NBS

455

Microchemical

Analysis Section

Summary of Activities

July 1967 to June 1968

***T °

F

*o.

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

^MMS^&MiM0i¥MW^i^MM^%)^^^^^
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3, 1901. Today, in addition to serving as the Nation's central measurement laboratory,

the Bureau is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To this end the Bureau conducts research and

provides central national services in three broad program areas and provides central national services in a fourth. These are: (1) basic measurements and standards,

(2) materials measurements and standards, (3) technological measurements and

standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, and the Center for Radiation Research.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the

United States of a complete and consistent system of physical measurement, coor- dinates that system with the measurement systems of other nations, and furnishes

essential services leading to accurate and uniform physical measurements throughout

the Nation's scientific community, industry, and commerce. The Institute consists

of an Office of Standard Reference Data and a group of divisions organized by the

following areas of science and engineering

:

Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic Physics—Cryogenics2—Radio Physics2—Radio Engineering2—Astrophysics2—Time

and Frequency.2 THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to methods, standards of measurement, and data needed by industry, commerce,

educational institutions, and government. The Institute also provides advisory and

research services to other government agencies. The Institute consists of an Office of

Standard Reference Materials and a group of divisions organized by the following areas of materials research:

Analytical Chemistry—Polymers—Metallurgy — Inorganic Materials — Physical

Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides for the creation of appropriate opportunities for the use and application of technology within the Federal Government and within the civilian sector of American industry. The primary functions

of the Institute may be broadly classified as programs relating to technological meas- urements and standards and techniques for the transfer of technology. The Institute

consists of a Clearinghouse for Scientific and Technical Information,3 a Center for

Computer Sciences and Technology, and a group of technical divisions and offices organized by the following fields of technology:

Building Research—Electronic Instrumentation — Technical Analysis — Product

Evaluation—Invention and Innovation— Weights and Measures —Engineering

Standards—Vehicle Systems Research.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement,

and application of radiation to the solution of Bureau mission problems and the

problems of other agencies and institutions. The Center for Radiation Research consists of the following divisions:

Reactor Radiation—Linac Radiation—Applied Radiation—Nuclear Radiation.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted ; mailing address Washington, D. C. 20234.

2 Located at Boulder, Colorado 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia 22151.
UNITED STATES DEPARTMENT OF COMMERCE

C. R. Smith, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 455

ISSUED OCTOBER 1968

Microchemical

Analysis Section:

Summary of Activities

July 1967 to June 1968

Edited by John K. Taylor

Microchemical Analysis Section

Analytical Chemistry Division

Institute for Materials Research

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C., 20402 - Price $1.25
FOREWORD

The Analytical Chemistry Division was established as

a separate division at the National Bureau of Standards on

September 1, 1963, and became part of the Institute for

Materials Research in the February 1, 1964, reorganization.

It consists at present of nine sections and about 100 technical personnel encompassing some 57 different analytical

competences from activation analysis and atomic absorption

to vacuum fusion and x-ray spectroscopy. These competences,

and in turn the sections which they comprise, are charged

with research at the forefront of analysis as well as awareness of the practical sample, be it standard reference

material or service analysis. In addition it is their

responsibility to inform others of their efforts.

Formal publication in scientific periodicals is a highly

important output of our laboratories. In addition, however,

it has been our experience that informal, annual summaries

of progress describing efforts of the past year can be very

valuable in disseminating information about our programs.

A word is perhaps in order about the philosophy of these

yearly progress reports. In any research program a large

amount of information is obtained and techniques developed

which never find their way into the literature. This

includes the "negative results" which are so disappointing

and unspectacular but which can often save others considerable work. Of importance also are the numerous small items

which are often explored in a few days and which are not

important enough to warrant publication—yet can be of great

interest and use to specialists in a given area. Finally

there are the experimental techniques and procedures, the

designs and modifications of equipment, etc., which often

must be covered in only a line or two of a journal article.

li
Thus our progress reports endeavor to present this

information which we have struggled to obtain and which we

feel might be of some help to others. Certain areas which

it appears will not be treated fully in regular publications

are considered in some detail here. Other results which are

being written up for publication in the journal literature

are covered in a much abbreviated form.

At the National Bureau of Standards publications such

as these fit logically into the category of a Technical Note

In 1968 we plan to issue these summaries for all of our

sections . The following is the fourth annual report on

progress of the Microchemical Analysis Section.

W. Wayne Meinke, Chief

Analytical Chemistry Division

111
PREFACE

This report summarizes the current program and activities

of the Microchemical Analysis Section of the Analytical

Chemistry Division. The Microchemical Analysis Section has

the primary mission to make contributions to the science and

technology of analysis of small samples. Its program includes

fundamental studies to improve the precision, accuracy and

sensitivity of analytical methods as well as the development

of new and improved methods of chemical analysis applicable to

wide areas of materials research. As a closely related activity, the section provides analytical measurements of high reliability to the various research programs of the Bureau and

to the Standard Reference Materials programs.

Research projects are active in the following analytical

competence areas: gas analysis by mass spectrometry and other

techniques; polarography ; coulometry; electroanalytical

measurements; microscopy; wet chemistry; conventional

elemental microchemical analysis

.

Activities during the reporting period are classified

either as research or analytical development. The classification is often arbitrary since nearly all of the analytical

applications have required considerable efforts of both kinds.

During the year, a number of analytical methods have been

developed or studied in sufficient detail to verify their applicability to the demanding requirements of standard reference material certification. An attempt has been made to

describe a number of these, briefly, yet with sufficient detail to make them understandable to an experienced analyst.

However, specific details will be made available to anyone

interested in such matters.

Much of the work during the year has been concerned with

the analysis of standard reference materials. In addition,

these materials have been used frequently to verify the

IV
accuracy of analytical procedures . They are referred to by

an Identification such as SRM #1604, for example. A catalog

containing full descriptions of these materials may be obtained from the Office of Standard Reference Materials,

National Bureau of Standards, Washington, D. C. 20 234.

In order to specify adequately the procedures, it has

been necessary occasionally to identify commercial materials

and equipment in this report. 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.

John K. Taylor, Chief

Microchemical Analysis Section

v
TABLE OP CONTENTS

PAGE

1. GAS ANALYSIS 1

A. Introduction 1

B. Research Activities 1

1. Determination of Atmospheric Oxygen .... 1

2. Trace Oxygen Analysis

3. Determination of Carbon Dioxide 6

4. Determination of Argon 7

C. Standard Reference Materials 8

1. Oxygen In Nitrogen 8

2. Sulfur Dioxide in Air 8

3. Hydrocarbon in Air 9

D. Research Materials Service Analysis 10

1. General 10

2. Analysis of Heavy Water 14

3. Reaction Product Analysis 1^

4. Gas Contaminant Identification 15

5. Atmospheric Oxygen Survey 15

2. POLAROGRAPHIC ANALYSIS 19

A. Introduction 19

B. High Precision Polarographic Analysis 19

1. Analysis of Lead and Zinc Cyclohexanebutyrates 19

2. Analysis of Copper-Zinc Alloys 22

C. Major Constituent Analysis 23

1. Analysis of Metal-Organic Complexes .... 23

2. Determination of Zinc in Corrosion

Products 25

D. Minor Constituent Analysis 25

1. Determination of Lead in Leaded Steel ... 25

2. Determination of Copper, Bismuth, and

Nickel in Solders 26

3. Determination of Copper and Zinc in

Aluminum Alloys 29

E. Small Sample Analysis 29

1. Analysis of Antimony-Bismuth Films .... 29

2. Analysis of Copper-Nickel-ChromiumAluminum Films 30

3. Analysis for Lead in Lead-Tin-Telluride . . 31

F. Trace Analysis 32

1. Determination of Trace Constituents in

Zinc 32

2. Determination of Trace Constituents in

High Purity Zinc 35

3. Determination of Copper, Lead, and Iron

in High-Purity Platinum 36

vi
PAGE

4. Determination of Copper and Iron in

High Purity Gold 38

5. Analysis for Pollutants 39

3. COULOMETRIC ANALYSIS 4l

A. Introduction 41

B. Research Activities 4l

1. Development of a Method for Precise

Analysis of Boric Acid 41

2. Determination of Strong Acid in Crystalline Boric Acid 44

3. Electrochemical Equivalents of Benzoic

and Oxalic Acids 46

4. Redetermination of the Faraday ...... 54

5. Effect of Photodecomposition of AgCl on

Coulometric Determination of Chloride ... 57

C. Analysis of Standard Reference Materials ... 59

1. Homogeneity Studies of Boric Acid 59

2. Effect of Relative Humidity on the

Stoichiometry of Boric Acid, Lot No.

