tests among many laboratories. Such

tests have been organized in the past by such organizations as the American Society for

Testing Materials and the Committee for Particle Size Analysis of the British Society for

Analytical Chemistry. The problem with this type of material is that one batch of powder

has to be set up as the initial reference material; it has then to be subdivided and quantities sent for characterization by various laboratories. Any future use of the material is

then destructive and one is faced with the dwindling supply of the reference material which

is eventually exhausted and the process has to begin again.

Various physical problems arise in the storage and handling of both ideal and operative

standards. For example, if one is using Dow latex materials to calibrate an instrument then

places the latex particles in the beam of an electron microscope and the energy levels of

the electron beam are not properly controlled, the latex particles can be distorted by heat

from the energy of the electron beam. On the other hand, if the particles are to be placed

in an electrolyte, such as is used in instruments of the Coulter Counter, or Cel lo-O-scope

type, then electrolytes can alter the structure of the particles.

520
With operative standards, such as cement powders used in permeability calibration

experiments, the inadvertent admission of moisture to the system can result in the deterioration of the powder when it is stored. At Laurentian University we are working on several

techniques to improve the methods of handling operative reference powder systems. In particular, a new type of storage container which can also act as a randomizing system shows

promise of being a useful system [9].

Industrial organizations wishing to avail themselves of operative and ideal reference

material must face the fact that the proper organization and operation of systems is expensive and that even after they have acquired subsamples from a parent population of reference

powders, they must exercise stringent control over operation and handling of such reference

material. Developments in the near future of these systems can be anticipated as the industrial community comes to the realization that many of the methods for characterizing

fineparticle systems are not primary methods which can be calibrated from physical theory

alone but which require this type of reference material. It may well be that any initial

attempt to establish a national centre for fineparticle reference systems may also have to

undertake an educational program to advise users of such systems of the pitfalls inherent in

the handling of fineparticle reference systems. The need for this educational program

arises directly from the fact that engineers concerned with the operative environment of a fineparticle system are not always trained in the necessary surface physics and statistical

descriptive theory associated with adequate storage and handling of fineparticle systems.

3. Semantic Problems Associated with the Provision of Reference Material

for Fineparticle Characterization

To illustrate some of the semantic problems of 'standard reference materials', let us consider the simple problem of comparing characterization data from a microscope examination,

settling velocity studies in a viscous fluid and electrozone evaluation of a particle. In the first technique, the particle to be characterized is observed directly under the microscope. When particles are studied by sedimentation technology, the fineparticle is placed

in a viscous fluid and allowed to sediment under the interacting forces of gravity and

viscous drag. The terminal velocity reached by such a particle can be related to the magnitude of the fineparticle. It is usual practice to interpret the settling velocity of the

particle in terms of the Stokes' Diameter of the particle which is that radius calculated by

assuming that the particle is equivalent in its behavior to a dense smooth sphere which has

the same settling velocity of that observed for the particle under study. In the electrozone

counters, such as the Coulter Counter equipment, the change in the electrical properties of

a cylinder of electrolyte, with and without the fineparticle under study, is correlated to

the magnitude of the particle. If a smooth hard sphere is used in all three experiments,

the measured diameter of the sphere will very closely correlate, provided that the flow i regime of the falling particle in a viscous fluid is in the laminar flow region.

Examine a typical problem which could arise in environmental science in which one needed to characterize agglomerates of spherical particles being emitted from a furnace.

(These particles could be carbon particles or agglomerated fly ash particles.) Assume that

various types of particles as shown in figure 1 needed to be evaluated. Consider now the

effect of the presence of agglomerates of individual particles on the data generated by the

three characterization procedures that have been briefly reviewed. First of all one notes

that the vocabulary for describing the shape of agglomerates is very underdeveloped and that

one is reduced to such terms as "straight" and "twigged" to describe the various agglomerates

of this diagram. If one regards the agglomerates of this diagram as forming the population

to be characterized, then the particles which have the same property as determined by the

various methods can be grouped. If the set of particles which have the same projected

length are organized, then the particles such as those indicated by the linkage in the

diagram would be identical. On the other hand, if attempts to draw up the classification of

particles according to their Stokes' Diameter (i, g. measured settling velocity) the same particle can have different diameters depending on the initial orientation of'the fineparticle when placed in the viscous fluid (see figure 1) and that apparently very different

particles can be identical from the Stokes' Diameter parameter (see fiaure 2).

521
Subunit Number

as Classi i'i cation

Parameter

o

OOOOCX) Many variations in

structure between these

extremes are possible

One particle at the bottom of

the cluster.

Figure 1. The descriptor classification of non-spherical particles can group together particles according to one descriptor parameter which

differ greatly when described by an alternate descriptor parameter.

This aspect of fineparticle characterization is illustrated graphically

for agglomerates of spherical particles.

522
ooo

Set of particles of the same size - descriptor parameter "Projected Length",

Possible members of the set of 'particles

of identical Stokes' Diameter'.

Possible members of the set 'all particles

of the same volume"

Figure 2. Many strangely different particles can be identical when

described by a single characteristic parameter. Calibration of

a characterization instrument using spherical smooth dense particles will result in this kind of descriptor group membership.

Again, with the electrozone equipment, one finds that the recorded particle diameters

of agglomerates entering the sensitive zone of the instrument will depend on the orientation

of the agglomerate. Also, problems may exist in that the analytical methods may cause degeneration of the operative magnitude of the agglomerate. Thus, the severe shear conditions present in the orifice, into which the particles are being sucked in an instrument

such as the Coulter Counter, could result in a break-up of the agglomerate system. This is

523
not predictable beforehand without a knowledge of the fineparticle to particle bond in the

agglomerate. In this connection it is interesting to note that in the extreme situation one could be collecting many agglomerates such as the particles of figure 1 in a method which

sucked all particles into a liquid suspension such as that used in the Greenberg impinger

[10]. Then, before such a suspension is characterized by any method, it may be subjected to severe ultrasonic agitation 'to disperse agglomerates'. Such Procrustean treatment may

result in the conclusion that all particles leaving the chimney stack are of one size! In using characterization data one has to have a concern for the operative environment in which

one will be using the characterization data. For example, if one has a concern for the rate

at which particles fall out from a chimney stack, one requires the Stokes' Diameter of the

agglomerate. If, however, one is interested in the possibility of the particles damaging

the human lung, then one is interested in a combination of the settling velocity of the

particle and its dimensions which control the ability of the fineparticle to lodge in the

structure of the lung. Thus, industrial hygiene studies call for a combination of the

descriptors involving both settling velocity and dimensional structure of the particle.

To clearly summarize the problem of appropriate standards when using different methods

of analysis, one can turn to the language of set theory and use the symbolism of Venn Diagrams. Basically, the population of fineparticles to be described can be represented by the

inclusive set shown in figure 3. When split into sets having the same descriptor parameter,

intuitively one expects to be able to split the original population into clearly defined

groups. However, the descriptor sets into which the parent population splits can have

membership requirements which cause an overlap of the set if one changes from the analytical

descriptors to the operative parameter descriptor sets based on Stokes' Diameter. Thus,

descriptor sets in a characterization study using projected diameters in microscope studies

will not give correct membership for the operative parameter descriptor sets. The fact that

different methods of characterization will give identical subsets for populations of dense

hard spheres is equivalent to saying that the difference between descriptor sets based on different physical measurements for non-spherical particles degenerate to zero for the case of fineparticles in which all particles are dense smooth spheres. Thus, a situation could

be envisioned in which scientists wished to calibrate an instrument to be used to characterize asbestos fibers in a study of industrial dust hazards from such a dust. If such an instrument was calibrated using an ideal standard spherical particle so that all particles were described in terms of Stokes' Diameter of the equivalent smooth dense glass sphere,

then the velocity with which the particles would settle in the factory area may be predicted.

One could be very wrong in predicting the hazard to the worker from particles lodging in his

lung. To obtain such shape dependent information by determining "1 odgeabi 1 ity" another

method of analysis would have to be used or one would have to calibrate the original equipment with asbestos fibers of known environmental hazard. Whichever way one goes, he faces a long and expensive calibration procedure.

524
Four subsets of particles with decreasing projected diameter

(microscope measurement).

All particles in micron range

(projected diameter)

All particles with Stokes' Diameter in the range 20-30/«m

(This group contains particles of different shape which

are outside the range 10 - 30/llfiby projected diameter . )

Figure 3. From a simple perspective, any characterization procedure should

be capable of uniquely classifying a population of fineparticles into

well-defined subsets. In practice, for non-spherical dense smooth particles, membership in any subgroup of a given 'size' range is not a welldefined concept. Descriptor groups formed by different physical methods

for characterizing particles which are identical for spherical groups

are not identical for non-spherical particles.

4. Summary

A growing sophistication in the characterization of fineparticle systems is leading to

•the demand for standard f ineoarti cles . However, it is easier to conceive of the notion of

standard fineparticle than it is to provide real systems. A great deal of work needs to be

carried out on the provision of ideal standards and their storage but such a program would

525
have to concurrently advise people that there may not be a direct link between the parameters

given by their instrument when calibrated with ideal standards vis a vis the operative

performance of the fineparticles that they are studying. The alternative route of providing

operative standards for industrially important powders is even more difficult to organize

since any standard powder established needs to be carefully handled, characterized and is

always a dwindling resource which has to be replenished at great time and effort at a later

date.

References

[1] "The Laurentian Handbook of Powder Science and Technology", published by the Institute

for Fineparticle Research, Laurentian University, Sudbury, Ontario.

[2] "Particles in the Bank", The Stanford Research Institute Journal", Third Quarter, 1961,

Vol . 5, Page 133.

[3] Duke Standards Company, 445 Sherman Avenue, Palo Alto, California, 94306.

[4] Particle Information Service, 600 South Spring Rd., Los Altos, California 94022.

[5] Dow Diagnostics, The Dow Chemical Company, P.O. Box 68511G, Indianapolis, Indiana

46268.

[6] Alliet, D. F., "A Study of Available Particle Size Standards for Calibrating Electrical

Sensing Zone Methods", Pow. Tech., 13, (1976) 3-7.

[7] Robillard, P. and Patitsas, A. G., "Determination of the Particle Diameter of Dow Latex

642-6 X 4 Independent Methods", Pow Tech. 9(1975) 247-255.

[8] "Something Old, Something New, Something Borrowed, Something Blue". A general interest

article describing the use of Dow Latex particles, published in Industrial Research,

August 1976, pages 46-49.

[9] Kaye , B. H., "The Various Techniques for Sampling Powder Systems". In press.

[10] Allen, T., "Particle Size Analysis", 2nd Edition, Chapman and Hall, Great Britain, 1976.

526
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1 977 )

THIN FILM STANDARDS FOR X-RAY AND PROTON-INDUCED X-RAY FLUORESCENCE

D. N. Breiter, P. A. Pella, and K. F. J. Heinrich

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

1. Introduction

Small samples such as air particulates and water residuals are increasingly being

analyzed by multielement x-ray techniques. They are usually presented for analysis on thin substrates ranging in thickness from 100 ng/cm^ to several mg/cm^. The use of thin

samples minimizes but does not eliminate corrections which are required due to x-ray self

absorption and/or proton energy loss effects. The accuracy of x-ray and proton-induced x- ray fluorescence spectrometry in many applications depends highly on the development and

application of accurate and useful thin-film standards.

2. Discussion

Thin-film reference materials can be homogeneous single- or multi-element film deposits

or particulates collected on or in thin backing materials. These materials when well

characterized for elemental composition and homogeneity can serve several functions in x- ray fluorescence and proton-induced x-ray fluorescence spectrometry. Such materials can directly improve the accuracy of certain calibration procedures. They can also be useful

in interlaboratory comparisons [1]^. Another area of application is the improvement of

the overall accuracy of the measurement process by aiding in the testing of mathematical

models for physical processes {e.g., x-ray self absorption, proton energy loss, particle

size effects) and background-peak stripping routines.

Homogeneous thin film standards can be prepared by a variety of techniques including vacuum evaporation or sputtering [2], filtration of powders from air or liquid suspension,

and evaporation of solutions deposited directly or via nebulization onto thin backing

materials [3,4,5]. Films may also be cast from polymer material which has been doped with

suitable organometall ic compounds [6]. Particulate standards can be prepared by filtration

of particles onto thin backing materials from air or liquid suspension [3,7]. These

particles may be finely ground and sieved minerals, spiked particulates [3], or ground

Standard Reference Materials [8]. The use of dried deposits of multielement solutions on wettable filter papers allows considerable flexibility in the composition of the standard

and an excellent quantitative transfer from well-characterized solutions. Homogeneity is

good as long as the filter paper is completely wetted before evaporation takes place and

is large enough so that edge effects are not significant. Unfortunately, some of the

thinnest available films of polyester and polycarbonate are not wettable. Use of such

thin films (<^lmg/cm^) is desirable to minimize the errors due to the absorption of light

element characteristic x-rays in the film and proton energy loss in the case of protoninduced x-ray fluorescence. Although the use of nebulizers in the deposition of multielement solutions allows one to use nonwettable surfaces, accurate quantitative transfer

of the solution to the thin backing filter is not possible. However, one does have excellent

knowledge of the elemental ratios which provide relative x-ray efficiencies. With the

^Figures in brackets indicate the literature references at the end of this paper.

527
addition of an absolute standard for a single element, such as a vacuum-deposited metal

foil, absolute calibration can be achieved [5].

While thin deposits of pure elements can be made by vacuum evaporation or sputtering

and have been used by many laboratories, they have generally not been weighed to better

than 3%. These deposits are generally 50-200 pg/cm^ on a ~1 mg/cm^ backing. If accurately

weighed by the best techniques available such deposits could possibly serve as primary

standards against which other deposits could be measured by x-ray spectrometry. A recent

approach to the manufacture of absolute element standards is the casting of polymer films

in which organometal 1 ics have been dissolved [6]. Further measurements of homogeneity,

stability, and element content will be necessary to assess the suitability of these

materials as thin film standards.

Thin-film metal standards containing various metal impurities are not susceptible to

the radiation damage which can affect standards based on hydrocarbon or organic matrices.

They could be formed by rolling precharacteri zed metals. However, uniformly rolling thin

foils which are several microns thick is difficult. If one is looking at characteristic

x-rays of an energy high enough so that the absorption correction errors due to thickness

uncertainties are sufficiently small, then one can weigh the foils and get useful mass- per-unit areas for the elemental constituents. This same consideration holds for the cast

polymer films mentioned previously. A second approach to thin metal foils is the characterization of already existing foils for homogeneity and composition. While use of commerciallymade foils results in a limited choice for elemental constituents, foil which has already

been made in large quantity by industrial processes is likely to be homogeneous if one

looks at different portions of a piece of foil which has been taken from a much larger

factory rolled sheet.

We have obtained commercially manufactured thin aluminum foil (6.3 pm, ~2 mg/cm^)

which is relatively pure. We have examined four square sections (~5 cm^) from a piece of

this foil for homogeneity by energy dispersive x-ray fluorescence, with a tungsten tube, a molybdenum secondary target, and a molybdenum filter. Homogeneity results were obtained

for a 2000-second run at 40KV and 66 mA for aluminum and the impurities iron and gallium

which are present at roughly the 6 yg/cm^ (3000 ppm) and 0.1 yg/cm^ (50 ppm) levels. The

number of counts and the estimated standard deviation of these counts obtained for aluminum,

iron and gallium under the above conditions were 28704 ± 539 (1.9%) 12019 ± 139 (1.2%),

and 1333 ± 36 (2.7%) respectively.

While homogeneous thin-film standards are very useful for the calibration of x-ray

spectrometric systems, particulate standards which are formed by the deposition of particles

from air or liquid suspension onto or into thin backing materials are most applicable to

the more specialized study of correction models for particle size and composition effects.

Particulate standards have been made from finely ground rocks and minerals [3]. Quartz

particulates (spiked with several elements) have been made by heating a mixture of quartz

particles and aqua regia in which metals have been dissolved until all nitric and hydrochloric acids are evaporated, all nitrates are decomposed, and nitrogen oxides volatilized [3]

An organic particulate standard was developed at the National Bureau of Standards by

grinding the Orchard Leaves SRM (1571) and filtering them via liquid suspension in cyclohexane

onto a membrane filter [8]. Particles are usually fixed on backing materials by a thin

hydrocarbon film such as paraffin. Since particulate standards generally serve more as a research tool than for calibration their development should rest largely on the specific

research need in question. Particulate standards do, however, serve as an important

calibration tool in applications where the particulate standard is very similar to the

unknown sample being analyzed.

Another approach to the manufacture of particulate standards is the deposition of

glass particles made from synthetic glasses which can be generated by fusion techniques

with a great variety of elemental components. By means of heating and aerosol separation

techniques, controllable size distributions of spherical particles with precharacteri zed

elemental concentrations can potentially be deposited on a variety of substrates. Finely

ground glass particles from the trace elements in glass standard reference materials (SRM

610-traces at the 500 ppm level) were found to adhere well to an adhesive material which

was applied to polycarbonate membranes. Ratios of elemental intensities measured by

energy dispersive x-ray fluorescence spectrometry were found to be repeatable and particles

528
were seen to be on the surface of the adhesive by scanning electron microscopy. Absolute

standards require the more difficult quantitative transfer of particulates to the support

membrane. This particular material would not be useful for calibration because of the

large number of interfering peaks. However, it might be useful as a material for testing

overlap and background stripping routines. Glasses made from elements with non-interfering

characteristic x-ray peaks could provide particles with controlled size distributions.

Small particles would be useful for calibration purposes while larger particles could be

used in establishing models for particle size effects. In contrast with the spiked

quartz particles mentioned previously [3], particles made from fused synthetic glasses

have elemental concentrations which are uniform throughout the particle.

Further use and development of accurate and appropriate thin film standards will

directly increase the accuracy obtainable in a variety of x-ray spectrometric applications.

References

[1] Camp, D. C. , Van Lehn, A. L. , Rhodes, J. R. , and Pradzynski , A. H., Intercomparison

of Trace Element Determinations in Simulated and Real Air Particulate Samples, X-Ray

Speatrometry 4, 123-137 (1975).

[2] Graham, M. J., and Bray, C. S., The Use of Evaporated Metal Film Standards in Thin

Layer X-Ray Fluorescence Analysis of Mixed Oxides, J. Sai. Instrwn. (J. Physics E)

(1969) Series 2, Vol. 2.

[3] Pradzynski, A. H. , and Rhodes, J. R., Development of Synthetic Standard Samples for

Trace Analysis of Air Particulates, astm Special Technical Fublication 598, pp. 320-

336, (ASTM 1976).

[4] Baum, R. , Walter, R. L. , Gutnecht, W. F., and Stiles, A. R. , Solution Deposited

Standards Using a Capillary Matrix and Lyophi 1 i zation , Proa. EPA Symp. on XRF Analysis

of Environmental Samples (Ann Arbor Press, 1976) (to be published).

[5] Giauque, R. D. , Garrett, R. B. , and Goda, L. Y., Calibration of Energy Dispersive X-Ray

Spectometers For Analysis of Thin Environmental Samples, Proc. EPA Sympsoium on XRF

Analysis of Environmental Laboratory Samples (Lawrence Berkeley Lab) LBL4481

.

[6] Thin Polymer Films as Calibration Standards for X-Ray Fluorescence Analysis, Adv. X-Ray

Analysis, Vol. 20, (1976-77).

[7] Semmler, R. A., Draftz, R. D. , and Pureta, J., Thin Layer Standards for the Calibration

of X-Ray Spectrometers, Proo. EPA Symp. on XRF Analysis of Environmental Samples (Ann

Arbor Press, 1976) (to be published).

[8] Pella, P. A., Kuehner, E. C. , and Cassatt, W. A., Development of a Particulate Reference

Sample on Membrane Filters for the Standardization of X-Ray Fluorescence Spectrometers,

Advances in X-Ray Analysis, Jl9_, pp. 462-472 (1976).

529

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued No/ember 1977)

REFERENCE MATERIALS FOR AUTOMOTIVE EMISSION TESTING

Theodore G. Eckman

General Motors Corporation

Mil ford Vehicle Emission Laboratory

Mil ford, Michigan 48042, USA

1, Introduction

The automobile industry has been actively engaged in the measurement of exhaust gas

characteristics for more than twenty years. Some of this research was a result of the air

quality problem that was becoming evident in the Los Angeles basin. In the late 1960's the

test results took on added significance since during that time the California and Federal

regulatory statutes came into force; California in 1966 and Federal in 1968.

With compliance testing came a new array of difficult problems for the automotive

industry. Perhaps the most obvious was, and still is, the very basic one of engineering

the product to meet the standards set forth. However, less visible, but of equal significance, were the problems encountered in measuring the exhaust constituents at the levels

necessary for compliance to these standards. Existing instruments demanded refinement, new

ones were developed, and test procedures were written. These efforts were undertaken in

order to lend assurance to both the automobile manufacturer and the government that a given

emission test gave an accurate appraisal of actual constituent levels in an exhaust gas

sample. Also, the state and Federal agencies charged with the enforcement of emission

standards had test facilities similar to the industry's. Not only were we required to

share our test data with these agencies but also it was reasonable to expect that data

reproducibility would be acceptable between the test facilities. Automobile emission

compliance testing (which is called "Certification") involves testing the same cars at both

the manufacturer's test site and, particularly in the case of Federal standards, the government's test site. The manager of an emission test location is often faced with a myriad of

problems, not the least of which sometimes is answering the question of why his test results

are not the same as those obtained by EPA in Ann Arbor or CARB in Los Angeles. To say,

that at present, correlation is perfect among test locations would be incorrect. However,

it is true that correlation between test facilities has improved greatly over the years.

This increase in correlation came by way of investing time and funds to improve areas such

as instrumentation, test procedures, adherence to driving schedules, data reduction, and so forth.

An area that was neglected to some degree in spite of its obvious importance was that

of the gas standards. No test, no matter how well performed, can be any more accurate than

the gas standards that are used to define the various analyzers' responses to the gases

they are intended to quantify. If, unknown to you, your gas standards are 10 percent off,

unknown to you the test results will also be 10 percent off. This, of course, neglects the

possibility of cancellation of errors which is hardly a textbook method advocated to insure

good results. Several calibration gas cross-check (correlation) programs between the

various testing facilities evolved in an attempt to improve correlation. To a degree they

were successful; several laboratories adjusted their gas concentration values to equal the

mean. However, what these programs did not address was any consideration of accuracy and

rightly so--since no primary standards existed that could be inserted into the programs.

This led us to search for very accurate standards to be provided by a party not involved in

either vehicle manufacturing or emission compliance testing. The National Bureau of

Standards (NBS) had for years enjoyed a position of prominence in the world-wide standards

community. It is for that reason that the automobile manufacturers and EPA turned to NBS

as a natural choice to fill the much needed standards role.
2. Discussion

In 1972, two significant events happened to initiate the availability of emission test

calibration gas standards. First, a conference was held here in Gaithersburg which was attended by a diversity of interests in vehicle emission standards; the automobile industry,

specialty gas vendors, NBS, and EPA. The purpose of the conference was to establish what

gases and concentrations were needed and what problems were likely to be encountered in the

issuance of these blends. The second event of significance was the signing of an interagency agreement between EPA and NBS whereby the Bureau was funded by EPA to perform the

research and the production of the first sets of standards.

The necessary gas standards, agreed upon principally by the automotive industry and

EPA, reflected the test levels anticipated for the Certification of 1975 model cars. Certification test programs for a particular year normally start about one year before

model introduction. For 1975 models, this meant that the standards were needed by no later

than the fall of 1973. In addition to this, several months were needed to correlate

existing standards with the Standard Reference Materials (SRM) gases. This established the

target at January 1973.

Current Federal and California standards require a vehicle manufacturer to limit the

levels of carbon monoxide, hydrocarbons (reported as propane), and nitric oxide from the

exhaust of the cars it manufactures. These standard levels are expressed in terms of grams

per mile. In addition to this, carbon dioxide is measured as a constituent for the determination of fuel economy. Early emission test standards were stated in terms of simple

concentration, for example, 275 ppm HC and 1.5 percent CO. However, this did not take into

account the volume of exhaust gas produced by various size vehicles. For example, a small

vehicle while it may have constituent concentrations twice that of a large car, may

actually contribute less to air pollution if its exhaust flow is less than half that of a large car. Therefore, a measurement method was developed, appropriately enough called

"mass testing" to allow the emission standards to be converted from a concentration basis

to a true mass basis.

If one were faced with the task of determining the mass of a particular gas in a mixture of contained gases, it would be a relatively simple task if you knew: a) the

volume of the enclosure; b) the concentration of the gas of interest; and c) the density of

the gas of interest. By knowing these three things the weight can be determined. With

this in mind, a search was made for some kind of instrument or device that could store the

exhaust from a vehicle for a finite time duration. It also had to be able to accommodate

different exhaust flows since a driving schedule was constructed, one which was generally

representative of typical urban driving. The method chosen involves the passage of the

vehicle's exhaust in its entirety through a Constant Volume Sampler (CVS) which is basically

a fixed displacement pump which moves a constant volume per unit time. For exhaust emission testing this volume is comprised of varying amounts of filtered air and the entire

exhaust of the test vehicle and is corrected to reference conditions (528°R and 760 mm Hg).

The vehicle is operated on a chassis dynamometer. Vehicle speed changes, required by the

test schedule, cause changes in the exhaust flow rate. As this exhaust flow rate changes,

the ambient air contribution to the total CVS volume changes in the opposite direction.

If, for example, a CVS demands 300 cfm and the vehicle is at idle producing only 20 cfm,

the remainder, or 280 cfm would be ambient air. During a moderate speed cruise when the

vehicle produces, for example, 50 cfm, the ambient contribution will drop to 250 cfm to

maintain the 300 cfm total demand of the CVS. Various CVS pump parameters are monitored

throughout the test to determine the exact volume for the test. The Federal test driving

schedule is 11.1 miles long and rather than store the entire volume of exhaust and CVS

makeup air, small representative samples are stored in plastic bags for concentration

analysis at the end of the test. After these concentration measurements are made, enough

is known to determine the mass levels. We know the volume of the sample, the concentrations,

and the densities of the constituents. From this we calculate the mass weight of each

pollutant generated during the test. By dividing by the mileage we know the grams per

mile. Again, it is important to recognize that it is not necessary to know what the volume

of exhaust was during the test cycle; how much was exhaust; and how much was CVS added air.

What is important is to know the total volume. As more air is added, the concentration

decreases and viae versa. This example, of course, relates only to one specific type of

532
vehicle. The actual certification process is very extensvie covering a fleet of, in the case of General Motors, hundreds of cars; some of them driven 50,000 miles and tested every

5000 miles. The number of vehicles a manufacturer must test is determined by selection

rules made by EPA and California.

So, one can see that the levels of CO, CO2, NO, and hydrocarbons that we measure are not true tail pipe values but are diluted by the test equipment in order to obtain mass instead of concentration readings.

At this point it was shown that a need existed for automotive emission reference

standards. This need was met by the Bureau with the issuance of the following Standard

Reference Materials.

Propane in Air. Nominal values (ppm); 3, 10, 50, 100 and 500. Available February 1973.

Carbon Dioxide in Nitrogen. Nominal values (percent); 1.0, 7.0, 14.0. Available

February 1973.

Carbon Monoxide in Nitrogen. Nominal values (ppm); 10, 50, 100, 500, 1000. Available

January 1974.

Nitric Oxide in Nitrogen. Nominal values (ppm); 50, 100, 250, 500, 1000. Available

ilovember 1974.

The Bureau had some initial reservations with respect to sales projections for these SRM's.

However as of May 1 of this year, a total of 930 cylinders of Standard Reference Materials

had been sold at approximately $300 each totalling over a quarter of a million dollars in

sales.

We all know that with the passing of time, things change. However, we continue to

need new SRM's. Contributing to this need are several factors. Two major ones are new legislation and the continuing decrease in exhaust constituent levels as required by more stringent automobile emission standards. The most immediate concern is the new fuel economy

regulations.

An interesting use of mass emission grams per mile results is the calculation of the

fuel consumed during the test. Basically, fuel economy can be determined by taking the

results of an exhaust emission test and using what is termed the "carbon balance" method of

fuel economy determination. The basic premise of this method is that any carbon that

enters an engine in the form of fuel (gasoline) exits at the tail pipe as various carbon

containing compounds. These compounds (HC, CO, CO2) each contain a known percentage of

carbon. Since these compounds are routinely measured during an exhaust emission test, the

total amount of carbon burned during the test is known. By assuming the total carbon

exhausted that came from the fuel and knowing the amourit of carbon in a gallon of qasoline,

one can calculate the volume of fuel used.

Recent fuel economy legislation enacted by Congress has two features which bear

pertinent mention at this point. First, passenger automobile fleet fuel economy figures

for various years have been set. The Energy Act has mandated a production weighted fuel

economy of 18 mpg for 1978, 19 mpg for 1979, 20 mpg for 1980, and 27.5 mpg in 1985. The

Act also provides for a penalty of $5 per 1/10 mpg below the applicable fuel economy standard times the total model year production. If an automobile manufacturer were to produce 5 million cars in a year and missed Federal fuel ecomony standards by just a tenth of a mile

per gallon, the manufacturer would be required to pay $25,000,000 in fines. A 2/10 miss--

$50,000,000 and so on. It seems needless to point out that we take this very seriously. A

great amount of effort is currently being expended at General Motors in an effort to meet

these standards. Our fuel economy results must be of highest quality so that the values we

report are as accurate as possible.

533
As mentioned previously, fuel economy is determined by measuring the amount of carbon

emitted by the engine, carbon in the forms of CO, hydrocarbons, and CO2. By far, the

largest amount (greater than 98 percent) of carbon is in the form of CO2. This puts a heavy burden on analyzing this compound accurately. Presently available CO2 Standard

Reference Materials of carbon dioxide in nitrogen are 1.0 percent, 7.0 percent, and

14.0 percent. However, mass testing due to its dilution characteristics leaves us with

carbon dioxide concentrations that seldom exceed 3.0 percent. Therefore, it is necessary

to better define the 0-4 percent range with SRM concentrations of 0.5, 1.0, 1.5, 2.0, 2.5,

3.0, 3.5, and 4.0 percent. Fortunately this need has almost been met. The funds to do the

research and development phase were provided to NBS this last Spring by the Motor Vehicle

Manufacturers Association. The SRM's have been produced and currently are undergoing

statistical batch analysis before release, which the Bureau anticipates will be in November.

Standard Reference Materials involving methane are also needed. In addition to meeting

Federal emission standards, the automobile manufacturers also must conform to California

standards. California recently has allowed a "methane credit" on hydrocarbon measurements.

What this simply means is that a certain fixed amount of hydrocarbons, which California

feels is representative of methane content in exhaust, may be deducted from hydrocarbon

that does not contribute to photochemical smog and it is for this reason that California

has made the allowance. Standard Reference Materials of 5, 10, 20, 40, and 80 ppm are needed for CVS type testing. In addition, higher ranges would be desirable for engine

concentration development work.

An area allied to emission testing but not involving the actual exhaust stream concerns

the fuel used for the tests. Two classes of chemical compounds contained in fuel are under

scrutiny, lead and sulfur. We are all aware of the somewhat controversial role that lead

has played in the area of automobile emissions. The only way the industry could meet

current standards on most vehicles was through the use of oxidizing catalysts (hydrocarbons

and carbon monoxide oxidized to carbon dioxide and water). Tests unequivocally demonstrated that alkyl lead bearing compounds in fuel poisoned the catalyst and it is for that reason that lead has been removed from fuel. However, test facilities cannot always be sure that gasoline used for emission test purposes is truely lead free. Therefore, lead in

fuel standards were needed. Fortunately, these have been provided by the Bureau and

standards of 0.03, 0.05, 0.07, and 2.0 g/gal are currently available.

In addition to lead, sulfur has posed somewhat of a problem; although not the problem

that EPA had originally believed it to be. However it is present in fuel and it is

routinely measured. Standard Reference Materials in the range of 0.02 to 0.06 percent by

weight are needed.

3. Conclusion

In conclusion, a need has existed in automotive emission testing laboratories for

Standard Reference Materials provided by the Bureau. This need has been ably met in

several areas; however, we look for continued support from the Bureau in assisting us with

the very difficult task of measuring emission levels by providing standards of the very

highest accuracy and credi tabi 1 i ty

.

534
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

LONG TERM INVESTIGATION OF THE STABILITY OF

GASEOUS STANDARD REFERENCE MATERIALS

E. E. Hughes and W. D. Dorko

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

A program to produce gaseous Standard Reference Materials has been in existence for

many years but only since 1972 has it constituted a significant part of the Standard

Reference Materials Program. Standards for calibration of calorimeters for assessing the

heating value of natural gas were issued for a time in the 1950' s. Standards of carbon

dioxide in nitrogen at atmospheric levels, concentrations of oxygen in nitrogen from 1 ppm

to 21 percent, and several low concentrations of methane in air were made available after

1968. The quantities of gas per sample were limited as were the sales. In 1972 the National

Bureau of Standards embarked upon a program to supply standards for automobile emission

measurements to the Environmental Protection Agency and to the industries involved, principally gas suppliers and automobile manufacturers. The interest in this program and the

resulting high sales volume of SRM's helped to define the true needs for gaseous SRM's and

the program has been steadily expanded since then.

The acceptance of these SRM's was not instantaneous and they were subjected to intensive scrutiny by the users. We have cooperated fully with the users in order to obtain as much confirmatory information as exists concerning the accuracy of these standards and

equally important, of the stability. We have conducted a project within the gaseous SRM

program concerned solely with stability of gas mixtures and in particular, with stability

of samples which have been purchased and used for known periods of time by other government

agencies and by industry. We have encouraged the return of standards for periodic recheck

of concentration from those laboratories which we feel are unusually competent in gas

analysis and who presumably have treated the standards with the care necessary to prevent

contamination. In addition, we have retained from each individual lot of SRM's a number of

samples which are periodically analyzed in our laboratories. The cumulative results and

observations of this project are reported below.

2. Stability of Gas Mixtures

Instability of a gas mixture contained in a cylinder generally refers to a decrease in

concentration of the component of interest, although in isolated cases instability may be seen as an increase in the component. Instability may result from physical adsorption of

materials on the walls of the container, a chemical reaction between the component and the

cylinder materials, or a reaction between the component and a second gas phase component.

In most cases, instability results from interaction between the container and the component

and the only significant gas phase instability encountered thus far is that between nitric

oxide and traces of oxygen. Further, instability seems to be quite dependent on the

condition within the individual cylinder and is not usually predictable either from a knowledge of the cylinder material or the gaseous components. Variations in traces of

moisture, grease or rust on the walls of the cylinder can cause varying degrees of instability. The impossibility of reproducing the surface conditions within a cylinder during

fabrication and treatment makes it impossible to produce cylinders which will all exhibit

•"he same degree of instability with regard to a particular gas mixture. Stability, however,

535
may be achieved if the surface is treated in such a manner that it is completely inert to

the particular gas mixture. This treatment may be only a thorough drying and evacuation

for relatively non-reactive compounds or a robust chemical treatment for more reactive

species. Stability of carbon dioxide mixtures in steel cylinders may be achieved simply by

using a clean and dry container. Carbon monoxide, on the other hand can only be stored

reliably in steel cylinders if the interior surface is completely coated with an inert wax. Cylinder materials, other than ordinary steel, may be substituted to achieve stability.

Stability is best studied by comparison of the concentration of a component in a cylinder to a sample of known concentration. The essential point in this procedure is

assuring the accuracy of the sample of known concentration. The procedures for assuring

accuracy and the precautions which are observed have been reported elsewhere [1].-^ At

this point while reference to known mixtures is adequate it is not always convenient. Much

information can be obtained concerning stability by analysis on a relative basis. Long

term intercomparisons of a group of samples at or near the same concentration will reveal

"drift" in the concentration of a sample by a change in the ratio of that sample to other

samples in the group. If a large amount of samples have been filled by transfer from a single source, an analysis of each sample will reveal the degree of instability of any

sample by agreement or lack of agreement to the average. If this series of analysis is

performed at some extended time after the original transfer of material then it is possible

to predict the stability of each sample for a considerable period of time in the future.

This is possible because of the nature of the concentration vs. time curve for unstable gas

mixtures. Figure 1 is a representation of some observations of the instability curves of

several different gaseous mixtures. There is always an initial negative slope to the

concentration line, the magnitude of the slope indicating the degree of instability. Thus,

for a mixture such as sulfur dioxide in steel cylinders the instability is evident after a very short period of time. The early data for the particular sample of carbon monoxide

shown would not have revealed the long term instability with such clarity. It should be

noted that the curves are based on analysis of a single mixture of each type. Other analyses of mixtures of the same compounds would have given curves similar in nature but quite

varied in slope because of the differences between each cylinder.

The gas mixtures of major interest are obviously those already issued as SRM's or those which are contemplated as potential SRM's. These include mixtures of carbon dioxide

in nitrogen, carbon monoxide in nitrogen and air, propane in air, methane in air, nitric

oxide in nitrogen and sulfur dioxide in nitrogen.