92511 63

3. Development of a Procedure for Precise

and Accurate Preparation and Aliquoting

of Separated Boron-Isotope Boric Acid

Solutions 65

4. Determination of Chromium in Ferrous

Alloys 70

5. Assay of EDTA by Acidimetric Coulometry . . 74

6. Analysis of Ion Exchange Beads 75

D. Analysis of Research Materials 78

4. ELECTROANALYTICAL MEASUREMENTS 80

A. Introduction 80

B. Research Activities 80

1. Improved Microdetermination of Silver by

Linear Null-Point Potentiometry .* 80

2. Fluoride Microanalysis by Linear NullPoint Potentiometry 83

3. Electrochemical Generation of Fluoride

Ion by Solid-State Transference 88

4

.

Analate Additions Potentiometry 91

5. Determination of Dissolved Oxygen Using

an Amperometric Oxygen Sensor 93

C. Analysis of Standard Reference Materials ... 96

1. Analysis of Silver 2-Ethylhexanoate .... 96

2. Analysis of o-Fluorobenzoic Acid 97

3. Analysis of Au-Ag Metal Microprobe

Standards 98

vii
PAGE

D. Analysis of Research Materials 100

1. Determination of Fluoride in Sodium

Carbonate Solutions 100

2

.

Determination of Fluoride in HF-HC1

Mixtures 101

5. MICROSCOPIC AND CLASSICAL MICROCHEMICAL ANALYSIS . . 102

A. Introduction 102

B. The Detection and Identification of Microamounts of Materials 102

C. Ultramicrochemical Standards . 103

D. Determination of Trace Quantities of Uranium

in Biological Materials 105

1. Background 105

2. Experimental 107

3. Results 108

E. Analysis of Standard Reference Materials . . . 109

1. Residual Fuel Oil 109

2. Miscellaneous Analyses 112

6. MISCELLANEOUS ANALYTICAL PROCEDURES 113

A. Determination of Sulfur in Plastic Clay .... 113

B. Determination of Carbon and Sulfur in

Copper Foil Il4

C. Analysis of Platinum-Chromium Alloys 115

7. INTERNATIONAL RESEARCH GRANTS PROGRAM 117

A. Introduction 117

B. Trace Metal Determinations in Silicates .... 117

C. Anodic Stripping Voltammetry with Superimposed

A.C. Potential 118

D. Studies of the Rotating-Film Electrode .... 118

E. Water Purification 119

F. Theoretical Studies of Electrochemical

Techniques 120

8. PERSONNEL AND ACTIVITIES 121

A. Personnel Listing 121

B. Publications 121

C. Talks 123

D. Committee Activities 124

E. Award 125

F. Standard Reference xMaterials Analyses 126

9. REFERENCES 129

viii
LIST OP FIGURES

FIGURE NO. PAGE

1. Modified Hersch cell for determination of

oxygen concentrations above 1 ppm 3

2. Apparatus for determining concentrations of

oxygen in inert gases at concentrations

above 1 ppm 4

3. Galvanic cell designed for the detection of

oxygen at concentration levels below 1 ppm ... 5

4. Photograph showing arrangement of cells in

series 6

5. Schematic of gas handling system for admitting

gases to oxygen analyzer at one atmosphere

from a container at lower pressure 16

6. Photograph of apparatus shown in figure 5 ... 16

7. Homogeneity studies of boric acid 44

8. Coulometric titration cell for precise

acidimetry 49

9. Effect of titration sequence and composite

number on the assay of boric acid 61

10. Effect of relative humidity in the balance

case on the approach of boric acid to H^BO

stoichiometry (15 min. exposure time) ..... 64

11. Effect of the humidity of the environment on

the assay of boric acid 65

12. Loading factor of ion exchange beads as a function of bead diameter 77

13. Fluoride electrode microcell 85

14. Apparatus for fluoride determination by

linear null-point potentiometry 86

15. Electrochemical cell for fluoride generation . . 89

16 . Fluoride generation cell 89

17. Oxygen cell and analyzer 94

18. Oxygen sensor response to dissolved oxygen ... 95

ix
1.

2.

3.

4.

LIST OF TABLES

TABLE NO. PAGE

Standard reference materials certified for

oxygen content 8

Summary of gas analytical services 11

Zinc in zinc cyclohexanebutyrate 20

Homogeneity check of six different bottles of

lead cyclohexanebutyrate 21

5. Determination of lead in various portions of

blended lead cyclohexanebutyrate 22

6. Analysis of metal-quinolates 24

7. Copper and lead in metal-organic complex .... 25

8. Copper in SRM 127a, 127b, and 1131 27

9. Nickel in SRM 127a, 127b, and 1131 28

10. Bismuth in SRM 127a, 127b, and 1131 28

11. Determination of copper and zinc in aluminum

alloys 29

12. Determination of bismuth and antimony in thin

film deposition source material 30

13. Lead in lead-tin-telluride 32

14. Copper, lead, and cadmium in pure zinc composition standard SRM 683 33

15. Determination of iron and aluminum in zinc SRM

683 and 728 34

16. Copper, cadmium, and lead in high purity zinc . . 35

17. Iron, copper and lead in high purity and doped

platinum ..... 37

18. Comparison of iron, copper, and lead determinations in platinum, SRM 680 and SRM 681 37

19. Iron in high-purity gold wire 38

20. Copper in high-purity gold wire 39

x
TABLE NO. PAGE

21. Impurities found in oxalic acid dihydrate . . .

22. Electrochemical equivalent of benzoic acid . .

23. Electrochemical equivalent of oxalic acid

dihydrate

47

52

53

55

59

60

24. Summary of values for the faraday

25. Effect of light on argentimetric titration

of KC1

26. Boric acid homogeneity studies

27. Assay of boric acid. Lot No. 92511. (equilibrated at 3^% relative humidity for at least

30 min. ) 62

28. Absorption of water by boric acid 63

29. Precision of aliquoting and analysis of boric

acid solutions 67

30. Effect of the size of boric acid solution

aliquot on the coulometric determination of

boric acid concentration 68

31. Concentration changes of solution (b) stored in

polyethylene bottle in room atmosphere 69

32. Stability of H_B0 solution stored in glass

bottles in 90-100% RH atmosphere 70

33- Determination of chromium in ferrochromium,

SRM 196 72

34. Results of analysis of three randomly selected

bottles for each of the two SRM cast irons ... 72

35- Analysis of SRM stainless steel for chromium . . 7 4

36. Assay of Na

2

EDTA 75

37- Analysis of RH ion exchange beads 76

38. Analysis of RC1 ion exchange beads 76

39. Analysis of calorimetric reaction products ... 79

XI
TABLE NO. PAGE

40. Results of the LNPP determination of silver ... 82

41. Results of fluoride determinations by LNPP ... 87

42. Oxygen sensor response to dissolved oxygen ... 95

43. Silver content of silver 2-ethylhexanoate .... 97

44. Au-Ag content of microprobe standards 100

45. Fluoride in sodium carbonate 101

46. Fluoride in HF-HC1 mixtures 101

47. Loss of volatile constituents from fuel oils . . 110

48. Analyses of residual fuel oils Ill

49. Determination of S0„ in clay 113

50 . Determination of sulfur in copper foil 11^

51. Determination of carbon in copper foil 115

52. Analysis of platinum-chromium alloys 116

xii
MICRO CHEMICAL ANALYSIS SECTION: SUMMARY OP ACTIVITIES

JULY 1967 to JUNE 1968

Edited by John K. Taylor

ABSTRACT

This report describes the research activities and scientific programs of the MIcrochemical Analysis Section of the

Analytical Chemistry Division of the NBS Institute for Materials

Research during the period July 1967 to June 1968. General

activities are reported in the areas of gas analysis, polarography , potentiometry , coulometry, chemical microscopy, and

classical microchemical analysis. Research activities described in some detail include: determination of trace amounts

of oxygen in gases, development of a coulometric method for

precise analysis of boric acid, improvements in microdetermination of silver and fluorine by null-point potentiometry,

the electrochemical generation of fluoride ion, preparation

of resin-bead particle standards, and determination of trace

elements by the nuclear track technique. A number of microchemical procedures which have been developed for the analysis

of a variety of materials are also included.