^Figures in brackets indicate the literature references at the end of this paper.

536
537
3. Carbon Dioxide

Carbon dioxide in nitrogen mixtures appear to be remarkably stable. Mixtures at

concentrations of about 350 ppm have not shown any evidence of change over a period of

seven years. This is not unexpected because of the relative inertness of carbon dioxide

and because of its high vapor pressure. If the container is dry, no significant adsorption

occurs and if it is clean and free of organic material carbon dioxide will neither be

created nor destroyed.

A further indication of stability is shown by the homogeneity of samples prepared in

bulk and transferred to many small cylinders. Only one sample out of over 300 in the

concentration range from 1 to 15 mole percent has shown any evidence of change over a period of three years.

4. Carbon Monoxide

The instability of carbon monoxide in steel cylinders has long been recognized.

Carbon monoxide mixtures are stable in stainless steel and aluminum containers but exhibit

an unpredictable and sometimes disastrous instability in steel cylinders. The mechanism of

instability appears to be the oxidation of carbon monoxide to carbon dioxide catalyzed by

iron oxides. Evidence for this mechanism is found in samples which show a large loss of

carbon monoxide but a gain in carbon dioxide. Initially, stability was achieved by coating

the interior of each cylinder with a thin coating of wax which effectively covered the

catalytic surface. More recently, aluminum cylinders have been employed which appear to be

quite inert to carbon monoxide. Analysis of the concentration of the carbon monoxide

content of 100 cylinders at a concentration of 49 ppm yielded an average of 49.4 ppm with a standard deviation on the average of 0.2 ppm. This value is within the imprecision limits

of the method and indicates a high degree of homogeneity and stability.

A number of SRM's contained in wax lined steel cylinders have been reanalyzed after

extensive periods of use in laboratories outside the National Bureau of Standards and no evidence of significant instability was observed.

5. Propane in Air

Early results concerning the stability of mixtures of propane in air were quite

encouraging. Mixtures ranging from a few ppm to 1000 ppm exhibited no instability. However,

when the first batch of SRM's. were prepared four of five mixtures appeared to show evidence

of instability. While the majority of samples in each mixture had a concentration within

measurement limits of the average, a number of samples were well below the average. A

careful examination of the method of preparation and filling, and of the sequence of filling,

revealed no obvious source of dilution or contamination. Samples in which the concentration

deviated from the average were retained and reanalyzed. The conclusion drawn from the

results was that the differences were real and represented instability due to some unknown

cylinder effect. A second batch of 265 samples did not show similar behavior and has been

found to be quite stable.

6. Nitric Oxide in Nitrogen

The nitric oxide molecule is not a particularly reactive molecule except in the

presence of water or oxygen. Nitric oxide mixtures cannot easily be stored in steel

cylinders without a rather strenuous pretreatment. The treatment may either be one which

dehydrates the interior surface with a strongly hydrophilic chemical or it may be passiva

by exposure to a high concentration of nitric oxide. Neither of these treatments is

desirable; the first may leave a residue of an undesirable chemical and the second may

leave residual nitric oxide. The nitric oxide can desorb after addition of the sample

resulting in a change in concentration.

538
The latter treatment, passivation with nitric oxide prior to filling with the sample,

has been used with moderate success to prepare SRM's. It is not successful in all cases and in each batch of SRM's produced by this method a number of samples were found to be

unstable. The instability was easily recognized during the first analysis. It was generally true that samples in a batch, which had concentrations significantly lower than the

average for the lot, continued to decline in concentration with time. Aluminum cylinders

treated to produce an inert and non-porous interior surface were found to be quite stable

relative to nitric oxide. Observations of the concentration of mixture ranging from 50 to

1000 ppm have shown no change in concentration over a period of about 2 years. Reanalysis

of samples in steel cylinders prepared at the same time have revealed a few changes in

samples that were originally considered stable.

7. Sulfur Dioxide in Nitrogen

Sulfur dioxide mixtures in steel cylinders exhibit an instability characterized by a rapid initial reduction in concentration followed by a slow steady decline. Samples

analyzed over a period of 4 years never appeared to reach equilibrium although the rate of

decline decreased significantly after six months. Sulfur dioxide shows no greater stability

in stainless steel or wax lined cylinders. Aluminum cylinders, however, appear to be

excellent containers for these mixtures. Analyses performed over an 18-month period with

mixtures of sulfur dioxide in nitrogen in aluminum cylinders indicate no loss of sulfur

dioxide. Four mixtures consisting of 28 samples each of four different concentrations

ranging from 500 to 2500 ppm have been analyzed. The analyses, performed at least one month after filling, indicates a high degree of homogeneity within the batch and consequently gives a large measure of confidence in the stability. The spread of values between the

28 samples in each batch is commensurate with the imprecision of the method of analysis.

The relative standard deviation of the average is between 0.25 percent and 0.37 percent for

each of the four lots.

8. Conclusion

The stability of current SRM's has been assured by continuing observation of representative samples of the SRM's. While some individual samples exhibit a degree of instability

this can usually be recognized with sufficient accuracy to reject these individuals as SRM's. The use of aluminum cylinders appears to be a solution to problems relating to the more reactive species.

References

[1] Hughes, E. E,, Development of Standard Reference Materials for Air Quality Measurement,

ISA Transactions ]±, 4, 281-91 (1975).

539

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMP Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

STANDARD REFERENCE MATERIALS FOR THE ANALYSIS OF ORGANIC VAPORS IN AIR^

Barry C. Cadoff

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

The increasing knowledge of the harmful long-term health effects of exposure to organic

solvent vapors has led to more stringent regulations that have lowered permissible concentration levels. These regulations have had their broadest impact on workers in industrial

environments but have also had influence on the emission of industrial effluents, particularly vinyl chloride. This paper discusses the preparation and analysis of Standard

Reference Materials (SRM's) for seven organic solvents, viz., benzene, m-xylene, p-dioxane,

1 ,2-dichloroethane, chloroform, trichloroethylene and carbon tetrachloride, and briefly

mentions the preparation of standards for the analysis of ambient levels of vinyl chloride.

2. Collection and Analysis of Field Samples

The method in widespread use for the sampling of industrial workplace atmospheres

employs a small glass tube containing 150 mg of charcoal granules (which strongly absorb

solvent vapors) and a pump which draws air through the tube. The charcoal tube is attached

with flexible tubing to the pump. The pump, which is battery-run, is small enough to fit

inside a person's pocket or can be clipped to the person's clothing. Thus, the apparatus

can be positioned near the face, or breathing zone, of the individual. After collection of

the sample, the tube is capped and sent to the laboratory where the charcoal granules are removed from the tube. The charcoal is then desorbed with carbon disulfide and the resulting

solution is analyzed using a gas chromatograph equipped with a flame ionization detector.

The role of SRM charcoal tubes is to provide a means for calibrating gas chromatographs for

this type of analysis. Each SRM contains one of the above-mentioned solvents and consists

of eight tubes: two tubes at each of four concentration levels.

3. Vapor Mixtures for the Filling of Charcoal Tubes

The method chosen for the preparation of charcoal tube SRM's closely simulates the

collection of field samples, i.e., a known volume of air containing an organic vapor is

drawn through the charcoal tube. The organic vapor mixture is prepared using partial

pressure procedures and is compressed and stored in a large cylinder; this provides a large

volume of stable gas sufficient for the preparation of several hundred charcoal tubes.

Using the ideal gas law, an approximate value for the concentration can be assigned.

However, these solvent vapors are often not "ideal" so their concentrations must be confirmed

by other means. One method, developed in this laboratory, is a gravimetric procedure using

a charcoal tube, which is weighed before and after a known volume of vapor mixture is

sampled [1]^. The weight gain can then be used to calculate the concentration of the vapor

mixture.

^This work was supported, in part, by the National Institute for Occupational Safety and

Health and the Environmental Protection Agency.

^Figures in brackets indicate the literature references at the end of this paper.

541
Lower concentrations are prepared by diluting the higher concentration mixtures and

storing these mixtures in cylinders. These dilute mixtures are assigned values based on their gas chromatographic response compared to the concentration mixture. These procedures

will be discussed in further detail.

4. The Absorption of Organic Vapor on Charcoal Tubes

To prepare the several thousand charcoal tubes required for the SRM's, an apparatus

was constructed which fills 20 tubes at a time. This apparatus consists of 20 critical

orifices (made from hypodermic needles having flow rates of approximately 0.9 liters/min)

mounted on a manifold which can be connected to a vacuum source [2]. The critical orifices were measured for flow rate and selected such that no orifice deviated from the average

flow rate by more than 0.8 percent. The blank charcoal tubes were obtained commercially

and samples were taken to obtain data on resistance to flow (pressure drop). The values

for the flow rates of the critical orifices and the values for the pressure drops of the

tubes could then be used to estimate the uncertainty or variability in quantity of adsorbed

solvent that could be expected for each batch of tubes. In use, a charcoal tube is mounted

atop each orifice and vacuum is applied to the manifold containing the orifices. The gas

mixture is allowed to flow into a glass enclosure which covers the tubes and manifold.

This enclosure is fitted loosely to ensure that sampling is conducted at ambient atmospheric

pressure. Flow rates are determined with a wet- test meter and total flow is calculated for

the ambient temperature and pressure conditions.

5, Analysis of Charcoal Tubes

A number of tubes were selected for analysis from each concentration level. The

charcoal was removed and desorbed with 1 ml of carbon disulfide. A 5 yl aliquot of this

solution was injected into a gas chromatograph and the area of the resultant peak was recorded. This peak area was assigned a value, expressed in yg/tube, by means of a calibration curve. The standard solutions used for the calibration curve were prepared by

dissolving known volumes of the particular solvent in carbon disulfide. This general

analytical procedure has been published by the National Institute for Occupational Safety

and Health (NIOSH) [3]. Modifications of this reported method will be discussed. Finally,

a comparison will be made between the results obtained from the analysis of the tubes and

the predicted results based on the total volume of vapor mixture sampled and the concen- tration of the vapor mixture.

6. Vinyl Chloride Standards

For the case of vinyl chloride, charcoal tubes were also prepared to serve as analytical

reference standards. The amount deposited on the tube corresponded to that which would

have been collected during 24 hours at a sampling rate of 0.2 liters/min, for several

concentration levels of vinyl chloride. The concentration levels were first chosen to be

0.1, 1.0, and 5 ppm and a few pilot tubes were prepared on this basis. The levels were

later changed to 0.014, 0.10 and 1.0 ppm and most of the tubes were prepared at these

levels.

The charcoal tubes, which were prepared for the Environmental Protection Agency, were

of a different design than the ones used for industrial atmospheric testing. These tubes

contained much larger quantities of charcoal and furthermore, the tubes exhibited a wide

range of pressure drops. Accordingly, it was necessary to measure the flow resistance of

each tube and to apply a correction to the nominal flow rate. These tubes were filled,

with standard mixtures of vinyl chloride in air, using the same sampling equipment described

earlier.

542
Selected tubes from each concentration level were analyzed, using carbon disulfide for

the desorption step. Gas chromatographic standards were prepared by the addition of gaseous

vinyl chloride to carbon disulfide, using a calibrated gas-tight syringe. Data on the

analytical results obtained and the results predicted on the basis of sample flow rate and

gas concentration will be compared.

7. Charcoal Tube SRM's

The choice of solvents and concentration levels for the SRM's were decided upon as a result of discussions with representatives of NIOSH. Table 1 lists each solvent and SRM

number and four target levels of concentration expressed in ppm. The nominal quantity of

solvent deposited on each tube is equivalent to the amount contained in a 10-liter sample

at one of the listed concentration levels. The concentration levels roughly correspond to

the following:

Level I: Limit of Detection

Level II: Safe Level of Exposure

Level III: Threshold Level

Level IV: Excess of Threshold Level

The actual quantities deposited differ somewhat from these amounts and will be specified in

the SRM certificate.

Table 1

Target levels of concentration

SRM No. Sol vent Concentration Level (ppm)

I II III IV

2661 Benzene 0.5 2 8 30

2662 m- Xylene 1 7 50 300

2663 p-Dioxane 0.5 4 30 200

2664 1 ,2-Dichloroethane 2.5 10 40 150

2665 Chloroform 2.5 10 40 150

2666 Trichloroethylene 5 20 80 300

2667 Carbon Tetrachloride 0.5 2 8 30

References

[1] Cadoff, B. C, Greifer, B., Pella, P. A., and Taylor, J. K. , Development of Contaminant

Generation Systems for Certification of Portable Air Sampling Instruments, NBSIR 74-573

(1975).

[2] Cadoff, B. C, Hughes, E. E., Alvarez, R. , and Taylor, J. K. , Preparation of Charcoal

Sampling Tubes Containing Known Quantities of Adsorbed Solvents, NBSIR 74-520 (1974).

[3] Organic Solvents in Air, Analytical Method No. P&CAM 127^, NIOSH Manual of Analytical

Methods (1974).

543

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

WORKING REFERENCE MATERIALS FOR LEAD CONTAMINATION ANALYSES OF AIR AND WATER

Alfred C. Eckert, Jr. and Dennis M. Mongan

Globe-Union, Inc.

Milwaukee, Wisconsin 53201, USA

1. Introduction

Cali, in a recent historical review of the National Bureau of Standards Standard

Reference Materials Program [l]'^ refers to problems in measurement compatibility between

laboratories that prompted the issuance of an NBS monograph in 1975 [2] to review certain

fundamentals of metrology as they apply to chemical analysis processes. He cites the need

for an accuracy-based measurement network that would automatically achieve compatabi 1 ity.

By definition, an accurate measurement is one that is both free of systematic error and

precise; thus it is directly related to the "true" value of the property being measured.

We find some measurement networks for which efforts to attain greater accuracy are not

warranted because their precision is undetermined or if determined, the precision is

insufficient for the system to benefit from standards more accurate than commercially

available "reagent" grade chemicals.

Cali points out that although approximately 60 man-years per year of high quality

specialized manpower are available at the NBS for work on Standard Reference Materials,

many times this amount of manpower would be required to produce reference materials for

many applications that need standardizing. He cites a new NBS service to help fill this

need: "General Materials'!, which are reference materials produced by other standards

organizations but distributed by NBS. In the NBS monograph, the authors recommend the use

of secondary reference materials as a means to reduce the demands on the NBS so that it can devote more of its resources to the development of needed primary reference materials.

They also mention that the use of secondary reference materials promotes wider use of

reference materials for standardization purposes. Both General Materials and secondary

reference materials are useful extensions of Standard Reference Materials where accuracy is

of primary concern, for example, where the precision of the measurement system is sufficiently good for the system to benefit from accurately certified standards.

We are using a further extension of the use of reference materials to measurement

systems that may not have sufficient precision to benefit from the use of higher quality

reference materials. We call these supplementary reference materials "working reference

materials" as they are produced within our own laboratory and used as working standards on

a daily basis. The working reference material (WRM) is analogous to the standard reference

material (SRM). To be useful, a WRM must be sufficiently homogeneous so that the dispersion in results due to material variability will be less than method imprecision. Beyond

this requirement, the usefulness of a WRM depends on how well it meets the following

criteria:

1. availability in sufficient quantity for repeated analyses (15 to 100 is a generally

useful range)

Figures in brackets indicate literature references at the end of this paper.

545
2. stability over extended periods of time (one month to one year is a generally useful

range)

3. resemblance to the material whose analysis it is used to monitor.

Although a WRM has no certified value for the quantity being measured, and therefore cannot

be used to determine absolute accuracy, it is used effectively to determine precision.

We use analyses of WRM's to evaluate the precision of analytical methods and in

particular to determine when the precision is sufficient for the system to benefit from the use of SRM's (or other highly characterized certified reference materials). Progress in

upgrading poor precision can be evaluated and monitored by analyses of WRM's.

In a form of "active harmonization," as discussed by Huntoon at the NBS Sixth Materials

Research Symposium [3], we use multiple analyses of WRM's both to maintain an active analytical quality assurance (AQA) program (evaluating analytical repeatability), and also in

occasional round robin programs (evaluating analytical reproducibility). It is WRM's that

make our active AQA program feasible for most of the analyses we perform. In most cases SRM's are either not available, are not directly applicable, or are too expensive for such

frequent use.

Maintaining AQA with materials other than SRM's is a direct extension of the thinking

expressed by Cali et at. when they suggest the use of a secondary reference material.

WRM's can serve an even wider area of analyses than secondary reference materials, extending

the use of such standards even further and reducing the demands on the NBS.

By the use of WRM's in our own laboratory and in round robin experiments, we have

found that until the repeatability and reproducibility of results obtained in practice for

air lead and water lead analyses in the parts per million and lower range are significantly

improved, any advantage in the use of SRM's for these analyses is difficult to justify.

Certainly, other projects involving more precise measurement systems must have greater need

for NBS SRM's.

2. Within Laboratory Use of WRM's

When an SRM is more expensive to develop and produce than the application warrants, or when there is insufficient time to wait for an SRM to be developed and produced, WRM's can

be used to make an active AQA program feasible. To maintain active, systematic AQA programs

within our laboratory, we intersperse WRM samples within each batch of regular samples.

This day-to-day use of a WRM is a more active form of AQA; the conventional use of a refer- ence material for calibration is a more passive form of AQA. In either case, the materials

may be primary or secondary reference materials or WRM's. AQA becomes more systematic when

the results of analyses of reference materials are systematically plotted on control charts.

WRM's in active AQA programs are advantageous not only when the feasibility of the program

depends on them, but also when their daily use can displace high volume use of more expensive SRM's.

Estimates of uncertainty in individual analytical results can be derived from active

AQA data. These estimates have the advantage over those derived from more passive AQA data

because they usually are based on more observations and the individual analyses are made

under conditions that more closely resemble the conditions of analysis of regular samples.

The value of larger numbers of observations is clearly illustrated in table 1 on air lead

data

.

546
Table 1

Interlaboratory Comparisons - Lead Analyses

WRM: BHD-74-5

100 X 2s/x X 2s//n

Estimated 95%

from n^ Probability

observations Limits

Laboratory n^ (%) Lower Upper (mg/filter) (mg/fi 1 ter)

ABCD vs X 24 28 22 39 0.146 X 0.008

ACD vs X G-U 18 11 8.2 16.5 0.156 0.002

A 6 6 3.7 15 0.139 0.004

B 6 50 31 125 0.141 0.03

C 6 5 3.1 12.5 0.168 max 0.003

D 6 8 5.0 20 0.136 min 0.004

G-U - AQA Analyses

(10/74 to 11/74)

67 12 10.2 14.5 0.156 0.002

G-U - Initial 18 10 7.5 15 0.153 0.002

Analyses (9/74)

3. Between Laboratories Use of WRM's

A classical example of inadequate harmonization between laboratories is cited by Cali

et at. [1], and discussed in an editorial aptly titled "The Wizards of Oops" [4]. For

example, results from three laboratories for contaminants in portions of a sample of water

from San Francisco Bay were: lead--3.30, 21, 50, and mercury--0.80, 0.10, 0.10 ppm. It is

unfortunate that more intelligent planning was not used in this case. The sample itself

could have been used as a WRM in an intelligently planned program of between laboratory

harmonization, preceding attempts to determine its actual composition. A round robin

program would have generated more meaningful data. The data obtained only indicate that

there is serious lack of between laboratories harmonization.

Comparison of analytical results between laboratories can be facilitated by use of WRM

samples, particularly in cases where SRM's are not available. In addition the cost and

custom design of WRM's often makes their use advantageous even when SRM's are available.

The use of WRM's makes it unnecessary to make between laboratories comparisons from

"split samples." Results from split samples usually give data that are inconclusive

because they can be interpreted only with great imprecision. Often, the same amount of

work on WRM's used in a program will give data that can be related to confidence or tolerance intervals with a greater degree of rigor.

WRM's are useful not only for simple harmonization experiments, but for programs of

varying complexity including the carefully structured procedures such as the ASTM Standard

Recommended Practice [5]. WRM's can often offer advantages by being designed to simulate

actual samples more closely than available SRM's. They are particularly advantageous for

harmonizations of analyses that are not made with sufficient frequency to justify the

development and production of an SRM.

4. Air Lead WRM's

We analyze some 800 air filter samples per month to verify that the lead content of

the air in our lead-acid battery plants is well below hazardous levels. The particulates

from the filters are dissolved in nitric acid containing H2O2, and lead in the solutions is

547
determined by atomic absorption spectrophotometry. Our routine AQA is derived primarily

from analyses of WRM samples interspersed with the regular samples; the WRM's are specifically designed for the purpose.

The WRM samples are filter discs (identical with those used in sampling the air in our plants), that have been inoculated with metered quantities of lead-containing particulates.

Material collected in the baghouse of a plant, representative of the material found in a typical plant atmosphere, is screened (-325 mesh). A quantity (75 to 100 mg) of the

screened material is suspended in 100 ml of water containing 1% surfactant (Triton X-100),

and the mixture is stirred magnetically at a speed sufficient to produce a 2 to 3 cm deep

vortex. While stirring continues, 200 pi portions of the suspension are withdrawn in a plastic tipped micropipet and placed dropwise on the filter discs. After air drying, the

filters are stored in individual plastic containers (Petri dishes).

This WRM has been useful in both repeatability and reproducibility programs. It is

stable indefinitely, prepared in batches for 75 to 100 determinations, and is virtually

identical with the plant samples it is designed to simulate. However, the plant samples

analyzed actually contain significantly less lead. It is at the upper limits that precision

is critical, and therefore the samples are appropriate for the purpose.

By preparing WRM's in this manner, we simulate filters that have been used in a plant

sampler to collect the particulates from 1 cubic meter of air containing 0.12 to 0.15 mg of

lead (the current OSHA maximum allowable limit is 0.15 mg/M^). The pooled uncertainty^

at 95 percent probability (confidence interval) of the preparation procedure and the analysis, performed by two experienced operators over a period of several days, is ±8 to ±10

percent at concentrations of 0.12 to 0.16 mg/filter. If the ±10 percent uncertainty is

divided equally between the procedure and the WRM preparation, the uncertainty in the WRM

is ±7 percent.

In the regular analysis, the instrument is calibrated with a series of dilutions of a stock solution of lead nitrate, and calibration samples are interspersed periodically

during the day with the regular samples. These do not qualify as desirable WRM's because

they are not carried through the whole analytical procedure.

Summarized in table I are data on within laboratory and interlaboratory results of 101

analyses of an air lead WRM. Of interest to within laboratory AQA is the comparison of the

uncertainty in individual results predicted from the initial 18 analyses (Row 8) with the

scatter experienced over a period of 2 to 3 months: ±10 percent; ±12 percent; the predicted uncertainty is lower, but well within its 95 percent probability limits shown in the

following two columns. However, the greatly improved confidence interval within which the

uncertainty is predicted shows the value of making 67 observations rather than 18: a range

of 4.3 instead of 7.5.

The interlaboratory data appear good; the lowest mean is only about 3 percent below

the highest. However in practice, analyses are usually not made on six independent samples;

the uncertainty in results within each of three of the four laboratories is ±5 to ±8 percent

This would seem to be useful, but the scatter in individual results based on our longer

range experience with the WRM is about twice as much. Also, the scatter in results from

one laboratory was ±50 percent, and the scatter in the pooled results by two approaches was

not encouraging.

Available standard reference materials for monitoring air filter analyses for lead

content (NBS SRM 2676) are filter discs with known quantities of nitrates of several metallic contaminants at three levels. Daily use of this SRM would be expensive ($80 per unit

of three filters). This SRM provides basis for evaluating accuracy at levels of 0.10, 0.03

^Uncertainty includes method imprecision plus materials variability. It does not include

systematic error so may not be accurate. This is a statistical uncertainty calculated

from replicative data.

548
and 0,007 mg/f i lter--al 1 below the range of our greatest interest; in fact, only the highest

level is in the range of our method. The lead is in the form of a solid salt, not the

oxide, mixed with various lead sulfates and other plant debris. Therefore, the SRM's check

only the determination, not the whole procedure. For instance, omission of the H2O2

addition in the dissolution step could affect the results from the WRM samples and from

"real" samples, but not from the SRM samples.

The precision experienced is hardly sufficient for this measurement system to benefit

from the use of SRM's. The inadequate precision of the analysis and the similarity of the

WRM to actual samples provides a good example in which use of a WRM results in economical

AQA, without the use of more costly SRM's.

5. Water Lead WRM's

The WRM's used for AQA of our water lead analyses are not as unusual as the WRM's used

for AQA of air lead analyses. However, we prepared some special WRM's for an interlaboratory experiment discussed below.

The WRM's used regularly are aqueous solutions (0.3 N in HNO3 promote stability)

containing known quantities of lead nitrate in the range most frequently of interest (0.1

to 5 ppm). These samples are stable for periods of a year or more. The quantity is

sufficient for about 30 determinations, and the similarity to normal test specimens is

apparently good. However, the data from the interlaboratory experiment show that impurities

in samples affect lead results significantly at lower concentrations (below 0.1 ppm).

Our AQA control charts for lead in water (figure 1) cover a period of about two years.

Two charts are maintained concurrently. One is for lead concentration in the range between

0.5 and 1 ppm, and the other at about 5 ppm. At the higher level, individual results over

both years were distributed within ±5 to ±7 percent of the mean at 95 percent probability

(confidence interval). At the lower level the first year's results were distributed within

±23 percent of the mean. During the succeeding year the distribution was improved to ±12

percent. In each case, repeatability predicted from six to ten initial determinations was

not significantly different from the repeatability experienced throughout the year.

However, the confidence interval of the estimated standard deviation was considerably

reduced and the initial estimates tended to be lower than experience showed.

An experiment was designed to illustrate how interlaboratory results can be expected

to compare with each other. Our laboratory participated with three others. The eight

WRM's used contained lead at four concentrations: 10, 1, 0.1, and 0.01 ppm. There were

two kinds of matrices, 0.3 N HNO3 and 0.3 N HNO3 plus selected "impurities":

• 0 5000 ppm each - Na2C03, KH2PO4

• @ 1000 ppm each - acetic, sulfuric, and phosphoric acids

- NaOH, FeClj, Al2(S04)3, glycerine

Six groups of twelve samples were sent to each laboratory at intervals of about one month;

the twelve samples in each group were sextupl icates from two WRM's. On two occasions,

samples from the same WRM's were submitted in two successive groups.

Results of the 288 analyses will be presented and discussed in detail in a later

publication. An abbreviated summary follows.

0 At 10 ppm, individual results were scattered about laboratory means within an estimated ±0.6 to ±4 percent at 95 percent probability (confidence level), and the means

all fell within the range of 9.1 to 10.5 ppm.

0 Results were progressively less satisfactory with decreasing lead concentration, and were significantly high at low lead concentrations in both the uncontaminated and in

the contaminated series of samples.

549
(lOOx^) 1974-75

-5.3%

DATES Feb Apr Jul Oct jlin

I I

I I I

1975

WRM 75-16

+ 66%

n=9

Aug Oct Jon

X=5.32

-6.6%

+t 8

95

+ 20-

WRM74-I

"'•6 +25%

X«.80

"-25%

LEGEND

dates: no scale

WRM 75-15

+ 11.5%

-11.5%

t s f PREDICTED

ICALCULATEDFigure 1: AQA control charts for lead in water cover a period of about two years.

550
0 At 0.01 ppm, laboratory means were high by factors as large as 2.5 and 6 for the

uncontaminated and contaminated samples respectively. Within laboratory imprecision

was up to ±59 percent for the uncontaminated samples and up to "±" 150 percent for the

contaminated samples. Intralaboratory disagreements by a factor of 2 were observed

between mean values of successive sets of samples from the same solution.

6. Conclusions

Working reference materials have helped us expand the use of active, systematic

analytical quality assurance (AQA). Especially in analyses of samples such as air filters

for lead, they have made it possible for the AQA evaluations to be based on data from

materials similar to the regular samples being analyzed.

Working reference materials have helped us make better evaluations of several parameters, such as:

0 The repeatability of our air lead analyses.

0 The reproducibility of air lead analyses from different laboratories.

0 The reproducibility of water lead analyses between laboratories at lead concentrations

ranging from 10 to 0.01 ppm, with and without selected contaminants.

The advice of a recent author in CHEMTECH is well illustrated: "Test your test: it's

cruder than you thinkl" [5].

References

[1] Cali, J. P., The NBS Standard Reference Materials Program: An Update, Anal. Chem. 48 , 802A-14A (1976).

[2] Cali, J. P., Mears, T. W. Michaelis, R. E. Reed, W. P., Seward, R. W., Stanley, C. L.,

Yolken, H. T., and Ku, H. H., The Role of Standard Reference Materials in Measurement

Systems^ NBS Monograph 148, U. S. Department of Commerce, National Bureau of Standards,

U. S. Government Printing Office, Washington, DC 20404 (1975). •

[3] Huntoon, R. D., Standard Reference Materials and Meaningful Measurements--An Overview,

in standard Reference Materials and Meaningful Measurements, Proceedings of the 6th

Materials Research Symposium, National Bureau of Standards, October 29 through

November 2, 1973, Gaithersburg, MD, Seward, R. W., Ed., U. S. Government Printing

Office, Washington, DC 20404 (1975).

[4] Cavanaugh, W. T., The Wizards of Oops! Materials Research and Standards 1_2, No. 1,

28 (1972).

[5] ASTM Committee E-3 on Chemical Analysis of Metals, Conducting Interlaboratory Studies

of Methods for Chemical Analysis of Metals, in 1974 Annual Book of ASTM Standards, Part

12, Chemical Analysis of Metals; Sampling and Analysis of Metal Bearing Ores, pp.

492-5, American Society for Testing and Materials, Philadelphia, PA 19103 (1974).

[6] Mitton, Parker, B., Test your test: It's cruder than you think!, Chemtech 4^, 248-53

(1974).

551

Part XI. COLLABORATIVE TESTING

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

COLLABORATIVE TESTING OF AIR POLLUTION METHODS

John B. Clements

Environmental Protection Agency

Research Triangle Park, NC 27711, USA

1 . Introducti on

Interl aboratory collaborative testing is one of the traditional means by which measurement methodology is validated and determined to be suitable for its intended purpose.

Interlaboratory collaborative testing has been used widely in such diverse fields as water

chemistry, metallurgy, food and related products and agricultural chemicals, as a means to assess measurement methodology. From the results of interlaboratory collaborative testing

one can estimate the precision capabilities of a method and in many cases method bias.

The basic concept of an interlaboratory collaborative test is the use of a method by

a variety of analysts, in different laboratories, to make measurements on a standard

reference material in order to estimate the precision, capabilities and bias of the method.

A simple example will illustrate how one obtains precision information from collaborative

testing results.

The results from a hypothetical interlaboratory collaborative test are presented in

table 1. In this very simple example imagine that a reference material was submitted to

five different laboratories who were asked to analyze the material four times using the

method under test. Further, imagine that the values ente^red under "Replicate Results" were obtained from these analyses. The column labeled "X-j" shows the average of the four

replicates for each of the five laboratories and the column labeled "S-j^" shows the

statistical variance of the replicate results for each of the five laboratories. Withinlaboratory standard deviation (S^^) and between-laboratory standard deviation (S^) can be

calculated. The within-laboratory standard deviation (S^) is obtained by averaging the

individual S-j^ and taking the square root of the average. The between-l_aboratory standard

deviation, Si, is obtained by calculating the variance of the array of Xi values and

applying a correction to account for the uncertainty caused by the rather modest number of

replicates.

This hypothetical and very much simplified example is presented to illustrate how

precision information is obtained from interlaboratory collaborative tests. Actual collaborative tests are considerably more complex in design and require a much more rigorous

statistical analysis to extract information from test results. It is extremely important

that collaborative tests be carefully and thoughtfully designed and the results be analyzed

in depth in order to obtain all available useful information.

555
Table 1

Results of hypothetical collaborative test

Lab Replicate Results M Si^

1 72 79 61 71 70.8 54.92

2 61 49 57 61 57.0 32.00

3 70 62 62 76 67.5 46.33

4 36 39 41 45 40. 3 14.25

5 58 57 58 53 56.5 5.67

\ U

<; 2 rC • 2

c0

= 153.17

5

= 30,. o6

\

-= 5.5

(2) = z(Xi -Xi)2 - 142,,44 - 7.66 = 134.

P

-1 4

(p = number of laboratories, 5)

2. Air Pollution Methodology

Although interl aboratory collaborative testing has a long history of use in a variety

of areas, its use in validating air pollution methodology is relatively recent. The

remainder of this discussion will deal with the collaborative testing of air pollution

methods with special emphasis on the Environmental Protection Agency's program directed at

the air pollution methods specified in Federal regulations. The American Society for

Testing and Materials (ASTM) has also conducted interl aboratory collaborative tests for some of their air pollution methods in their Project Threshold.

A listing of pollutants which are the subject of National Ambient Air Quality Standards

and the designated reference methods is shown in table 2. The combination of industries

and pollutants which are the subject of Standards of Performance for New Stationary Sources

is shown in table 3 and the pollutants which are the subject of National Emission Standards

for Hazardous Air Pollutants are shown in table 4. There are detailed methods specified

for measuring the indicated pollutants in the various stationary source emissions with the

exception of asbestos where no methodology exists.

Many of these methods have been subjected to interl aboratory collaborative tests.

Our experience has shown that a complete and systematic examination before collaborative

testing is required even for those methods and measurement principles with fairly extensive

histories of usage. From this experience we are convinced that the effort expended in

this pre-test method examination is necessary for a successful methods validation and

standardization program.

556
Pol 1 utant

Table 2

Reference method for ambient air quality standards

Reference Method

Total suspended particulates

Sulfur dioxide

Carbon monoxide

Photochemical oxidants

Hydrocarbons

Nitrogen dioxide

high volume samples

pararosani 1 ine (PRA)

nondispersi ve infrared spectrometry (NDIR)

ozone-ethyl ene chemi 1 uminescence reaction

gas chromatographic separation of methane and flame

ionization measurement of nonmethane fraction

original method withdrawn: now being replaced

Table 3

Pollutant/source combination in standards of performance for new stationary sources

Source

Power Plants

Incinerators

Cement Plants

HNO3 Plants

H2SO4 Plants

Asphalt Plants

Petroleum Refineries

Secondary Lead Smelters

Secondary Brass and Bronze Plants

Iron and Steel Plants

Sewage Treatment Plants

Copper, Zinc, Lead Smelters

Primary Aluminum Plants

Phosphate Fertilizer

Coal Preparation Plants

Ferro-alloy Plants

Electric Arc Steel Furnaces

Pol 1 utant

Particulate, SO2, NOx

Particulate

Particulate

NOx

SO2, Acid Mist

Particulate

Particulate, CO, SO2

Particulate

Parti culate

Particulate

Particulate

Particulate, SO2

Fl uorides

Fl uorides

Particulate

Particulate, CO

Particulate

557
Table 4

Pollutant/source combinations in national emission standards for hazardous air pollutants

Source Pol 1 utant

Be, BeO, Be Alloy Beryllium Emissions

Processing Plants and Machine Shops

Hg Ore Recovery Plants Mercury Emissions

Chloralkali Plants

Asbestos mills, Roadway surfacing. Asbestos Emissions

various manufacturing process,

various demolitions

A. Pre-col laborati ve test evaluation

The method should first be examined for technical accuracy, clarity and completeness

of detail. Regardless of the inherent capabilities of a measurement principle, there is a significant risk that a method may not give reliable results if it is poorly written, has errors in critical spots or lacks procedural details. If a method is deficient in these

aspects it may need to be rewritten.

The method should then be subjected to a thorough and rigorous laboratory evaluation.

This evaluation typically includes investigations of sample collection efficiency, integrity

of calibration procedures, reagent stability, variation of method response as a function

of pollutant concentration and effects of interferences. It may be said that these are

the jobs of the researchers and should be done at the time the method is developed. This

is true in principle but experience has shown that many times such investigations were carried out in a rather superficial manner and significant deficiencies of the method were

not uncovered.

One very powerful technique for efficiently examining a number of variables with a surprising small number of experiments has been described by Youden [1]^ and given the name Ruggedness Testing. Statistically designed fractionated factorial experiments are

the basis of Ruggedness Testing, but as described by Youden this testing does not require

sophisticated statistical techniques. Our experience shows that Ruggedness Tests are well

within the capabilities of professionally trained chemists and that they are very useful

in methods evaluation [2].

B. The collaborative test

Methods which survive the above evaluation process are then candidates for interlaboratory collaborative tests. There are unique problems in air pollution methodology which

complicate the usual collaborative testing procedure. In particular, there is a problem

in obtaining a reference material that can be used as a test material by the participants.

A sample that simulates polluted air with its interferences and contains the pollutant in

known amounts is difficult to prepare, particularly if there is a requirement that replicate

samples be distributed to a number of test participants. Collaborative testing stationary

source emission test methods presents a set of particularly difficult problems. It is

enormously expensive to measure source emissions in replicate, the sampling portion of

emission test methods are a major part of the total method and it is physically difficult

to obtain adequate replicate measurements.

Figures in brackets indicate the literature references at the end of this paper.

558
Collaborative tests have been conducted by submitting reference materials to test

participants. The preferred procedure is to gather the test participants at a common site

and then make simultaneous measurements of ambient air or a stack emission using the

method under test, A report describing the test and its results is essential. From the

information gained from the collaborative test a final version of the measurement method

can be prepared and recommended as a standard method.

This sequence of steps has evolved with time from a more simple and naive approach

used earlier. In earlier efforts at standardizing air pollution methods, particularly

those specified in Federal regulations, the assumption was made that these were well

written, fully described and adequately researched methods needing no further evaluation.

For this reason pre-collaborative test evaluations were all but eliminated and plans were

made for method collaborative testing after only a limited amount of evaluation. Experience

has shown that this was a poor assumption. While it is true that the methods are based on sound measurement principles, occasionally procedural details were too sketchy to ensure

that different users would use the methodology in the same way. Too many options were sometimes permitted and faulty or incorrect instructions were sometimes encountered. The

effort invested in pre-collaborative testing evaluation of methods has done much to eliminate

these problems. We now take all methods introduced into the validation program through

the above pre-collaborative test evaluation sequence.

3. Collaborative Test Results

The results of the collaborative testing program are much too extensive to discuss in

detail and are presented here in summary form. Tables 5 and 6 present the essential

statistical results from the collaborative testing carried out on EPA's reference methods

and the original reports should be consulted for details. Our experience in evaluating

and collaboratively testing one of EPA's methods will now be presented to illustrate why

we now believe so strongly in precol laborati ve test method evaluation.

Table 5

Summary results from collaborative testing of ambient air methods

A. High-volume procedure for total suspended particulate matter [3]

This test was carried out by having twelve laboratories simultaneously sample the

ambient air at a common site over a four day period. The following results were obtained:

(a) The relative standard deviation for a single analyst variation is 3.0 percent.

(b) The relative standard deviation for multi laboratory variation is 3.7 percent.

(c) The minimum detectable amount of particulate matter is 3 yg, which is equivalent

to 1 to 2 pg/m^ for a 24-hr sample.

B. Pararosanil ine procedure for sulfur dioxide [4,5]

The 30-min sampling option was tested collaboratively by 14 laboratories, and the

following results were obtained:

(a) The standard deviation for within-laboratory variation varies linearly with

concentration from 15 yg/m^ at 0 to 36 yg/m^ at 1000 yg/m^.

(b) The standard deviation for between-laboratory variation varies linearly with

concentration from 29 yg/m^ at 0 to 70 yg/m^ at 1000 yg/m^.

(c) No systematic error bias or inaccuracy was detected, and the lower limit of

detection is 25 yg/m^ (95 percent confidence level).

559
The 24-hr sampling option prescribed in the reference method was collaboratively tested

by four laboratories, and a statistical analysis provides the following results:

(a) The standard deviation for within-laboratory variation varies linearly with

concentration from 18 yg/m^ at 100 ug/m^ to 51 pg/m^ at 400 yg/m^.

(b) The standard deviation for between laboratory variation varies linearly with

concentration from 37 yg/m^ at 100 yg/m^ to 104 yg/m^ at 400 yg/m^

(c) The 24-hr sampling method appears to have a concentration dependent bias which

becomes significant at the 95 percent confidence level at about 400 yg/m^.

Observed values tend to be lower than expected SO concentration levels.

C. NDIR procedure for carbon monoxide (CO) [6]

This reference method was collaboratively tested by supplying 16 laboratories with

cylinders containing carbon monoxide in air of varying concentrations which were unknown

to the test participants. A statistical analysis of the data provided the following

information about the procedure.

(a) The standard deviation for within-laboratory variation is 0.57 mg/m^

(1 ppm CO = 1 .15 mg/m3 CO)

.

(b) The standard deviation for between-laboratory variation varies non-linearly with

concentration with a minimum of 0.85 mg/m^ at 20 mg/m^ and ranges as high as 1.4 mg/m^ in the concentration of 0 to 60 is mg/m^.

(c) The minimum detectable limit is 0.3 mg/m^.

D. Four procedures for nitrogen dioxide [7,8,9,10]

Standard Deviation

Method Wi thi n-Laboratory Between- Laboratory

TGS

Sodi urn Arseni te

Continuous Chemi luminescent

Continuous Colorimetric

8 yg/m3^

7 yg/m^^

6°?

6°?

11 yg/m3^

12 yg/ni3^

12%*^

14%^

^Absolute value, not concentration dependent.

'^Relative standard deviation, absolute value is dependent on concentration.

560
Table 6

Summary results from collaboratively testing of stationary source methods

A. Precision estimates for those parameters where standard deviation was proportional

to the mean value, 6

Standard deviations,

percent of mean value (6)^

Method Parameter, units 0 °b Ref.

2 Velocity, ft/sec 3.9 5.0 3.2 11

2 Volumetric flow rate, ft^/hr 5.5 5.6 1 .

1

11

5 Particulate matter, mg/m^ 10.4 12.1 6.1 12

6 SO2 , mg/m^ 4.0 5.8 4.2 13

7^ NOx, mg/m^ 6.6 9.5 6.9 13

NOx, mg/m3 14.9 18.5 10.5 13

8 H2SOL mist (including SO3),

mg/m^

58.5 66.1 30.8 14

104 Be, g/day 43.5 57.7 37.9 15

= within-laboratory deviation; = between-laboratory standard deviation, o[_ = laboratory bias.

^Pooled power plant/pilot combustion plant data.

Nitric acid plant data.

B. Precision estimates for those parameters where standard deviation was independent of

the mean value,

Standard deviations,

parameter units^

Method Parameter, units a Ob Ref.

3 C02> percent 0.20 0.40 0.35 16,17

3 O2, percent 0.32 0.61 0.52 16

5 Moisture fraction 0.009 0.012 0.008 16,12

8 SO2, mg/m^ 123.0 115.0 99.0 14

9 Opacity, percent 2.05 2.42 1 .29 18

10 CO, mg/m^ 14.3 32.3 29.0 19

o = within-laboratory deviation, = between-laboratory deviation, a]_ = laboratory bias.

561
A. Method 5 for particulate emissions from stationary sources

A very important test method is EPA's method for measuring particulate emissions from

stationary sources. In this method, designated Method 5 of the Standards of Performance for

New Stationary Sources, a sample of pollutant-laden flue gas is withdrawn from a stationary

source using a probe to traverse the entire cross sectional area of the stack in a prescribed

manner. The sample of flue gas is filtered externally to the stack to obtain the mass of

particulate matter. Appropriate meters are used to measure the volume of gas withdrawn and

the concentration of particulate matter in the sample is calculated. Other measurements are concurrently made which permit the determination of the total volumetric flow rate from the

stack and appropriate determinations are then used to calculate a mass emission rate for the

stack.

B. Method 5 collaborative tests

We have collaboratively tested Method 5 at several different kinds of emission sources

such as coal fired power plants, municipal incinerators and a Portland cement plant. Earlier

collaborative tests of Method 5 made some severe compromises which likely had an adverse

effect on the test results.

In the earlier studies we conducted all collaborative tests of Method 5 by assembling

sampling teams at a source and designed the test to have the teams sample the stacks

simultaneously at the same point within the stack. Because of the physical limitations at

the sampling point on the stacks in the sources, only 4 sampling teams could be accomodated

in these tests. A replicate of 4 is not really sufficient for between-laboratory variation

estimation.

Blocking of the samples into units when emissions were constant also proved to be

difficult because process conditions varied somewhat in spite of efforts to keep them

constant.

The results from the earlier tests seemed to show that Method 5 suffered from poor

precision. For example, within- and between-laboratory standard deviations, as a percent of mean values, were estimated to be 25.3% and 38.7%, respectively, from tests at a municipal

incincerator [20]. However, single-laboratory studies showed that Method 5 is capable of

considerably better precision under carefully controlled conditions, using a special multiple

probe assembly [21 ]

.

In the earlier collaborative tests, we had assumed that Method 5 was written in sufficient detail to assure that different users would execute it in a proper and reproducible

manner. For this reason, test participants were allowed to use the method in accordance

with their interpretation of the method's instructions. However, it is now apparent that

the method lacked sufficient clarity in some critical areas and it was revised to make it

clearer, remove some options and give more explicit details on its use.

The revised version was again collaboratively tested at a municipal incinerator [12].

The second test made use of a specially designed sampling system and a unique test design

which permitted unambiguous replicates to be obtained even if the process changed during the

test. The second test permitted eight samples to be taken simultaneously, thus strengthening

the statistical conclusions made from test results. Also, we assured ourselves that only

competent sampling teams were accepted as test participants and that the test coordinator

exercised sufficient control to assure that the participants operated the method properly.

The results of the second collaborative test of Method 5 at a municipal incinerator

showed that the precision estimates for Method 5 were considerably improved from the earlier

results. Within- and between-laboratory standard deviations, as a percent of mean values, were estimated to be 10.4% and 12.1%, respectively [12]. The test also showed that successful execution of Method 5 requires care and close attention to detail. In the hands of a competent test team who will use such care and attention. Method 5 is capable of giving

satisfactory and precise results.

562
The author wishes to acknowledge with appreciation the efforts of members of the

Quality Assurance Branch who have contributed so significantly to the air pollution methodology evaluation program. Specific recognition is made of M. Rodney Midgett, W. J. Mitchell.

John H. Margeson, R. G. Fuerst, M. E. Beard, J. E. Knoll, and E. C. Ellis. Dr. H. F. Hamil

and Dr. H. C. McKee of the Southwest Research Institute and Mr. P. C. Constant of the

Midwest Research Institute are also acknowledged with appreciation for their assistance in

planning and coordinating the collaborative tests under contracts with the Environmental

Protection Agency.

References

[1] Youden, W. J., Statistical Techniques for Collaborative Tests, The Association of

Official Analytioal Chemists, Washington, DC (1973).

[2] Beard, M. E. and Margeson, J. W., An Evaluation of Arsenite Procedure for Determination

of Nitrogen Dioxide in Ambient Air, EPA-650/4-74-048 (Environmental Protection Agency,

November 1974)

.

[3] McKee, H. C, Childers, R. E., and Saenz, 0., Collaborative Study of Reference Method

for the Determination of Suspended Particulates in the Atmosphere (High Volume Method)

,

PB 205-892 (June 1971 )

.

[4] McKee, H. C, Childers, R. E., and Saenz, 0., Collaborative Study of Reference Method

for Determination of Sulfur Dioxide in Atmosphere (Pararosaniline Method) , PB 205-892

(September 1971 )

.

[5] McCoy, R. A., Camann, D. E., and McKee, H. C, Collaborative Study of Reference

Method for Determination of Sulfur Dioxide in the Atmosphere (Pararosaniline Method - 24-Hour Sampling), EPA-650/4-74-027 (Environmental Protection Agency, December 1973).

[6] McKee, H. C. and Childers, R. E., Collaborative Study of Reference Method for the

Continuous Measurement of Carbon Monoxide in the Atmosphere (Non-Dispersive Infrared

Spectrometry), PB 211-265 (May 1972).

[7] Constant, P. C, Sharp, M. C, and Scheil, G. W., Collaborative Testing of Methods

for Measurement of NO2 in Ambient Air, Vol. I, Report of Testing, EPA-650/4-74-019e

(Environmental Protection Agency, June 1974).

[8] Constant, P. C. , Sharp, M. C. , and Scheil, G. W., Collaborative Test of the TGS-ANSA

Method for Measurement of Nitrogen Dioxide in Ambient Air, EPA-6 50/4-74-046

(Environmental Protection Agency, September 1974).

[9] Constant, P. C, Sharp, M. C, and Scheil, G. W., Collaborative Test of the Continuous

Colorimetric Method for Measurement of Nitrogen Dioxide in Ambient Air, EPA-650/4-75-

011 (Environmental Protection Agency, Feb. 1975).

[10] Constant, P. C, Sharp, M. C, and Scheil, G. W., Collaborative Test of the Continuous

Chemiluminescence Method for Measurement of Nitrogen Dioxide in Ambient Air,

EPA-650/4-75-013 (Environmental Protection Agency, Feb. 1975).

[n] Hamil, H. F. and Thomas, R. E., Collaborative Study of Method for Determination of

Stack Gas Velocity and Volumetric Flow Rate in Conjunction with EPA Method 5,

EPA-650/4-74-033 (Environmental Protection Agency, Sept. 1974).

[12] Hamil. H. F. and Thomas, R. E., Collaborative Study of Particulate Emission Measurements by EPA Methods 2, 3 and 5 Using Paired Particulate Sampling Trains (Municipal

Incinerators), EPA-600/4-76-014 (Environmental Protection Agency, March 1976).

563
[13] Hamil, H. F. , Laboratory and Field Evaluation of EPA Methods 2, 6, and 7, EPA-650/4-

74-039 (Environmental Protection Agency, October 1973).

[14] Hamil, H. F., Camann, D. E., and Thomas, R. E., Collaborative Study of Method for the

Determination of Sulfuric Acid Mist and Sulfur Dioxide Emissions from Stationary

Sources, EPA-6S0/4-75-003 (Environmental Protection Agency, November 1974).

[15] Constant, P. C, and Sharp, M. C, Collaborative Study of Method 104 - Reference

Method for Determination of Beryllium Emission from Stationary Sources, EPA-650/4~74-

023 (Environmental Protection Agency, June 1974).

[16] Hamil, H. F. and Thomas, R. E., Collaborative Study of Method for Stack Gas Analysis

and Determination of Moisture Fraction with Use of Method 5, EPA-650/4-74-026

(Environmental Protection Agency, June 1974).

[17] Mitchell, W. J. and Midgett, M. R., Field Reliability of the Orsat Analyzer, Jour. APCA

26^(5) :491_495 (Environmental Protection Agency, Research Triangle Park, NC, 1976).

[18] Hamil, H. F., Thomas, R. E., and Swynnerton, N. F., Evaluation and Collaborative

Study of Method for Visual Determination of Opacity of Emissions from Stationary

Sources, EPA-650/4-75-009 (Environmental Protection Agency, January 1975).

[19] Constant, P. C, Scheil, G. , and Sharp, M. C, Collaborative Study of Method 10 - Reference Method for Determination of Carbon Monoxide Emissions from Stationary

Sources, EPA-650/4-75-002 (Environmental Protection Agency, January 1975).

[20] Hamil, H. F. and Thomas, R. E., Collaborative Study of Method for the Determination

of Particulate Matter Emissions from Stationary Sources (Municipal Incinerators)

,

EPA-650/4-74-022 (Environmental Protection Agency, July 1974).

[21] Mitchell, W. J., and Midgett, M. R. , Method for Obtaining Replicate Particulate

Samples from Stationary Sources, EPA-650/4-75-025 (Environmental Protection Agency,

July 1975).

564
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

INTERLABORATORY COMPARISON OF NEUTRON ACTIVATION AND

ATOMIC ABSORPTION ANALYSES OF SIZE-CLASSIFIED STACK FLY ASH

J. M. Ondov, R. C. Ragaini, R. E. Heft

Division of Biomedical and Environmental Research

Lawrence Livermore Laboratory

Livermore, CA 94550, USA

and

G. L. Fisher, D. Silberman, B. A. Prentice

Radiobiology Laboratory

University of California

Davis, CA 95616, USA

1. Introduction

Expanding national electric power requirements have made the evaluation of potential

biomedical hazards associated with coal combustion increasingly important. High-temperature

combustion of coal mobilizes significant quantities of potentially toxic species in stack

emissions [1-3]^ on respirable particles, in part, through a vapor condensation mechanism

[4-5]. Indeed, the greater mass of volatile elements occurs in thin surface layers [3],

thereby potentially increasing biological availability.

We have undertaken a collaborative study to evaluate the biological availability and

toxicity of coal fly ash. The first phase of the study is the chemical and physical

characterization of fly ash. We have collected (nonisoki neti cally ) kilogram quantities of

fly ash in the stack breeching downstream from an electrostatic precipitator (ESP) at a large western coal-fired electric power plant. Coal burned at the plant was rated at

8760 Btu/lb and contained 23% ash, 0.52% sulfur, and 11% moisture. Precipitator efficiency

was estimated to be 95% during sample collection.

Fly ash was collected over a period of several weeks in January and February 1976,

using a special sizing system that aerodynami cally sized the fly ash in situ during

collection [6]. The individual fractions were mixed to insure homogeneity, and were

analyzed for 35 elements by instrumental neutron activation analysis (INAA) at the Lawrence

Livermore Laboratory (LLL) and for 18 elements by atomic absorption spectroscopy (AAS) at

the UC Davis Laboratory. Mass median diameters for particles in each fraction were determined by centrifugal sedimentation at LLL, and by Coulter analysis at U.C. Davis. Results

from the two methods were in excellent agreement. Mass median diameters determined by

centrifugal sedimentation are 17, 6, 3.8, and 2.5 ym for fractions 1 through 4, respectively.

^Work performed under the auspices of the U.S. Energy Research and Development

Administration under Contract Nos. W-7405-Eng-48 and E(04-3)-472.

^Figures in brackets indicate the literature references at the end of this paper.

565
A. Neutron activation analysis

Fly ash fractions were analyzed with techniques previously described [7] for routine

analysis of environmental programmatic samples. Briefly, three 100-mg portions of each of

the four fractions were pressed into 1 . 7-cm-diameter pellets with 100 mg of AviceP

(cellulose binding material) per pellet. The fly ash pellets were irradiated in the 3-MW

Livermore Pool-Type Reactor simultaneously with elemental monitors and iron flux monitors.

Two separate irradiations were performed, one lasting 15 sec at a flux of 2 x 10^^ n/cm^-

sec for short-lived activation species and the other for 72 min at a flux of 2.5 x 10^^

n/cm^-sec. Gamma-ray spectra of the radioactive species were measured with Ge(Li) detector

systems coupled with 4096-channel analyzers. The full width at half maxima for the systems

ranged from about 1.8 to 2.1 keV for the 1332-keV gamma-ray peak of ^°Co. Samples were counted for 10-, 20-, and 40-min periods after a 10-min decay period following the 15-sec

irradiations. After the 72-min irradiations, samples were counted for 133 min after a 3-

day period, and again for 333 min after another 15-day decay period. Spectral data were

analyzed on a CDC-6600 computer with the GAMANAL code [8], which fits peaks with Gaussian

and exponential functions and smoothed background functions.

In addition to blank corrections for Avicel, corrections for neutron-induced fission

of naturally-occurring ^^sy gpcl (n,p) reactions were also determined and applied. To

insure integrity of the analyses, five 100-mg portions of NBS fly ash SRM 1633 were irradiated and counted simultaneously with the fly ash fractions.

B. Atomic absorption analysis

Atomic absorption analyses were performed on NBS SRM fly ash and on the four fly ash

fractions. Sample preparation involves a room temperature dissolution with HF and H3BO3.

The sample is dispersed in double-distilled, deionized water. The dispersion is added to

49% (W/V) HF and then tightly capped in a teflon bottle. After shaking the mixture over- night, 5% (W/V) HqBOs is added. After an additional 4 hours of shaking, only a small

quantity (1 to 3%) of undissolved black residue, presumably carbon, remains. Resuspension

and filtration produces a clear solution.

Initially, sodium and potassium values were high because of contamination of the boric

acid. However, cation exchange of saturated boric acid solutions resulted in low and

reproducible sodium and potassium blanks. Ionization of Si, Al , Na, K, and Ti by flame

temperatures was controlled with a 2000 ppm cesium nitrate diluent. Molecular absorption

in the flame by Ca and Mg compounds was controlled with a 5000 ppm SrCl2 diluent. Chromium

was analyzed after dilution in 2% NHi+Cl to suppress iron interferences. Nickel was determin

o o ed at 3524A rather than the standard 2320A wavelength to take advantage of lower background

o o absorption. Lead and cobalt were analyzed at 2833A and 2407A, respectively; and a backo o ground correction was derived from absorption at 2805A and 2394A respectively.

2. Results and Discussion

A. NBS SRM 1633 analyses

In table 1 are listed the results of current analyses of NBS fly ash SRM 1633 by INAA

and AAS, as well as NBS certified values [9] and previously published values [10]. The

average of up to five individual determinations is given for elements measured by INAA.

The uncertainties listed are the largest of: twice the standard deviation, the range, or our estimate of the minimum possible accuracy. Atomic absorption spectroscopy values are

^Reference to a company or product name does not imply approval or recommendation of the

product by the University of California or the U.S. Energy Research & Development Administration to the exclusion of others that may be suitable.

566
the averages and ranges of two-to-four determinations on two independent samples. Intercomparison of INAA and AAS results (table lA) for NBS fly ash analyses indicates ^8%

deviation for elements analyzed by both methods, with the exception of Ca (15%). The

relatively large uncertainty in the INAA analysis of Ca is due to poor counting statistics.

Agreement of all the results from INAA and AAS in table lA with previously published or NBS-certif ied values is within <:10% and <:15%, respectively. Only for Cr did both the INAA

and AAS determinations deviate from the reference value by more than the uncertainty in our

data. The agreement between INAA and AAS analyses of Cr is probably fortuitous; both Cr

analyses appear to be low relative to the NBS value.

TABLE 1

Comparison of elemental concentrations in NBS fly ash (SRM 1633) (pg/g unless % indicated)

A. INAA and AAS Analyses

AAS'^ Literature

Element INAA^ Average Range values^

Al {%) 12+1 [4] 12.6 0.7 12.7+0.5

Ba (%) 0.251+0.02 [5] 0.23 0.01 0.27+0.02

Ca (%) 5.0+1 .1 [5] 4.3 0.2 4.7+0.6

Co 40+2 [5] 42. 6. 41.5+1.2 (38)^

Cr 118+6 [5] 120. 4. 131+2'^

Fe 6.0+0.3 [5] 6.2 0.1 6.2+0.3

K (%) 1 .7+0.2 [5] 1 .71 0.04 1 .61+0.15

Mn 499+25 [4] 477. 5. 493+7^

Na (%) 0.31+0.03 [5] 0.32 0.02 0.32+0.04

Ni 1 00+20 [3] ICQ. 7. 98+3^

Ti {%) 0.68+0.11 [3] 0.74 0.08 0.74+0.03

In 220+5 [5] 201. 8. 210+20^

B. AAS Analysis Only

Be - 12.6 0.5 12^

Cu - 119. 5. 128+5^

Cd - 1.7 0.2 1.45+0.06^

Mg (%) - 1.2 0.1 1.8+0.4

Pb - 78. 2. 70+4^

567
Table 1 (continued)

C. INAA Only

Literature

t 1 ement * TNAfl^ i linM V U 1 o

As 61+4 [5] 61+6^

Ce 146+17 [5] 146+15

Cs 8.2+0.5 [5] 8.6+1 .1

Dy 12.1+0.6 [4] —

Eu 1 .9+0.2 [5] 2.5+0.4

Ga 45+7 [5]

Hf 8.2+0.8 [5] 7.9+0.4

La 76+14 [5] 82+2

Nd 66+7 [5] —

Rb 1 30+30 [5] 125+10(112)^

Sb 6.9+0.3 [5] 6.9+0.6

Sc 26.9+1 .4 [4] 27+1

Se 10+2 [5] 9.4+0.5°

Sm 13.4+0.7 [5] 12.4+0.9

Sr (%) 0.13+0.02 [5] 0. 17+0. 03(. 138)®

Ta 1 .8+0.3 [5] 1 .8+0.3

Tb 1 .5+0.4 [5] 1.9+0.3

Th 24+2 [5] 24.8+2.2(24)®

U n.1+1.7 [5] n.6+0.2^

V 270+60 [3] 21 4+8^

W 4.8+1 .5 [5] 4.6+1 .6

Yb 5.7+0.6 [5] 7+3

INAA values are averages of the number of determinations given in parentheses.

Uncertainties given are the largest of: twice the standard deviation, the

range, or our estimate of the accuracy.

'^AAS values reported are the averages and ranges of two independent determinations.

^Ref. 10.

^Ref. 9.

®Ref. 9, information value only.

568
Agreement between results of Be, Cu, Cd and Pb determinations, measured only by AAS

(table IB), and NBS-certi f ied values was very good. The AAS Mg (1.2%) result was 33% lower

than the literature value. However, the literature value used in this case (1.8 + 0.4) is an average of only two independent laboratory INAA determinations (1.5 ± 0.16 and 2.08 ± 0.43)

which differed greatly. The AAS value is in good agreement with the lower INAA literature

value, which also had the lower uncertainty. In this work, accurate Mg analyses could not

be performed by INAA because of a large interference from the ^'^

l\] {n ,p)^'^Mg reaction. Of

the 31 elements determined by INAA, 27 were within 8% agreement with either the NBScertified informational values or previously published values [9]. Large differences

between reference and current values were found for V, Eu, and Yb (26, 20, and 19% agreement,

respectively). However, those reported here agree within the uncertainties in data.

Preliminary analyses for Dy, Ga, and Nd not previously published are also given.

B. Sized fly ash fractions

In table 2 are listed INAA and AAS analyses of the four sized fly ash fractions. Of

the 12 elements for which comparisons between the two methods could be made, 9 agreed

within <15% of the mean of the INAA and AAS values. For the remaining three elements (Ca,

Ti , and Zn) the uncertainties in the INAA data and ranges of AAS determinations overlapped.

Agreement between the two techniques was found to be ^]07o for 32 of the 48 comparative

analyses. Results of analyses for elements determined by AAS only, and by INAA only are listed in B and C of table 2, respectively.

The results indicate that little or no enrichment occurs with decreasing particle

size for Si, Al , Ca, K, Na, Ni , Ti , Mg, Ce, Co, Cs, Dy, Eu, Hf, La, Nd, Rb, Sc, Sm, Sr,

Ta, Tb, Th, and Yb. This may reflect the low volatility of these elements. Silicon

concentrations appear to decrease with decreasing particle size. Significant enrichment

with decreasing particle size was observed for the following elements: Cd > Se > As > Zn > Sb > Mo > Ga > W > Pb > V > U > Ba > Cu > Cr > Be > Mn > Fe. These observations agree

with the results of analyses of particle fractions collected with an in-stack cascade

impactor at the same generating unit [11,12].

The data in table 2 have been used to calculate concentrations of selected toxic

elements that can be transported by fly ash particles to a lung target cell, the pulmonary

alveolar macrophage. Assuming the macrophage phagocytizes 10 particles with the average

chemical and physical properties of Fraction 4, the resulting concentrations of most toxic

elements would be substantially higher than concentrations found in normal lung tissue.

569
HI 00

r— (T. O O O

O

O —

o

o 5 00 f— ro o

00

r- O

00o O 00 lO

o in I 71 ?l Ti Tl

C\J O CO ^ <^ Csj

• C\J CO

in ^ o ,— .— I— c\j o

?i" ?i ?i °i 7i ?i Ti

" <\j r-^ «± I— o 1^ f— «T ir>

. rn . • Ln o — o

4-> u

01N

1/1

»-> n)

s.

•»-> c

0)u

O)E

<u

o

c

o

n)Q.Eo

01 ro cn

(D c L. o OJ> o

10

i.

Li.

cn 00o o

r— >»• O I— o

O r- O

O

roo

•3- O

O

o

roo

CM OCM O ro ro LO I— 00

ro o

00

ro ,

O 00 lO

CT> ""T

I— CM I

I '^i '~i ""i "^1 "^1 + 1 +1 +1 ±1 ±' ±1 CM 00 CM cr» <T> o r— CM . — LO

ro ro

o

?l Ti

00 I—

vo

. CO O rO 1—o

CM

• O CM + 1+1

1— ^ VO o • CO

i. Ucn CMo oo' CM LO LO

Ash Ran o o LO O o o o

o o o o ro O o LO o o

>. AAS

Ll- 0) LT) ro C71 o LO LO

TD « CM CM ro O 00

0) c

o •a- o CM 00 ro o o cn

t- > LO C^ ro 00

+> CM

(/) u

tn ID

lO (.

Ll- CJ

1 CMo LO 00 CM

roCM CM

CMOO

O

LO

LO LO

00 .—

CO

cn CO LO CM

. 00 • CM • CM. O, O. O, LO O, O, t— , O I— O

+ 1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 rorOLOrocJ^O^r^|— C0ro«^

I— CM • • -a- . ro • 'd' LO

• CM VO CM • CM 1

Or— O O

±1

01cn O <n c O

<o

C£. O o o O ro o o

<U 00 cn LO CM LO

to CO LO LO

i-01 ro o CM cn CO CM O > CM

LOO

ro O r—

CM O

C3 C>

I LO

CM 00

LO

•a- c> ro cr> r~ CM

01

L/l >,

<oc

«r

I/) s

-DCD3

00o ro CMO + 1 ?l + 1 +

ro cn LO

CM CO o

O t—

+ 1 00

O, O, 00, o, + 1 +1 +1 +1

LO «a- r- CM

. O CM

CM • CM • o .—

O, LO, ±1 +1

00 <—

o

Z 01 JD

1— 5 OO o •1- t- c z 1— rvi

C7> J3 210.00

570
Table 2 (continued)

C. INAA Only

Fraction 1 Fraction 2 Fraction 3 Fraction

T M A A ^ T M A A

1 IN MM INAA

As 13.7+1.3 56+14 87+9 132+22

Ce 113+4 122+5 123+6 120+5

Cs 3.2+0.1 3.7+0.2 3.7+0.2 3.7+0.2

Dy 6.9+0.3 8.5+0.9 8.1+0.3 8.5+0.8

Eu 1.0+0.1 1 .2+0.2 1 .2+0.2 1 .3+0.4

Ga 43+12 116+52 1 40+23 'l 78+90

Hf 9.7+0.4 10.3+0.3 10.5+0.3 10.3+0.5

La 62+3 68+4 67+11 69+3

Mo 9.1+2.5 28+1 .4 40+5 50+9

Nd 45+4 47+4 49+7 52+6

Rb 51+3 56+4 57+3 57+8

Sb 2.6+0.1 8.3+0.4 13.0+0.7 20.6+0.7

Sc 12.6+0.5 15.3+0.6 15.8+0.6 16.0+0.2

Se 19+2 59+2 78+2 198+20

Sm 8.2+0.3 9.1+0.4 9.2+0.4 9.7+0.4

Sr 410+60 540+1 40 590+1 40 700+210

Ta 2.06+0.09 2.3+0.2 2.5+0.3 2.7+0.1

Tb 0.90+0.05 1 .06+0.06 1.10+0.07 1 .13+0.06

Th 25.8+0.6 28.3+0.6 29+1 30+2

U 8.8+1 .9 16+3 22+4 29+4

V 86+44 178+17 244+18 327+40

W 3.4+0.2 8.6+1 .6 16+2 24+2

Yb 3.4+0.4 4.1+0.4 4.0+0.2 4.2+0.3

INAA values are the weighted averages of three determinations. Uncertainties

given are the largest of: twice the weighted standard deviation, the range, or

our estimate of the accuracy.

571
References

[I] Bertine, K. K. , and Goldberg, E. D. , Saience 173, 233 (1971).

[2] Gordon, G. E., Zoller, W. H. , and Gladney, E. S., Tvaoe Substances in Environmental

Health-VII, D. D. Hemphill, Ed. pp. 167-174 (Univ. of Missouri, Columbia, 1973).

[3] Linton, R. W. , Loh, A., Natusch, D. F. S., Evans, C. A., Jr., Williams, P., Saience

191 , 852 (1976).

[4] Natusch, D. F. S., and Wallace, J. R. , Science 186, 695 (1974).

[5] Kaakinen, J. W., Jorden, R. M. , Lawasani , M. H., West, R. E., Environ. Soi. Teahnol.

9, 862 (1975).

[6] McFarland, A. R. , Fisher, G. L. , Prentice, B. A., and Bertch, R. W. , ^ Fraationator for

Size-Classification of Aerosolized Solid Particulate Matter, ( Radi obi ol ogy Laboratory,

University of California, Davis, 1976) Annual Report, UUC 472-123, in press.

[7] Ragaini, R. C, Heft, R. E., and Garvis, D. G. , Neutron Activation Analysis at the

Livermore Pool-Type Reactor for the Environmental Research Program, Lawrence Livermore

Lab., Rept. UCRL-52092, (July 1976).

[8] Gunnink, R. , and Niday, J. B., The Gamanal Program, Lawrence Livermore Laboratory,

Rept. UCRL-61061, Vols. 1-3 (1973).

[9] Certificates of Analysis, Standard Reference Materials SRM 1632 and 1633, Office of

Standard Reference Materials, National Bureau of Standards, U.S. Dept. of Commerce,

Washington, D.C. 20234.

[10] Ondov, J. M., Zoller, W. H., Olmez, I., Aras, N. K. , Gordon, G. E., Rancitelli, L. A.,

Able, K. H. , Filby, R. H., Shah, K. R. , and Ragaini, R. C. , Elemental Concentrations

in the National Bureau of Standards' Environmental Coal and Fly Ash Standard Reference

Material, Anal. Chem. 47, 1102 (1975).

[II] Ragaini, R. C, and Ondov, J. M. , Trace Contaminants from Coal-Fired Power Plants,

Proc. Int. Conf. Environ. Sens. Assess., Las Vegas, NV, 1975, p. 17-2; Lawrence Livermore

Lab., Rept. UCRL-76794 (1975).

[12] Ondov, J. M. , Ragaini, R. C, and Biermann, A. H., Wet Scrubbers vs. Electrostatic

Precipitators, Lawrence Livermore Laboratory, Rept. UCRL-78359, (1976).

572

11
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1 977 ).

COLLABORATIVE TESTING OF A CONTINUOUS CHEMILUMINESCENT METHOD FOR

MEASUREMENT OF NITROGEN DIOXIDE IN AMBIENT AIR

John H. Margeson

Environmental Monitoring and Support Laboratory

U. S. Environmental Protection Agency

Research Triangle Park, North Carolina 27711, USA

and

Paul C. Constant, Jr., Michael C. Sharp, and George W. Scheil

Midwest Research Institute

425 Vol ker Boulevard

Kansas City, Missouri 54110, USA

1. Introduction

A continuous chemi 1 uminescent method for measurement of NO2 in ambient air was subjected

to a collaborative test. The method involves calibration of a monitoring instrument by gas

phase titration, NO + O3 NO2 + O2. Ozone atmospheres - analyzed by the 1 percent neutral

buffered potassium iodide method - were used to analyze an NO cylinder which was then used

to calibrate the NO2 response of the instrument and to generate NO2 for calibration of the

NO2 response.

2. Objective

The objective of the collaborative test was to determine the bias and precision of the

method. Volunteer collaborators were used. All collaborators were asked to follow the

method description provided to them and to analyze their NO cylinder prior to coming to the

test site. The at home analysis of the cylinder was done to minimize biasing the test

results

.

3. Experimental

The collaborative test was carried out by having 10 collaborators sample ambient air

and the same ambient air spiked with a reliable source of NO2 for four days (September 23-

27, 1974) at a common site in Kansas City, Missouri; NO2 concentrations of 60 to 308 yg/m^ were sampled.

The integrity of the NO2 spike was maintained by (a) using a high ambient air flow

rate, 50 liters/min., to minimize NO2 residence time in the sample generation system and

the possibility of losses due to reaction with water vapor, and (b) using Teflon parts in

the sample generation system. The integrity of the spike was confirmed by monitoring the

NO2 concentration in the ambient air with and without the spike.

573
4. Results

The results of the test show that, based on one-hour average concentrations, the

within laboratory standard deviation is 6 percent of the concentration over the range 60 to

308 yg Wz/m^, and the between laboratory standard deviation is 14 percent of the concentrations over the same range. The results also show that the method has an average bias of

-5 percent over the above concentration range. The lower detectable limit of the method

was determined to be 22 yg/m^.

Additional information can be obtained from EPA report No. 650/4-75-013. This report

is available from: U.S. Environmental Protection Agency, Office of Forms and Publications,

Highway 70 Warehouse Facility, Durham, North Carolina 27711.

574
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg , Md. (Issued November 1977).

COLLABORATIVE TESTING OF EPA METHOD 11

Joseph E. Knoll and M. Rodney Midgett

Quality Assurance Branch

Environmental Monitoring and Support

Research Triangle Park, North Carolina

Laboratory

27711, USA

and

George W. ScheiT

Midwest Research Institute

Kansas City, Missouri 64110, USA

1. Introduction

The Quality Assurance Branch, Environmental Monitoring and Support Laboratory, has

been engaged in a systematic program to standardize or validate EPA source test methods,

which are used to determine compliance with Federal emission standards. Of fundamental

importance to this program is collaborative testing. By this process, the method is

observed in the hands of typical users, practical field problems are brought to light and

information about precision and accuracy is obtained. This information is then compiled,

made available to the public and is valuable for developing quality assurance programs,

compiling users manuals and assessing compliance measurements.

EPA Method 11 determines the hydrogen sulfide content of petroleum refinery fuel gases

and process gases. H2S is collected as the cadmium salt and is measured iodimetrical ly

.