Key Words: Coulometric analysis, Gas analysis, Methods of

chemical analysis, Microchemical analysis,

Microscopic analysis, Polarographic analysis,

Specific ion electrodes.

xm

1. GAS ANALYSIS

A

.

Introduction

The functions of the Gas Chemistry Laboratory are threefold; research into gas analytical methods, the analysis and

production of gaseous standard reference materials, and service analysis of research materials and other materials.

These functions are not independent of each other but rather

are interrelated. For instance, much of the research is directed toward the analysis of standard reference materials

and some of the service work requires prior development of

analytical methods. For this reason there will be some overlapping of the three sections of this portion of the report.

B. Research Activities

1. Determination of Atmospheric Oxygen

In a previous report [1], initial research on a method

for the determination of atmospheric oxygen was described.

This work has since been completed and published [2]. The

method involves reaction of the oxygen with either phosphorous

or a sodium-potassium alloy. When corrected for the difference

in carbon dioxide, which is removed when using the sodiumpotassium alloy, the results are identical. It was found that

the cylinder of air examined had an oxygen content of 23.157

weight percent with a 95% confidence limit of 0.017% based on

36 determinations. This value is equivalent to 20.959 mole

percent. The currently accepted value for the concentration

of oxygen in the atmosphere is 20.9^5 ± 0.002 mole percent [3].

The contents of the cylinder from which the 36 samples were

obtained was analyzed for its carbon dioxide content. This

was found to be quite low and when the correction for the reduced carbon dioxide content was applied to the original value,

the corrected value became 20.953 mole percent. In order to

resolve the still remaining discrepancy of 0.008 mole percent,

a sample of pure dry atmospheric air was obtained. It was

1
compared with the cylinder sample and a difference of 0.008

mole percent was observed. Thus, the discrepancy was resolved

and the validity of the gravimetric method was proved. These

results are also in substantial agreement with the results

obtained by Benedict in 1912 [4],

2 . Trace Oxygen Analysis

Considerable effort has been devoted to the development

of absolute methods for the determination of oxygen in gases

.

Such methods are needed to accurately analyze a series of

standard reference materials consisting of nitrogen containing

oxygen at levels ranging from a few parts per million up to

a thousand parts per million or more.

An attempt was made to determine low concentrations of

oxygen in inert gases by expanding the sample into a closed

Hersch-type cell [5] and integrating the current produced by

the oxygen. A knowledge of the coulombs produced, in addition

to the cell volume and sample pressure, should allow calculation of the oxygen concentration. After considerable experimentation, this method was abandoned, since results were

generally non-reproducible. The major problem was obtaining

a reproducible value for the cell volume; this seemed to

fluctuate due to varying rates of loss of water vapor.

An attempt was made to determine the oxygen content of

some of the intermediate mixtures by gravimetric methods. Two

reagents were tried; manganous oxide (MnO) , and phosphorous

coated on silica gel. The MnO appeared to be quite ineffective

in removing all the oxygen and the results were very low. The

phosphorous reagent was prepared by dissolving phosphorous in

carbon disulfide and then soaking silica gel in this solution.

The solution was then evaporated and the reagent was packed

into absorption tubes. Again the results were disappointingly

low. Therefore, gravimetry as a method for the determination

of oxygen at low concentrations was abandoned.
A successful method for the analysis of trace concentrations of oxygen in inert gases was developed utilizing a modification of the Hersch cell [5]. The cell design used for

analyses, which are described later, is shown in figure 1. The

cell consists of a cathode made from ribbons of silver foil

one mil in thickness and an anode consisting of a small sheet

of lead, separated from the silver by a Teflon sheet. The

electrolyte was a two-molar solution of sodium hydroxide.

Four cells are connected in series to assure complete

electrochemical reduction of the oxygen. The current output

in terms of the voltage drop across appropriate resistors is

measured at two different flow rates . The difference in

voltage is a direct measure of the difference in the rate of

consumption of oxygen and hence allows a calculation of the

absolute oxygen content. The apparatus with its attendant

valving, volume measuring device and saturator to allow correct

calculation of the volume is shown schematically in figure 2.

TIGHTLY PACKED SILVER FOIL COATED WITH ELECTROLYTE

NICHROME LEADS

LEAD IMMERSED

IN ELECTROLYTE TEFLON INSULATOR GLASS TUBE

RUBBER STOPPER

/

COPPER TUBE

I CM

Figure 1. Modified Hersch cell for determination of

oxygen concentrations above 1 ppm.
TO GAS CYLINDERS

PRESSURE GAUGE

"-Hgh^

U CELLS IN

K ^>

\ PRECISION y RESISTORS |

TO VACUUM

PUMP

BUBBLE FLOWMETER

LEADS TO SELECTOR

SWITCH AND RECORDER

GAS SATURATOR

Figure 2. Apparatus for determining concentrations of

oxygen in inert gases at concentrations above

1 ppm.

This method is described in a publication [6] which should

be consulted for experimental details. The results of an

experiment are calculated from the equation

where

M

0,

M

, (E -E )T x 10 ( PPm) " °' 2127 (f

f-f^)p >

x 10 = oxygen concentration in parts per million

by volume (ppm)

E. = the sum of all cell outputs at the initial

flow rate (mV)

E

f

= the sum of all cell outputs at the final

flow rate (mV)

f. = initial flow rate (cm /s)

f

f

= final flow rate (cmJ /s)

T = temperature in degrees Kelvin

r = load resistance of cell (ohms)

p' = atmospheric pressure corrected to dry air

at room temperature (atmospheres).

4
Using this new technique, oxygen concentrations as low as one

ppm may be determined. Below one ppm, residual currents, produced by leakage or diffusion of atmospheric oxygen into the

system, tend to obscure the small currents produced by the

oxygen in the gas being analyzed.

An improved apparatus designed for concentrations of

oxygen below the ppm level has been designed. This cell design

is shown in figure 3 and the complete apparatus is shown

photographically in figure 4. In use, all joints are lubricated with a small amount of high vacuum grease and tightly

clamped.

/\. NICKEL LEADS

7/12 JOINT

TO GAS HANDLING SYSTEM

TO SIMILAR CELL

12/5 JOINT

35/20 JOINTS

GLASS TUBE LEAD IMMERSED IN ELECTROLYTE

I CM

Figure 3. Galvanic cell designed for the detection of

oxygen at concentration levels below 1 ppm.
Figure 4. Photograph showing arrangement of cells in

series

.

3 . Determination of Carbon Dioxide

A previous publication from this laboratory described a

method for the accurate determination of low concentrations of

carbon dioxide in nitrogen [7]. A method has now been developed

for the accurate and direct mass spectrometric analysis of

carbon dioxide in air. In essence, it consists of removal of

the oxygen with phosphorous with subsequent mass spectrometric

analysis with an accuracy of better than 1% . Samples are collected in bulbs containing phosphorous which are immediately

analyzed by comparison with one of the NBS standard reference

materials consisting of carbon dioxide in nitrogen (SRM's

1601, 1602 and 1603) .
Using this method, a large number of samples were collected

in a rural area near the National Bureau of Standards site at

Gaithersburg, Maryland. The results are of great interest because they indicate rapid fluctuations in the carbon dioxide

content of the atmosphere. This is in agreement with observations made by Dr. C. D. Keeling of the Scripps Oceanographic

Institute [ 8]

.

The National Bureau of Standards method for determination

of atmospheric carbon dioxide has also been described in a

publication [9]

.

4 . Determination of Argon

Moissan, in 1903 3 made a world-wide survey of the argon

content of the atmosphere [10]. His value of 0.934 mole percent

has recently been challenged by Sinya Oana, whose value is

0.917 mole percent [11]. Both of these investigations utilized

the same method, that is removal of all the reactive constituents of the air with calcium with subsequent measurement of the

residual pressure presumed to be argon.

We have attempted to determine the argon by an independent

method based on high pressure mass spectrometry, in which a

comparison is made between a carefully prepared standard and

a sample of clean dry atmospheric air. This procedure consists

of carefully weighing a quantity of nitrogen in a bulb after

which slightly more than one percent of argon is added and the

bulb reweighed. This is used to calibrate the mass spectrometer by measuring the mass (40) to (28) ratio. A sample of

ordinary air is then measured in the same manner. Preliminary

results indicate that the true value for the concentration of

atmospheric argon may be lower than that reported by either of

the previous investigators . Their high results may be due to

the equilibrium pressure of nitrogen over calcium nitride.

Much further work will be necessary before a definitive value

can be given.
Table 1.

SRM No.

1604

1605

1606

1607

1608

1609

C . Standard Reference Materials

1

.

Oxygen In Nitrogen

Certified gas standards consisting of oxygen in nitrogen

have been prepared, analyzed, and are now being distributed

by the Office of Standard Reference Materials. These are

summarized in table 1.

Standard reference materials certified for

oxygen content

.

Oxygen Concentration

0.000303 ± 0.000004 mole percent

.00103 ± .00001 mole percent

.0112 ± .0001 mole percent

.0212 ± .0002 mole percent

.0978 ± .0007 mole percent

20.95 ± .02 mole percent

The methods of analysis have been described earlier in

this report.

Work is currently in progress on three new gaseous standards. These are sulfur dioxide in air, carbon monoxide in air,

and a hydrocarbon in air.

2

.

Sulfur Dioxide in Air

The major problem with sulfur dioxide is its reactivity.

Consequently, the first phase of this program was concerned

with selection of a suitable container. Initially, three duplicate mixtures were prepared in stainless steel cylinders.

Of each duplicate pair, one was equipped with a brass valve

and one with a stainless steel valve. The nominal concentrations of sulfur dioxide in nitrogen were 6, 115, and 2350 ppm

by volume, respectively. The mixtures were periodically

analyzed over a period of one month by the peroxide method [12]

and it was observed that the 6 ppm mixture continually decreased while the values for the higher concentration remained

constant within the limitation of the experimental error.

8
Subsequently, two more mixtures were prepared in larger

stainless steel cylinders . The concentrations were 15 and 300

ppm. Periodic analysis of these samples produced results with

a spread of less than ± 1% from the mean.

Portions of the 15-ppm mixture were transferred to two

mild steel cylinders . The concentration of sulfur dioxide

immediately dropped to 8 ppm in one cylinder and to 4 ppm in

the other. These concentrations continued to decrease significantly over a period of two weeks

.

Because of the observed behavior, effort will be devoted

at present to certification of standards containing relatively

high concentrations of sulfur dioxide. These standards will

be useful for source control rather than atmospheric analysis.

Concurrently, further investigation will be continued to determine a suitable container for the lower concentrations.

3 . Hydrocarbon in Air

A proposal to produce a series of hydrocarbon-in-air

standards was accepted and work has begun on their preparation

and analysis . Mixtures will be made using methane as the

hydrocarbon component and the concentrations will be approximately 100, 10, and 1 ppm.

Hydrocarbon analyses are to be performed using an instrument utilizing flame ionization. In order to use this instrument, calibration standards are necessary. The relationship

between hydrocarbon concentration and instrument response

should be linear. Hence, a standard of relatively high concentration (200-300 ppm) and one of zero concentration could be

used to calibrate the instrument for subsequent analysis of

mixtures of hydrocarbon in air.

A standard containing 207 ppm methane in nitrogen was

available; this concentration was determined by converting

the methane to carbon dioxide and determining the carbon dioxide

mass spectrometrically as well as from the measured pressure

involved in compounding the mixture.
Using the flame-ionization technique, with the above calibrant, the hydrocarbon content of several cylinders of compressed air was found to be in the 3-ppm range. To provide

air of zero hydrocarbon concentration, removal of the hydrocarbon contained in the compressed air was necessary. Neither

a column of molecular sieves nor a column of cooled, activated

charcoal inserted in the air line, were effective in completely

removing the hydrocarbon in the compressed air. However, it

appears that a Vycor tube filled with cupric oxide and heated

to about 1050°C will remove all hydrocarbon in air passed

through it. Using this technique, the same instrument response

is obtained when air containing about 4.5 ppm hydrocarbon, air

containing about 2 ppm hydrocarbon, and nitrogen containing

about 0.2 ppm hydrocarbon are passed through the hot cupric

oxide into the instrument. Preliminary results using the 207-

ppm mixture and compressed air passed over hot copper oxide

(after which the air is presumed to be hydrocarbon free) as

calibrants, indicate that results from the hydrocarbon analyzer

are reproducible. For example, an air sample, analyzed on three

different days, gave results of 2.98, 2.91 and 2.92 ppm hydrocarbon.

After several mixtures are analyzed to verify the linearity

of response and also to provide calibration standards at the

lower levels, work will proceed on the preparation of the

standard reference materials

.

D. Research Materials Service Analysis

1. General

The analysis of research materials is a significant part

of the activities of this laboratory. The nature of samples

range from relatively pure materials to very complex mixtures.

Typically, there are complicating factors that preclude a

routine determination. Frequently, method development or modification is involved.

10
Analyses performed during the past year are summarized in

table 2. Several of the more interesting determinations are

outlined below.

<v able 2. Summary of gas analytical services.

A. Mass Spectrometric Analysis

Number of

Material Samples Sample Size Determined

Organic Substances

Reaction 1 2 ml STP Molecular weight

product

Ethane 1 10 ml STP

Gases evolved 1 10" moles

from plastics

2

Inorganic Substances

Air Cylinder

Hp, CH., C0

2

, butane

p-xylene, p-tolualdehyde

co

2

Condensates 1 10 ml STP COp, HC1, HpS

from reaction

NpO 1 Cylinder Hp, Op, Ar

Air 1 Cylinder Hp

He 1 50 ml STP Hp

Np 1 Cylinder He

SP

5

C1 2 Cylinder SOFp, SOp, SOpFp,

SiF„

11
Table 2. (Continued)

Number of

Material Samples Sample Size Determined

Atmospheres

within sealed

tape recorders

Inorganic-Organic Mixtures

500 ml STP Organic vapor contamination of the

Np atmosphere

Product of

reaction

2 0.1 ml STP Hp, CHjj

Reaction

atmosphere

2 2 ml STP Hp, CH^, Np,

2

,

H

2

1 10 ml STP CH^, HpO, Air

Air 1 Cylinder CH

4

Air 1 Cylinder Pentane

Isotopically Altered Compounds

Helium-3 3 30 ml STP He-4, Hp, HpO, Np

Helium-3 19 30 ml STP He-4

Nitrogen-15 1 100 ml STP Nitrogen-l4

Carbon-13 2 0.07 ml Carbon-12 ethyl

enriched ethyl acetate

acetate

Helium-3 1 Cylinder Helium-4, HpO, Np

Op, Ar, COp

D

2 2 1 ml STP HD, Hp

D

2

3 Cylinder Hp, HD

12
He

He

NO,

Table 2. (Continued)

Pure Chemicals

1 500 ml STP

1 Cylinder

1 Cylinder

N

2

, 2, Ne, Ar

CH lp C

2 Hg,2

Impurities

B. Nuclear Magnetic Resonance Analysis

Material

Reaction

products

Number of

Samples

Unsaturated

hydrocarbon

plus reactant

Sample Size

5 ml of a 1056

solution

5 ml of a 1056

solution

Determined

Structure

Change in the ratio

of saturated to un- saturated material

over a period of

time

C. Gas Chromatographic Analysis

Material

Preservative

solutions

Bromo organic

compounds

Number of

Samples

3

2

Sample Size

10 ml

10 ml

Determined

Methanol, ethanol,

water, formaldehyde

Purity

D. Preparation of Gas Mixtures

Compounded one mixture of Ik ppm carbon monoxide in

nitrogen.

Compounded for methane in air mixtures

(a) 2.02 ppm

(b) 2.02 ppm

(c) 8.09 ppm

(d) 8.09 ppm.

13
2. Analysis of Heavy Water

A method was developed and is now being used to monitor

the deuterium oxide content of heavy water contained in the

NBS nuclear reactor. The preliminary work has been described

in the report of last year [1], The method consists of comparing the absorption of a sample of deuterium oxide to that

of a standard at 2.95 u using an infrared spectrometer. The

standards are prepared from a sample of deuterium oxide of

known concentration. A series is prepared by the careful addition of weighed quantities of water to weighed quantities

of deuterium oxide.