Originally, a CdS0i+/Cd(0H)2 mixture was used as the absorbing medium, but this also collected thiols, which caused a serious interference. Investigations at EPA's Environmental

Monitoring and Support Laboratory and at Midwest Research Institute resulted in the development of an absorbing solution that circumvented this problem. It consists of 0.015 M

CdS0i+/H2S04 at pH 3.0 and has been used in the measurements reported in the present study.

Selection of collaborators was accomplished as follows: Qualification samples were

submitted to 22 laboratories and 10 were selected at random from among the 15 laboratories

that submitted results free from gross errors. The collaborative test took place at the

Midwest Research Institute in Kansas City, Missouri. The collaborators furnished their own equipment, followed the revised test procedure and made all measurements in duplicate. Two

separate kinds of gas samples were employed. The first consisted of three cylinders of H2S

in research grade methane. These cylinders were analyzed by the bottled gas manufacturer,

both before and after the test. The second type of sample was prepared using a source

simulator. This system was used to generate known levels of H2S in commercial natural gas,

while also adding quantities of interferences and other compounds normally found in refinery

fuel gases. These consisted of constant amounts of propylene (4 percent), SO2 (50 ppm),

methyl mercaptan (100 ppm) and ethyl mercaptan (56 ppm). Regulation was achieved using

glass capillary flow controllers and calibrated flowmeters. The primary calibration of H2S

levels in the source simulator was by the calculated dilution factors. Further checks were

made using a potentiometric titration with standard silver nitrate and by flame photometric

gas chromatography analysis.

2. Experimental

575
3. Results

Each of the ten collaborators measured the cylinder samples in duplicate and repeated

them three days later. These results are listed in Table 1. Using the source simulator,

five runs were made at a level of approximately 200 mg H2S/m3, five runs at approximately

400 mg H2S/m2 and six runs at a level of approximately 100 mg H2S/m^. The sixth run also

contained carbon oxysulfide (COS) at a level of 100 ppm. These results appear in Table 2.

Table 1

H2S concentration (mg/m^) determined by collaborators for standard cylinder samples

Cyl inders Collaborators

1 2 3 4 5 6 7 8 9 10

#1

No. 1 157.7 116. 0 88.9 93.1 90.8 93 0 92 9 100. 1 87 3 100.9

103 mg/m^ 118.9 117. 1 82.8 90.4 92.3 93 0 89 9 100. 6 87 9 90.6

No. 2 364.1 366 3 331 .0 334.9 330.2 342 0 343 9 297 1 329.0

350 mg/m^ 377.4 354 7 333.0 335.7 323.6 339 0 332 4 314 8 332.5

No. 3 204.5 193 3 171.0 181 .7 172,1 177 0 228 9 176 9 166 5 177.7

184 mg/m^ 199.5 197 3 168.0 179.5 173.6 179 0 227 2 172 4 168 4 170.1

Test #2

No. 1 117.3 101 1 94.9 93.4 88.8 95 0 100 9 83 8 111 1 95.5

103 mg/m^ 107.2 97 4 94.3 91.0 89.9 95 0 102 1 90 3 106 8 94.1

No. 2 329.8 309 4 328.0 333.2 317.4 338 0 355 7 284 3 312 5 330.9

350 mg/m^ 346.8 305 6 338.0 333.9 318.6 334 0 335 1 286 4 312 8 333.9

No. 3 192.4 186 8 175.0 179.7 170.1 180 0 189 3 155 8 173 9 184.5

184 mg/m3 190.1 184 3 183.0 178.1 169.7 174 0 182 8 153 2 174 7 180.1

576
Table 2

H2S concentration (mg/dscm) determined by collaborators at test levels A, B, C

H2S Collaborator^

Level present 1 2 3 4 5 6 7 8 9 10

la

lb 180 187.9199.2

271.0

277.9

184.2 181.0181.7

181.7

180

182

191.83

179. 72

b/ 122. 2-' 144.5^^

170.79

176.43

219.1

221.5

2a

2b 180 191.9 203.9

210.0

214.2

174

177

182.8 176.0

177.3

173.8

174

177

180.34

173.29

114.2-^'

150.1-^^

164.02 172.82

205.8 205.6

A 3a

3b 188 215.1 208.2

221.9

204.1

194

194

196.6

193.2

190.3

189.3

195

196

175.55

187.19

144.4

157.4

183.88 188.94

224.6

216.3

4a

4b

191 213.8 216.0

212.2 203.8 236^/

198.4

197.6

193.7 195.9197

199

230.466

190.750

164.7 204.8

183.91

186.81

193.6 217.7

5a

5b

192 223.2

218.5

211.1 214.1

197 200.7 202.4194.2

194.7

200

204

202.66

196.13

167.0

220.8

184.25

191.05

224.3

227.1

la

lb 342 375.3 333.7

356.3

351.2

338

346

334.8

333.3

328.4

327. 7

337

339

347.99 337.70

b/ 312. 6-' 315.15

321.98

364.3

369.9

2a

2b 380 406.7

407. 7

399.0

340.3

376

364

375.0

374.0

364.8

362.1

375

386

439.55

417.51

331.6

314.5

290.51 354.18

392.6

401.

1

B 3a

3b 378 384.2

395.

1

392 .2 388.4369 373379.7

373.5

365.3 361.0

377 376439.61

426.05

366.3 356.3

342.31

354.03

388.6

394.1

4a

4b 426 447.7 432.8

. 420.4 446.6

399

393

395.1 402.2386.1

383. 7

402

405

416.55

408.72

416.9

393.2

372.88

384.65

411.2

409.4

5a

5b 426 434.2

415.5

436.4

427.2

397 403404.1

399.4

382.4

390.0

400

405

424.32 422.01

378.5

371.7

384.43

375.27

420.8

417.3

la

lb 100 109.3108.5

114.0

116. 7

111

112

115.99

113. 7

108.6

109.4

113

113

118.61 116.34

110.8

110.6

109.61

115.31

182.66

144.4

2a

2b 100 107.4 105.0

118.2 117.7114

113

114.3

111.6

111.1 111.8113

112

119.86

112.98

102.4

103.0 50.19^^

144.9 143.05

C 3a

3b

99 115.3 110.9

121.7

122.2

113

112 Hi . 1 110. 7

109.5 109.4111 119

117.73

113.48

99.4 100.4

102.20

115.13

142.9

143.8

4a

4b

97 127.0

123.9

123.3 114.4110

114

112.0

111.9

110.6

110.4

114

115

118.95

115.22

109.7

109.9

114.48

118.31

138.9

143.9

5a

5b

102 128.4 127.6

120.4

118.6

113 116116.9

115.4

115.5

115.6

114

113

128.71

116. 74

113.7

107.9

123.08 118.03

150.3

146.1

6a

6b 100 123.1 122.6

117.9

121.3

117 117

111.5

112.8

113.5

112.5

120

116

120.76

112.99

106.6 105.8121 .52 125 . 24

151.1 129.0

a/ Each collaborator ran two trains simultaneously each run.

b/ Error during sampling or analysis. Sample deleted.

577
Only two percent of the measurements were not carried through successfully. -Other

points were rejected as a result of applying Grubbs' test for multiple outliers [1].^

This test is based on criteria tabulated for ratios of the sum of squares of deviation for

a reduced sample (obtained by omitting the possible outliers) to the sum of the squares for

the entire sample. The method has the advantage that it does not suffer from problems of

repeated application or from masking. Use of Grubbs' criteria resulted in the elimination

of only three of the 118 cylinder gas sample data points. These are underlined in Table 1. Measurements made at the beginning of the test agreed with those made three days later,

since mean values agreed statistically and there was little change in precision. This

indicated that day and experience were not significant factors in the results and that

polling the data was justified. Analysis of the pooled data revealed a negative bias that was a function of concentration within the range studied. It had an average value of

-4.8 percent and may be attributed to incomplete absorption of hydrogen sulfide from the

gas sample or to incomplete recovery of cadmium sulfide from the impingers. The standard

deviation was also an increasing function of concentration. The coefficient of variation

and the within laboratory and between laboratory coefficients of variation were also

calculated and are listed in Table 3. The bias, which is also listed, has a magnitude that

is approximately equal to the coefficient of variation.

Table 3

Precision and accuracy summary

Standard gas Source simulator

cyl inders samples

Total coefficient of variation, % 7.0 6.6

Within lab coefficient of variation, % 4.3 4.6

Between lab coefficient of variation, % 5.5 4.7

Relative bias, % -4.8 +2.8

Source simulator measurements were made at approximately the same concentration levels

as the standard cylinder gases (Table 2), but with five runs per level. Application of

Grubbs' criteria eliminated 17 data points. Analysis of variance was performed and is

summarized in Table 3. These values are very similar to the values determined from the

standard cylinder gas data. It may therefore be concluded that no deterioration in precision resulted from the interferents present in the source simulator samples. However,

when the average bias was calculated, the pattern obtained was unlike that which appeared

in the standard gas cylinder measurements. The bias was positive at low H2S concentrations

and became negative at higher concentations. The range of the bias did not exceed the

precision of the data. The positive bias values obtained at low H2S concentration may

reasonably be attributed to the interfering substances present in the source simulator

samples

.

4. Conclusion

The primary results of this collaborative test are shown in Table 3. The precisions

are good and the biases are small and stable. Method 11 has been shown to yield accurate

measurements over a range of H2S concentrations and in the presence of substantial interference levels. The method functioned well under simulated field conditions.

^Figures in brackets indicate the literature references at the end of this paper.

578
References

[1] Grubbs, F. E. and Beck, G., Extension of Sample Sizes and Percentage Points for

Significant Tests of Outlying observations, Technometvics 1_4, 847-854 (November 1972).

579

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

EVALUATION OF INTERLABORATORY COMPARISON DATA

BY LINEAR REGRESSION ANALYSIS

Donald E. King

Ontario Ministry of the Environment

Laboratory Services Branch

P. 0. Box 213, Rexdale, Ontario M9W5L1

1. Introduction

The Ontario Ministry of the Environment Laboratory Services Branch has been increasingly involved in inter laboratory comparison studies with municipal, industrial and com- mercial laboratories in Ontario whose data could be used in assessing routine water and

waste water quality. The objective has been not only to determine that differences exist

in some instances, but to attempt to define the nature of the disagreement so as to

provide advice as to the possible corrections required. The approaches presently under

development permit the use of linear regression techniques by ensuring that intercomparison samples cover the range of analytical concentration of interest. However, in the course of applying linear regression analysis to such data it has become apparent that

this technique, if misapplied, can easily lead to improper conclusions; such as to the

presence or absence of bias between laboratories. At the same time it is able to direct

attention to several potential areas of interlab incompatibility.

By rights, linear regression analysis should not be applied when comparing methods or laboratories where the precision of observation, or analytical measurement, is similar.

However, its ready availability and simplicity make it attractive to the average scientist

or engineer who has little or no formal training in statistics. The more elegant techniques are unknown to most of us and may require information and appreciation of purpose

not readily available.

Linear regression is a statistical tool and like all tools must be applied with care

in recognition of the assumptions inherent to it. Since the inclusion of linear regression programs in even hand-held calculators increases the possibility of misuse, the

purpose of this paper is to demonstrate the effects of such misuse and thereby provide a mechanism for checking the validity of linear regression findings when applied to the

evaluation of interlaboratory comparison data.

2. Review of Linear Regression

In order to point out the problems in interpreting regression and correlation data,

it is important to appreciate their derivation. Therefore the following is a review aimed

at clarifying the difference between what linear regression gives us and what in fact is

required in order to assess interlab differences.

Given Paired Data : (XiYi), {X2Y2), ... (Xn Yn)

Average : I = EX/n; T = EY/n

Deviation : x = (X-X); y = (Y-Y)

Variance : s^ = I.x^/{n-^), s^ = T.y^/{r\-^)

581
The following review is sini£l2.f ied by discussing the data (X,Y) in terms of deviations {x,y) from the averages {X,Y).

For calculation purposes, ix^ = zX^ - nX^

lyZ = - nY2

ixy = zXY - nXY.

Linear Regression : assumes that the variability in the Y data set can be 'explained' as partially dependent upon_a_corresponding change in the X data. The reference point for

these deviations is at (X,Y). It is assumed that none of the scatter seen in a plot of Y versus X is caused by uncertainty in the X or independent variable. Given a deviation x

and a suitable coefficient b the corresponding deviation y = bx can be estimated. The

remaining deviation in y is 'unexplained' by regression and b is calculated to minimize

this residual variance.

Residual 'Unexplained' Deviation : {y - y) = (Y - Y)

Residual Variance : s^^^ = i{y - y)^/{r)-2)

This is clearly a variance based on the moving average Y rather than Y. By substituting

y = hx this equation can be rewritten

where r^ is shorthand for [ixy)'^ /ix'^iy'^

Correlation Coefficient r: by comparing the equations for s^ and Sy.^ it can be seen tha

r'-^ is the fraction of Zy^ 'explained' by using b. The correlation coefficient r is frequently used to determine whether sufficient ^/-data scatter has been explained to justify

the statement that b 7^ 0. It tends to unity as data scatter is reduced.

The use of b minimizes the residual variance but is overly sensitive to error in points

distant from (X,Y).

= Ey2(i_r2)/(n-2)

Regression Coefficient b^: b = y/x = zxy/zx^

Variance of r: - {^-r^) / {r\-2)

Variance of b: si = ^/ix^

n V" X

Therefore sg = s^{zy^/^x^) = s^is^/s^

The equation y = bx can be written Y = a + bX

where a = Y - bX, or 'inverted' X - a' + b'Y

where b' = 1/b and a' = -a/b

582
The symbol " indicates the assumed dependent variable for regression purposes and the

symbol ' indicates the equation coefficients for calculating X rather than Y. The intercept

coefficient a is the value of Y at X_ f_ 0 whereas a' is the value of X at Y = 0. Since

this line rotates about the point (X,Y) an error or uncertainty in 'b' magnifies the error

or uncertainty in 'a'

.

3. Interlaboratory Comparison

Many intercomparisons are poorly designed. One or two samples are distributed,

analyzed, and the resulting data is averaged. Based on some criteria, outliers from the mean are identified but there is no way to identify the nature of the discrepancy. The

Youden technique is better in that, if properly applied, it can discriminate between

random and systematic error. There are situations where this assessment could be wrong.

Since there are two sources of systematic error, one in the blank determination and one in

slope calibration, it is possible for the two errors to cancel in certain ranges of

concentration. Some studies compare two laboratories based on a series of samples and use

the t-test to_demons^trate that no (statistically) significant difference exists between

the averages X and Y, and therefore no difference between laboratories. Yet regression

analysis may demonstrate a slope difference of 5 to 10 percent.

Usually when comparing laboratories we can expect similar levels of precision of

observation. However other factors may affect the overall data^ s_catter in unknown ways.

Since linear regression puts extra weight on points far from (X,Y), one or two large

errors may grossly affect the estimates of b and a, particularly when little data is

available. Suspect points should therefore be deleted in the initial evaluation. (If the

line is found to pass through these points they in fact will confirm what otherwise might

have been an unusual finding.) The residual scatter in a plot of Y versus X, about the

regression line is measured by s^ . This will be the sum of several variances. Thus

y-x ox oy h

where s^ = observational variance lab X OX

s^ = observational variance lab Y oy

s^ = variance due to sample handling, eta.

When natural samples are being split in the field, or sample homogeneity is not

certain, s^ can be quite significant. Usually one knows his own analytical or observational variance, e.g. , s^^. If Sy.x>>SQx then either Soy or Sh is dominant and it is

proper to assume initially that X is the independent variable (unless Sk may be entirely

assignable to lab X). If Sy.^ ~ ^

Sq^ then s^ may be negligible and the two labs will

have equal precision. If Sy.^ = Spx then lab X is the most significant source of data

scatter, and therefore should not nave been chosen as the independent variable.

Data compatibility depends more upon freedom from systematic error than upon com- parable precision of analysis. We expect, and hope to find no significant difference

between laboratories at zero concentration, and a ratio of 1:1 between paired results over

the concent£atj_on range of interest. However, since regression analysis provides es- timates of X, Y and b, any error in the estimation of 'b' will magnify the estimated

difference 'a' between labs at the detection limit. Unfortunately this is the area in

trace analysis where data compatibility is most important and most difficult to achieve so

that estimates must be valid.

In the following discussion emphasis is placed on the potential for error in 'b' and

'a' resulting from misapplication of the linear regression technique. The variances s^.x

and s^ are of no value in estimating the extent of such error, since they measure precision

not accuracy.

583
4. Interlaboratory Regression

When comparing two laboratories over a range of concentration on the basis of a limited amount of paired data, it is usually invalid to assign all of the data scatter to

lab Y, (often lab Y is the other guy), and yet linear regression does exactly this. In the absence of other information, 50 percent of the time the wrong data set will be

arbitrarily defined as the dependent variable, and therefore the calculated regression

coefficient will be invalid. Obviously there are two regression lines both of which must

be examined. These are:

Y on X regression: Y = a^ + bjX

X on Y regression: X = a2 + b2Y

The latter equation can be 'inverted' for comparison with the former. Thus

X on Y invert: Y = aa + b2X

The relationship between bi and b2 is as follows.

Since bj = ixy/Zx'^

and b2 = l/b2 = ^y'^lYxy

thus bib2 = Zij^lY.x'^ - s2/s2

and bi/b2 = {ixy)'^/zx'^iy^ = r^

Therefore, since r^ < 1 , bj is always less than b2. If, in fact, it were proper to

assign all scatter to the Y data set then b^ would be a valid estimate of the slope

relating labs Y and X and b2 would be in error high by lOOCl-r^) percent. If the opposite

were true, b2 would be correct and bi would be low by the same amount. Of course the

truth lies somewhere between these extremes shown in figure 2. In fact, if the data

scatter can be equally a ssig ned to both laboratories then both bi and b2 will be in error

by an equal amount and /BTb^will be the best estimate, if r^ = 1 , bj = b2 = /b7b7.

If Sh is negligible or evenly attributable to both data sets, then a difference of

about 2X in the analytical precision of the laboratories is sufficient to define the

better lab as the independent variable and make bi the better estimate.

There is a way to resolve this dilemma. The most valid estimate will be one which is

most independent of the data set selected. Thus if the total set is randomly or otherwise

divided into subsets and b^ , b2 and /bTb^ are calculated for each subset, one of them will

be appreciably more 'stable' for all subsets.

5. Division Into Subsets

The following data (Tables 1 and 2) was used to prepare figure 1 to demonstrate the

difference between the Y on X and X on Y (inverted) regression lines. If this data set is

subdivided in any one of four ways other estimates of bi and b, can be obtained, (see

fig. 3);

584
Figure 1.^ The least squares line of best fit minimizes

^ iy - yV given the deviations a: = X - X.

585
^

assumed / ^

distribution

*

of readings •

• y^^Y = a, + b,X

• / • /

A Sox

1 . 1 • 1 1 1

V assumed distribution

? of readings

'Sox * /

5^ ^ X = a'2 + b'2 Y

-

/ • / A Soy

1 1 . 1 1 1 . 1 •

X DATA Y DATA

Y = a2 + b2X

y

\//( / / Y = a^ + biX

/ / *

*

- X • bi and b2 represent extremes

1 1 1 1 1 I 1 1 1

1

Y = ao boX

\/

/ /

V / ^

V unknown /,/ /

y bo = >/bi b2

jf Soy = Sox

y / unknown

1 1 1 1

X DATA

Figure 2. For any set of data two regression lines can be calculated. Their

validity depends on the ratio of the respective precisions of observation.

(NOTE: figure 2 consists of 4 separate figures a), b), c) and d).)

536
Figure 3. Use of data subsets may verify regression line validity.

In this case ba varies by less than 2 percent whereas bj varies over a range of 18 percent. (NOTE: figure 3 consists of 4

separate figures .

)

587
Table 1. Raw data in mg/l

a) b) c) d)

AA

nD An A

/I /I 44 /I o 48 38 36 24 28 57 53

27 33 57 65 35 30 17 25

42 X 51 75 66 82 * 77 34 40

49 41 63 60 50 * 46 55 "k 49

30 37 52 55 41 44 83 74

46 52 43 39 30 27 78 "k 75

21 23 46 *

51 22 26 41 46

38 36 50 * 45 38 37 38 44

17 21 57 * 52 70 * 64 60 * 58

35 32 70 * 64 45 47 22 26

Lab A = data set Y

Lab B = data set X

Table 2. Slope and intercept estimates

ratio mg/l

bi b2 ai 32 Y X

1) 1.058 1.226 -2.98 -10.59 45.0 45.4

2) 1.181 1 .228 -7.98 -10.13 46.1 45.8

3) 1.117 1.370 -4.69 -19.19 59.3 57.3

4) 1 .370 1.249 -1.62 -10.47 31 .8 33.4

All) 1.134 1.228 -6.14 -10.40 45.6 45.6

The four subsets examined were:

1) columns a) and b)

2) columns c) and d)

3) high data marked by asterisk

4) low data remaining

588
Except in case 3) the X on Y inverted regression estimates are very stable and the

slope estimates fall in a range of about 2 percent. This suggests that the overall

precision of data submitted by lab B is worse than that from lab A. The Y on X regression

data is not a good predictor of the blank difference between labs and is lower in the

slope estimate by about 8 percent. In case 3) /b7b7 = 1.237 and the corresponding intercept estimate is -11.58, in fair agreement with the b2 estimates for the other subsets.

This suggests that in the higher range the precision of the two labs is more equal.

In this example r varies from 0.89 for sets 3) and 4) to 0.98 for set 2). The

residual standard deviation varies from Sy.^ = 4.1 to 5.7 so that the standard deviation

for lab A probably falls between 1 and 3 mg/1 whereas lab B probably falls in the range 3

to 5 mg/1. These estimates can be compared to known values if available.

Obviously when comparing two laboratories only relative biases can be detected. No

knowledge of the absolute accuracy is gained unless the data set contains known standard

reference materials. There should always be a plausible explanation for any significant

bias observed between laboratories. Since most laboratories concentrate on slope control,

it is not usual to observe severe slope differences. Blank control tends to be neglected.

6. Multilab Intercomparison

In some recent studies distributed by the Quality Control laboratory of the Ontario

Ministry of the Environment, a mix of natural, standard, and spiked samples (6 or more)

have been distributed to as many as 10 to 15 laboratories and analyzed for 6 to 9 parameters. The inter-comparison design is intended to permit linear regression analysis, but

successful interpretation of the study depends upon the development of a concise format

for presenting the massive amount of data generated, in a format readily appreciated by

the participants. If the data is plotted and a linear regression equation given, most

readers will be lead to the appropriate deduction. How can this be done when perhaps 100

diagrams are needed.

A procedure is being developed, however, for attacking this type of study based on 'difference linear regression' which is outlined below. As noted already regression

requires that the X data set be more precise than the Y data. Since the standard deviation for an average is better than that for the individual data, the X data set is chosen

to be the average reported by all participants on a given sample.

What we want is to examine the difference between the individual laboratory's data

and any suitable reference value such as the average for each sample. Therefore why not

calculate D = (Y-X) and regress D on X so that

if d = (D-D) = [y-x)

then b3 = ixd/ix'^

sg^X = z(d-d)2/(n-2)

r^ = [ixd)'^ /id'^Zx'^

and d = is the regression equation.

But by comparing d to y = bix and noting that {d-d) = {y-y) it becomes apparent that

bj = bi - 1 , a3 = ai and Sp,^ = Sy.x- Only

""p.x

^'^ different. It can be shown by substitution that

r2 = r2(bi -l)2/(bi^ + r2 - 2bir2)

589
In comparing methods or labs bj tends to unity so that r itself is of little use. However

bs will tend to zero and therefore rp.v can be used to determine whether bi is significantly

(statistically) different from unity, (see Table 4).

[This is a very useful feature since r^.^ can be used to determine whether b^ is

different from any reference value 'bp' one may want to choose simply by regressing D on X where D = (Y-b^X) and = (b^-bp). In fact it could be used as a s^tatistical control over instrumental response to sta^ndards. The t-test would confirm Y (new standards) not

different from the usual value (X) and r^^^ would confirm response unchanged from the

usual value b .] r Figure 4 compares, visually; plots of Y versus X, X versus Y, D versus X and D versus

Y for a very simple data set shown in table 3.

Figure 4. Comparison of Y on X, X on Y, D on X and D on Y data

plots and regression lines. (NOTE: figure 4 has two parts

a) and b) .

)

590
Table 3. Data used for plots of Y vs. X, X vs. Y, D vs. X and D vs. Y.

V - on 9 c; 9 c; CO CD /U 7n 7C 7C /U /D /b

X

= 10 30 12 32 60 80 62 82

X

= 47..5, Y = 46.0 > paired-t = 0.39

r

= 0,,927,

•^D-X = 0 .362, Tp^Y = 0.015

Y

= 7..74 + 0.864X (Y on X)

Y

= 1 ..225 + 1 .0060X (X on Y invert)

D

= 7,.74 + 0.136X (D on X)

X

= -8..956 + 1.157Y (Y on X invert)

X

= -1..218 + 0.9941Y (X on Y)

D

= 1

.

,218 + 0.00594Y (D on Y)

Figure 5 shows y on x and D on X plots from a recent intercomparison study. Difference

plots occupy much less space for the same amount of information. (Note the data set was chosen to demonstrate X precision poorer than the Y precision. Therefore the valid re- gression is X on Y or D on Y)

.

Figures 6, 7 and 8 demonstrate how three laboratories compare for nine parameters

relative to reference averages for each of six samples calculated from data submitted by six

participants. (One laboratory submitted duplicate results for some parameters). Only six

parameters were analyzed directly by each laboratory, the other three were calculated from

the data supplied to permit comparison and to demonstrate interchange of nitrate and ammonia

due to sample aging. The vertical scale covers differences D ranging between ±10 percent of

the maximum X given. Even without the data, relative precision and accuracy can be assessed

readily and interactions between parameters can be observed.

7. Summary

Linear regression techniques can be successfully used to compare laboratories provided

the precautions described are taken. The use of difference linear regression permits multilab, multi-parameter, mixed sample and standards intercomparisons to be evaluated whereas at

present data from such studies when attempted sit unevaluated. Proper evaluation should

clarify and identify possible sources of bias and should not leave this task to the participant alone.

591
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592
0.3

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Ammonia in l\latural Samples

Y = 0.004 + 1.02 X

r = 0.995

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0.1 0.2 0.3

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0.2

0

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(•5

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D = 0.004 + 0.018 X

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Figure 5. Interlaboratory comparison of a series of natural

samples analyzed for ammonia. Note the clarity of presentation in the difference plot.

593
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594
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595
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596
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

POTENTIAL ENFORCEMENT USES OF EMISSION TEST COLLABORATIVE STUDIES

Louis Paley

Division of Stationary Source Enforcement

Environmental Protection Agency

Washington, DC 20460, USA

and

Walter S. Smith

Entropy Environmentalists, Inc.

Research Triangle Park, NC 27711, USA

1. Introduction

Over twenty-eight documents have been written by EPA or their contractors on the

subject of collaborative studies of stationary source emission measurement methods. These

delineate the results of evaluations conducted on nine of EPA's reference test methods

(No's 2,3,5,6,7,8,9,10 and 104). The results of these studies have been used for various

purposes by the scientific and legal community. The purpose of this paper is to describe

three major ways in which enforcement agencies can utilize the results of collaborative

tests.

The primary application of these results for enforcement is in estimating the reliability of test methods. Since most agency determinations of the status of compliance of

a source are based on emission measurement data, the degree of reliability of this data is

of the utmost importance.

2. Discussion

The between-laboratory standard deviation is the statistic provided by the collaborati

studies which best quantifies a method's reliability. This term estimates the degree of

agreement to be expected among different laboratories who independently collect and analyze

"identical" samples. The between-laboratory standard deviation is frequently called

standard deviation of reproducibility, or just "reproducibility". A value twice that of

the "reproducibility" indicates the limit within which one can have 95% confidence in his

final value.

Compliance with the New Source Performance Standards (NSPS) and the National Emission

Standards for the Hazardous Pollutants (NESHAP) is based upon an average of more than a single run. Since EPA collaborative results have been based on a single run or sample,

these results must be adjusted by dividing them by the square root of the number of runs required to be averaged in the standard. For example, the reproducibility of Method 5 (particulate matter) collaborative test results at a municipal incinerator was 12.1%.

Conversion_of that data to the three-run basis is accomplished by dividing the reported

value by /3, thus yielding a three-run reproducibility factor of 7.0%. These values and

the associated values for the 95% Confidence Level are presented below for several

reference test methods.

597
Table 1

Reproducibility values and associated values for

the 95% confidence level of EPA reference test methods

Method

2

5

6

7

8

Parameter

Volumetric Flow

Particulate Matter

( i nci nerator

)

SO2 (power plant)

NOx (power plant)

Sulfuric Acid Mist

(Sulfuric Acid Plant)

Reproduci bi 1 i ty

(% of mean value)

3.2

7.0

2.4

2.7

38.2

95% Confidence

Level

(% of mean value)

6.4

14.0

4.8

5.4

76.4

Quantities recalculated from those given in the collaborative test reports in order to

reflect the number of runs required by the NSPS and NESHAP.

Once enforcement personnel have a good estimate of the reliability of a method as it

is applied to a specific category of sources, they can make a more intelligent judgment of

the compliance status of a specific source. As an example of this application, consider

the submittal of valid Method 5 test data by the operator of a municipal incinerator.

Agency personnel can be 95% confident that if a second test team conducted a valid test at

the facility, while it was under identical emission conditions, the second set of results

would be within 14% of those obtained by the first team.

Most cf the collaborative tests have indicated that the reference test methods are very reproducible. However, in the case of the sulfuric acid mist test, and the early

particulate tests, for example, the results appeared to indicate that Method 8 is not very

reproducible. It is unclear to what degree this result is affected by limitations of the

method, poor quality assurance procedures of testers, the spatial and temporal variations

of the emission stream during the tests, or other problems. Until tests, which have this

degree of uncertainty, are carefully repeated to evaluate and pinpoint this variability,

enforcement agencies must be very cautious when using this data.

A second application of the collaborative tests is to identify any problem area associated with the design and use of reference test methods. The most important finding

of this type were the necessity for having highly reliable methods, which are clearly and

thoroughly written; and for the implementation of effective quality assurance procedures

as an integral part of all emission testing programs. The collaborative studies showed

that at that time a crude state of the art existed among some "average" stack sampling

laboratories. In some cases, obvious gross errors were the norm. The most recent test

demonstrated that the presence of qualified on-site observers and the use of meaningful

quality assurance procedures can reduce the probability of most of the gross errors.

3. Conclusion

Because of the identified problem areas in the methods, proposed revisions for these

methods were published in the June 8, 1976, Federal Register. The majority of the revisions

centered around (1) more detailed explanations; (2) more detailed calibration procedures;

and (3) detailed quality assurance procedures.

598
Another valuable use of collaborative studies is to give the tolerances one should

consider when setting revised or additional standards for existing sources. When such a standard is written it should contain (or reference) a specific testing method. As in the cases of EPA's NSPS and NESHAP standards, the standard should take the method's reproducibility factor into account. For example, if the agency decides that a certain type of source needs to be restricted to ten pounds per hour in order to obtain suitable ambient

air quality, and the measurement method has a 10% reproducibility factor, then the standard

should be set at 8.3 pounds per hour in order to ensure (with 95% confidence) attainment

of the desired ambient air quality.

599

Part XII. AIR POLLUTION, WATER ANALYSIS

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

ION CHROMATOGRAPHY - A NEW ANALYTICAL TECHNIQUE

FOR THE ASSAY OF SULFATE AND NITRATE IN AMBIENT AEROSOLS

James D. Mulik, Ralph Puckett, Eugene Sawicki

Environmental Sciences Research Laboratory

U. S. Environmental Protection Agency

Research Triangle Park, NC 27711, USA

and

Dennis Williams

Northrop Services Corporation

Research Triangle Park, NC 27711, USA

1. Introduction

There are many methods currently available for the assay of sulfate and nitrate in

ambient aerosols. These methods appear to be inadequate because of poor sensitivity

and/or selectivity or are cumbersome to use. H. Small, T. S. Stevens and W. C. Bauman

[1]^ recently reported a new technique called ion chromatography (IC). The technique,

uses ion exchange chromatography, eluant suppression, conductimetric detection and is

ideal for the analysis of sulfate and nitrate in ambient aerosols.

Ion exchange chromatography with conductimetric detection has been attempted in the

past for the assay of anions and cations with little success because of the high background

produced by the electrolyte or eluant used. Dr. Small uses a novel technique of eluant

suppression, which allows the use of a universal conductivity detector. Eluant suppression

is carried out by means of a second ion exchange column that reduces or suppresses the

unwanted eluant ions without affecting the eluting ion species. This communication

describes the first successful application of ion chromatography to the analysis of sulfate

and nitrate in ambient aerosols.

2. Experimental

A Model 10 Ion Chromatograph (Dionex Corp., Palo Alto, Calif.) was used for the

analysis of water soluble sulfate and nitrate in ambient aerosols. A schematic of the

flow system is shown in figure 1. The flow system consists of a separator or analytical

column, suppressor column, four solvent reservoirs, injection valve with 0.5 ml sample

loop, two Milton Roy fluid pumps, conductivity detector, and a valving system to direct

the flow through various parts of the instrument. The system uses air activated Teflon

slider valves throughout.

Figures in brackets indicate the literature references at the end of this paper.

603
WASTE

FIG. 1 Ion Chromatograph Flow System

604
For the analysis of sulfate and nitrate the separator column (500 mm x 3 mm I.D.)

contains a strong basic anion exchange resin and the suppressor column (250 mm x 6 mm

I.D.) contains a strong acid ion exchange resin. For the data described herein the eluant

is .003 M NaHCOg .0024 M Na2C03 prepared in distilled deionized water. The water should

have a conductivity of less than 10"^ ohm"^ cm"i.

The separator column separates anions in a background of carbonate eluant which then

pass into the suppressor column where the sample anions and the carbonate eluant are converted to their acid form and pass unretarded into the conductivity detector. The

carbonate is converted into carbonic acid, which has a very low conductivity (eluant

suppression), whereas the nitrate and sulfate are converted to nitric and sulfuric acid,

which have a high conductivity. Thus, producing the sensitivity that, heretofore, has

been unattainable.

3. Results

The minimum detectable level (MDQ) of sulfate and nitrate was found to be 0.1 yg/ml

:

the MDQ can be increased by going to a larger sample loop.

The relative standard deviation is 3 percent for sulfate and 1 percent for nitrate at

the 95 percent confidence level for 10 replicate injections at the 5 pg/ml level.

Our initial experiments with the IC technique involved the assay of hi-vol glass

fibre filter strips (3/4 in x 8 in) containing known amounts of sulfate and nitrate. The

strips were extracted by soaking in 25 ml distilled water overnight. The strips were washed three times with 5 ml of distilled water through a Buchner funnel and the final

volume brought to 50 ml. Aliquots of the 50 ml were taken for injection into the ion

chromatograph. In most cases it was necessary to make dilutions. The concentrations

found by IC compared to the actual spiked concentrations are shown in table 1.

Table 1

Glass fiber hi vol filter strips impregnated with sulfate and nitrate standard

N03 yq/Strip 504= yg/Strip

Sample # Added Found (I.e.) % Diff. Added Found (I.e.) % Diff.

6195 1381 1441 + 4.0 477 477 - 6.0

6196 1381 1286 - 7.0 477 467 + 2.1

6197 1381 1385 + 0.1 477 438 - 1.5

7089 1116 936 -16.0 3857 3553 - 7.8

7090 1116 1100 - 1.4 3857 3769 - 2.3

7091 1116 993 -n .0 3857 3786 - 1.8

8189 229 218 - 5,0 5078 4530 -10.8

8190 229 240 + 5.0 5078 5183 + 2.1

8191 229 201 -12.0 5078 5251 + 3.4

5184 Blank 0.61 Blank 7.3

The large negative bias shown in several samples is probably due to the extraction

process and not to the analytical technique. It emphasizes the need for an improved

extraction procedure.

Several common anions that might possibly interfere with the IC method for analysis

of sulfate and nitrate are shown in table 2. The concentration of sulfate and nitrate was

5 yg/ml with the interfering anions at the same concentration.

605
Table 2

Common anions that may interfere with the IC method

for analysis of SO4 and NO3

Anions SO1+ NO3"

F 1 uon de None None

Chloride None None

Bromide None None

Nitrite None None

Sul f i te None None

Si 1 icate None None

Carbonate None None

Phosphate None None

Sulfide None None

Our earlier research [2] showed that bromide and phosphate would interfere because

they could not be resolved from the nitrate with the 250 mm anion analytical column.

Bromide and phosphate are no longer interferences as shown in table 2 because we are now

using a 500 mm anion analytical column which resolves the bomide and phosphate from nitrate

Several water extracts of actual ambient aerosols were assayed by the IC procedure.