The heavy water for installation in the NBS reactor consisted of 75 drums, each containing 55 gallons of deuterium

oxide. The values obtained on analysis of these drums ranged

from 99.73 to 99.80 mole percent deuterium oxide. These values

could be determined to ± 0.005 mole percent.

Periodic analyses of the deuterium oxide in the reactor

have shown little additional contamination by light water.

3 • Reaction Product Analysis

Another analysis involved an experiment in kinetics which

was solved using a nuclear magnetic resonance spectrometer

(NMR) . The problem was to determine the rate at which various

reactants would add across the double bond of an unsaturated

organic molecule. The reactant and unsaturated molecule were

added to an NMR tube at a very low temperature. 'The tube was

sealed and stored at low temperature until analyzed, at which

time it was quickly warmed to the temperature of the NMR probe

and a spectrum of the significant peaks was obtained. These

peaks, occurring in regions corresponding to saturated and unsaturated bonds, were periodically measured and their areas

determined. Prom thes^ data it was possible to determine the

rate constant for the reaction.

14
2| . Gas Contaminant Identification

A third problem was concerned with the premature failure

of sealed tape recorders carried in space satellites. The

project in which these recorders were used was sponsored jointly

by the National Aeronautics and Space Administration and the

European Space Research Organization. Their suspicion was

that possible volatile organic substances might be contaminating

the supposedly inert atmosphere within the recorders causing

failure of the tape or the coating on the tape.

Recorders prepared by both groups were obtained. They

were placed in an oven under conditions similar to what they

would experience in actual usage. Samples of the atmospheres

within the recorders were then removed through a small valve

inserted into the recorders. The samples were then examined

mass spectrometrically . Some samples were introduced directly

while others were passed through a cold trap. In the case of

these, the volatiles were pumped away with subsequent warming

and those substances not volatile at the low temperature were

determined.

Varying amounts of organic materials were found in each

recorder. This data will be used by the concerned agencies

together with their knowledge of the components in the recorders

in order to remedy the problem.

5 . Atmospheric Oxygen Survey

An example of a combined service and development project

is a cooperative effort between the Environmental Science

Services Administration and the National Bureau of Standards

for the investigation of a method for the determination of

atmospheric oxygen in samples of air collected on a world-wide

cruise of the research ship Oceanographer . It was necessary

for the Bureau to develop a technique which would allow analysis

of small samples at atmospheric pressure with an accuracy of

0.01 mole percent or better. The apparatus is shown schematically in figure 5 and photographically in figure 6.

15
c

METAL TO GLASS BALL JOINT V5

MERCURY LEVELLING BULB

V4

XJ

V3

U-TUBE MANOMETER

V2

NITROMETER TUBING

Figure 5- Schematic of gas handling system for admitting

gases to oxygen analyzer at one atmosphere from

a container at lower pressure.

Figure 6. Photograph of apparatus shown in figure 5

16
In use, the sampler is connected at B, the mercury is

transferred to the levelling bulb and stopcock 2 is closed.

The whole system is evacuated through valve 2 at line C with

only valve 4 closed. Valve 2 is then closed and the cylinder

valve is opened allowing the sample to fill the system. Valve

3 is then closed and stopcock 2 is opened slowly until enough

mercury has entered the reservoir to bring the pressure to

about a torr above atmospheric. Stopcock 2 is then closed,

valve k is opened momentarily to equalize the pressure with

the atmosphere. Valve 4 is then closed and measurements of

the oxygen content are made using an instrument utilizing the

paramagnetic properties of oxygen. Next, the system enclosed

by valves 2, 3, 4, 5, and stopcock 1 is evacuated. Valve 2 is

then opened and a new sample is allowed to flow into the restricted portion of the system. Mercury is again allowed to

flow into the reservoir after opening stopcocks 1 and 2.

Valve 5 is opened and the pressure is raised again to slightly

over one atmosphere

.

The same procedure is followed in introducing more samples

from the same flask. The procedure can be continued as long as

there is sufficient mercury in the reservoir to allow compression of the sample to one atmosphere. The tubing is 1/4-in.

soft copper and the operation is so rapid and the cell volume

is so small that no contamination from previous samples from

the same container trapped in the reservoir or manometer is

likely to occur.

Because the measurements are made at atmospheric pressure,

a barometer capable of estimation of the atmospheric pressure

with a repeatability of ± 0.03 mm is necessary to correct all

calculations to the same pressure.

Personnel aboard the Oceanographer will sample air at

selected locations by filling one-liter stainless steel flasks

which will be evacuated immediately before sampling. The

sample will be drawn through a probe sufficiently long to

17
obtain an uncontaminated sample of air. The air is dried by

means of a drier filled with magnesium perchlorate attached

to the probe. It is anticipated that at least 50 samples will

be collected from this cruise. Subsequently, a second research

ship, the Eltanin, will obtain a similar number of samples

which will also be analyzed in the same manner.

The apparatus will allow about five samples per container

to be analyzed.

(E. E. Hughes, W. D. Dorko, and J. M. Ives)

18
2. POLAROGRAPHIC ANALYSIS

A. Introduction

The polarographic program during the past year has been

largely devoted to the analysis and development of methods of

analysis of standard reference and other research materials.

Since a scarcity of reliable methods exists in many areas of

microchemical, trace, and high precision analysis, considerable effort has been exerted in these directions in this

laboratory. The resultant polarographic methods were demonstrated to be advantageous in most cases in sensitivity, accuracy, and time required for analysis. Some of the procedures

will be given in the following report as well as some collaborative data obtained by other analytical techniques for the

same materials

.

B

.

High Precision Polarographic Analysis

1 . Analysis of Lead and Zinc Cyclohexanebutyrates

Procedures utilizing the improved comparative polarographic method developed here [13] have been applied to

several organic standard reference materials . Not only were

the methods used for the certification analysis, but also

provided quick and accurate information on sample homogeneity.

The procedure for the determination of zinc in zinc

cyclohexanebutyrate , SRM 1073b, was as follows: After drying

over phosphorous pentoxide for about 48 hours, samples weighing approximately 0.6 g were slowly ashed to about 700 °C.

The residues were then wet ashed with nitric acid and hydrochloric acid, evaporated to dryness, dissolved In 10 ml of

concentrated hydrochloric acid and water and diluted to one

liter. Zinc was then measured comparatively at about - 1.0 V

vs . a mercury pool anode using reference solutions prepared

in the same manner from melting point zinc, SRM 43e.

19
Preliminary analyses of nine separate lots of the sample

showed no significant differences . The lots were then combined by rotating and tumbling in a large jar. Pour samples

were taken from the blended material, identified as follows:

top, 1/3 down, 2/3 down, bottom. Quadruplicate determinations

were made on each sample except the one taken 2/3 down which

was analyzed in triplicate. The results are shown in table 3-

Table 3. Zinc in zinc cyclohexanebutyrate

.

Sample Standard

designation Zinc, percent deviation, s Top 16.68 0.06

1/3 down 16.60 .14

2/3 down 16.67 .06

Bottom 16.67 .09

General average 16.66

The method for the determination of lead in lead cyclohexanebutyrate, SRM 1059b, was as follows: After storing

in a desiccator over phosphorous pentoxide for about 24 hours,

samples weighing about 0.27 g were ashed slowly to 500 °C.

The residues were dissolved in 10 ml of hydrochloric acid and

diluted to one liter. Lead was then measured comparatively

at about - 0.5 V vs . a mercury pool anode using solutions

prepared from melting point lead, SRM 49d, as reference

standards

.

The material was received in 12 bottles, each containing

about 150 g of the compound. Six bottles were selected at

random and four were analyzed in duplicate and two in triplicate. The results are shown in table 4. It is seen that the

average deviations between different bottles were somewhat

greater than those between replicates on a single bottle,

suggesting that the differences found between bottles were

real

.

20
Table 4. Homogeneity

of lead cycl<

check of six different

ohexanebutyrate

.

bottles

Sample

designation Pb,

36,

, %

.55

Avg

det<

. dev.

ermina

0.14

per

.tion

Average

Pb, %

36.41

Deviation

from general

average

0-4 0.35

36,,26

0-10 36,

36,

.59

.70

.06 36,,64 .12

0-11 37,

37.

37.

.38

.29

.43

.05 37..37 .61

0-12 36,

36,

,62

.76

.07 36,.69 • 07

0-20 36,

36,

36,

.31

.55

,48

.09 36,.45 .31

S-29 36,

37.

,66

,12

.23 36..89 • 13

General

average

36,.76 .11 .26

The several lots were then combined and blended by rotating and tumbling in a large jar. Four samples were taken

from the blended material and identified as follows: top,

1/3 down, 2/3 down, bottom. Duplicate determinations were

made on each sample by the method already described. The

results are shown in table 5-

A high degree of agreement is shown between duplicates,

with an average deviation of about 0.02% absolute or 0.05%

relative . There is still an apparent small discrepancy between

the values found for the four samples, but it is within the

tolerances for homogeneity required for this standard.

21
Table 5- Determination of lead in various portions of

blended lead cyclohexanebutyrate

.

Deviation

Sample Avg . dev. per Average from general

designation Pb , % determination Pb , % average

Top 36.715 0.023 36.692 0.038

36.668

1/3 down 36.760 .035 36.725 .071

36.690

2/3 down 36.560 .005 36.565 .089

36.570

Bottom 36.650 .015 36.635 .019

36.620

General

average 36.654 .020 .054

2 . Analysis of Copper-Zinc Alloys

Polarography is a superior technique for precise analysis

of copper base alloys as illustrated for the following sample.

A binary copper-zinc alloy which came to our laboratory

through the service analysis program was found by electron

microprobe analysis to be especially micro-homogeneous. Since

their criteria for homogeneity are considerably more rigorous

than for many other techniques, it seemed desirable to have an

accurate analysis on this particular sample in order that it

could be used as a microprobe standard. Since the microprobe

measurements are precise to within about 0.5% or better, an

accuracy greater than this was desired for the copper-zinc

analysis

.

The procedure used was as follows: Approximately 0.2-g

samples of metal drillings were dissolved in dilute nitric

acid, and evaporated to dryness. The residues were dissolved

in hydrochloric acid and diluted to one liter with pyridine

and water so that the final concentration was approximately

0.5 M in both pyridine and pyridinium chloride. The solutions were measured by comparative polarography, using re22
ference solutions prepared from melting point copper, SRM 4|?d,

and melting point zinc, SRM 43e. The results showed a composition of 76 . 75% copper and 23.21% zinc with average devia^-

tions in both cases of less than 0.1%.

C . Major Constituent Analysis

1 . Analysis of Metal-Organic Complexes

Single cell cathode ray polarography is particularly

suitable for the rapid determination of many metal constituents in organic or biological matrices.

For some studies made in the Polymers Division by Dr. E,

Horowitz and Miss M. Solarczyk on the behavior of certain

transition metal-polymer systems, the exact composition of

some copper, nickel, zinc, manganese, or iron-8-hydroxyquinolates prepared by them was needed. The methods used were as

follows : Fifty mg of the copper quinolate was treated with

0.5 ml of sulfuric acid and several additions of nitric acid

to destroy organic material. The samples were then fumed to

dryness and the residues were dissolved in 4 ml of hydrochloric

acid and water. Eight ml of pyridine was added, the samples

were diluted to 100 ml, and copper measured at about - 0.4 V

vs. the mercury pool anode. Nickel was determined in a similar manner except the peak was measured at about - 0.8 V

vs . a mercury pool anode

.

Zinc was determined in the same supporting electrolyte

as copper and nickel after slow ignition of 50-mg samples.

Zinc was then measured at about - 1.1 V vs. the mercury pool

anode

.

Manganese was determined using 50-mg samples after slow

ignition. The residue was dissolved in a few drops of hydrochloric acid, evaporated to dryness and diluted to 100 ml with

0.1 M potassium chloride. Manganese was then measured at

about - 1.6 V vs . a mercury pool anode.

23
The organic material was destroyed in 25-mg samples of

two different iron quinolate samples by fuming with perchloric

acid and nitric acid. The residues were dissolved in 2.5 ml

of 1+1 perchloric acid, 12.5 ml of 2 M sodium acetate, 2.5 ml

of 0.1 M EDTA, and diluted to 25 ml. Iron was then measured

at about - 0.3 V vs. the mercury pool anode. The results on

the quinolates are shown in table 6.

Table 6. Analysis of metal-quinolates

.

Cu, %

16.11

Ni, %

11.55

11.69

Zn, %

16.55

16.26

Mn, %

14.66

14.52

Fe, %

Pound 13.57

13.51

13.54

13.65

Reported 16.1 11.6 16.4 14.6 13.5 13.6

Small crystals containing major-constituent amounts of

copper and minor-constituent amounts of either cadmium or lead

were analyzed for both metals concurrently in the same solution by cathode ray polarography . The samples which were

copper pyridine N-oxides doped with small amounts of either

cadmium or lead, were of interest in some electron-spin

resonance studies made in the Inorganic Materials Division.

Organic material was destroyed in a 25-mg sample of the

copper-cadmium compound by fuming with nitric acid and perchloric acid. The residue was dissolved in 0.5 ml of 1+1

hydrochloric acid, diluted to 50 ml, and copper was measured

at about - 0.25 V and cadmium at about - 0.7 V vs. a mercury

pool anode. The results showed 19.4$ copper and 0.36$ cadmium

The copper-lead sample was analyzed in a similar manner

using approximately 30-mg samples except that it was necessary

to utilize the subtractive mode of operation of the cathode

ray polarograph for the determination of the lead. The peak

resulting from the reduction of the small amount of lead,

following the very large copper peak, is not well enough

defined for quantitative measurement. By using a solution in

the second cell containing an amount of copper similar to

24
that of the sample and no lead, the large copper peak is

electrically subtracted and a well-defined lead peak results.

Copper was measured in the single cell at about - 0.25 V vs.

a mercury pool anode . and lead, by the dual-cell mode of

operation at about - . 5 V vs . a mercury pool anode. Results

are shown in table 7.

Table 7. Copper and lead in metal-organic complex.

C opper, percent L ead, percent

Sample no . 1 19-81 0.17

Sample no. 2 19.95 .19

Reported 19-9 .18

2 . Determination of Zinc in Corrosion Products

A small amount of corrosion product resulting from the

contact of a mixed hydrazine rocket fuel with the zinc coating

of a rocket fuel container was submitted for determination of

zinc. Knowledge of the zinc content would then give an indication of the amount of corrosion which had occurred. A 3-mg

sample was dissolved and evaporated to dryness with nitric

acid and perchloric acid followed by dissolution in a pyridinepyridinium chloride supporting electrolyte. Zinc was then

measured at about - 1.1 V vs. a mercury pool anode and found

to be 30.4%.

D. Minor Constituent Analysis

Cathode ray polarography has been very useful for the

determination of a number of elements in solders and steel.

The methods developed could be used directly without timeconsuming separations

.

1 . Determination of Lead in Leaded Steel

A method described last year [1] for SRM 130a has been

utilized for analysis of a leaded steel needed to verify

conformance with the lead specification. A 400-mg sample

was dissolved in 10 ml of 1+1 hydrochloric acid and saturated

25
potassium chlorate solution was added to oxidize carbides and

the solutions evaporated to about 6 ml. The iron was then

reduced by gentle heating with hydrazine hydrochloride and

5 ml of saturated sodium formate and 2 ml 0.5% starch solution. After dilution to 25 ml, lead was measured at about

- 0.5 V vs . a mercury pool anode.

2 . Determination of Copper, Bismuth, and Nickel in

Solders

Methods were developed for the determination of bismuth,

copper and nickel in lead-tin solders, SRM 127b and 1131.

Bismuth and copper or nickel and copper could be determined

concurrently in the same supporting electrolyte; however,

for the certification analyses, they were each measured in

a separate supporting electrolyte. The methods are as follows:

For the determination of copper and, under some conditions,

bismuth, 1-g samples were dissolved in a 4+1 mixture of hydrobromic acid and bromine, 10 ml of perchloric acid was then

added and the solutions evaporated to perchloric acid fumes

several times to remove tin. SRM 127a was also taken through

the procedure as a control. The solutions were then boiled

vigorously to convert the lead bromide to perchlorate and diluted to 25 ml. Ten-ml aliquots were evaporated to dryness

twice with nitric acid and the residues dissolved in 1 ml of

5% nitric acid and 4 ml of a 20% sodium tartrate solution.