These extracts were also analyzed by the methyl thymol blue colorimetric procedure for

sulfate and by the copper cadmium reduction colorimetric procedure for nitrate. The

comparison of the sulfate and nitrate analysis by the IC technique to that of the two

colorimetric procedures is shown in table 3. The excellent agreement between the IC

procedure and the two colorimetric procedures for nitrate and sulfate indicate that IC is

certainly a promising method for both sulfate and nitrate.

Table 3

Comparison of ion chromatographic (IC) method with colorimetric

methods for sulfate and nitrate in actual ambient aerosols

S0^= (yq/ml) NO3- (yq/ml )

Sample Ion Methyl Ion Cadmi um Number Chromatography Thymol blue Chromatography Reduction

1 65.1 66.2 9.23 14.8

3 79.4 72.9 21 .2 20.4

5 29.2 30.9 6.4 7.0

7 52.9 53.2 23.6 23.5

9 35.5 35.3 9.3 9.6

11 88.8 82.1 4.3 4.5

13 23.6 25.1 5.2 5.9

15 35.9 36.5 17.5 18.2

17 47.6 48.7 12.3 12.4

4. Conclusion

Although additional research is needed on interferences, repeatability, and accuracy,

sufficient information has been presented herein to demonstrate that the ion chromatographi

technique can measure sulfate and nitrate in ambient aerosols with a sensitivity and

selectivity that heretofore has been unattainable. One of the most attractive features of

the IC method is that it has the potential of becoming a multipollutant analyzer. The

development of ion chromatography for the assay of other pollutants such as NH^"*", gaseous

NH3, aliphatic amines, sulfite, nitrite, phosphate, halides, SO2 and NO2 is also under

investigation.

606
References

Small, H., Stevens, T. S., Bauman, W. C. , Anal. Chem. , 47_, 1801 (1975).

Mulik, J., Puckett, R. , Williams, D., Sawicki, E., Analytiaal Letters 9{7) 653 (1976).

607

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

THE USE OF A GAS CHROMATOGRAPH-MICROWAVE PLASMA DETECTOR FOR THE

DETECTION OF ALKYL LEAD AND SELENIUM COMPOUNDS IN THE ATMOSPHERE

Donald C. Reamer, Thomas C. 0' Haver and William H. Zoller

Chemistry Department

University of Maryland

College Park, Maryland 20742, USA

1. Introduction

Considerable interest in the determination of organo-metal 1 ic compounds has been

generated by studies which indicate that organic mercury and arsenic compounds are present

in natural waters and in the atmosphere. Organic forms of heavy metals are generally more

toxic to man due to increased solubility. Atmospheric levels of organic mercury have been

found in the ng/m^ range [1]^ and organic arsenic in the sub ng/m^ range [2]. Arsenic,

mercury, lead, and selenium are now known to be methylated by microbial organisms. The

high atmospheric enrichment of elements, such as selenium, has prompted investigators to

propose a vapor phase for these enriched elements due to their volatility resulting in

their possible release from natural or anthropogenic processes [3]. Selenium is one of

the elements found to have an enrichment factor of 10,000. While bi omethylation of

selenium is known to occur, there is little information as to the species present in the

atmosphere. The origin of organic lead compounds--lead additives to gasoline--is well

known, but, there is still a need for more data to ascertain the environmental effects of

this pollutant.

2. Discussion

During atmospheric sampling, the high concentration of organics and water present in

the atmosphere relative to that of organo-metal 1 ic species can cause interferences requiring analytical techniques that can satisfactorily measure down to these levels while

maintaining a relatively interference-free performance. Several instrumental methods have

been employed for the determination and identification of organo-metal 1 ic species; gas

chromatography-atomic absorption for atmospheric organic lead [4], membrane probe emission

detection for organic mercury and arsenic in air and water [1,2,5], and gas chromatographymicrowave plasma detection (GCMPD) for organic arsenic environmental samples [6]. Electron

capture has been used as a GC detector for organo-metal 1 ic analysis, but suffers from poor

sensitivity to some metal species and instability due to fouling by contaminants from

column bleed.

The GC-MPD has proven its sensitivity and selectivity for a number of metal species,

primarily in a chelated form. This paper describes the applicability of a GC-MPD system

with wavelength modulation for background correction for the analysis of atomospheric

samples of alkyl lead and selenium species. The GC-MPD system is basically the same as that described by McCormack, Tong, and Cooke [7], with some instrumental modifications.

The system is comprised of a transparent quartz capillary which contains the effluent from

the GC. The capillary is contained within a 3/4 wave cylindrical microwave cavity. The

argon plasma contained within the capillary is generated by a 200-watt Microtron microwave

^Figures in brackets indicate the literature references at the end of this paper.

609
generator. The signal is viewed at right angles to the quartz capillary, which is parallel

with the entrance slit of the monochromator . The wavelength modulation system, which is

similar to that described by Epstein and O'Haver [8], consists of a torque motor and a 1 in. X 1 in. x 1/8 in. quartz plate mounted at the entrance slit within the monochromator.

The desired wavelength of the monochromator is modulated, via the vibrating quartz plate, over a small wavelength interval and the resulting ac component of the signal is measured

by a frequency-selective ac detector system. Wavelength modulation was used to remove two

types of background interferences: broad band emissions resulting from organic molecular

species in the sample and residual impurities in the argon and background plasma emissions.

The high concentrations of organics in atmospheric samples, relative to that of alkylmetals, makes it difficult to achieve good chromatographic separation prior to the sample

entering the plasma region. For selenium analysis at 196 nm, the 193 nm atomic carbon

line generates a sloping continuum-type background interference, which can be substantially

reduced with wavelength modulation. For the analysis of organic lead compounds at 405.78

nm, there are few interfering emission lines, so wavelength modulation is not as necessary.

The selectivity ratio of the selenium 196 nm emission line, when compared to methanol, is

approximately 6 x 10^ in the dc mode and 6 x 10^ in the ac mode. The selectivity ratio of

the lead 405.78 nm emission line, when compared to methanol, is approximately 1 x 10^ in

the dc mode and 8 x 10^ in the ac mode. Consequently complete resolution of the solvent,

organic species and alkyl-metal species is not required in the ac mode. The GC conditions

can be selected somewhat to enhance selectivity and sensitivity.

The detection limits, defined as the amount of the element which produces a signal

twice the size of the background noise, was approximately 12 pg for dimethyl selenide and

40 pg for tetraethyl lead in the ac mode and 7 pg for selenium and 26 pg for lead in the

dc mode.

Approximately one percent hydrogen was added to the argon during the tetraethyl lead

analysis to minimize a memory effect which occurred within the quartz capillary. Some of

the lead, after being decomposed in the hottest portion of the plasma, plated onto the

quartz walls. When the next aliquot was injected, the solvent removed some of this lead

from the walls producing an erroneous lead signal following elution of the solvent. The

intensity of repeated injections was also reduced as a result of this lead plating.

Hydrogen was found to be better than nitrogen or oxygen in reducing this lead depositing

effect.

The sorbent collection system for tetraethyl lead employed a Teflon cartridge tube

filled with ten percent SE-52 on 80/100 mesh Chromosorb-P. The collection tube was maintained in a methanol-dry ice slurry during sampling and stored in dry ice prior to analyzing.

Samples of ambient air were drawn through a 0.2 ym Nuclipore filter and the sample cartridge

at a flow rate of 0.3 m^/h. The filter retained lead particulates, and the passed vapor

phase of tetraethyl lead was quantitatively retained by the sorbent. The recovery of the

organic lead was accomplished by a two-step procedure. Since low power microwave plasmas

are sensitive to water, it was necessary to remove the water by freeze drying. A miniature

freeze drying system was used to desorb the trapped gases within the sorbent and the water.

The drying procedure removed the water and volatile lead species. Following this step the

aqueous sample was extracted with benzene. The recovery and accuracy of this method was evaluated by collecting simulated air samples which were spiked with 200 ng of tetraethyl

lead. The overall efficiency of the method ranged from 83 percent to 108 percent at this

concentration level

.

Gas and particulate samples were collected for two-hour intervals. The particulate

lead samples were digested for six hours on a hot plate in a solution of 25 ml water, 1 ml

of perchloric acid and 25 ml of a 4:1 mixture of nitric acid and hydrochloric acid. The

Nuclipore filters and standards were analyzed by flameless atomic absorption using a Varian

Model 63 carbon rod furnace. The GC-MPD optima for tetraethyl lead analysis are shown in

table 1. The results of the samples collected in the Baltimore Harbor Tunnel are presented

in table 2. The organic lead values are in the same range as those reported by other

methods [9,10]. The average percentage of organic lead to particulate lead is approximately

1 .9 percent.

610
Table 1

Operating parameters: GC-MPD optima for tetraethyl lead analysis

GC system: Pb:

Se:

10% SE-52 on 80/100 mesh Chromosorb-P

(2 ft X 1/8 in)

15% Carbowax 20M on 60/80 mesh Chromosorb-W

(10 ft X 1/8 in)

Quartz capillary:

Carrier gas

:

Carrier gas flow rate:

Column temperature:

Injection temperature:

Microwave power:

1.0 mm i . d . , 6.0 mm o . d

.

Argon - 1% hydrogen

Pb-75 ml/min, Se-20 ml/min

Pb-90, Se-70

Pb-130, Se-160

Pb-lOOW, Se-30W

Monochromator

:

Slit height:

Spectral bandpass:

Wavelength

:

Modulation interval

:

Photomultiplier tube:

1 2 mm

.22 nm Pb-405.78,

.38 nm Jarrel-Ash

Se-196 nm

R106

Table 2

Results of air analyses from the Baltimore Harbour tunnel

ug/m^ Volume of Air

Sampling time Sampled (m^) Tetraethyl Lead Particulate Lead

12 - 2 pm 0.7 — 19.1 ± 1.7

2 - 4 pm 0.6 0.8 ± .023 20.6 ± 1.6

4 - 6 pm 0.6 0.13 ± .02 19.8 ± 1.4

6 - 8 pm 0.6 0.07 ± .013 14.9 ± 1.2

8 -10 pm 0.6 0.12 ± .014 16.3 ± 1.1

3. Conclusion

In conclusion, the GC-MPD is well suited for atmospheric organo-metal 1 ic analysis due

to its sensitivity and selectivity for volatile metal -containing species. The limitation

of this GC detector lies in the preparation of the sample for introduction into the plasma.

Due to its susceptabi 1 i ty to overloading, the plasma can be quenched, if the concentration

of sample or solvent is too high. Preliminary results indicate that the addition of hydrogen

in the plasma has minimized the other problem in this system— the development of carbon and

other metals deposits. This study has shown that the GC-MPD system with wavelength modulation can be used for atmospheric alkyl-lead analysis. The instrument has also been shown

to have the capability of detecting minute amounts of volatile selenium compounds, but a quantitative collection system has yet to be fully developed.

611
Refe rences

[1] Johnson, D. L. and Braman, R. S., Environ. Soi. and Technol. 8, 1003 (1974).

[2] Johnson, D. L. and Braman, R. S., Chemosphere 6_, 333 ( 1975).

[3] Zoller, W. H. , Gladney, E. S. and Duce, R. A., Saience 183, 198 (1974).

[4] Chau, Y. K. , Wong, P. T. S. and Saitah, H., J. of Chromat. Sai. H, 162 (1976).

[5] Soldano, B. A., Bien, P., and Kwan, P., Atmospheric Environ. 9_, 941 (1975).

[6] Talmi, Y., Anal. Chimi. Acta 74, 107 (1975).

[7] McCormack, A. J., Tong, S. C, and Cooke, W. D. , Anal. Chem. 37, 1470 (1965).

[8] Epstein, M. S. and O'Haver, T. ,C., Spectroahimiaa Acta 30B, 135 (1975).

[9] Purdue, L. J., Enrione, R. E., Thompson, R. J., and Bonfield, B. A., Anal.

Chem. 45, 527 (1973).

[10] Harrison, R. M. , Perry, R. , and Slater, D. H. , Atmospheric Environ. 8_, 1187

(1974).

612
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

THE DUTCH NATIONAL AIR POLLUTION MONITORING SYSTEM—

A FOCAL AND REFERENCE POINT

T. Schneider

Rijks Instituut voor de Vol ksgezondheid

Nederland

1. Introduction

Over the last few years environmental monitoring has become an important issue in the

Netherlands. Scientific, technological and political thinking has been focussed on it;

instruments and techniques have been developed. The Netherlands have one of the highest

densities of population in the world together with major industrial centers. Meteorological conditions and wind direction in this part of the world are extremely variable and

so are pollution conditions. Not only will the emission in a given air space vary from day

to day and hour to hour but so will its chemical composition and place of origin. Complicating the matter is the fact that this country's neighbors, Belgium and West Germany, are also heavily industrialized. So, in addition to the pollution generated internally, the

Netherlands must often cope with that coming across international boundaries, from the

industrial concentrations in the Ruhr area and northern Belgium. It is not surprising,

therefore, that the history of monitoring and surveillance is a long one in the Netherlands.

Using a multitude of methods and laboratories, a national picture was not exactly easy to

obtain. In the late sixties a decision was taken to create a national air pollution monitoring network to achieve comprehensive surveillance throughout the country. It was designed to provide ultimately the following information: A reliable estimate of the

quantity, composition and origin--international as well as national--of the pollution; data

for establishing trends in the degree of pollution from year to year and the influence of

zoning decisions, growth of industry, traffic and pollution on these trends; evaluation of

the effectiveness of abatement strategies; and information for short-term warning purposes,

to allow forecasting of undesirably high degrees of pollution under unfavorable dispersion

conditions.

2. Discussion

The network consists of 217 monitoring stations, of which 109 form a regular base line

grid covering the entire country. The remaining stations cover special topographical

features, such as densely inhabited areas, large industrial centers and areas along the

national borders. Each station is equipped to monitor, on a regular basis, one or more polluting components in the atmosphere and to transmit the data to its regional center.

Some of the stations also monitor meteorological factors such as wind velocity and wind

direction. In the first phase the network is equipped with monitors for SO2 and wind speed

and wind direction only. The capabilities of approximately 80 stations will be expanded to measure in addition CO, NO, NO2, and O3. The first monitors for the measurements of these

pollutants have recently passed the tests and the first series will be installed this year

in one of the regions (South Holland) of the network. Each measuring instrument is calibrated by remote signal from the computer in a regional center. At each region information

is collected every minute; minute values and hourly averages are calculated. The central

communication unit, located in the National Institute of Public Health (R.I.V.) in Bilthoven,

automatically collects information from the regions and stores it on magnetic tapes and

discs. It calculates and presents hourly averages on a line printer. It checks pollution

levels in the regions. Threshold values are set and monitoring stations exceeding these

values are automatically indicated by lights on an illuminated map. All these and additional information can be presented on a CRT display, a logging typewriter, an analog recorder

613
or punched papertape. A facility for minute to minute check and control of the whole

network is available. The information stored on magnetic tape is processed off-line for

statistical and model studies. The continuously recorded information is also processed to

national and regional surveys every month, every six months and every year to study trends

in pollution levels.

For an optimal interpretation of network data additional measurements are carried out

using mobile units. In this way the density of measurement in space is increased temporarily in order to obtain information on possible occurring spatial structures. The concentration fields as reconstructed with optimal interpolation parameters, are compared to

measured transport patterns along dynamic traverses.

Apart from this mobile addition to the network, the effect of air pollution on plants

is studied at 30 stations of the national network. Special indicator plants, specific for

one or more pollutants are used. Among the indicators used are spinach as an indicator for ozone and SO2, Petunia as an indicator for ethylene, tobacco as an indicator for ozone, and

grass and lettuce as an indicator for PAN. Ozone damage on tobacco plants especially was found all over the country, which for ozone indicates the importance of a surveillance over

a large area.

A prominant role in the whole of the national system is reserved for the final refer- ence point of the system, the dynamical calibration unit in Bilthoven. Here all instrumental methods to be used in the Dutch network (and others in between) have been examined.

Although most of them were rejected at first we finally succeeded in convincing a few

manufacturers of the advantages of the development of air pollution monitors that could

pass even the severe tests specified by the RIV. These tests were executed on the calibration unit built especially for this purpose. The unit consists of an air cleaning device

(compressor and heatless dryer with dust filters) that deliver dry gas with a dewpoint

below -60°C and without CO2, CO and NO. The massflow is selectable between 0 and 50 K liters/min. A specially constructed evaporation block is used to supply water

vapor to the carrier gas. The "pollution" is added using permeation tubes (SO2, H2S,

CH3SH, NO2); permeation tubes and photolysis of NO2 for NO or UV radiation of O2 and

comparison with NO2 from a permeation tube for O3; or cylinders traceable to NBS (CO, NO

and C2HL,).

The permeation tubes are kept at a temperature of 25 ± 0.03°C. The flow of the mixing

gas is determined by a volumemeter with optical regulation (inaccuracy ^ 0.5 percent).

Taking into account the uncertainties in the permeation rate and in the air flow, the

inaccuracy of the total system is for SO2 - H2S - vinylchloride and CO .< 1%; for NO2 2%,

for NO (photolysis) .< 3% and O3 (gasphase titration) ^ 4%.

Specifications that are determined at the calibration unit are among others: lower

detectable limit, inaccuracy, precision, interference, sensitivity, lag time, rise and fall

time, zero drift and span drift. External factors that are determined are: influence of

temperature and humidity.

The control of the most important characteristics--zero drift and span drift--should

be performed regularly at the monitoring station itself. For this purpose a portable

calibration unit has been developed. With this unit a dynamic multi-point calibration can

be performed in the field which uses a mixture of known amounts of SO2, supplied by permeation tubes, with known volumes of cleaned air. The flow rate is controlled by two

thermostated critical orifices in conjunction with a vacuum pump. The overall error in the

calculated test gas concentration is ^ 4 percent.

614
3. Conclusion

Details such as those for the calibration and reference systems given above could also

be outlined for the necessary maintenance and servicing systems used in connection with the

Dutch national network. The final interest lies in the receipt of the signals of reliable

measurements of all the stations at the national center in Bilthoven. Once a reliable

monitor has been developed a transmission network can be constructed to carry the signals

from a station to the regional and national centers. In the end it is just as important,

if not more so, that a reliable system remains a reliable system. To reach that goal a load of hard but rewarding work has to be performed.

615
»
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

ANALYSIS AND CALIBRATION TECHNIQUES FOR MEASURING AIRBORNE PARTICULATES

AND GASEOUS POLLUTANTS

I. Delespaul, H. Peperstraete and T. Rymen

Chemistry Department

Belgian Nuclear Research Centre

MoT, Belgium

1. Introduction

A. Heavy metals network

Since May 1972, the daily average levels of Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn have been measured in airborne dust, collected in fifteen stations [1,2P. The lay-out of

this network is given in figure 1. The large cities of Antwerp, Brussels, Charleroi and

Liege have three stations each. Background levels are measured in Oostende (seaside) and

Botrange (inland). A pilot station at Mol is used for further control of the network.

NETHERLANDS

LUXEMBURG

Figure 1. Belgian network for the determination of heavy metals

(ZM-network)

.

^Figures in brackets indicate the literature references at the end of this paper.

617
2. Experimental

Samples are collected on a 24-hour basis, using high-volume samplers with cellulose

filters. Filters are changed manually each morning at 9:00 a.m. Emission spectrometry has

been retained as the analytical technique because it is a good compromise between detection

limit, accuracy, speed and price. The set-up is composed of a direct reading spectrometer

(MBLE-SM 150), a multisource (ARL-6900 F), a measuring unit (MBLE-PV 8700), a POP 11/20

computer with interface and teletype, and a direct link to the central IBM 370 multi-user

computer.

Sample preparation starts by cutting a 5 cm^ portion from a loaden filter and wetting

it with a solution containing 10 mg NaCl (buffer) and 2 micrograms In and Pd (Internal

standards). These filter strips are ashed at 440 °C for 2 hours, and mixed with 100 mg

graphite powder. A fraction of this mixture is pressed in a L 4006 graphite electrode from

NCC, and excited in a 7.5 A D.C. arc for 30 seconds.

The calibration of the spectrometer is made with synthetic reference samples obtained

either by dry mixing of oxides or by absorbing aliquots of solutions of the metals onto

filter paper. Drift on the calibration is cross-checked by repeating previously analyzed

samples. The accuracy is controlled by intercomparison with neutron activation, atomic

absorption spectrometry and x-ray fluorescence [3,4]. These calibration data are given in

table 1.

Table 1

Emission spectrographi c calibration data

Element Wave length Detection Upper limit Deviation^ on Accuracy'^

limit of working duplicate

range samples

(10"^ cm) (ng/m3) (ng/m3) (%)

Ba 5535 5

Cd 2288 4

Co 3453 5

Cr 4254 1 Cu 3247 1.5

Fe 3734 12

Mn 2576 7 Ni 3492 2.5

Pb 4057 20

V 4379 4

Zn 1 2138 10

Zn 2 3345 60

1000 21.5

500 8.5 1.06

1000 — 1.03

150 18.9 0.89

1250 8 1.04

25000 9.1 1.13

1150 7 1.01

1500 28.6 0.99

5000 8.1 0.96

600 13.8 0.96

60

50000 12.6 0.96

^ Deviation = 1 00-^ " ^ number of duplicates

J

_ 1st reading - 2nd reading

1st reading + 2nd reading

Expressed as the ratio of the emission spectrometric result to the mean of the results of

the other methods.

618
3. Results

Interpretation is made on a yearly basis starting from the measurements stored in the

data bank. The cumulative frequency distribution is calculated for each station. The

results give the possibility to specify the variability of the daily levels, their average

and highest level over a long period. An example of the visualization of the general

situation for Pb over the Belgian area is given in figure 2.

LUXEMBURG

Figure 2. Median values and 95 percentiles of the daily Lead

levels in Belgium during the period 5/73-4/74.

A. Gaseous inorganic pollutants

Gaseous pollutants are sampled to provide information on local pollution levels in

urban and industrial areas. The sampling period is of the order of . 5 to 1 hour and is

usually performed with several samplers simultaneously. The general approach consists in

locating the possible sources by simultaneous sampling up-wind and down-wind, by operating

a continuous monitoring station in the area, and by completing the campaign by an "at

random" sampling for statistical evaluation.

Campaigns were organized for measuring SO2, NO, NO2, NH3, Cl~ and F~ for periods

ranging from two months to two years with an average daily amount of 30 to 60 samples. The

most commonly applied analytical techniques are summarized in table 2. The sampling device

is shown in figure 3.

619
Table 2

Analysis of inorganic gaseous pollutants

^/ 1\ 11 utf^ U U U nt1 1 u Sampl i ng utr LcL L 1 Ui 1 i lib Lr Ulllcil La 1 m "t" iiietnou Vol ume Time limit method

ug/m^

S02 colorimetry [5] 30 I 1/2 h 15 coulometry & flame

NO&N02 colorimetry [6] 12 I 1/2 h 18 chemil amines cence

NH3 colorimetry*" 30 £ 1/2 h 15

cr col orimetry*^ 60 £ 1 h 5 coul ometry

F" ion selective 60 a 1 h 0.5

electrode

colorimetric method with Nessler reagent

colorimetric method with diphenyl carbazon

1 - SAMPLE INIET

2 - IMPINGER

3 - DRYER

4 - PUMP

5 - TIMER

6 - ROTAMETER

Figure 3. Sampling device for

inorganic pollutants.

Calibration of methods and apparatus is achieved with a multi-component calibration

device (fig. 4). Permeation tubes or pulsed injection are used as pollutant sources. Permeation tubes are made on a routine basis for SO2, NO2, Cl2> H2S, CH3SH and NH3 and have

permeation rates in the range of 0.2 to 6 yg of pollutant per minute. The stability of the

permeation rate at constant temperature is of the order of 2 percent. Pulsed injection

introduces 0.050 or 0.100 m£ amounts of pollutants in a gas stream at a rate of 10 injections

per minute.

620
VENTILATION

CHANNEL

1

1. SOLENOID VALVE

2. FLOW CONTROLLER

3. THREE WAY

SOLENOID VALVE

4. MASS FLOWMETER

5. MANOMETER

6. TEMPERATURE

REGISTRATION

7. PERMEATION TUBE

8. THERMOSTATIZED

COLUMN

9. DUST FILTER

AEROSOL GENERAL

19 11. CONOENSOR

12 OVERFLOW

13 MIXING CHAMBER

14 SOLENOID VALVE

15 MANIFOLD

16 THERMOSTAT

17 CRYOSTAT

18 ROTATION PUMP

19 WATER CONTAINER

Figure 4. Mul ti component Calibration device

4. Conclusion

A. Gaseous organic pollutants

The well known differences among organic pollutants with regard to their adverse

health effects, either direct (vinyl chloride, polynuclear aromatic hydrocarbons [7-10]) or indirect {via their participation in photochemical smog formation [11-14]), obviously

raises the necessity of an individual tracing. Moreover, because of the very low permissible

levels, extremely sensitive quantities and reliable sampling techniques are required.

As a rule, pollution measurement campaigns were performed in two steps: a preliminary,

intended to establish an order of priority for the pollutants present in the area to be

controlled, and the actual quantitative campaign, performed by sampling in the field and

analysis in the laboratory, in conjunction with an automatic control station ,in the field.

Samples are collected by aspiration of air in "multi-wall" sampling bags, that were

previously controlled against adsorption and memory effects. The sampling set up is shown

in figure 5. The sampling time is normally set at 30 minutes. In the automatic field

station, an integrated air mixture representing 30 minutes sample is analyzed. During the

preliminary campaigns, preconcentration of the pollutants on activated charcoal [15,16] was

used a few times alternatively with direct sampling.

Pollutants are analyzed by gas chromatography. During the preliminary campaign conditions

instruments are set for a sensitive detection of all the pollutants which are suspected to

be present. Uhile this information is accumulating, gas chromatographic conditions are progressively adjusted for fast, sensitive and accurate quantitative analyses. Examples are

given in table 3.

621
1 - ALUMINUM CILINDER

2 - SAMPLING PIPE

3 - HERMETICAL SEALS

4 - SAMPLING BAG

i - AUTOMATED PUMPING SYSTEM WITH TIMER 51 OF AIR ARE SAMPLED

IN 30 MINUTES

Figure 5. Set up for direct sampling.

Table 3

Instrumental conditions for organic pollutants

Area

Vinylchloride

plant

Paint industry

Prior pollutants

ethylene

vinylchloride

1.1 dichloroethane

1 . 2 dichloroethane

dichloromethane

1.1.1. trichl oro- ethane

trichloroethylene

tetrachloroethylene (x)

benzene

toluene

ethyl benzene

(m+p) xylene

(°)

(x)

(x)

g.c. conditions

alumina F, column 5' x 1/4"

operating at 110 °C _^

carrier gas : N2, 60 mi min"

detection: flame ionization, 150 °C

tricresyl phosphate 5 % on chromosorb

W, AW, 80-100 mesh, 7'xl/4", operating

at 60 °C.

carrier gas : N2, 15 mi min'

detector : flame ionization, 150 °C

-

1

tricresyl phosphate 5 % on chromosorb

W, AW, 80-100 mesh, 7'xl/4", operating

at 65 °C _j

carrier gas : N2, 30 ml min~

detector: (°) flame ionization

(x) electron capture

(53Ni), 150 °C)

1,2,3 tris (2 cyanoethoxy) propane

15 % on chromosorb W, AW, 8'xl/4"

operating at 65 °C _^

carrier gas : H2, 60 ml min

detector : flame ionization, 150 °C.

622
Calibration of the instruments is carried out with standard mixtures prepared from

gases or liquids. The first step consists of the injection of a known volume of liquid or gas in an evacuated 1 litre flask. After evaporation of the liquid, the flask is filled

with nitrogen up to atmospheric pressure. A suitable volume of this primary mixture is then

injected in a line while nitrogen is flowing through and entering a sampling bag. The total

volume of nitrogen used to fill the bag is measured with a wet gas meter. Calibration with

these mixtures proved to be better than 5 percent, based on 20 consecutive preparations over

a period of 6 months.

The over-all efficiency of the analytical procedure is checked by duplicate measurements

and correlation between analyses in the laboratory and in the automatic field station. For

the area of the vinyl chloride plant the reproducibility of duplicate results are: ethylene

3.9 percent, vinyl chloride 4.9 percent, 1.2 dichloroethane 9.5 percent.

Finally it should be mentioned that, when combined with the information about sampling

place and meteorological conditions, the results obtained always allowed the identification,

among a set of plants, of the major sources for the detected pollutants.

This work was sponsored by the Belgian Ministry of Public Health under the form of

contracts and was carried out in cooperation with the official instances.

References

[I] Ministry of Public Health - S.C.K. /C.E.N. Mol Onderzoek naar de niveaus van luchtverontreiniging door zware metalen Jaarverslag 1974.

[2] Ministry of Public Health - S.C.K. /C.E.N. Mol Onderzoek naar de niveaus van luchtverontreiniging door zware metalen Jaarverslag 1975.

[3] De Regge, P., Lievens, F., Delespaul, I., Monsecour, M., Intercomparison of Neutron

Activation Analysis with Other Instrumental Methods for the Elemental Analysis of

Airborne Particulates, International Symp. Vienna, March 15-19, 1976.

[4] Kretzschmar, J. G., Lievens, F., De Rijck, Th. , Verduyn, G., Delespaul, I., The Belgian

Network for the Determination of Heavy Metals. Submitted for publication in Atmospheric

Environment

.

[5] West and Gaeke, Anal. Chem. 28, 1816 (1956).

[6] Saltzman, Anal. chem. 26, 1949 (1954).

[7] Levine, S. P., Hebel , K. G., Bolton, J., and Kugel , R. E., Anal. Chem. 47, 1075 A

(1975).

[8] Kennaway, E. L., Brit. Med. J., 1_, 564 (1924).

[9] Cook, J. W., et al., J. Chem. Soe., 395-405 (1933).

[10] U.S. Environmental Protection Agency, Air quality data for 1968, Pub. AVTT)-0978 (1972).

[II] Leighton, P. A., Photoahemistry of Air Pollution, Academic Press, New York (1961).

[12] Haagen, A. J., Smit, and Wayne, L. G., Air Pollution (A. C. Stern, ed.) 2nd ed. Vol. 1, A. P. New York, p. Ill (1967).

[13] Altshuller, A. P., J. Air Poll. Contr. Assoe., J6^, 257 (1966).

[14] Masters, G. M., Intro, to Environ. Science and Tech., J. Wiley & Sons, Inc., 1974.

[15] Grob K., and Grob, L., J. of Chromatography, 62, 1-13 (1971).

[16] Burghardt, E., and Jeltes, R., Report B 216-11, IG-TNO, Delft (1974).

623
(
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1 977).

FACTORS GOVERNING THE CONTENTS OF METALS IN WATER

D. J. Swaine

CSIRO Division of Mineralogy,

North Ryde, New South Wales, Australia

1. Introduction

If the current deluge of data in environmental science is to be meaningful, certain

fundamental aspects must be considered. In the case of heavy metals in natural waters,

more needs to be known about

(a) the meaning of the content of a metal in water

(b) the factors governing the state of metals in water

(c) reactions at the sediment-water interface

(d) how to sample, preserve the sample, and analyze, in order to obtain real results even at levels of the order of 1 in lO^.

The total content of a metal in water is made up of a soluble part (inorganic and

organic; usually defined as that passing a 0.45 pm filter, an insoluble part (particulate

matter) and that associated with living matter. A variable proportion of the total amount

associated with the particulate matter is adsorbed on clay, on organic matter, on iron and

manganese oxides, and on thin films of these oxides on minerals or rock particles. These

various forms of a metal in water may differ chemically, ranging from simple complexes to

highly dispersed colloids. The solubility and form a metal may have in water depend on several factors, perhaps the most important ones being pH, oxygen concentration, salinity

and the nature of the major ions present.

2. Discussion

The significance of these factors has been established by laboratory experiments on the extraction of different rocks by saline solutions (A. M. Giblin and D. J. Swaine,

unpublished work). In most natural waters of low salinity, pH and oxygen concentration are

the main factors. Adsorption has a major role in the distribution of trace constituents

between water and solids. What happens in a particular case depends on the metal, the

nature of the solids present and on the chemical environment, typified by pH , oxygen con- centration, salinity and the kind of ligands present. In many natural waters, a relatively

high proportion of the total metal content may be adsorbed on the particulate matter, but

this depends on the factors mentioned above, and in general the status of a metal must be

considered in terms of a dynamic system.

Reactions at the sediment-water interface are relevant to the supply of metal ions to

natural waters. In the uppermost layer of a sediment there is a zone of intense biological

activity, centered on the bacterial breakdown of organic matter. This in turn causes

changes in pH, oxygen concentration and organic matter, and increases in the levels of

carbon dioxide. Metal ions may compete for bisulphide ions and organic matter of humic

acid or fulvic acid types. Some metals in recent sediments were found to be preferentially

625
bound to humic acid, while others were mainly associated with sulphide phases [1]^. Perhaps

the depletion of organic matter with consequent decrease in biological activity causes the

consolidation of the sediment, resulting in stabilization of pH and oxygen concentration.

Movement of metals to the sediment-water interface is thereby markedly reduced. A better

understanding of the supply of metal ions from sediments to water requires research on the

kinetics of reactions of metals in sediments. Such studies are essential for a proper

evaluation of the effects of metal-rich effluents discharged into natural waters. The

dilemma posed by the accumulation of metals in sediments cannot be completely resolved

until we have estimates of the rate at which a metal will move from the sediment into the

overlying water.

3. Conclusion

The analytical chemistry of metals in waters is difficult, and should take into

account geochemical aspects dealing with origin, composition, distribution and migration of

metals in aquatic systems. In sampling, it is essential to realize that the system is

dynamic and that geochemical cycles involving inputs from man's activities are imposed on a natural background. Such a notion is similar to the use of blank determinations in analysis.

Just as the level of a metal in a blank should be very low, so the level of metals in many

natural waters may also be low. The various factors already discussed are pertinent to

sampling. It is imperative that the analytical chemist is involved at all stages, namely

sampling, analysis and assessment of results, otherwise meaningful results for total con- tents and for species cannot be expected.

The dual role of many metals, namely essentiality and possible toxicity, can only be

properly assessed by careful and reliable analysis, and likewise legislation for waterquality parameters should rest ultimately on the work of the analytical chemist.

A plea is made for the consideration of the meaning of the content of a metal in water

and of the various factors governing the state of metals in water, so that data will be more realistic.

References

[1] Nissenbaum, A. and Swaine, D. J., Geoahim. Cosmoohim. Acta 40^, 809, 1976.

^Figures in brackets indicate the literature references at the end of this paper.

626
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

EFFECTS OF WATER SOLUBLE COMPONENTS OF REFINED OIL

ON THE FECUNDITY OF THE COPEPOD, Tigriopus Japoniaus

1 Colin Finney and Anthony D'Agostino

New York Ocean Science Laboratory

Montauk, NY 11954, USA

1. Introduction

Crude and refined oils spilled in open waters often remain unnoticed and their impact

unmeasured. However, when they occur in shallow waters and are wind-driven to shore the

biota of intertidal zones invariably becomes heavily impacted [1]^. Considerable information

has accumulated on the severity of kills resulting from massive spills [2,3,4,5]. There

is evidence that certain micro-organisms metabolize oil [6], but the photosynthetic ability

of phytoplankton [7] and sea weeds is impaired [8]. Likewise, there is abundant but

contrasting information on the tolerance of several intertidal invertebrates [9,10,11] but

no data on the effect of petroleum products on trophic relationships and fecundity of

marine organisms. Recently, Kontogiannis and Barnett [12] studied the acute toxicity of

"crude oil" on Tigri-opus oalifomicus. They concluded that the oil killed mainly by

preventing the diffusion of oxygen but speculated that the observed mortality may have

been caused also by toxic water soluble substances.

Tigriopus spp. are herbivorous harpaticoid copepods unbiquitous to intertidal zones

and tidal pools [13]. Most species are easily reared in the laboratory; one strain has

been kept for well over 15 years feeding on Tetraselmis maoulata and other micro-organisms

[14]. The relatively short duration of its life cycle and its consistent reproductive

behavior through many successive generations, make these species ideally suited for

bioassaying the effects of water soluble fractions of refined oils on growth and fecundity.

T. japoniaus was reared in a microcosm shared by two algal prey species and several

types of bacteria. This trophically linked assemblage was stressed with lethal and

sublethal concentrations of the water soluble fractions of fuel oils.

2. Materials and Methods

The water soluble fractions (WSF) of #2 and #6 American Petroleum Institute reference

fuel oils were extracted by dispersing twenty-five cm^ of the oils in 250 cm^ of sterile

charcoal -treated and filtered seawater. The mixtures were agitated at 25 strokes/min for

24 hours in a 4°C ambient temperature chamber to prevent bacterial degradation. The oil

and water mixtures were allowed to settle in separatory funnels for 24 hours at 4°C. The

water phases containing the WSF were recovered and filtered through 0.22p membrane filters

These stock solutions were considered to contain 100% of the extractable WSF and from

these appropriate dilutions were made for inclusion in the test media.

^Present address: College of Marine Studies, University of Delaware, Lewes, Delaware 19958

"^Figures in brackets indicate literature references at the end of this paper.

627
Details on the maintenance of the stock cultures of Tigriopus, its food algae, and the

criteria and procedures used for the standardization of the test method were published

elsewhere [15]. Briefly, gravid females of T. japonicus were placed into test tubes (screwcapped 20 X 125 mm, Pyrex) containing: 10 cm^ of a test medium, consisting of charcoaltreated sea water of salinity 30°/oo enriched with micronutrients , essential metals and

vitamins [15], the food algae Rhodomonas lens and Isochrysis galbana, and the appropriate

quantities of WSF of #2 and #6 fuel oil extracted in sea water.

A single dose response test consisted of 90 tubes, grouped into 6 sets of 15 replicates

each. One set of 15 tubes functioned as controls, the remaining 5 sets contained serial

dilutions of WSF. The parent females were removed as soon as the nauplii had hatched,

usually within two days. The resulting progeny was expected to develop into ovigerous

females within 21 days, corresponding to the mean generation time for T. japoniaus when

reared under optimal laboratory conditions [15]. The test period lasted 48 days and

allowed the development of two complete generations of Tigriopus. Three tubes from each

set were harvested on day 3, 6, 12, 24, and 48. The contents were fixed with a drop of 3%

(v/v) formaldehyde solution. Tigriopus was sorted into the different developmental stages

and counted.

The number of bacteria found in the microcosms varied between 6.1 x 10^ to 9.9 x 10^

cells/ml. Seven types were consistently identifiable by their characteristic colony

developed on 2215 Marine Agar, cell morphology, motility and gram staining.

The initial food algae inoculum gave 78 x 10^ cells/ml in the test media and it was expected to provide ad libitum feeding for the duration of the experiment provided that the

WSF did not inhibit further growth of the algae. Algae counts ranged from 5.1 x 10^ to

8.5 X 10^ cells/ml at the 48th day and end of the test period in both the controls and the

WSF stressed microcosms. The only significant deviations occurred in test tubes containing

high concentrations of WSF #6 fuel oil. In these the algal and bacterial counts exceeded

the above by one or more order of magnitude probably because there was no predation of

algae or bacteria since Tigriopus died shortly after inoculation.

In order to facilitate numerical treatment, tabulation and graphical representation of

the data, it was found convenient to group the 12 different developmental stages of

T. japonicus into 7 events, to which, in turn were assigned numerical values corresponding

to the fraction of the life cycle which they represented (table 1). This expedient permitted scoring of the populations found in the experimental tubes and the computation of a single developmental index value which simultaneously expressed both survival and growth [15].

Table 1

Values assigned to grouped developmental events in the life cycle of T. japonicus

Developmental events Code

Fractional value of

life cycle

1st filial generation Fi 0.00

Naupliar stages 1-3 Fi>Ni.3 0.09

Metanaupliar stages 4-6 0.20

Copepodite stages 1-5 Fi »Ci_5 0.37

Adult (copepodite stage 6) A 0.50

Gravid female I- 0.78

2nd filial generation F2 1 .00

Naupliar stages 1-3 F2>Ni.3 1 .09

628
3. Results

WSF of #2 fuel oil proved very toxic. At concentrations of 100 and 75% (v/v) the

females were moribund within 2-3 days. Similarly, at 50 and 25% although the gravid females

survived 3 or more days, no hatching took place. At 10% nauplii hatched successfully but

survival and growth was suppressed. After 48 days, the population was made up of mature

adults but there were no gravid females (Table 2).

Table 2

Development of T. japoniaus stressed with water soluble fractions of fuel oil

Elaspsed time in days

Culture Conditions 3 5 12 24 48

WSF^ of #2 oil , % (v/v)

10

^b

9 9 32 56 50

25

&c *d

50 f

75

100

WSF of #6 oil , % (v/v)

10 9 20 35 50 81

25 9 9 20 37 50

50 9 9 9 20 20

75 9 9 9 9 9

100 |d

Controls ±S.D. 9^±0 20±7 29+5 46±6 70±

^Water soluble fraction extracted in sea water.

'^Developmental index value, calculated, mean of 3 replicates.

^Nauplii unhatched, gravid female alive.

"^Gravid female dead, nauplii unhatched.

^Mean and ± S.D. of 30 replicates.

The WSF of #6 fuel oil was relatively less toxic. At 100% (v/v) gravid females aborted

the egg sacs within 3 days or less and died, at 75% the nauplii were able to hatch but

seldom developed past the third naupliar stage. Development stopped at the 4th or 6th

naupliar stage at 50% and continued to mature females at 25%. Tigriopus cultured with 10%

WSF of #6 fuel oil in the medium showed growth comparable or better than the controls, on

the 48th day nauplii of the F2 generation reached stages 4-6 while the control tubes

carried F2 nauplii in stages 1-3 (Table 2).

629
4. Discussion

Water soluble extracts of crude and refined oil are toxic to marine life. The pelagic

copepods Aoartia olausii and Oithona nana died within 3 to 4 days following exposure to Ipl

of oil per liter of sea water [10]. The response of barnacle larvae was less certain.

Smith [16] reported that crude oil had no discernible effect on the survival of nauplii of

Elminius modestus, but Spooner [17] found for this species a 1 hour TL50 value of 100 ppm.

Crude oil in concentrations of 0.5 to 5% (v/v) were toxic to oyster and sand shrimp.

Tigriopus japonious was less tolerant of the water soluble extract of the #2 than that

of #6 fuel oil. This response was expected since Notini and Hagstrom [18] showed that

light fuel oil spilled on an intertidal Fuous community and eliminated all gammarids while

a similar spill of heavy fuel oil only slightly reduced the number of epiphytic species

associated with this sea weed. The toxicity of the water extract of the #2 fuel oil is

attributed to its relatively high content of low boiling aromatic hydrocarbons. Fuel oil

#2 may give as much as 400-600 pi of WSF per liter of sea water [19]. A 48-hour extraction

of #6 fuel oil gave 5.53 ppm of WSF in sea water [20]. Obviously, both the type of oil as well as the method used for the extraction may influence the quantity of WSF in sea water.

Assuming that the extraction of #6 fuel oil, for this study, gave a concentration of

WSF of the same order of magnitude as that reported by Bender et al. [20] then the results

would indicate that Tigriopus could tolerate approximately 0.553 ppm of WSF without loss of

fecundity. The growth and fecundity of Tigriopus was dependent on the continued well-being

of the algae and bacteria sharing the same stressed microcosm, hence these also were tolerant

of the water extract of #6 fuel oil.

The significantly larger population densities of bacteria and algae observed in those

test tubes which were carrying concentrations of WSF lethal to Tigriopus suggest that the

algae and bacteria were more tolerant than Tigriopus.

The test method utilized in this study permitted the measurement of growth and fecundity

of an harpacticoid chronically stressed by sublethal concentrations of water soluble extracts

of fuel oil. Concomitantly, since the fecundity of the harpacticoid depended on the sus- tained availability of nutritionally adequate food algae and/or bacteria [14] then the

reproductive behavior of the herbivore reflected the viability of the prey species as associated entities in a trophically linked complex. Successful production of the F2

generation should be the principal and perhaps only criterion for the identification of

potentially toxic concentrations of pollutants.

[1] Straughan, D., Factors causing environmental changes after an oil spill, J. Petroleum

Technology, 250-254 (March 1972).

[2] Ottway, S. M. , A review of world spillages., 196-1971. Oil Pollution Research Unit,

Orielton Field Center, Pembroke, Wales (1972).

[3] Rutzler, K. , and Sterrer, W. , Oil pollution damage observed in tropical communities

along the Atlantic seaboard of Panama, Bioaaienae, 20 222-224 (1970).

[4] Bellamy, D. J., Clarke, P. H. , John, D. M. , Jones, D. , Whittick, A., and Darke, T.,

Effects of pollution from the Torrey Canyon on littoral and sublittoral ecosystems.

Nature, 216_, 1170-1173 (1967).

[5] O'Sullivan, A. J. and Richardson, A. J., The Torrey Canyon disaster and intertidal

marine life. Nature 2}±, 448-450 (1967).

5. Conclusion

References

630
[6] Ahearn, D. G. and Meyers, S. P., eds., The microbial degradation of oil pollutants.

Workshop, Georgia State University, Atlanta, PiJdI. No. LSS-SG-73-Ol, Center for Wetland

Resources, Louisiana State University, Baton Rouge (1973).

[7] Nuzzi , R. , Effects of water soluble extracts of oil on phytoplankton , in Proceedings

of Joint Conference on Prevention and Control of Oil Spills, American Petroleum

Institute, Washington, D. C, pp. 809-813 (1973).

[8] North, W. J., Neushul , M. , Clendenning, J., and Clendenning, K. A., Successive biological

changes observed in a marine cove exposed to a large spillage of mineral oil, in Symp.

Poll. Mar. Miaro-Org. Prod. Petro., Monaco, pp. 335-354 (1965).

[9] Horn, M. H., Petroleum lumps on the surface of the sea. Science, 168 , 245-246 (1970).

[10] Mironov, 0. G., Viability of some Crustacea in seawater polluted with oil products,

Zool. Zh., 68 (1), 1731-1735 (1969).

[11] Chipman, W. A. and Galtsoff, P. S., The effects of oil mixed with carbonized sand on aquatic animals, U. S. Fish and Wildlife, Special Report, 1_, 1-52 (1949).

[12] Kontogiannis , J. E. and Barnett, C. J., The effect of oil pollution on survival of

the tidal pool copepod, Tigriopus califomicus. Environ. Pollut., 4_, 69-79 (1973).

[13] Fraser, J. H., The occurrence, ecology, and life history of Tigriopus fulvus (Fischer),

J. Mar. Biol. Ass., UK, 20, 523-536 (1936).

[14] Provasoli, L. Conklin, D. E., and D'Agostino, A., Factors inducing fertility in

aseptic Crustacea. Helgolander wiss. Meeresunters , 20, 443-454 (1970).

[15] D'Agostino, A. and Finney, C, The effect of copper and cadmium on the development of

Tigriopus japonicus. Pollution and Physiology of Marine Organisms, J. Vernberg, ed.

,

Academic Press, NY, pp. 445-463 (1974).

[16] Smith, J. E., Torrey Canyon - Pollution and Marine Life, Cambridge University Press,

pp. 1-196 (1970).

[17] Spooner, M. , Some ecological effects of marine oil pollution. Proceedings, Joint

Conference on Prevention and Control of Oil Spills, American Petroleum Institute

(Washington, DC, 1969).

[18] Notini, M. and Hagstrom, A., Effects of oils on a Baltic littoral community as studied

in an outdoor model test system, ms Special Publication 409, 251-254, U. S. Department

of Commerce, Washington, DC (1974).

[19] Gordon, D. C, and Prouse, N. J., The effects of three oils on marine phytoplankton

photosynthesis. Marine Biology, 22 (4), 329-333 (1973).

[20] Bender, M. , Hyland, J., and Duncan, T., Effects of an oil spill on benthic animals in

the lower York River, Virginia, Marine Pollution Monitoring (Petroleum) , NBS Special

Publication 409, 257-259, U. S. Department of Commerce, Washington, DC (1974).

631

Part XIII. CHEMICAL CHARACTERIZATION OF AEROSOLS

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

A COMPARISON OF ELECTRON MICROSCOPE TECHNIQUES FOR THE

IDENTIFICATION OF ASBESTOS FIBERS

C. 0. Ruud, P. A. Russell, C. S. Barrett and R. L. Clark

Denver Research Institute, University of Denver

Denver, Colorado 80208, USA

1. Introduction

It is fairly well accepted that airborne and waterborne asbestos poses a potential

health hazard. Sources of asbestos in the environment include asbestos and other mineral

mining and beneficiation operations, manufacturing of asbestos-containing consumer products,

fugitive dust sources, such as unpaved roads, consumer use of asbestos-containing products,

and natural weathering of minerals. Natural asbestos minerals are found in many portions

of the country since asbestiform mineralization occurs in rocks that are ubiquitous to all

mountainous regions and to a large percentage of the earth's crust. Although many varieties

of asbestos minerals exist, only six are generally recognized as having commercial importance. These are chrysotile, which is a sheet silicate serpentine mineral, and amosite,

tremolite, actinolite, crocidolite and anthophyl 1 ite, which are chain silicate amphibole

minerals, and which originate in entirely different geologic formations from chrysotile.

Chrysotile constitutes about 95 percent of the world's production of asbestos.

Analytical techniques that have been proposed for the determination of concentrations

of asbestos in the environment include x-ray diffraction, differential thermo-analysi s

,

infra-red spectrometry and other methods which do not provide fiber size information. The

methods which provide size information are optical, scanning electron and transmission

electron microscopy. Because fibers are found in the natural environment that are often

less than a micron in diameter and because there is no definite information on toxicity

dependence with fiber size, any valid technique for asbestos fiber concentration determination must be able to provide reliable fiber species identification and accurate size

measurements. This limits the methods of examination to electron microscopy. These

include transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

The scanning electron microscope (SEM) with energy dispersive (ED) x-ray microanalysis

has been suggested as a means of identifying asbestos fibers. The SEM has the resolution

necessary to detect very small fibers, on the order of 100 angstroms in diameter; however,

even with an x-ray microanalysis attachment the identification of fibers is not positive

o and x-ray microanalysis requires a fiber at least 400A in diameter. SEM's with field

emission electron sources, however, may be able to produce adequate x-ray spectra from

smaller fibers.

Ambiguities of asbestos fiber identification may also arise from x-rays produced by

adjacent or adhering particles, from uncertainties in determining the exact chemical

composition of an asbestos mineral due to its chemical change in the environment or from

the fact that a given mineral can exist over a wide range of compositions. Furthermore,

the position and attitude of a fiber in the electron microscope can give apparent variations in composition.

On the other hand, many researchers consider the transmission electron microscope

(TEM) coupled with selected area electron diffraction (SAED) the only reliable method for

identifying asbestos fibers. This method has some disadvantages. However, its overriding

I 635
advantage is that for the most part it is specific with respect to the identification of

chrysotile or amphibole fibers, and it permits accurate size measurement of the fiber even when that size is on the order of a few hundred angstroms in diameter. The highly magnified shadowgraph obtained in transmission electron microscopy is nearly always an accurate

representation of the length and width or diameter of the fiber. Chrysotile fibers are usually circular bundles of fibrils or round single fibrils. Often the fibrils can be

distinguished by the fact that they are tubular and the hollow center can be seen in the

electron microscope image. This tubular appearance is unique for chrysotile but not

always present, and therefore if a fiber does not appear to be hollow, this does not rule

out that it is chrysotile. Amorphous material can be attached to the surface and fill the

tubes, thereby giving the appearance, as far as density is concerned, that the fiber is

solid. At any rate, it is well to have an identification method in addition to morphology

for chrysotile, and it is imperative for the amphibole minerals since non-asbestos materials

can appear in the electron microscope to be fibrous, i.e., they may have a 3:1 length-towidth ratio. Also many chain silicate non-asbestos minerals fracture in the same general

way as the asbestos minerals so that morphology does not lead to a reliable identification.

The most effective additional identification method is selected area electron diffraction.

2. Methods and Material

This laboratory has mainly been concerned with distinguishing fibrous submicroscopic

asbestos from non-asbestos minerals. In order to compare the relative ability of SEM with

ED and TEM with SAED to distinguish the asbestos and non-asbestos fibers, we selected

several silicate minerals from our collection of rather well characterized minerals.

These were ground to fine particles and in every case, even the non-asbestos minerals,

fibers were observed in the electron microscope. Six asbestos minerals and seven non- asbestos sheet and chain silicates were studied and the results from the two electron

microscope methods were studied.

3. Discussion

The SEM-ED elemental spectra of the asbestos minerals were indistinguishable from

certain of the non-asbestos minerals. In every case, the TEM-SAED patterns showed characteristic layer line and spacing patterns for the asbestos minerals which were always

distinguishable from the non-asbestos mineral. TEM-SAED analyses is therefore considered

the only technique capable of identifying and sizing asbestos particles collected in a low concentration environment.

A more complete treatment describing the procedures and results of this study will be

published in micron.

636
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

DETERMINATION OF REDUCING AGENTS AND SULFATE IN AIRBORNE PARTICULATES

BY THERMOMETRIC TITRATION CALORIMETRY

L. D. Hansen, D. J. Eatough,

N. F. Mangelson, and R. M. Izatt

Thermochemical Institute

Brigham Young University

Provo, Utah 84602, USA

1. Introduction

While extensive determinations of the' elemental composition of airborne particulates

have been made, very little information is available concerning the oxidation states of the

elements in these particulates. Also, very little is known about the compounds existing in

the particulates. Specific information on the oxidation states and compounds is extremely

important in an environmental sense because the behavior of an element in the environment

can differ markedly with oxidation state and with the other species with which it is combined. Toxicity and movement in the biosphere for example are both affected by the oxidation state and chemical combination of an element. Specifically we are interested in the

speciation, S, N, and As in airborne particulates.

2. Methods

For the studies we wished to do it was desirable to have a rapid, inexpensive, broadly

applicable, and sensitive method for the determination of specific species in airborne

particulates. The classical types of spectrophotometric methods do not lend themselves

well for this type of analysis because of the complexity of the samples involved. Electron

spectroscopy for chemical analysis (ESCA) has successfully been applied to this problem, but

it is slow, the equipment is expensive, and the procedure is complex enough that it cannot be

used as a routine method. Since there did not seem to be any other options available for a direct analysis of the solid particulate, we elected to extract the sample and then analyze

the supernatant solution. The extractant chosen was 0.1 M HCl , 0.005 M FeCla for reasons

that have been previously given elsewhere [1]^.

The analysis of the extractant solution for specific species could be accomplished by

a variety of methods, however, the one chosen should be as free as possible from interferences and should give unequivocal evidence of the identity of the species as well as quantitative data on the amount present. Thermometric titrimetry seemed to best fill these

requirements.

A thermometric titration of a 0.1 M HCl, 0.005 M FeCls extract of a sample of airborne

particulates with K2Cr207 solution provides enough data to identify (from the AH value for

the reaction) and quantitatively determine (from end-points) a number of reducing agents

with a sensitivity in the nanomole range. To date, we have done extensive studies on S(IV)

and Fe(II) and preliminary work on S(II), S°, As(III), alcohols, aldehydes and olefins [1].

In order for another substance to interfere with a species of interest it must have the

same AG and AH values for reaction with Cr207". No such interferences have been found.

^Figures in brackets indicate literature references at the end of this paper.

637
If species specific reagents are available, direct injection enthal pimetric determinations of non-oxidizable species can conveniently be combined sequentially with the thermometric titration to determine such species. We have used BaCl2 to determine sulfate sulfur

and have recently developed a method using sulfamic acid to determine nitrite nitrogen.

Details of the methods for S(IV) and sulfate have been published [1].

3. Results

Thus far we have identified and determined significant amounts of S(IV), sulfate,

Fe(II), As(III), Sb(III), and nitrite in samples of airborne particulates from various

locations [2,3]. We have also found a reducing agent in a sample from New York City of

unknown identity which is much more strongly reducing than Fe(II) and which reacts with

Cr207" with liberation of more heat than Fe(II). We conjecture that it is an oxidizable

nitrogen compound (not nitrite) which has not been detected as yet by any other method.

Being as powerful a reducing agent as it is, it almost certainly has implications for human

health.

We have done extensive work on the oxides of sulfur in airborne particulates collected

along the Wasatch front in Utah. A map of the area showing our sampling sites is given in

figure 1. High-Vol samples were collected from the workroom environment (reverberatnry

furnace and converter) at the smelter and at several sampling stations in Utah and SaTt

Lake valleys. The copper smelter located near the southern tip of the Great Salt Lake is

the major stationary source of sulfur oxides in this area. The major industrial sources of

metal containing aerosols are the copper smelter and a steel mill located near Provo, Utah.

638
Figure 1. High-vol collection sites, and major point sources <^ , in the study region.

The samples obtained at Magna, Kearns, Salt Lake City and Cedar Fort were collected on days when the wind direction was from the smelter towards the sampling site. The sample

obtained at Provo and at the two locations north of the steel mill were collected when the

wind direction brought the emissions from the steel mill across the sampling site. The

Springville and Ogden data are probably representative of normal rural and urban environments in the study area when not influenced by the plume from the two major metallurgical

facil ities.

Table I gives the results of our analyses of the High-Vol samples for sulfite and

sulfate. Samples of the particulates collected from inside the smelter have also been

analyzed by ESCA and S(IV), S(VI) and S(II) were shown to be present [5].

639
Table I. Concentration of Sulfite and Sulfate

in Collected Particulates.

1.

1- r— r- wt% SP

Location

Kilomi from

;

m

o

Part.

Size.M

SP*3 s(iv).

so^-

s(vi).

Smel ter 0 7 >7.0

1.1-7.0

<1.1

TSP

1450+690

680+750

500+630

2630+2000

2.1+0.4

1.9+0.5

1 .5+0.4

1.9+0.4

2.0+1.1

6.6+4.2

16.0+15.8

5.9+4.2

Magna 4 3 >7.0

M-7.0

<1.1

TSP

31+9

47+11

29+4

107+22

1.2+1.0

2.8+1 .0

2.1+0.9

2.3+1.0

17.7+1.8

30.7+5.2

28.9+9.8

26.2+4.1

Kearns 15 2 >7.0

1.1-7.0

<1.1

TSP

22+1

34+8

24+3

80+12

1.1+0.3

2.7+0.3

1.1+0.6

1.8+0.1

16.7+0.5

19.5+15.1

22.5+12.2

19.9+9.9

Salt

Lake

City

26 2 >7.0

1.1-7.0

<1.1

TSP

21+2

33+1

24+5

78+8

1.9+0.1

2.8+0.1

1.7+1.2

2.2+0.4

16.7+9.7

21.5+1.3

17.4+0.4

18.9+3.0

Cedar

Fort

44 1 >7.0

1.1-7.0

<1.1

TSP

21

28

15

64

1.3

2.5

1.7

1.9

19.9

46.5

19.1

31.4

Ogden 62 2 >7.0

1.1-7.0

<1.1

TSP

43+n

67+30

49+18

1 59+59

0.5+0.1

0.5+0.4

0.2+0.2

0.4+0.2

5.4+2.7

8.0+0.7

10.7+4.2

8.2+1.7

Steel

Mill

7' 3 >7.0

1.1-7.0

<1.1

TSP

30+9

25+1

15+4

70+13

0.9+0.3

1.2+0.3

0.9+0.2

1.0+0.1

12.9+2.8

43.1+6.6

17.5+2.8

24.8+2.6

Springville

20^ 1 >7.0

1.1-7.0

<1.1

TSP

59

46

49

154

0.42

0.48

0.39

0.43

6.6

35.8

19.8

19.5

^SP is the suspended particulates, either total, TSP,

or indicated size fraction.

^Kilometers from the steel mill-

(Note: Uncertainties in all Tables are standard

deviations.

)

640
The concentration of sulfite in the particulates apparently remains constant at about

2 percent as long as the majority of the particulates are derived from the copper smelter

plume. The sulfite concentration in aerosols produced by the steel mill facility is about

1 percent by weight. Background levels of sulfite for the area appear to be about 0.5

percent of the total particulate mass. In contrast, concentrations of sulfate in the

ambient air near the smelter are much higher than concentrations found in particulates

inside the smelter facility (near the converter and reverberatory furnaces) and are comparable to levels found in ambient aerosols influenced by the steel mill emissions. The

background levels of sulfate (Ogden and Springville) appear to be highly variable.

Sulfite ion has been shown to form complexes with Fe^"*", Hg2+, Ag"*", and Cu^"*" in aqueous

solution [6,7]. The mos^_stable complex is formed by Fe^"*". An excellent correlation

exists between Fe and SO3 concentrations in the particulates collected from inside the

smelter. A Mossbauer spectrum of a composite sample indicates the iron is present in the

trivalent state. These data suggest Fe(III) and SO3" form a complex in the aerosol. The

reaction of SO2 gas with metal oxides in particulates to form metal sulfite complexes may

be an important reaction in terms of sulfite toxicity since it provides a mechanism by

which sulfite, together with metal ion catalysts can be deposited deep in the lungs.

4. Summary

To summarize our work on sulfur oxide speciation, sulfite species which are stable to

air oxidation have been shown to exist in aerosols produced by a copper smelter. The data

suggest the sulfite exists as an Fe(III) complex. Formation of these sulfite complexes is

not correlated with either SO2 gas or sulfate. There have been ambiguities in past epidemiological studies on the combined toxicologic effects of SO2 and particulates. These

differences may, in part, be due to differences in the actual sulfur species present in the

aerosols, suggesting that complete sulfur speciation in aerosols and the toxicity of newly

identified species, such as the metal-sulfite complexes, should be investigated further.

Samples of flue dusts from the flue pipes of two copper and three lead smelters have

also been analyzed for reducing agents and sulfate by the methods given above [4]. The

results are given in Table 2. Sulfite and Fe(II) were identified in the dust samples from

both copper smelters and in the sample from one lead smelter. As(III) was identified in one sample only. The assignment of the species in samples 2 and 3 which is oxidized by

Cr207 with a aH value of -11.5 kcal/eq is not confirmed by other measurements but is

believed to be Sb(III).

In summary, thermometric methods of analysis are rapid, inexpensive, and broadly

applicable to speciation studies of environmental samples.

This work was supported in part by the Energy Research and Development Administration

and by the National Institute for Occupational Safety and Health.

641
Table 2

Species Analyzed Thermometrically in a 0.1 M HCl , 2.5 mM FeCla

Extraction of Each Sample, Given as wt% of the Total Sample

ome 1 ter

Type 5(1V; as bU3 as oUi+ A e- ^ T T T ^ MS ^ 1 i 1 )

Cu 1.54 ± 0.10 5.0 ± 1.9 2.1 ± 0. 2 11.7 ± 0.7 n.d.

Cu 0.69 ± 0.10 15.5 ± 0.5 3.5 ± 0. 3 n.d.

a

n.d.

Pb n.d. 7.5 ± 0.5 n.d. n.d. 1.35 ± 0.13

12.9 ± 0.43

Pb n.d. 1.7 ± 0.7 n.d. n.d. 1.14 ± 0.13

Pb 0.85 ± o.n 6.9 ± 3.0 2.3 ± 0 4 n.d. n.d.

^n.d. = not detected above background levels.

References

[1] Hansen, L. D. , Whiting, L., Eatough, D. J., Jensen, T. E., and Izatt, R. M., Anal.

Chem. 48, 634 (1975).

[2] Smith, T. J., Eatough, D. J., Hansen, L. D. , and Mangelson, N. F., Bull. Environ.

Cont. Tox. , in press.

[3] Hansen, L. D. , Eatough, D. J., Mangelson, N. F., Jensen, T. E., Cannon, D., Smith, T. J.,

and Moore, D. E., Proa. Int. Conf. Environ. Sensing Assessment, Las Vegas, Nev.,

September 1975. Paper #23-2.

[4] Eatough, D. J., Mangelson, N. F., Hill, M. W., Izatt, R. M. , Hansen, L. D., and

Christensen, J. J., Final Report to NIOSH on Analysis of Copper and Lead Smelter

Dust Samples, 19 March 1976.

[5] The ESCA spectra were obtained by Robert G. Meisenheimer, Lawrence Livermore Laboratory,

Livermore, California.

[6] Hansen, L. D., Eatough, D. J., Whiting, L., Bartholomew, C. W. , Cluff, C. L., Izatt,

R. M., and Christensen, J. J., Transition Metal-SOs' Complexes: A Postulated Mechanism

for the Synergistic Effects of Aerosols and SO2 on the Respiratory Tract, Trace

Substances in Environ. Health, VII., University of Missouri Press, 1974, p. 393.

[7] Sillen, L. G. and Martell, A. E., Stability Constants of Metal-Ion Complexes, Special

Publication No. 17, The Chemical Society, London, 1964.

642
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

DETERMINATION OF ACIDIC AND BASIC SPECIES IN PARTICULATES

BY THERMOMETRIC TITRATION CALORIMETRY

D. J. Eatough, L. D. Hansen, R. M. Izatt and N. F. Mangelson

Thermochemical Institute

Brigham Young University

Provo, Utah 84602, USA

1. Introduction

Recent reports on studies of pH of rain water in the northeastern United States [1-3]^

and in isolated storm events around fossil fuel burning stations [4-6], a copper smelter

[7] and an urban center [8] indicate SO2 (and presumably NOx) [7,9] emissions result in an increase in the acidity of precipitation. In these studies there is a direct relationship

between measured sulfate concentration and pH, although the impact of the point source compared to ambient levels on both sulfate and pH is not always predominant [5]. The role

SO2, H2SO4 and related particulate emissions may play in long range transport of acidity is

not well understood [9-13]. While it is often assumed that H2SO1+ plays a primary role in

determining the acidity of such precipitation, [1,2,9] a recent study by Frohliger and Kane

[11] indicates that acid rains in the northeast are buffered by a weak acid and not by

H2S0it. They assume that only one buffering agent is present although the agent is not

identified by their study. Total acidity and pH measurements by Brosset [13] in precipitation samples collected over Sweden are interpreted to show hydrolysis of Al^"*" and/or Fe^"*" controls acidity of these samples in spite of high SOl concentrations.

Acidic species in particulates are not much better understood. Raman spectroscopy,

[14] thermal degradation techniques, [15,16] and the conversion of H2S0tt to a perimidylammonium sulfate [15] have been proposed for the determination of sulfate, bisulfate and

sulfuric acid species but have not been shown to be applicable to the study of ambient

aerosol species. The most widely used techniques for identification of acid sulfate

species in the environment involve the semi-quantitative sensing of neutral and acid sulfate

aerosols by nephelometric [17,18] and infrared [19] techniques, and the quantitative extraction of H2SO4 from NaHSOi+ and NH1+HSO1+ by organic solvents [20,21]. These results suggest

that aerosols originating from the coastal areas are acidic in nature, while those originating from continental or urban sources are weakly acidic or neutral with respect to

HSO4 species. Reported studies, however, do not investigate the acidity of particulates

beyond these sulfate species. Thus it appears that techniques which give more detailed

information for the study of acidic species in both particulates and precipitation would be

valuable. We report here initial studies on the development of one possible technique.

2. Procedure

We have completed preliminary studies on acidic and basic species in flue dust samples

collected from two copper and three lead smelters and a single Hi-Vol New York City particulate sample. Acidic and basic components of the aqueous extracts (1 mg sample/ml H2O) of

these samples were characterized as follows:

a. The pH of the water extract solution was measured.

b. Parallel pH and thermometric titration data were obtained for all samples by titrating

aliquots of the water extract with HC10i+ to pH = 1.5 and with NaOH to pH = 12.5.

^Figures in brackets indicate the literature references at the end of this paper.

643
c. The pK and aH values were determined for proton ionization of the species titrated at

the pH of the initial extractant solution using a published technique [22]. In addition, the pK and AH values for all proton ionizable species were determined for some samples. Based on these values species were identified where possible [23-25].

d. Cold water soluble sulfate was also determined by acidifying the water extract to

0.1 M HCl and determining sulfate thermometrical ly by BaSOi+ts) precipitation [26].

3. Results

The combined pH and calorimetric acid and base titration data allow the identification

of all weakly acidic species in the aqueous extracts of the samples. As the data are complex for the acidic and neutral flue dust samples, the available information is illustrated only for a basic flue dust sample and the New York City particulate sample. The pH and

calorimetric titration curves for the aqueous extract of the flue dust sample, Lead-1 , are given in figure 1 and the data are summarized in table 1. The assignments are based on comparisons with available literature data [23-25] and on x-ray fluorescence spectroscopic

analyses for Ca and higher atomic number elements. The concentration of Ca^"*" is consistent

with the elemental data. The assignment of the group with pK = 7.8 and AH-j = -0.2 to

phosphate is reasonable. It should be noted that the pH titration curve in the region from

pH = 9 to pH = 5 for sample Lead-1 is very different from that for the more acidic flue

dust samples. Several species with AH-j values ranging from 6 to 12 kcal/mol are seen for

the acid samples. These species are transition metal ions which hydrolyze in this pH

region. Such species are not discernable in the acid-base data for Lead-1 and are indeed

not present as confirmed by the elemental analysis.

Table 1

Species identified in the acid-base titrations of the aqueous extraction

of flue dust sample lead-1

Probable

species pK

Ca2+ 10.6

PO^" 7.8

30^. PO^" <3.6

AHj (kcal/mol) mmol/g wt%

13.1 1.26 4.9 ± 0.5

-0.2 0.31 2.9 + 0.5

0.0 2.5

644
NANOEQ/mg OF SAMPLE

Figure 1. Calorimetric and pH titration data for the aqueous extract of sample Lead-1

lead smelter dust.

The most striking result from the aqueous extraction studies is the apparent wide

range of acidities in the dust samples as summarized in table 2. The two copper smelters

give an acidic pH for the extraction. Large quantities of metal ions are also extracted.

This is apparent from the x-ray fluorescence analyses and was also verified by the acidbase titrations where hydrolysis of Fe(III), Ca(II), Pb(II), Zn(II) and Fe(II) was readily

apparent. Based on the determined pK and AH values, the species which act as buffers for

the extraction solution at the extraction pH are probably hydrolyzed Fe(III) and Al(III)

species. The extraction pH values for the lead smelters vary from acidic to basic. It is

most probable that the species which control the pH of the extraction solutions for lead

dust samples 1, 2, and 3 are Ca(II); Fe(III) and H2SO4; and Pb(II), Zn(II), and Cu(II);

respectively.

645
Table 2

Species analyzed in an aqueous extraction of flue dust samples

Acid buffer group at extraction pH

Smelter type Extraction pH mmol/g £K AH(kcal/mol

)

Copper - 2 4.23 0.10 3.9 -1.3

Copper - 3 4.39 5.09 <3 -0.9

Lead - 1 8.9 1 .26 10.6 13.1

Lead - 2 3.79 5.13 3.7 -0.9

Lead - 3 7.2 0.46 7.2 8.6

Elemental concentrations determined by x-ray fluorescence, wt%

Ca Fe Cu Zn Pb As Cd

Copper - 2 0.8 0.9 7.4 2.6 n.d.^ 1.9 n.d.

Copper - 2 0.8 0.8 2.6 1.6 0.2 5.9 n.d.

Lead - 1 3.0 0.02 0.03 0.04 n.d. n.d. n.d.

Lead - 2 0.9 0.4 0.3 1.0 1.2 0.6 1.0

Lead - 3 0.1 0.2 0.8 0.4 1.8 0.07 0.9

n.d. -• not detected above background or sensitivity level

s

It has been previously reported that benzaldehyde will selectively extract H2SO1+ in

aerosol samples [20,21]. Possible presence of acid sulfate species in sample Lead-2 was checked by extracting 35 mg of the sample with 2 ml of benzaldehyde. The insoluble material was then removed by centri fugation and 1.0 ml of the benzaldehyde was extracted with

10.0 ml of H2O. The resulting aqueous solution was then analyzed for total sulfate and for

acid species by calorimetric titration with NaOH. The calorimetric titration curve indicated strong acid (aH[\j - -12.9 ± 1.2 kcal/mol) and two weak acids (aH[^ = -5.7 ± 1.2 and

-1.0 ± 0.7 kcal/mol) were present. The weak acids were identified as Cu^"*" and/or Zn^*

and Ca2+ based on the measured AHf^ values for reaction of these ions with NaOH. The

results of these determinations, together with data from the aqueous extraction of the same sample are summarized in table 3. Twelve percent of the sulfate in the sample was extracted by benzaldehyde. Mass balance from the data in table 3 indicates this sulfate was extracted as bisulfate salts of Ca^^ and Cu^^ and/or Zn2+. These bisulfate salts quantitatively account for the observed pH (table 2) in the aqueous extraction. There is,

therefore, no evidence for H2SO4 in the sample. Strong acid was not extracted from any of

the other flue dust samples by benzaldehyde.

Table 3

Comparison of results for SO4', H+, Ca2+ and Cu^^ + Zn2+ in H2O and benzaldehyde

extractions of lead-2 smelter dust sample, given in mmol/g of sample

Solvent soil

^ 2x(Cu2+ + Zn2+) 2xCa^+

H2O 1.79 ± 0.08 --- 0.38 ± 0.10 0.58 ± 0.04

Benzaldehyde 0.22 ± 0.03 0.22 ± 0.04 0.06 ± 0.02 0.13 ± 0.02

646
The calorimetric and pH acid-base titration curves for the titration of an aqueous

extract of the New York City particulate sample are given in figure 2 and the results

obtained from these data plus independent determinations of sulfate are summarized in table

4. The initial pH of the extract solution was 5.2, indicating the aerosol is not strongly

acidic. The elemental data, table 4 and table 5, also indicate that the particulate sample

does not contain sulfate as an ammonium or a transition metal salt. The low levels of V and Ni suggest the sample does not contain emissions from oil burning point sources. The

increased solubility of iron and lead in the acid as compared to the aqueous extract is the

only substantial change in elemental extraction noted with the marked change in acidity of

the extractant solution. The extraction pH of this sample is controlled by the carboxylic

acid groups. The data also indicate that this sample would not have much buffering capacity

if exposed to moderate levels of acids, i.e., SO2 or NOxThis work was supported in part by the Energy Research and Development Administration

and by the National Institute for Occupational Health and Safety. Appreciation is expressed

to T. J. Kneip, New York University for furnishing the New York particulate sample.