Copper was then measured at about - 0.3 V vs . a mercury pool

anode. Bismuth could also be measured at about - 0.5 V; however, in view of the relatively small volume and high concentration of lead tartrate, it was thought that some co-precipitation of bismuth might occur with the lead tartrate and that

the amounts of bismuth present in the sample might be better

determined at higher dilutions. The results are shown in

table 8 as well as those later obtained by other techniques.

The polarographic values represent individual samples while

those by other techniques are averages as reported by the

analysts

.

26
Table 8. Copper in SRM's 127a, 127b, and 1131.

Copper, percent

Neutron

Sample Polarographlc Spectrograph! c activation Average

127a

( cert

.

0.004)

0.0037

.0038

.0040

127b .011

.011

.011

.010

1131 .010

.009

.011

.012

o.ona 0.010 b 0.011

.oio a .011

M. M. Darr, Spectrochemical Analysis Section.

P. D. LaFleur, Activation Analysis Section.

For the determination of nickel in the solders, 2-g

samples were dissolved and tin was removed in a manner similar

to that described above for the determination of copper. The

samples were diluted to 100 ml and 1 g of sodium sulfate was

added to precipitate lead. The solutions were mixed well,

lead sulfate was allowed to settle, and a 25-ml aliquot was

taken from the clear supernatant liquid. The aliquot was

evaporated to dryness, the residue dissolved in 3 ml 1+6

hydrochloric acid and 2 ml of pyridine and nickel measured

at about - 0. 85 V vs. a mercury pool anode. Copper could

also have been measured in the same solution at about - 0.4 V.

The results are shown in table 9.

27
Table 9. Nickel in SRM's 127a, 127b, and 1131.

Nickel, percent

Sample Polarographic Spectrographic Spectrophotometric

127a 0.0025

{ cert . no?l

0.002) • UU ^ 1

127b .011 0.015 a 0.011b

.012

1131 .011 .0l4 a .009 b

M. M. Darr, Spectrochemical Analysis Section.

E. R. Deardorff, Analytical Coordination Chemistry Section

Bismuth was determined using 2 -ml aliquots of the solution from which the aliquots for copper were taken. The aliquots were evaporated to dryness with hydrochloric acid and

dissolved in 5 ml of 5% hydrochloric acid. Bismuth was then

measured at about - 0.2 V vs . a mercury pool anode. The

results are shown in table 10.

Table 10. Bismuth in SRM's 127a, 127b 3 and 1131.

Bismuth, percent

Sample Polarographic Spectrographic

127a (cert.

0.036)

0.038

.038

127b .065

.065

1131 .066

.068

0.062 a

.064 a

M. M. Darr, Spectrochemical Analysis Section.

28
3 . Determination of Copper and Zinc in Aluminum Alloys

Copper and zinc may be very conveniently determined

polarographically in aluminum alloys . Preliminary attempts

to use a pyridine-pyridinium chloride supporting electrolyte

did not give very precise results, probably owing to some

occlusion of copper by the gelatinous aluminum hydroxide precipitate. A copper-zinc-aluminum alloy received was analyzed

by dissolving 50-mg samples in dilute hydrochloric acid, diluting to 25 ml with 0.1 N hydrochloric acid and measuring

copper at about - 0.2 V and zinc at about - 1.0 V vs . a mercury pool anode. An aluminum-copper alloy was analyzed

in a similar manner. The results are shown in table 11 and

represent the average of four determinations

.

Table 11. Determination of copper and zinc in

aluminum alloys

.

Sample Zinc, percent Copper, percent

Cu-Zn-Al I.89 ± 0.03 5.63 ± 0.04

Cu-Al 3.83 ± .04

E. Small Sample Analysis

The work on samples weighing as little as several hundred

yg has continued. Methods developed in this laboratory have

played a vital role in determination of the composition of

thin metallic films being developed for electronic circuitry

by Harry Diamond Laboratories and also of thin films developed

in research programs at the Naval Ordnance Laboratory. The

methods have been extended to include the analysis of the

source material remaining on a tungsten filament after vacuum

deposition of the film onto a glass slide.

1 . Analysis of Antimony-Bismuth Films

The method developed for the determination of both bismuth and antimony in thin films is described in ref. [1].

The samples analyzed during the past year have ranged from

about 70 to 97% bismuth and the total sample weight has been

29
as little as 184 yg. Ordinarily, samples are too small to

weigh so that composition is calculated from the analytical

measurements 3 assuming no differential losses during analysis

One sample of the binary source alloy was submitted for

analysis in sufficient quantity that preliminary weights

could be taken, hence an additional check on the accuracy of

the method was provided. The results for this alloy are

shown in table 12.

Table 12. Determination of bismuth and antimony in thin

film deposition source material.

Wt found, mg

Wt taken, mg Bismuth Antimony Total

332.7 238.1 91.0 329.1

The apparent error of - 1% is well within the limit of

single cell polarographic measurements. Greater accuracy

could of course be provided if needed by use of the comparative mode of operation of the cathode ray polarograph.

2 . Analysis of Copper-Nickel-Chromium-Aluminum Films

A number of thin films have been analyzed for copper,

nickel, chromium, and aluminum largely by the methods described in ref. [14]. The amounts ranged from 2 to 100 yg of

copper and aluminum, 43 to 3600 yg of nickel, and 35 to 900

yg of chromium. A number of filaments used for vaporizing

the source material were also submitted for analysis in order

to determine the amount of unvaporized material remaining.

The source material was removed by prolonged digestion in

quartz with nitric acid, then with nitric acid and hydrochloric

acid. Some tungsten was also dissolved and precipitated as tungstic oxide. The resulting solutions were diluted to 25

ml and 10-ml aliquots were taken for the concurrent determination of copper and nickel in a pyridine-pyridinium sulfate

30
supporting electrolyte and 5-ml aliquots for the determination of chromium in 1 M sodium hydroxide as already described

in ref . [14].

For the determination of aluminum, 5-ml aliquots were

evaporated to dryness with 5 drops of hydrochloric acid, the

residue dissolved in 2 drops of 50% hydrochloric acid, transferred to a separatory funnel and diluted to 10 ml with H„0.

Two ml of acetic acid and 10 ml of 2 M sodium acetate were

added to give a pH of about 4.5. Ten ml of a saturated

sodium diethyldithiocarbamate solution was added and copper

and nickel extracted with 15, 10, 10, and 5-ml portions of

chloroform. One ml of 6% cupferron was added, the solution

allowed to sit for 2 minutes and aluminum was extracted with

15, 10, 5, and 5-ml portions of chloroform. The extracts

were evaporated to dryness in quartz. One ml of perchloric

acid and 2 ml of nitric acid were added and the solutions

were boiled and evaporated to dryness to destroy organic

material. The residues were treated with 10 drops of 50$

hydrochloric acid, evaporated to dryness on low heat, and dissolved in 0.5 ml of 6 M perchloric acid. Five ml of 2 M

sodium acetate and 2 ml of Superchrome Garnet Y were added,

the solutions diluted to 50 ml and transferred to polyethylene

bottles . After heating in a water bath for 10 minutes and

cooling, aluminum was measured on the cathode ray polarograph

at about - 0.7 V vs . a mercury pool anode. The aluminum found

ranged from 14 to 25 yg with a blank of 1.7 ug.

3 . Analysis for Lead in Lead-Tin-Telluride

Several lead-tin-telluride film source materials were

submitted for the determination of lead with a desired error

of less than 1% . In the previous thin film samples, both lead

and tin determinations were needed necessitating separations

as described in ref. [1] . However, lead alone may be determined in 1 M sodium hydroxide with no interference from

tin. The material was dissolved in nitric acid and perchloric

31
acid, evaporated to dryness, the residue dissolved in hydrochloric acid and made 1 M in sodium hydroxide. Lead was then

measured on the cathode ray polarograph. The results illustrating the precision achieved are shown in table 13

.

Table 13. Lead in lead-tin-telluride

.

Sample Lead, percent Average deviation, percent

R-28 31.256 0.092

31.440

2236-34 31.641 .067

31.774

P. Trace Analysis

The bulk of the work in trace analysis in this laboratory

during the past year has been devoted to the analysis of and

development of methods of analysis for ppm and ppb-level constituents of several high purity metal standard reference

materials . The polarographic methods developed are very sensitive and selective and give results in excellent agreement

with those obtained by other techniques

.