Figure 2. Calorimetric and pH titration data for the aqueous extract of a New York City

particulate sample.

647
Table 4

Acid and base species determined in the aqueous extract (1 mg sample/ml H2O)

of a New York City particulate sample

Species

Carboxylic acid

Phenol and

Ammoni a

Al kyl amine

sor

HSO^, H2SO4

AHj (kcal/mol)

0.85 ± 0.07

9.10 ± 0.5

12.65 ± 0.05

4.7

9.3

10.9

ymol/g sample

50 ± 10

23 ± 5 23 ± 5

120 ± 80

1340

not present

wt%

0.04 ± 0.01

12.9

Table 5

«

Sulfate and sulfite values determined thermometrical ly and elemental values determined

by x-ray fluorescence spectroscopy for aqueous and O.IM HCl extractions of the

New York City particulate sample, given as wt% of the total sample

S{IV) S{VI) S Sol vent as SO^ as SOi^ as SOt^

H2O

0.1 M HCl 0.16

12.9

9.8

17.2

17.5

Ca V Mn Fe Ni Cu Zn Pb Br

1.80 0.03 0.03 0.03 0.04 0.04 0.35 0.17 0.36

2.09 0.07 0.04 3.75 0.05 0.25 0.39 2.16 0.58

References

[1] Position Paper on Regulation of Atmospheric Sulfates, U.S. Environmental Protection

Agency, EPA-450/2-75-007, (Sept., 1975).

[2] Likens, G. E., and Bormann, F. H., Acid Rain: A Serious Regional Environmental

Problem, Science, 184, 1176 (1974).

[3] Cogbill, C. V., and Likens, G. E., Acid Precipitation in the Northeastern United

States, Water Resour. Res., 1_0, 1133 (1974).

[4] Li, T. -Y., and Landsberg, H. E., Rainwater pH Close to a Major Power Plant, Atmos.

Environ., 9, 81 (1975).

[5] Granat, L., and Rodhe, H., A Study of Fallout by Precipitation Around an Oil -Fired

Power Plant, Atmos. Environ. 7_, 781 (1973).

[6] Jones, H. C, Tenn. Valley Auth. Rep. E-EB-74-1 (1974).

[7] Larson, T. V., Charlson, R. J., Knudson, E. J., Christian, G. D., and Harrison, H.,

The Influence of a Sulfur Dioxide Point Source on the Rain Chemistry of a Single Storm

in the Puget Sound Region, Water, Air, Soil Pollut., 4, 219 (1975).

[8] Hogstrom, U., Residence Time of Sulfurous Air Pollutants from a Local Source During

Precipitation, Ambio, 2_, 37 (1973).

[9] Likens, G. E., and Bormann, F. H., Science, 188, 958 (1975).

[10] Newman, L., Science, 188, 957 (1975).

648
Frohliger, J. 0., and Kane, R. , Precipitation: Its Acidic Nature, Science, 189 , 455

(1975).

Tabatabai , M. A., and Laflen, J. M. , Nitrogen and Sulfur Content and pH of Precipitation in Iowa, J. Env. Qual., 5_, 108 (1976).

Brosset, C, Air-Borne Acid, Ambio, 2, 2 (1973).

Stafford, R. G., and Chang, R. K. , Absolute Raman Scattering Cross Sections of Sulfate

and Bi sulfate and Their Application to Aqueous Aerosol Monitoring, International

Conference on Environmental Sensing and Assessment, 23-5, Las Vegas, NV, (Sept. 1975).

Maddalone, R. F., Thomas, R. L., West, P. W. , Measurement of Sulfuric Acid Aerosol and

Total Sulfate Content of Ambient Air, Env. Sci. Tech., 1_0, 152 (1976).

Huntzicker, J. J., Izabelle, L. M., and Watson, J. G., The Continuous Monitoring of

Particulate Sulfate by Flame Photometry, International Conference on Environmental

Sensing and Assessment, 23-4, Las Vegas, NV (Sep. 1975).

Vanderpol , A. H., Carsey, F. D., Covert, D. S., Charlson, R. J., and Waggoner, A. P.,

Aerosol Chemical Parameters and Air Mass Character in the St. Louis Region, Science,

190 , 570 (1975) Atmos. Environ., 8, 1257 (1974).

Charlson, R. J., Vanderpol, A. H., Covert, D. S., Waggoner, A. P., and Ahlquist, N. C,

Sulfuric Acid - Ammonium Sulfate Aerosol: Optical Detection in the St. Louis Region,

Science, 184, 156 (1973).

Cunningham, P. T., and Johnson, S. A., Spectroscopic Observation of Acid Sulfate in

Atmospheric Particulate Samples, Science, 1 91 , 77, 1976.

Leahy, D., Siegel, R., Klotz, P., and Newman, L., The Separation and Characterization

of Sulfate Aerosol, Atmqs. Environ., 9, 219 (1975).

Tanner, R. L., Leahy, D., and Newman, L., Separation and Analysis of Aerosol Sulfate

Species at Ambient Concentration Levels, 1st Chemical Congress of the North American

Continent, Mexico City, (December 1975).

Izatt, R. M., Hansen, L. D., Eatough, D. J., Jensen, T. E., and Christensen, J. J.,

II. Recent Analytical Applications of Solution Calorimetry, in the book Analytical

Calorimetry, Vol. 3, Plenum Press, N.Y. (1974).

Sillen, L. G., and Martell, A. E., Stability Constants of Metal-Ion Complexes,

Special Publication No. 17, The Chemical Society, London, (1964).

Christensen, J. J., Eatough, D. J., and Izatt, R. M., Handbook of Metal Ligand Heats

and Related Thermodynamic Quantities, Marcel Dekker, New York, (1975).

Izatt, R. M., and Christensen, J. J., Heats of Proton Ionization, pK, and Related

Thermodynamic Quantities, in Handbook of Biochemistry, 2nd edition, H. A. Sober, Ed.,

Chemical Rubber Co., Cleveland, OH (1970).

Hansen, L. D., Whiting, L., Eatough, D. J., Jensen, T. E., and Izatt, R. M. , The

Determination of Sulfur(IV) and Sulfate in Aerosols by Thermometric Methods,

Anal. Chem., 48, 634 (1976).

649

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1 977).

SINGLE-PARTICLE ANALYSIS OF THE ASH FROM THE DICKERSON COAL-FIRED POWER PLANT

John A. Small 1 and William H. Zoller

Department of Chemistry

University of Maryland

College Park, Maryland 20740, USA

1. Introduction

The scanning electron microscope equipped with a Si-Li x-ray detector is becoming

increasingly important in the identification and analysis of particulate emission from

anthropogenic sources [1-3]^. To date, most of the work in single-particle analysis of

emission sources has been confined to morphological studies and qualitative elemental

analysis. In addition, these studies have not included a detailed investigation of the

emissions from a single source. This paper contains the results of a single-particle study

of both the exhaust system and plume of the Dickerson power plant in western Maryland. The

samples were collected from four different locations in the exhaust system of the plant and

at a distance range of 0-5 km in the gas plume. The different samples were analyzed by

scanning electron microscopy and x-ray microanalysis for particle morphology and semiquantitative elemental composition [4]. In addition the samples were also analyzed by

instrumental neutron activation analysis for bulk element composition.

The Dickerson power plant is operated by the Potomac Electric Power Company and is

located approximately 50 km northwest of Washington, DC. The locations of the different

sampling ports are shown in fig. 1. The plume particulate samples were collected with an instrumental aircraft.

2. Morphological Study

The results from the morphological study of the different ash samples are shown in

figures 2-8. Figure 2 Is a secondary electron image of a particle identified as partially

burned coal. This particle shape was observed in all in-plant samples and was concentrated

in the bottom and in the economizer ashes where it accounted for 75 percent and 30 percent of

the observed particles, respectively. In addition, this particle type accounted for 5 percent of the precipitator ash and over 80 percent of the particles collected on the first

stages of the in-stack impactor. The particle size was generally larger than 100 ym. The

partially burned coal forms when the pulverized coal remains in the burners long enough to

melt the alumino-silicate minerals. The material was mainly aluminum and silicon with

small amounts of potassium, calcium, iron, and titanium.

^Current Address: Analytical Chemistry Division, National Bureau of Standards,

Washington, DC 20234, USA.

^Figures in brackets indicate literature references at the end of this paper.

^Elements lighter than atomic number 11 cannot be analyzed using the solid state

detector.

651
-stock

Dickerson Generating Station

Figure 1. Locations of the different sampling ports.

Figure 2. A secondary electron image of a particle identified as partially burned coal.

652
Figure 3. An example of ash particle formed from the high-iron regions of the coal. This

particle type is characteristic of particles which are mainly iron with very small amounts

of silicon and aluminum.

Figures 4 and 5. Examples of particles that are formed from regions of the coal which

are high in iron and have modest amounts of silicon and aluminum.

653
Figure 6. Secondary electron image of a smooth sphere.

2|jnn

Figure 7. On in-plant ashes, this material

was in the form of amorphous surface

structures on large ash particles.

Figure 8. In this plume sample, the

material was more crystalline in struc

ture and often formed individual

particles.
Figure 9. Plots of the average elemental

concentrations normalized to aluminum

for the various collection locations.

B.A £A PPT SP P COLLECTION LOCATION

Figures 3, 4, and 5 are examples of ash particles which are formed from the high-iron

regions of the coal such as pyrite inclusions. The particle type shown in figure 3 is

characteristic of particles which are mainly iron with very small amounts of silicon and

aluminum. The particles are generally spherical in shape with diameters greater than 50 ym

and were found mainly in the economizer ash. The shape also was observed to some extent

in the bottom and in the precipitator ash samples. The surface texture is the result of

the rapid cooling and solidification of the material in the flue-gas stream.

Figures 4 and 5 are examples of particles that are formed from regions of the coal

which are high in iron and have modest amounts of silicon and aluminum. These particles

are spherical with diameters larger than 10 ym and were found primarily in economizer and

precipitator ash samples. During the solidification of these particles, the light element

fraction separates from the iron matrix so that the main particle is predominantly iron and

the surface structure is predominantly aluminum and silicon.

Figure 6 is a secondary electron image of a smooth sphere. This shape was the most

predominant shape observed in the field samples. It was observed most often in the precipitator ash, stack ash and plume ash where it accounted for 80 percent, 80 percent, and

100 percent respectively of the observed particles. The size variation of the particles

was from 0.5 ym to over 100 ym in diameter. The elements Al , Ca, Fe, K, S, Si, and Ti were determined by x-ray analysis of the spheres. The particles are formed from the melting and

solidification of the silicate mineral phase of the coal.

The final morphological classification is shown in figures 7 and 8. This classification

was relatively rare, accounting for less than two percent of the total number of particles

observed. The material was Ca and S with smaller amounts of Si, Al , K, and Fe. On inplant ashes, this material was in the form of amorphous surface structures on large ash

particles (see fig. 7). In the plume samples shown in figure 8, the material was more crystalline in structure and often formed individual particles. This shape may be the

result of sulfur dioxide gas reacting with ash particles to form calcium sulfate crystals

which grow as the material ages in the plume.

655
3. Elemental Analysis

^

The results from x-ray microanalysis of the different samples were used in three ways.

First, they were used to determine the variability in composition of the different ash

particles. Second, they were used to study elemental distributions and correlations in the

ashes collected at the different locations in the plant and plume. Finally, the results

from single-particle analysis were compared to the results from bulk-sample analysis by

instrumental neutron activation.

The elemental concentration of the different particles was determined by comparing the

characteristic x-ray peaks for the particles to the peaks generated by a series of flat

polished standards. The resulting ratio was then corrected for atomic number effects,

matrix absorption and secondary fluorescence [5]. The oxygen concentration was determined

by difference. The resulting concentration estimates are semi -quantitative since no corrections were made for particle shape and size.

The elements observed in the ash samples include Al , Ca, Fe, K, Mg, P, Si, and Ti

.

The frequency of occurrence for the different elements is given in table 1. It shows that

almost all particles have Si, Al , and Fe, about half have K, Ti , S, and Ca and only a few

have Mg and P. The variation in elemental concentration of the different ash particles is

shown in table 2. This table separates the particles by collection location and reports an average and standard deviation. The different elements, observed in particles collected

from that location, indicate that on a single-particle basis the ash samples are relatively

inhomogeneous

.

Table 1

Frequency of occurence of detectable amounts of various elements observed by

SEM/X-Ray analysis

Element

Si

Al

Fe

K

Ti

S

Ca

Mg

P

Percent of particles

97

97

89

56

55

53

48

13

9

Table 2

Average concentration (in wt. %) + standard deviation for elements analyzed by SEM/XRF

Sample

Bottom Ash

Electrostatic

Precipitator

Ash

Suspended

Particles

Airplane

Si Al K Ca Ti Fe

6.7+ 5.6 5.3±3.6 0.4 ±0.5 0.7 ±1.0 0.48±0.34 0.52±0.28 14.0±24.0

Economizer Ash 12.0±14.0 7.1±4.0 2.5 ±2.3 0.76±0.48 0.64±0.19 56.0±29.0

9.5± 5.2 7.3±3.8 2.4 ±2.9 1.9 ±1.1 1.6 ±1.4 0.58±0.52 8.0±13.0

13. 0± 6.0 9.5±4.0 0.88±1.2 1.1 ±0.5 0.70±0.40 0.57±0.36 4.7± 3.3

9.2± 5.8 5.9±3.1 1.5 ±1.9 1.0 ±1.2 1.3 ±1.4 0.46±0.42 2.6± 2.3

656
The distribution of the different elements is shown in figure 9 which contains the

plots of the average elemental concentrations normalized to aluminum for the various

collection locations. B.A. is bottom ash, port one (see fig. 1), E.A. is economizer ash,

port two, ppt is electrostatic precipitator ash, port three, S.P. is suspended stack

particles, port four and P. is plume ash. All the elements studied except iron have a minimum value for the aluminum ratio in the suspended stack particles and a maximum value

for both the bottom and plume ash samples. The plots for the elements potassium and

possibly calcium have a second minimum in the economizer ash and decrease steadily to a minimum in the plume ash.

In addition to elemental distributions, the concentrations can also be used to study

correlations between elements. The most consistent correlation is between silicon, aluminum

and possibly titanium. This correlation is expected since these elements are all associated

with the mineral phase of the coal. Calcium and sulfur also correlate fairly well but only

in the precipitator, stack and plume ash. This may reflect the growth of calcium sulfate

on particle surfaces.

A comparison of results from x-ray microanalysis and macroanalysis by instrumental

neutron activation is given in table 3 for the elements Al , Ca, Ti , and Fe. The absolute

concentrations are substantially different for the two methods of analysis which reflects

the uncertainty in single-particle quantitative analysis. The two techniques with concen- tration values normalized to aluminum are in much better agreement. Most of the values

agree within the uncertainty limits of the techniques and elemental trends such as the high

Fe/Al ratios for the economizer ash are observed in both analytical methods.

Table 3

Values for elemental concentrations and Al ratios from INAA and SEM/XRF analyses

Element

Concentrations in wt. %

INAA X-ray

Al ratios

INAA X-Ray

Bottom ash

Al

Ca

Ti

Fe

12.0

< 0.96

0.60

9.3

6.7

0.48

0.52

14.0

0.08

0.05

0.8

0.07

0.09

2.0

Economizer ash

Al

Caa

Ti

Fe

9.4

0.70

15.0

7.1

0.64

56.0

0.07

1.6

0.09

8.0

Precipitator ash

Al

Ca

Ti

Fe

13.0

0.96

0.69

12.0

7.3

1.6

0.58

8.0

0.07

0.05

0.92

0.04

0.08

1.1

657
Table 3 (continued)

Stack ash

Al

Ca

Ti

Fe

4.0

0.4

0.24

2.3

9.5

0.70

0.57

4.7

0.1

0.06

0.58

0.10

0.06

0.47

Plume ash

Al

Ca

Ti

Fe

b

b

b

b

b

b

b

b

0.07

0.05

0.43

c 0.10

0.078

0.44

c

^No Ca values from SEM/XRF.

'^Absolute concentrations could not be compared since airplane values are in yg/m^.

""Values from background-corrected airplane plume filter APF28 taken 0-8 km from

Dickerson stacks.

4. Concl usion

The results from the single particle study of the Dickerson power plant provided

information on particle shape and origin, sample homogeneity and elemental composition

which was not available from bulk analysis. In addition, for a select number of elements,

the semi-quantitative analysis of a relatively small number of ash particles was used to

predict elemental trends and correlations which were in good agreement with results from

bulk analysis. In these applications, scanning electron microscopy is an excellent complimentary technique to bulk analysis for the investigation of anthropogenic emission sources.

[1] Waller, R. E., Brooks, A. G., Cartwright, J., An Electron Microscope Study of Particles

in Town Air, J. Air Wat. Poll. 1_, 799 (1963).

[2] McCrone, W. C, Delly, J. G. , The Particle Atlas, 3 2nd ed., (Ann Arbor Science

Publishers, Inc., Ann Arbor, 1973).

[3] Moyers, J., Progress Report, ATM Sciences Laboratory, Dept. of Chemistry, University

of Arizona, (1974).

[4] Small, J. k. , An Elemental and Morphological Characterization of The Emissions from

the Dickerson and Chalk Point Coal-Fired Power Plants, Ph. D. Thesis, University of

Maryland (1976).

[5] Colby, J. W. , Magic IV A Computer Program for Quantitative Electron Microprohe Analysis,

Unpublished report. Bell Telephone Laboratories, Allentown, Pennsylvania (1974).

References

658
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977).

LASER-RAMAN MONITORING OF AMBIENT SULFATE AEROSOLS

R. G. Stafford, R. K. Chang, and P. J. Kindlmann

Yale University

Department of Engineering and Applied Science

New Haven, Connecticut 06520, USA

1. Introduction

Presently there is a need for an analytical instrument which is capable of accurately

measuring the concentration of sulfates in aerosols at ambient conditions. Ambient sulfate

concentrations have ranged from 2 ug/m^ to 54 yg/m^, depending on the location [l,2]i.

The major sulfur constituents in aerosols are believed to be (NH[+)2S04 and H2S0[t [2-4].

The greatest percentage of these compounds lies in the accumulation mode (0.1 - 1 ym

diameter) of an aerosol size distribution [5].

Experimental methods now employed for the measurement of aerosol pollutants involve a collection phase where interparticle reactions may occur on the collecting surfaces,

especially since the particle concentrations are considerably enhanced by the collection

process [6,7]. The data resulting from these methods are therefore not necessarily indicative of the original aerosol composition. Considering the chemically reactive nature of

atmospheric aerosols and gases, a method which can measure in situ the concentration of

sulfate in aerosols would provide a more reliable analytical approach.

We wish to report on the progress attained in utilizing a laser-Raman scattering

technique to measure directly, without filter collection, the concentration of sulfate

compounds in aerosols. During the initial phase of this project, we investigated the

feasibility of measuring the concentration of sulfate and bisulfate in aqueous aerosols by

the Raman scattering technique [7,8]. We have now successfully detected laboratory generated (NH4)2S0t+ aerosols in a continuously flowing system at concentrations down to less

Two experimental setups will be described in this section. The first is a cw laserRaman system which was used to measure the concentration of sulfates down to the low ppb

range. The second is a pulsed laser-Raman system which was used to investigate the advantages that should be gained by going from a cw to a pulsed laser system. These advantages

and associated problems will be treated in the following section.

For the cw laser approach, the experimental setup was a modification of the standard

90° system used in our original laser beam single-pass system [7]. In the standard system,

the Raman signal is collected in a direction perpendicular to the plane defined by the

direction of the incident laser beam and its polarization, with a single pass of the laser

beam through the sample region [9-11]. The new arrangement is shown in figure 1. The

incident cw laser beam at 4880A and 340 mW is from a Spectra-Physics Model 165 argonkrypton laser. The laser beam is partially trapped by an optical cavity formed by concave

mirrors Ml and M2. These mirrors have high reflectivity, multi-layer dielectric coatings.

This multi-pass scheme is a modification of an optical cell originally devised by Hill and

^Figures in brackets indicate literature references at the end of this paper.

2. Experimental

o

659
Hartley [12]. Ours is a simplified version using concave spherical mirrors rather than

elliptical mirrors. The two mirrors are positioned so that their equal radii of curvature

are coincident. In this configuration, a beam incident from outside the cavity and passing

near the coincident radii of curvature will be partially trapped and forced to undergo many

bounces before escaping out the other side. The focal region contains two images, each of

which intersects many passes of the laser beam. A third concave mirror M3 redirects the

Raman scattered photons that would normally be lost back towards the collection optics.

The Raman photons are collected by lens LI and imaged by lens L2 onto the entrance slit of

a Spex Model 1400 double monochromator. The monochromator was equipped with Jobin-Yvon

holographically ruled gratings, 1800 grooves/mm, blazed for 3500 - 7000 A. An RCA C31034

gallium-arsenide photomultipl ier tube (PMT) was kept at -20°C for photon counting. The dark

count rate was approximately 7 Hz with a 4 mm x 10 mm photocathode. The Raman signal is

then amplified and monitored by a photon counter.

The sample region was contained in a specially designed cell which directed the test

sample through a nozzle into the laser beam. A flowing system was maintained by exerting

positive pressure at the nozzle entrance and pumping at the exit port. Both standard gases

and aerosols were used as test samples. The gas samples were pure N2, 10 ppm of NO2 in N2,

and normal laboratory air. The aerosols were generated by a commercial unit (Sierra Instruments Model 7330 fluid atomization aerosol generator) from water solutions of (NH4)2S0i+

and Na2S0i+. The molarities of the solutions used were 1 M, 0.1 M, 0.01 M, and 0.001 M. The aerosol generator contained an impactor which effectively removed all particles with

diameters greater than 2 ym. The exiting aerosols were collected on a substrate and

analyzed with an electron microscope to confirm that no aerosols with diameters larger than

2 ym were being admitted into the sample region. The mass flow rate from the generator was calibrated using a liquid nitrogen cold trap which collected the particles that passed

through the impactor.

The pulsed system utilized a high-power ruby laser (Spacerays) operating in the normal

mode condition in a single-pass configuration. The setup is shown in figure 2. The laser

beam diameter was stopped down to 1/4 inch and had a 0.5 msec halfwidth. The maximum

energy was 4.1 J. The beam was focused into the sample region by a 1 cm focal length

aspheric lens. The spot size diameter was 120 ym. After passing through the sample region,

the beam was directed onto a scattering plate. Two silicon photodiodes, PDl and PD2,

monitored the scattered laser signal. PDl operated in a saturation mode to deliver a gate

pulse to the photon counter, so that photon counts from the PMT were accepted only at times

coincident with the laser pulse. PD2 integrated the laser signal to give a voltage proportional to the total laser energy. The energy measurement electronics were calibrated with

a TRG Model 100 thermopile. Mirrors Ml, M2, and M3 of figure 1 have not yet been incorporated into the pulse of figure 2.

3. Results and Discussion

The multiple-pass optical cavity is the chief source of the enhancement of our signal/

noise ratio. This enhancement allows a consequent increase in sulfate concentration measureo ment sensitivity. In the single-pass scheme with the 4880 A line at 340 mW and a monochromator slit width of 1 mm and height of 10 mm, we obtained 5700 Hz from the PMT for the

2330.7 cm-^ line of atmospheric N2. Including mirrors Ml, M2, and M3 as shown in figure 1, we achieved 5.22 x 10^ Hz, a gain of approximately 92. For these condi.tions, the background count rate at the 981 cm"^ line of sulfate was approximately 25 Hz with ambient air

flow from the aerosol generator.

As an initial test of our calibration of the system with atmospheric N2, we sampled

two gases: atmospheric CO2 (0.0314 percent ambient concentration [13] and a standard

commercial mixture of 10 ppm of NO2 in N2. Both concentrations were easily detected and

measured with respect to ambient N2.

660
LlI

hUJ

o

cr

ho

LU

CL

cn

<

cr

I

LU

<

orO

o

<

o

LU

UJ

< LU

O

CM

UJ

m

O

o

o

I-

<

o

(r. I

o

o

Figure 1. Schematic of a laser-Raman scattering instrument used for the detection of

laboratory generated sulfate aerosols. The Raman signal induced by a cw laser is enhanced

by a multi-pass optical cavity.

661
LU

hUJ

o

(r

Io

UJ

CL

<

I

UJ

<

Q

UJ

>

LU

q:

UJ LU

LU

LU

_l

CQ

OO

O

\-

<

O

q:X

o

o

Figure 2. Schematic of a laser-Raman scattering instrument utilizing a pulsed versus cw

laser. A gate pulse from a photodiode (PDl) is used for coincident photon counting from

the photomul tipl ier (PMT).

662
Before measuring the Raman scattering from (NHi+)2S0i+ aerosols, we first calibrated the mass flow rate of the aerosols passing through the impactor of the aerosol generator. We

found that only approximately 1.0 percent (+50 percent) of the original solute from the IM

solution was getting past the impactor. This yielded a molecular concentration of sulfate

at the nozzle of the sample cell of approximately 8.2 ppm (±50 percent).

The Raman spectrum of the line of SO4 at 981 cm"' ^or these (NlHj^)S04 aerosols [14-

16] in the flowing system is snown in figure 3. The slitwidth of 1 mm for our monochromator

corresponds to approximately 14.1 cm"'' at the 981 cm"i position, which is also approximately

the halfwidth of the Raman line. We are therefore capturing the significant portion of the

Raman photons for this transition. Since the concentrations of ambient N2 and the laboratory generated sulfate aerosols are known, and the Raman cross section for N9 is also known

[17], a rough estimate can be made of the effective Raman cross section for 981 cm"'

line of (NHtt)2S04 aerosols. Previously, we had determined the cross section [7] for the

completely dissociated sulfate anion in aqueous solution, 0504^°^^'

solution case that a^Q'^°^°Va^^^^°^^ = 21.2 (±60 percent). Since the aerosols are in a water saturated vapor state, the sulfate anions are clearly not dissociated, even for such

high-humidity conditions. In fact, this cross section agrees favorably with that obtained

by Wright and Krishnan [16] on solid (NHJ2SO4 powder: OsoI^^^^SOr^"^ " ^^^^^ ^^^^^

result has a ±50 percent uncertainty. This result of a significantly larger cross section, even under high-humidity conditions, is very encouraging since it means that our sensitivity

is significantly greater than we had previously estimated.

Next we measured the sulfate Raman signal while decreasing the aerosol generator's

solution molarity from 1 M to 0.001 M in decade steps. From our previous calibration, this

corresponds to sulfate concentrations of 8.2 ppm down to 8.2 ppb at the sample cell. The

results are shown in figure 4. The abscissa represents the stated concentrations. The

ordinate gives the ratio of the sulfate signal at 981 cm"^ to that of the N2 signal at

2330.7 cm"i [17]. The sulfate signal at 8.2 ppm was clearly seen for a 1 sec integration

time per wavelength step. The signal at 8.2 ppb was seen only for 1000 sec integration

times. What is most noticeable in figure 4 is that the ordinate ratio is linear with concen- tration. This indicates that the different aerosol diameter distributions at different

concentrations are not causing significant deviations in scattering efficiency, as would

certainly be the case for Mie scattering [18].

The ultimate limiting sensitivity is governed by several factors. The most important

are masking effects, such as fluorescence and PMT dark counts. In figure 3, the sulfate

signal is perched on a relatively flat background. However, as the sulfate concentration

decreases, the background also decreases. This background may arise from aerosol fluorescence or fluorescence from optical elements in the system. The latter fluorescence may be

induced by Mie scattering from the aerosols of the incident laser beam into the collection

optics. Another possible source of fluorescence is the atmospheric pollutant NO2. The

fluorescence of NO2 has been extensively studied and it can occur in ambient concentrations

which might limit the detection threshold of sulfates [19, 20].

To combat these problems, we chose to incorporate a pulsed laser into our system. By

using gating electronics, the dark count rate is decreased linearly with a decrease in the

laser pulse width. In addition, for fluorescent lifetimes greater than the laser pulse

width, the interference from such fluorescers is correspondingly decreased. In the case of

NO2, the fluorescence efficiency is a strong function of the laser wavelength. We found

o o that by going from the 4880 A line of our cw laser to the 6943 A line of a pulsed ruby

laser, the fluorescence efficiency of the NO2 at the sulfate 981 cm"^ position should

decrease by a factor of 143 (±20 percent).

663
E

co

<

(ZH) nVNOIS NVI^Vd

_i

Figure 3. Raman scattering spectrum of (NHi+)2S04 aerosols. The \>i line at 981 cm for the

o

SOi^. anion was monitored. The 4880 A line from a cw argon-krypton laser was used. The

spectrum was scanned at an effective 1 Hz rate. The sulfate molecular concentration was approximately 8.2 ppm (±50 percent).

664
o

10 TTl 1 1 I I I I I I

I

1

1 I I I I II 1 1—I I I I I Ul

CD

LU

10"

<

(T 10-^

LU

iD

O

ct:

I10

r5

3

10" L I I I 11 I L

!0 100

ml

1000

J I I 1 1 II 10.000

SULFATE CONCENTRATION (ppb)

Figure 4. Graph of the sulfate Raman signal versus sulfate concentration, normalized to

the Raman signal for ambient N2. The accuracy in the sulfate concentration calibration

measurement was approximately ±50 percent.

Flowing (NH4)2S04 aerosols were tested with the pulsed ruby laser system as shown in

figure 2. The maximum average laser intensity that the sulfate aerosols were subjected to was approximately 73 MW/cm^. This corresponds to a 4.1 J pulse of 0.5 msec halfwidth and

120 ym spot size. However, a normal mode pulse from a ruby laser is typically composed of

a pulse train of many spikes rather than presenting a smooth profile [21]. In our case these spikes had halfwidths of 0.5 psec. The peak intensity in the focal region is therefore much greater than the average intensity. Under these conditions, the aerosol might be

strongly perturbed. The Raman scattering and heating of single fine particles down to 0.7

ym diameter by a focused cw laser has been investigated by Rosasco et at. [22]. They

encountered no heating problems for NaNOa mounted on a substrate. In our flowing system,

the sulfate aerosols have no substrate to dissipate heat easily. To check for possible

heating effects, the sulfate line was monitored with increasing laser intensity. No

665
abnormal increase in background fluorescence was seen up to an average intensity of 73

MW/cm^. In addition, the anti-Stokes component of the 981 cm"^ line was checked. Presence

of a strong anti-Stokes signal would indicate heating of the aerosols to high temperatures

by the laser [23]. Since no such effect was seen, we do not believe that the aerosols are being sufficiently perturbed to interfere with a concentration measurement.

The PMT and photon counter were checked for saturation effects which would affect

linearity. These can arise from the 0.5 ysec spike behavior of the laser normal mode

pulse. Raman photons might arrive in bunches closer than the pulse pair resolution time of

the photon counter. However, no such saturation was seen up to the full intensity previously mentioned.

Now that we are assured that using a high-power pulsed laser causes no serious experimental problems, we intend in the future to construct an optical cell similar to that used

in the cw system. If the previous optical enhancement factor of 92 can be reached with the

ruby laser, then the measurement sensitivity for sulfate concentration should be considerably improved.

4. Conclusion

Our experimental program for detecting sulfate aerosols in situ has accomplished to

date the following: 1) A Raman spectrometer using a cw laser for detecting flowing sulfate

aerosols has been constructed with a sensitivity significantly greater than previously

achieved. 2) Laboratory generated (NH4)2S0it aerosols in a flowing system have been measured

at concentrations down to the 10 ppb range. 3) The feasibility of using a pulsed ruby

laser system to partially eliminate interference effects and to increase the detection sensitivity has been discussed and some favorable initial experimental results have been obtalnea.

Work supported in part by the Northeast Utilities Service Company, Hartford, Connecticut.

References

[1] Schoff, R. A., Bew England Consortiim on Environmental Problems, Publication No.

RPTR-75-1 (September 1974).

[2] Keesee, R. G., Hopf, S. B., and Moyers, J. L., International Conference on Environmental Sensing and Assessment, Vol. 2, 23-6 (IEEE, New York, 1976).

[3] Junge, C. E. and Ryan, T. G., Quart. J. Roy. Meteorol. Soo. 84, 46 (1958).

[4] Brosset, C, AMBIO 2, 2 (1973).

[5] Stevens, R. K. and Dzubay, T. G., IEEE Trans. Nucl. Sai. NS-22 , 849 (1975).

[6] Forrest, J. and Newman, I., APCA Journal 23, 761 (1973).

[7] Stafford, R. G. and Chang, R. K. , International Conference on Environmental Sensing

and Assessment, Vol, 2, 23-5 (IEEE, New York, 1976).

[8] Stafford, R. G. and Chang, R. K. , Seventh International Laser Radar Conference,

Menlo Park, California (November 4t7, 1975).

[9] Fouche, D. G. and Chang, R. K., Ap-pl Rhys. Lett. 18, 579 (1971 ).

[10] Penney, C. M. , Goldman, L. M. , and Lapp, M., mture Rhys. Sci. 235, 110 (1972).

666
[11] Fenner, W. R. , Hyatt, H. A., Kellam, J. M., and Porto, S. P. S., J. Opt. Soa. Am.

63, 73 (1973).

[12] Hill, R. A. and Hartley, D. L., Appl. Opt. 13., 186 (1974).

[13] American Institute of Physios Handbook (McGraw-Hill Book Co., New York, 1972).

[14] Herzberg, G., Moleoulojc Spectra and Molecular Structure II (Van Nostrand, New York,

1966).

[15] Ananthanarayanan, V., Indian J. Fure Appl. Phys. ]_, 58 (1963).

[16] Wright, M. L. and Krishnan, K. S., Stanford Research Institute Report, EPA-R2-7Z-219

1973.

[17] Fouche, D. G. and Chang, R. K., Appl. Phys. Lett. 20, 256 (1972).

[18] Kerker, M., The Scattering of Light and Other Electromagnetic Radiation (Academic

Press, New York, 1969).

[19] Gelbwachs, J. A., Birnbaum, M. , Tucker, A. W., and Fincher, C. L., Opto-Electronics

4, 155 (1972).

[20] Fouche, D. G., Herzenberg, A., and Chang, R. K. , J. Appl. Phys. 43, 3846 (1972).

[21] Ross, D., Lasers, Light Amplifiers^ and Oscillators (Academic Press, New York, 1969)

[22] Rosasco, G. J., Etz, E. S., and Cassatt, W. A., Appl. Spectry. 29, 396 (1975).

[23] Lapp, M. and Hartley, D. L., Combustion Sci. and Tech. 12, 123 (1976).

667

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

CHEMICAL CHARACTERIZATION OF PARTICULATES IN REAL TIME BY A LIGHT SCATTERING METHOD

C. C. Gravatt

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

This paper describes a new light scattering method for the characterization of particulate matter as to its chemical composition. Specifically, it is possible by this method

to distinguish carbon, absorbing and metal containing particles from other materials, and

in some instances to distinguish among various types of carbon containing and metallic

particles. This technique can be applied either to the characterization of individual

particles or to aerosols containing many particles. In many situations some degree of

chemical characterization of particulate matter would be advantageous, and the present

technique is especially attractive since it can be accomplished without the collection and

subsequent chemical analysis of a sample. This is a light scattering method in which the

scattered radiation is monitored in such a way as to provide information related to the

chemical composition of the particle or aerosol.

The following is a brief introduction to the important optical parameters to be used

in this discussion. The total index of refraction, m, of any substance can be considered

as a complex quantity

m = n - i k ( 1

)

with real component n and imaginary component k. Both n and k are functions of the

wavelength of the radiation, x, and the absorption spectra of a substance gives the wavelength dependence of k. Light scattering is sensitive to both n and k and this dependence

is most pronounced in those cases where the size of the particle and the wavelength of the

light are of similar magnitude. Consider a beam of ligjit of intensity, io> and wavelength,

Aq, traveling in the direction given by a unit vector, ko, and scattered by a sample at 0.

A ray scattered in the direction given by unit vector, 1<, is measured to have intensity,

i , by a detector located a distance R from the jample. The scattering angle, 0, is the

angle between the directions defined by 'i<o and1<. The scattering plane is that plane

containing the sample and the unit vectors 1< and1<o. For the purposes of the present

discussion, it is also necessary to define the state of polarization of the incident

radiation, and the following notation will be adopted. If the polarizer is oriented such

that the direction of polarization is in the scattering plane, then the scattered radiation

is represented by i/, . If it is oriented such that the direction of polarization is normal

to the scattering plane then the scattered radiation is represented by ij..

2. Single Particle Case

Consider that there is a single particle located at 0 and that the scattered intensities i// and ij^ are measured as a function of e. It is found that the scattered intensities

are also a function of the particle size, index of refraction, and shape, and that this

dependence can be expressed quantitatively by the theory of Mie. In order to investigate

the effect of index of refraction on the scattering behavior of particulates, the scattering curves (i,, or i^ vs. e) have been calculated for a wide range of indices of

669
refraction and particle size using a modification of the procedure given by Dave [1]^. From

a comparison of a number of these scattering curves a certain pattern was noticed; specifically that the i// curves for materials with k = 0 differed markedly from those for materials

with k > 0 over the angular range from 0 = 30° to 0 = 90°. There is at least a one order

of magnitude difference in the i„ values for these two types of materials over the 0 range

30° to 80°. A more complete analysis of this effect has shown that the angular region

from 0 = 40° to 0 = 70° for \„ is extremely sensitive to the magnitude of the k value of

the particle index of refraction and can be used for chemical characterization of the

particles.

By employing a light scattering particle sizing instrument, and adding to it an optical system which collects light scattered by each particle over the angular range of

40° to 70° for i,^ , it should be possible to classify particles which are larger than 0.3 ym

as to whether they are non-absorbing (k = 0), carbon-like, or metallic. In many cases it

should also be possible to distinguish among the types of metals.

There are a number of possible applications of a single particle instrument as described above, in addition to the obvious ambient air pollution monitoring use. There

are applications in coal mine and industrial plant monitoring in which it is of interest

that not only the total particle size distribution be measured but also the fraction and

size distributions of carbon containing or metallic particles be measured. It should be

possible to tag certain dust particles with a dye of some type and then make the measurements at the absorption wavelength of the dye. These particles could then be used in

various studies as tracer particles. In addition to the above applications in air, it

should be possible to perform analogous studies in liquids, such as water. It would be

necessary to reevaluate the most effective angular range since the index of refraction of

the background would be different for the liquid case, but the general phenomena is the

same. Thus one could characterize particulates in liquids as to their chemical composition

and perform tracer studies with dye containing particulates.

In this section the chemical characterization technique will be extended to a device

that monitors an aerosol containing many particles rather than measuring a single particle

at a time. The specific application to be discussed is a smoke detector (f i re-producedaerosols) but several additional applications are possible. For an instrument which will measure the light scattered by an aerosol it will be necessary to consider two additional

factors which were not of importance in the single particle case. These factors are the

total number of particles in the beam, and the particle size distribution of the sample.

The optical configuration of the instrument is as follows. The light source is

either an incandescent bulb or a medium pressure mercury arc. An incident light system is

of straightforward design and produces a reasonably well collimated, linearly polarized

beam of uniform intensity and of approximately 1 cm^ in cross section. ' The 55° (i,^ ) scattered light detector system has an aperture of approximately ±15° and employs a photodiode-op-amp combination as the light detector.' The output of this detector is a quantity proportional to l„ where

3. Multi-particle Case

I + Nnl„ n} (2)

D

^Figures in brackets indicate the literature references at the end of this paper.

670
Na is the number of absorbing (carbon-like) particles of diameter D, Nn is the corresponding

number of nonabsorbing particles, I//a and 1//^ are the scattering intensities integrated

over the angular range 40° to 70° for the absorbing and non-absorbing particles respectively.

Although not explicitly shown, all the N and I^^ terms are functions of the particle diameter

and the sum extends over all particle sizes in the sample, l,, is relatively large for an aerosol containing non-absorbing particles and is relatively small for an aerosol containing

a large number of carbon-like particles.

There is also a second scattered light detector system normal to the plane of polarization centered at an angle of 90° with an aperture of ±10°. This system also uses a photodiode-op-amp combination as the light detector. The output of this detector is a quantity proportional to Ij where

The N terms are the same as defined above, and the Ij. terms are the scattered intensities

normal to the plane of polarization integrated over the angular range 80° to 100°. Ix is

approximately proportional to the total number of particles in the beam, independent of

whether they are absorbing or not. The theoretical studies have shown that almost any 20°

angular range in i^ can be effectively used as a term proportional to the total particle

density.

In order to evaluate the effect of particle size distribution it was necessary to

theoretically study the response of the instrument to changes in the particle size distribution. The distribution used in these studies was the Junge universal distribution

which gives the number of particles, N, of diameter, D, as a function of two parameters, A

and b. The parameter b has been measured for a number of aerosols and is generally on the

order of 4. The larger the b the more strongly the distribution is shifted to favor the

small particles. Theoretical analysis for a number of cases has shown that the smoke

detector response, I,, , is a valid measure of the carbon content of an aerosol provided

the particle size distribution has a b value of 6 or less.

The actual response of the smoke detector was measured for a number of aerosol samples.

It was shown that the instrument is effective in distinguishing fire-produced aerosols and

other types of absorbing materials from non-absorbing aerosols.

(3)

N = AD

-b

(4)

References

[1] Dave, J. v., IBM Report Z20-Z2Z7^ Palo Alto, Calif. (May 1968).

671

Part XIV. LABORATORY ACCREDITATION - PANEL DISCUSSION

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg , Md. (Issued November 1977).

THE NATIONAL VOLUNTARY LABORATORY ACCREDITATION PROGRAM

T. R. Young

National Bureau of Standards

Washington, DC 20234, USA

1. Introduction

A summary of the evolution of the National Voluntary Laboratory Accreditation Program

(NVLAP) helps to identify issues that may need consideration when contemplating the establishment of laboratory accreditation programs. NVLAP was established by the Department of

Commerce on February 25, 1976, after several years of study and communication with affected

parties in state and Federal government and in the private sector. NVLAP provides a national voluntary system whereby laboratory accreditation programs can be established for

specific product areas having need. The purpose of such programs is to examine and accredit

the professional and technical competence of testing laboratories that serve regulatory and

non-regulatory product evaluation and certification requirements. Detailed procedures and

definitions utilized by NVLAP are contained in Title 15, Code of Federal Regulations, Part

7 [1]-^. Additional descriptive material regarding NVLAP including background, a review of

procedures and discussion of NBS's supporting technical role is contained in proceedings of

briefing sessions held in June 1976 in Los Angeles and Washington, DC [2].

2. Discussion

Proposed establishment and procedures for NVLAP were initially announced in the

Federal Register in May 1975 [3]. The public review period that followed, including two

public hearings, provided over 150 substantive critiques from Federal and state agencies,

professional and trade organizations, industries, testing laboratories and individuals.

This public review raised principle issues resulting in significant revisions of the

proposed procedures.

The proposed procedures provided for appointment by the Secretary of Commerce of

laboratory accreditation boards for each class of technology for which a need for accredited

testing laboratories is determined. Thereafter, establishment of accreditation programs

for testing of products within the class of technology would be considered upon request.

This presumed the existence of general and concurrent needs within classes of technology

for accreditation of laboratories to test all, or many, of the various products within the

class. The public review of the proposed procedures indicated that this assumption is not

generally valid. Needs for laboratory accreditation tend to vary with the product that is

tested. Thus needs for laboratory accreditation applicable overall to classes of technology or technical disciplines may be difficult to assess and to justify. Therefore, the

proposed procedures were revised to allow initiation of accreditation services on a product

by product basis as needs are determined. To counter the potential for establishment of

innumerable and possibly duplicative separate services that might result from this approach,

the revised procedures allow the grouping of similar or related products when initiating

accreditation services. In addition, the procedures provide for review of applications for

accreditation with reference to the applicant's prior accreditations. Only those examination requirements not met in previous accreditations would be applicable to the laboratory's

additional accreditation.

Figures in brackets indicate literature references at the end of this paper.

675
The second principle issue that arose during public review of the proposed NVLAP

concerned participation of the private sector in development of accreditation services.

The proposed procedures provided for an advisory committee of private and public members

for each board of accreditation. A board, consisting of Federal employees, would be

required to consult with its advisory committee when developing accreditation criteria.

However, only the board would make final recommendations regarding accreditation criteria

and operational aspects of the program. Many comments received during public review

indicated that a voluntary program should provide for more direct and equal involvement of

the private sector, particularly in regard to development of accreditation criteria.

Accordingly, the procedures were revised to provide for accreditation criteria committees

in lieu of separate boards and advisory committees. These criteria committees, composed of

government and private sector members, develop and recommend accreditation criteria to be

promulgated by the program.

The third significant issue concerned coordination with other laboratory examination

and accreditation programs in the private and government sectors. Although, the proposed

procedures vaguely referred to support of coordination efforts, they lacked general or specific provisions regarding promotion or arrangement of coordination with other programs

that may exist or be in development. Many comments, during public review, addressed this

deficiency. They considered a major benefit of NVLAP to be its focus for coordination of

laboratory examination and accreditation programs. Such coordination could work to reduce

the duplication of laboratory examination efforts, reduce confusion regarding the criteria

used and promote reciprocal recognition of laboratory assessment programs, domestically and

internationally. In response, the procedures were revised to include such coordination as

a goal of the program. For initiation of laboratory accreditation programs under NVLAP,

provisions were added requiring consideration of existing programs in the public or private

sectors. These provisions include consultation with government agencies that may be

impacted by programs established under NVLAP. In particular. Federal regulatory agencies

may halt, by written objection, the establishment of programs that would adversely affect

their existing or developing laboratory accreditation programs.

Other revisions in the program's procedures resulted from NVLAP's exposure to public

review. Correspondence and transcripts of public hearings obtained in this review,

together with a summary and analysis of such response is available for inspection and

copying at the Department's Central Reference and Records Inspection Facility.

References

[1] Federal Register, Vol. 41, Number 38, Feb. 25, 1976 (pg. 8163-8168).

[2] NVLAP Proceedings, American Council of Independent Laboratories, 1725 K Street, N.W.

Washington, DC 20006.

[3] Federal Register, Vol. 40, Number 90, May 8, 1975 (pg. 20092-20095).

676
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

THE NATIONAL LABORATORY CERTIFICATION PROGRAM FOR WATER SUPPLY

Charles Hendricks

Environmental Protection Agency

Washington, DC 20460, USA

1. Introduction

In 1970, the Department of Health, Education and Welfare undertook a study of public

water systems:

- 36% of the tap samples contained one or more bacteriological or chemical constituents

exceeding the limits in the Public Health Service Drinking Water Standards.

- 11% of surface water samples exceeded the recommended organic chemical limit of 200

parts per bill ion.

- 77% of the plant operators were inadequately trained in fundamental water microbiology.

- 46% of the plant operators were deficient in chemistry relating to their plant

operation.

- 79% of the systems were not inspected by State or county authorities in the year

prior to the study.

- 85% of the systems did not analyze a sufficient number of bacteriological samples.

For these and other compelling reasons. Congress enacted the Safe Drinking Water Act

in 1974, "to assure that the water supplied to the public is safe to drink." The basic

structure of the Act, as it pertains to public water systems, calls for the establishment

of: (1) maximum contaminant levels for contaminants in drinking water; and (2) criteria

and procedures, including quality control measures, to assure compliance with such maximum

contaminant levels.

To implement the National Laboratory Certification/Quality Assurance Program, EPA has

proposed for discussioh a three-step framework to certify all water supply laboratories by

the effective date of the Revised Primary Regulations (March 1979). Also included were

specific alternatives to the basic plan and either the three-step framework or any one of

the alternatives could be adopted. The June 1976 draft of the Criteria and Procedures

Manuals are currently in the review process and the second draft is expected in late

October 1976.

2. Technical Requirements and Evaluation Criteria

EPA believes that adequate quality control must be an integral part of the day to day

operations of laboratories analyzing drinking water samples to help insure the availability

to the public of a safe and dependable supply of drinking water. Accordingly, EPA has

developed a set of manuals in chemistry (organic and inorganic), radiochemistry and microbiology which set forth fundamental techniques, training standards, and evaluation criteria

677
for the operation of analytical laboratories responsible for analyzing samples from public

water systems. EPA recognizes that there are many excellent State certification programs

for microbiology currently in operation, and it is EPA's intention that only those portions

of the National program be incorporated where they may be needed to augment present State

programs

.

3. Regulatory Basis for a National Laboratory Certification/

Assurance Program

Under the present Implementation Regulations (Section 142.10(b)(3) and (b)(4) of the

Interim Primary Drinking Water Regulations - Implementation {Federal Register, January 20,

1976), there are two requirements for a laboratory certification/quality assurance program.

First, the State must be able to supervise the analysis of samples from public water

systems. In order to do so, States must have access to laboratories capable of accurately

measuring the contaminants regulated by primary drinking water standards. Second, the

State must undertake a program to certify all laboratories conducting analyses for public

water systems. In order to attain and maintain primary enforcement responsibility, both

of these requirements are mandatory under the Interim Primary Drinking Water Implementation

Regulations.

4. Proposed Implementation Plan

The Implementation Regulations key the requirement for the certification of State

principal laboratories to a date for the establishment of a National Quality Assurance

Program. It is important to recognize that the implementation of the National program

must take into account the availability of resources and a commitment to carry out the

assigned responsibilities. To fulfill EPA's initial responsibility under paragraph (b)(4)

of the Implementation Regulations, EPA will approve designated State principal laboratories

on an interim basis using the Criteria and Procedures Manuals as guidelines. After the

promulgation of the Revised Primary Drinking Water Regulations (September 1977) and the

establishment of the National Laboratory Certification Program, EPA will begin to certify

State principal laboratories upon request. All State principal laboratories will be

certified by March 1979 using the revised Criteria and Procedures Manuals which will be

based upon the Revised Primary Regulations. The revised Criteria and Procedures Manuals

will be developed in sufficient time to be released with the Revised Primary Regulations.

EPA's proposed framework for the implementation of the National Laboratory Certification/Quality Assurance Program is as follows:

Step 1 - Between now and the promulgation of the initial laboratory certification

manual

s

EPA will grant "interim approval" to State principal laboratories if the State

determines that they are in compliance with the requirements of the Interim Primary

Regulations and with the State laws in effect when the State applies for primacy. In addition, the State must designate an official to serve as the State Laboratory

Certification Officer and submit a plan for developing a process to certify local

laboratories. Thus, processing of State requests for primacy will not be delayed.

Step 2 - Between Fall 1976 and September 1977 (anticipated promulgation of Revised

Primary Drinking Water Regulations)

EPA will grant "approval" of the State principal laboratories after visitation

and review using the initial laboratory certification manuals. Whether the manuals

will serve as guidelines or as mandatory requirements will be addressed after the

public review of the program. In addition, the States will be required to begin a certification program for local laboratories; local laboratories could be "approved"

if the laboratories were in compliance with State laws in effect when the State

attains primary enforcement responsibility.

678
step 3 - Between September 1977 and March 1979 (anticipated effective date of the

Revised Drinking Water Regulations)

Prior to September 1977, EPA/Office of Research and Development will lead efforts

to produce a revised laboratory certification/quality assurance manual consistent

with the Revised Drinking Water Standards. Thereafter, EPA would formally certify

State principal laboratories. In order to qualify for certification, the State

principal laboratories must be in conformance with all of the requirements in the

revised manuals. All State principal laboratories would be certified by March 1979.

The States will also be required to formulate certification programs for local

laboratories based on the technical requirements of the r^evised manuals or their

equivalent as developed by the State, Depending upon the option chosen by EPA, the

local laboratories must be certified before the effective date of the Revised Primary

Drinking Water Regulations.

579

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement,

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

LABORATORY ACCREDITATION

C. Eugene Hamilton

Dow Chemical

Midland, Michigan 48640, USA

By definition. Laboratory Accreditation is a system by which to examine, evaluate and assure an acceptable level of competence of a laboratory to test, analyze or inspect a material and to provide valid reliable data. With this definition in mind, the problems,

frustrations and progress toward developing water laboratory practice guidelines within

the ASTM D-19 Committee on Water is presented.

The first procedural step in ASTM is the agreement upon a written scope statement for

the planned activities. The following scope statements were developed for the Laboratory

Practices Section Activities:

0 to develop standard practices detailing the requirements and guidelines by which

laboratories engaged in the analysis and characterization of water and water related

material can be evaluated for reliable performance and operation.

0 to develop standard practices and guidelines for laboratories engaged in the analysis

and characterization of water, waste water, and water related material to enable them

to provide valid reliable data.

These two statements differ conceptually between "reliable performance and operation"

and "valid reliable data". This conceptual difference has not been unanimously resolved.

Operationally the scopes are very similar, since "valid reliable data" is the best measure,

if not the only measure of laboratory performance. The section developed five interrelated

necessary parts of laboratory practices which will assure "valid reliable data". Namely,

No one part is more or less important than any other; each part must be adequate to fulfill

the purpose of the laboratory.

From the results of the D-19 member questionnaire on current laboratory practices, at

the end of this paper, a priority was established to develop standard practices for the

parts in this order:

1. Records, Documentation, Chain of Custody, eto.

2. Quality Control

3. Personnel and Training

4. Facilities (including instrumentation)

Written documentation was missing for many common (good) practices of the laboratories.

That is, most laboratories practiced procedures which yield "valid reliable data" but also

most of these laboratories did not document these actions or programs.

Physical Facilities

Training

Quality Control Records

681
Thus a Standard Practice for Laboratory Records has been prepared, but not yet approved

by the subcommittee or the main Committee D-19 on Water or ASTM ballots. The other segments

are being prepared for future consideration.

These Standard Practices will help a person, or a laboratory determine the conformity

of its practices for Records, Personnel, Training, Facilities and Quality Control, which

will produce "valid reliable data".

Laboratory Activity Survey

Total

1. What is the scope of your laboratory activity?

Water analysis:

industrial process water 88

waste water:

Sanitary 63

Industrial 110

high purity water 59

drinking water 71 other 35

Water-formed deposit analysis 63

Evaluation of water treatment materials 57

Other 11

2. Describe the breadth of your testing service.

Waters (industrial process and drinking);

inorganic parameters 121

organic parameters 82

microbiological parameters 56

pesticide/chlorinated hydrocarbons 48

marine 32

radiological 21 toxicology 31

Waste & effluent waters:'

biological 67

inorganic parameters 116

brines 44

organic parameters 83

microbiological parameters 50

marine 26

pesticide/chlorinated hydrocarbons 46

toxicology 34

radiological parameters 18

Water-formed deposit analysis:

spectrographic 43

x-ray 23

microscopic 40

wet chemical 73

radiological 10

organic residue analysis 38

Ion exchange material:

capacity 45

cross-linkage 15

582
Membranes 21

Flocculants 34

Activated Carbon 35

3. Is you laboratory an: in-plant lab 34

central services lab 57

independent testing lab 23

company affiliated testing lab 26

university affiliated testing lab 4

regulatory agency lab 20

specialty service lab a-g., NMR; EM; GC/MS; eta. 17

other 12

4. What is your personal relationship with the laboratory?

administrator 57

supervisor 71 customer (user) 8

other (worker) 18

5. Do you sell your laboratory services?

Yes 64

No 77

6. Do you utilize on stream in-line monitoring for process control

and/or effluent quality?

Yes 68

No 65

7. How is data provided by your lab used:

process control 63

identify treatment requirements 89

monitoring treatment product performance 74

identify and quantify pollutants 105

monitor effluent quality 104

NPDES permit 77

waste treatment plant design 44

drinking water quality 64

design parameters 55

research - 86

other 7

8. Please indicate the number and distribution of your laboratory staff.

18.8 permanent 3.9 part-time

10.6 professional 9.5 technician

9. Do you have a formal training program for your laboratory analysts?

Yes 61

No 80

10. Do you have a formal internal quality control program?

Yes 100

No „ 50

11. Please check appropriate items your program covers. ^^^^ Covered

precision studies 40

accuracy studies 35

683
recovery studies 36

"blind" standard analysis 28

identified standard analysis 47

replicate sample analysis 36

"spiked" sample analysis 24

12. How often do you prepare ^ calibration curves? o/ ^ n i r j % of Analyses Covered

each time test is run 69

weekly 31

monthly 40

other 44

13. Do you service you instrumentation in-house?

Yes 84

No 76

14. Do you utilize manufacturers and/or outside service for the following:

Atomic Absorption Units 98

Infrared Spectrophotometers 60

UV Spectrophotometers 64

Gas Chromatographs 65

Analytical Balances 109

Other 9

15. Which of the following areas of analysis do you feel require our priority attention for development of guidelines? If more than one - please rank in order of importance.

1st 2nd 3rd

A. industrial process water quality 29 20 28

B. waste water quality 75 26 4

C. drinking water quality 26 25 14

D. other 13

684
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464 Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gai thersburg , Md. (Issued November 1977)

CERTIFICATION OF WATER, AND WASTEWATER LABORATORIES:

A PROFESSIONAL CHEMIST'S VIEW

H. Gladys Swope

Waste Management and Pollution Control

214 N. Allen Street

Madison, WI 53705, USA

1. Introduction

Under the National Pollutant Discharge Elimination System (NPDES) which is part of

Public Law 92-500, both industry and municipalities are required to meet certain permit

requirements before discharging a waste into a watercourse. The most recent Water Quality

Safety Act, Public Law 92-523, requires that certain chemical analyses, in addition to

bacteriological analyses, are required of all water supplies serving the public. Under

NPDES such requirements necessarily require that analyses be made.

It is very easy to obtain a number by any analytical method you so choose, but unless

the person doing the work is not only qualified but honest, careful and understands the

meaning of the results obtained, how good is this number? There is even more involved

than just the analysis. Taking of the sample itself and the manner of collection all have

a bearing on whether the permit or law is met. Therefore, it is necessary for those of us who are professional chemists to try to see that anyone taking a sample or making a laboratory analysis be required by law to do it properly.

The questions involved are: First, are the people who make such analyses qualified,

and what are the requirements for qualification? The next question is quality assurance.

Perhaps the personnel are qualified but does the laboratory take time to be sure that the

results are correct? Are the solutions standardized properly? Are the instruments working

correctly, etc.? Are duplicates run to check the precision of the analyst? Every laboratory should make an analysis with the thought in mind that this work should be good

enough to stand up in court.

2. Discussion

Over two years ago questions were asked of the Committee on Environmental Improvement

of the American Chemical Society as to what was being done about laboratories that were springing up to run water and waste analyses by people who were not qualified. It was

known that almost, if not all states, required certification of laboratories running

bacteriological analysis of water, but what about chemical analysis? A letter was sent

out in November of 1974 by the American Chemical Society to all of the' state Boards of

Health and to the environmental or sanitary engineer in each state asking if they certified

laboratories, both public and private, and whether they had any requirements for the

qualifications of chemists. It was a most pleasant surprise that not only did everyone

reply, but in most cases they wrote fairly detailed letters, Most, however, had no arrangements for certifying laboratories and certainly not for the qualifications of

chemists in these laboratories, but in almost every case bacteriological laboratories

testing for milk and water, had to be certified.

685
The words, certification, accreditation, registration, informal and formal approval,

may or may not have equivalent meanings. The replies to the survey indicated that the

following states had no uniform approval procedure for environmental laboratories or of

analytical chemists:

Al abama^

Alaska

Arkansas

Colorado

Delaware

District of Columbia

Florida

Idaho

Illinois

Indiana

Kansas

Louisiana

Maine

The following states have some form of approval for environmental laboratories:

California (mandatory registration)

Connecticut (mandatory registration, except for air analyses)

Hawaii (voluntary certification)

Iowa (approval of laboratories that do analyses of water supply and wastewater samples)

Massachusetts (voluntary certification of laboratories in the fields of water

bacteriology and water chemistry)

North Carolina (certification of water treatment laboratories and laboratories that

conduct chemical analysis of wastewaters)

Oklahoma^ (mandatory certification for county health laboratories)

Ohio (approval or certification of laboratories that do water and sewage analysis)

South Carolina (control program for chemical laboratories which analyze samples for

water treatment plants)

Utah (certification). They have a very well documented program.

Vermont (state regulations provide for approval but lack of funds prevent implementation)

Virginia (informal approval of independent laboratories doing tests in connection with

stream discharge permits)

The following states have introduced legislation to approve environmental laboratories:

Arizona (license); Illinois (approval); Kansas; Montana; Pennsylvania (accreditation) and

Wisconsin (water and milk analyses only).

Two states have introduced legislation for some form of approval of analytical

chemists: California (licensing) and Ohio (registration).

Maryland

Michigan

Minnesota

Mississippi

Missouri

Montana

Nebraska

Nevada

New Hampshire

New Jersey

New Mexico

New York

North Dakota

Oregon

Pennsylvania

Rhode Island

South Dakota

Tennessee

Texas

Virginia

Washington

West Virginia

Wyoming

Wisconsin^

^Since this survey a paper was published by Dr. John F. Regnier, Director of the Alabama

Environmental Health Administration Laboratory. Water and waste samples are analyzed by

the state and they have been developing a consolidated environmental laboratory capability.

^Since this survey a law has been passed in Wisconsin for the certification of laboratories

making water and milk analyses.

^Since the survey, the Oklahoma Water Resource Board certification has emphasized the

evaluation of laboratory performance through reference sample analysis.

686
Twenty states have indicated the need for some form of regulation of analytical laboratories and/or analytical chemists:

Alabama

Alaska

Kansas

Minnesota

Missouri

Montana

Nebraska

Nevada

New Jersey

Oklahoma"*

Colorado

Delaware

Florida

Idaho

Pennsylvania

Rhode Island

South Carolina

Tennessee

West Virginia

Illinois

Hawaii has mandatory licensing of personnel performing analyses of pollutants affecting health and safety and voluntary certification of laboratories.

There is a practical problem, however, that presents itself in the case of small

industries and small municipalities (10,000 or less population). They may not have the

funds to pay for a full-time chemist. Therefore, arrangements will have to be made in

which either the person making the analysis has been trained properly by a qualified

chemist or simplified analyses which are geared to the less technical person and have been

approved by the proper authority, may be substituted for the EPA methods. Even then, the

person using a simplified method should be trained by a professional chemist.

Since the original survey, a paper appeared in the January 1976 issue of Environmental

Scienae and Technology [1]^, in which Dr. J. E. Regnier reported on a survey he sent out to

the various states in which he was primarily interested in workload, staffing, budgets and

facilities. He received 27 replies which represented 17 states and three federal

laboratories

.

In the February 25 issue of Federal Register, the Department of Commerce discussed a procedure for a national voluntary laboratory accreditation program [2].

Howard J. Sanders of Chemical & Engineering News [3] had a special report in the March

31, 1975 issue discussing the licensing and registration or certification of chemists.

It appears there are many pros and cons regarding the certification of laboratories

and the licensing or certification of chemists, but in the interests of chemists themselves

and to protect the public from people who are not qualified to do chemical work, there

should be some legal basis for protecting both chemists, their laboratories and the public.

[1] Regnier, John E. , Operating Environmental Laboratories, Env. Soi. & Tech., 10, 28-33

January 1976.

[2] Department of Commerce, Procedures for a National Volimtary Laboratory Accreditation

Program^ Federal Register^ 41, No. 38, 8163-8168 February 25, 1976.

[3] Sanders, Howard J., Do Chemists Need Added Credentials?, Chem. & Eng. News, 53^, 18-27,

March 31, 1975.

''Since the survey, the Oklahoma Water Resources Board has an annual certification program

for laboratories for all laboratories that analyze and submit data to their agency.

^Figures in brackets indicate the literature references at the end of this paper.

References

687

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 464. Methods and Standards for Environmental Measurement

Proceedings of the 8th IMR Symposium,

Held September 20-24, 1976, Gaithersburg, Md. (Issued November 1977).

LESSONS TO BE LEARNED FROM CLINICAL LABORATORY ACCREDITATION

William F, Vincent

Director, Cyto Medical Laboratory

Bloomfield, Connecticut 06002, USA

Consultant on Laboratory Quality Control

Laboratory Division

Connecticut State Department of Health

Hartford, Connecticut 06101, USA

1 . Introduction

The question of laboratory accreditation, certification, or licensure is one which has

been actively discussed by governmental officials and analysts in recent years. This

decade has often been characterized as the "age of the consumer" and concurrently with consumer demands for better quality and quality assurance for both products and services, a rising interest has developed by consumer groups, professional and trade organizations and

governmental agencies at all levels in establishing programs which will effectively monitor

the quality of the products and services received by the consumer. Additionally, as increased emphasis is placed on laboratory data to be used as a monitoring device, it

becomes obvious that there has to be a reasonable way to assure that laboratory analyses

are approximately accurate and reproducible. The answer obviously is a program for

laboratory "accreditation".

2. Discussion

As we discuss the topic of laboratory accreditation, there are several questions that

must be asked and be eventually answered: First, is there really a need for laboratory

certification? To answer this, one must measure the accuracy, precision, and reproducibility of the laboratory data being generated by a given laboratory or laboratories. There

has been a sufficient number of proficiency testing surveys by governmental agencies,

complaints to state officials, and other examples of inferior laboratory analyses to allow

one to draw the general conclusion that a form of laboratory accreditation is needed in

order to protect the public and even the laboratory community.

Second, if accreditation is needed, who should carry out the program of laboratory

accreditation? There are several possible alternatives--governmental agencies (State or Federal), private professional associations or combinations of those.

Third, to what degree should accreditation be practiced? A program could be developed

that accredits the laboratory as an entity or the laboratory could be accredited by specialty. One could even go as far as to accredit a laboratory on a test-by-test basis. There

is also the question of personnel qualifications. As part of the accreditation process,

just the education, experience and training of key personnel such as the director and

supervisor could be evaluated. An alternative is to insist that all personnel in the

laboratory, who are performing analyses meet certain minimal requirements.

Fourth, should accreditation be voluntary or mandatory, that is, should every laboratory by virtue of law or statute be required to be accredited?

689
Fifth, who should pay for the accreditation program? Accrediting programs can be very

expensive. Should the individual laboratory pay the entire bill or should the program be

supported by government funds?

An excellent way of beginning to answer these questions is to take a close look at the

accreditation of laboratories performing clinical analyses. It was not unreasonable that

the clinical laboratory would be the first to fall under close scrutiny in terms of the

quality of work performed. A clinical laboratory analysis can be a very direct effect on the health of the patient. Even a small misjudgment on the part of clinical analysts has

led to the death of a patient. Because of the severe implications, a great deal of emphasis

has been placed, especially in recent years, on monitoring the quality of the tests performed in the clinical laboratory. With few exceptions (notably the private physician

performing tests on his or her own patients,) almost every clinical laboratory in the

nation is regulated by a state agency, the Federal government (Medicare or Interstate) or

both. In recent years, relatively good programs have been developed for laboratory registration and licensure that could serve as a model for programs to be developed for environmental laboratories. However, whenever analysts from non-clinical areas sit down to talk about

laboratory accreditation, they like to believe that they are the first to do so. The truth

of the matter, as this writer sees it, is that the clinical laboratory was subjected to

accreditation procedures such as proficiency testing, inspections, personnel evaluation,

quality assurance programs, etc. long before the average environmental analyst knew what

the words meant. Rather than trying to "reinvent the wheel," we would be well advised to

take a very close look at the clinical field. In some cases, there are programs which can

be adapted with very little effort. For example, in Connecticut, a program of proficiency

testing of environmental laboratories was started using the same format, computer programs,

eto. as was used for evaluating the proficiency of clinical laboratories performing

clinical chemistry.

The Federal Safe Water Drinking Act authorizes the Environmental Protection Agency to

establish guidelines for the certification of laboratories performing bacteriological,

chemical, organic, and radiological analyses in support of the monitoring activities

mandated by the Federal act.

The EPA Work Group on Laboratory Certification was charged with the responsibility of

preparing guidelines for use in the certification of laboratories. To a limited extent,

the draft guidelines do reflect the lessons that were learned from clinical laboratory

accreditation.

The EPA guidelines stress that the program should be conducted by the state agency,

that is, the state should have "primacy." As a consequence, state agencies will be actively

encouraged to develop certification programs which are "equal to or more stringent than"

the Federal guidelines. Unlike the EPA guidelines, the Federal Interstate Licensure Program

for clinical laboratories gives very little encouragement to the state to develop adequate

programs. The Federal reluctance to surrender licensure to the states eventually led to some rather estranged feelings between many of the states and the Center for Disease Control.

The EPA guidelines, while they place heavy emphasis on the role state agencies hopefully will play, do not provide for equivalency status for private professional accreditation

programs. It is worth noting this fact as it may lead to a much better Federal /State

relationship. In the case of the Federal Clinical Laboratory Improvement Act of 1967

governing laboratories engaged in interstate commerce, very little encouragement was given

to state agencies. However, the act contained a separate section dealing with private

organizations which made it easier for a private organization to substitute its accreditation program for the Federal licensure than it was for a state agency to do so. As a rule

of thumb, if an accreditation program is to be mandatory, its implementation is best left

in the hands of a governmental agency.

The subject of personnel qualifications has been closely related to laboratory accreditation in the clinical area. The controversy surrounding this subject, while existent, has

not been as great as that involving state agency status as an accrediting body as mentioned

earlier. The biggest problem has been--just how far does one go in incorporating personnel

690
qualification regulations into an accrediting program? For the clinical laboratory, there

have been almost as many different approaches as there have been programs! Some of these

are:

(a) A program which does not consider the experience, training and education of

laboratory personnel but stresses, rather, inspection and proficiency testing of

the facility as an entire entity.

(b) Certification of only the laboratory director. He or she may be required to have

a doctorate in medicine, chemistry, bacteriology, etc, and subsequent to graduation four or more years of full-time clinical laboratory experience. In some cases, the director may have to be board-certified by a national accrediting body

such as the College of American Pathologists or the American Acaden\y of Medical

Microbiology.

(c) Certification of the laboratory director and the supervisors.

(d) Certification of all laboratory personnel including laboratory trainees. Many

persons feel that this is the besL approach and should be conducted nationally in

order to give technologists the mobility to move from one state to another as job

opportunities present themselves.

While certain minimal requirements with regard to personnel education, training and

experience appear to be desirable and necessary, there has to be a reasonable and gradual

approach if one is to prevent basically well qualified laboratory personnel from being

excluded from the field or severely limited in terms of job opportunities. One of the

biggest problems that has confronted clinical laboratory certification has been precisely

this type of situation. For example, under Federal Medicare regulations, certain minimal

requirements have been set for medical technologists. Individuals not meeting those

requirements must pass an examination by the end of 1977. While this appears to be an equitable approach at first glance, it has created many problems with the consequence that

many very capable technologists may be unemployed at the end of 1977. Many of these individuals were trained in a specific area such as hematology, bacteriology, or clinical chemistry and know very little about the other clinical laboratory specialties. The Federal

regulations, however, require that they pass an examination in all areas which for many

will be virtually impossible. Consequently, as accreditation programs are developed for

environmental laboratories, care must be taken to prevent this type of situation. The best

way to do this is to limit the input from professional societies who will favor regulations

and personnel qualification criteria favoring their membership.

3. Conclusion

Now that mandatory laboratory accreditation is around the corner, thanks to the Safe

Water Drinking Act, government agencies and professionals must begin to look closely at the

problem. As mentioned earlier, many lessons can be learned from the trials and tribulations

of the clinical laboratory programs. Laboratory accreditation, in order to achieve its

goal, must be evolved gradually and realistically rather than as a massive undertaking. As

experience has shown in the latter case, one may end up with unrealistic and even detrimental criteria for accreditation.

691 * U. S, GOVERNMENT PRINTING OFFICE: 1977 O - 248-136
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. 1 UllRl ir"ATinM OR R P POR T MO 0 C,^t,*t X^^^^r- €r\^w^

""'""sh^e'eT

"^""^ NBS SP-464

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Methods and Standards for Environmental Measurement

ir^ roceedings oi tne otn iviateriais r\esearcn oymposium

Held September 20-24, 1976

5. Publication Date November 1977

6. Performing Organization Code

7. AUTHOR(S) William H. Kirchhoff Editor

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Worlc Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as 9.

13. Type of Report &. Period

Covered

Final

14. Sponsoring Agency Code

15. SUPFLEMbN lAKY NOlt^?

Library of Congress Catalog Card Number: 76-608384

16. ABSTRACT (A 200-word or less (actual summary of most si^iticant information. It document includes a significant

bibliography or literature survey, mention it here.)

This book presents the Proceedings of the 8th Materials

Research Symposium on "Methods and Standards for Environmental

Measurement" held at the National Bureau of Standards,

Gaithersburg , Maryland, on September 20 through September 24,

1976. The Symposium was sponsored by the NBS Institute

for Materials Research in conjunction with the Office of Air

and Water Measurement.

The volume contains extended abstracts of the invited

and contributed papers in topics of concern at the time of the

symposium: Accuracy, the analysis of trace organic compounds

in water, multielement analysis, the physical and chemical

characterization of aerosols, in situ methods for water

analysis, the application of laser technology to atmospheric

monitoring, ambient air quality monitoring, the chemical

characterization of inorganic and organometallic constituents,

reference materials for environmental measurement and finally,

environmental laboratory certification and collaborative testing.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Accuracy; Aerosol; Air; Collaborative Testing; Laboratory Accreditation;

Laser Technology; Multielement Analysis; Pollutants; Speciation;

Standard Reference Materials; Trace Organics; Water

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