1 . Determination of Trace Constituents in Zinc

The methods developed for the concurrent determination

of copper, cadmium and lead in zinc and results on some of

the samples have already been described in ref. [1]. The

methods proved extremely useful for both homogeneity testing

and certification analysis of both standards. Lots 1, 2, and

3 of zinc, SRM 728, were shown to be homogeneous with respect

to these elements, however, inhomogeneities were suspected in

lots 2 and 3 of zinc, SRM 683. Additional samples of lots 2

and 3 were, therefore, submitted for analysis. Samples from

each lot, weighing 10.5 to 10.9 grams, were dissolved in 30

ml of concentrated hydrochloric acid and diluted to 50.0 ml

with water. Duplicate 20-ml aliquots of each solution were

evaporated to dryness and the salts dissolved and diluted to

10.0 ml with 0.1 N hydrochloric acid.

32
Table 14 lists the results of the individual determinations and the average value for each sample, as well as the

general average value for each element. The agreement between

duplicate determinations is considerably better than between

samples, particularly for lead, thus indicating some inhomogeneity of the material.

Table 14 . Copper, lead, and cadmium in pure zinc

composition standard, SRM 683.

Sample designation Copper, ppm Lead, ppm Cadmium, ppm

2B36-1 6.13 9.60 0.93

6.36 9 .60 .91

6.25 9761)" .92

2-A36-1 6.17 11.58 1.06

6.25 11.47 1.06

2-B15-1 6.32 10.28 1.19

6.32 10.28 1.17

6T32" 10.2 8 T7TB"

2-A15-3 6.65 11.58 1.21

6.65 - 11.58 1.21

6765" 11.58 1.21

3-A15-1 6.49 11.29 1.16

6.71 11.62 1.18

6T6"0" 11.46 1.17

3-B15-1 6.47 11.53 1.12

6.65 11.87 1.19

6756"" 11.70 1.16

3-A26-1 6.43

6.61

6.52

9.63

9.63

9.63

1.11

1.14

1.12

6.44 10 .83 1.12

0.06 0.06 .01

General average

Pooled average deviation

per determination

Average deviation of .14 .85 .07

samples from general

average

As a result of these measurements and also of residual

resisitivity ratios obtained at the NBS laboratory in Boulder,

lots 2 and 3 were not used and only lot 1 was considered to

have sufficient homogeneity for certification.

33
Determinations of iron and aluminum were also needed for

both zinc standards. Limited time was available for these

determinations; hence it seemed desirable to develop a direct

method requiring no separations. The use of the Solochrome

Violet RS or Superchrome Garnet Y complexes of iron and

aluminum as discussed earlier in ref. [1] was first considered

because of the extreme sensitivity of the method. It was

found, however, that the presence of zinc caused a depression

of the normal aluminum and iron-dye complex peak heights

.

This difficulty was circumvented by preparation of the standard

curve with addition of increasing amounts of iron and aluminum

to the zinc sample to be analyzed. Although iron and aluminum

could be determined concurrently in the same solutions with

Solochrome Violet RS , it was found that better results for

aluminum could be obtained with Superchrome Garnet Y. Equivalent amounts of lead, which is a possible interference in the

method, were also added to the calibration standards. The

results are shown in table 15.

Table 15 . Determination of iron and aluminum in

zinc SRM 683 and 728.

ts Certified

SRM Element

Al

Found,

2.8

ppm s

0.7

n

6

7r

0.7

value

683

683 Fe 2.3 .6 6 .6 2.2

728 Al 2.8 .8 9 .6

728 Pe 2.5 A 6 .4 2.7

Additional verification of this work is planned involving

separation of the iron and aluminum. However, the blank resulting from the additional operations and reagents required

may cause difficulties.

34
2 . Determination of Trace Constituents in High Purity

Zinc

A small amount of exploratory work has been done on the

determination of copper, cadmium and lead in the high purity

zinc, SRM # 682, by anodic stripping. The instrumental sensitivity was more than adequate for the determinations at this

level, however, the blank value, particularly for copper and

lead, limits the amount which can be determined. All the con- tainers used were subjected to repeated cleaning with hot con- centrated hydrochloric acid until an actual analysis of 0.1 N

hydrochloric acid solution which had been heated in the container showed no higher contamination than that of 0.1 N

hydrochloric acid alone. A blank was also measured after

each sample to verify lack of contamination of the electrolysis vessel. The method used was as follows: Approximately

1-g samples were dissolved in 7 ml of hydrochloric acid and

evaporated to dryness. The residue was dissolved in 5 ml of

0.1 N hydrochloric acid and the anodic dissolution peaks were

measured after pre-electrolysis into a mercury drop extruded

from a micrometer syringe. The results are shown in table 16

It should be noted that one erratic polarographic result for

lead of 0.2 ppm was obtained. It is not known if this is the

result of chance contamination or of actual sample inhomogeneity

.

Table 16. Copper, cadmium, and lead in high purity zinc.

E£m

Spark source

Atomic Spectro- mass

Element Polarographic absorption photometric spectrometry

Cu 0.03 0.044 a 0.040b

Cd .05 0.1

Pb .03

T. C. Rains, Analytical Coordination Chemistry Section.

R. W. Burke, Analytical Coordination Chemistry Section.

R. Alvarez and P. Paulsen, Spectrochemical Analysis Section.

35
3. Determination of Copper, Lead, and Iron in High- Purity Platinum

For the polarographic determination of traces of iron in

SRM 680 and iron, copper, and lead in SRM 68l, complete

separation of platinum should be achieved. Several methods

were considered such as dithizone extraction (copper and lead),

cupferron extraction (iron), and ion-exchange (copper, lead,

and iron) . A cupferron extraction procedure was first tried

with both samples and complete iron recovery with standard

solutions was achieved. The procedure was somewhat inconvenient to use, however, owing to the precipitation of ammonium

chloroplatinate resulting from the cupferron hydrolysis during

the extraction. However, the organic layer could be passed

through a filter paper plug, eliminating any precipitate in

the extract

.

The procedure was as follows : One-gram samples of SRM

68l or 0.5-gram samples of SRM 680 were dissolved in aqua

regia and evaporated to incipient dryness three times with

hydrochloric acid. The residues were dissolved in 1 ml of

hydrochloric acid and water and diluted to 10 ml in a separatory funnel. One ml of 6% cupferron was added and the iron

cupferrate extracted with four 5 -nil portions of chloroform.

The organic layer was evaporated to dryness and fumed with

nitric and perchloric acids to destroy organic matter. The

residues were dissolved in 0.5 ml of 6 M perchloric acid,

2.5 ml 2 M sodium acetate and 1 ml of 0.05$ Solochrome Violet

RS, and diluted to 25 ml. The solutions were allowed to stand

15 min, then iron was measured on the cathode ray polarograph

at about - . 8 V vs . a mercury pool anode. An alternate ion

exchange separation procedure was also tried with SRM 681 in

which iron, copper-, and lead were eluted with 0.1 M and 8 M

hydrochloric acid and all three determined concurrently in an

oxalic acid, ammonium hydroxide, ammonium chloride supporting

electrolyte. Iron was measured at about - 0.1 V, copper,

36
- 0.2 V, and lead, - 0.6 V vs . a mercury pool anode. The

results are shown in table 17.

Table 17- Iron, copper and lead in high purity

and doped platinum.

ts

Sample Element Found, ppm s n Vn

680 Fe 0.75 0.2 2 1.8

681 Fe 5.0 1.0 6 1.0

Cu 5.2 2.0 5 2.5

Pb 10.3 0.7 5 0.9

These elements were also determined by a number of other

techniques and a summary of all the results obtained is shown

in table 18

.

Table 18. Comparison of iron, copper, and lead

determinations in platinum, SRM 680

and SRM 681.

ppm found

(Dther

NBS analyst s Isotope

a j- • b dilution ActivaSample

ElementPolarographicmass spectrometry

tion

analysis A

C

B

C c

c Cert,

value

680 Fe 0.75 1.4 2.6 0.6 0.7

681 Fe 5.0 3.5 6.2 5-6 5.0

Cu 5.2 6.0 5.0 6.3 3.0 5.6 5.1

Pb 10.3 14 8.5 15.0 9.1 12.0

R. A. Alvarez and P. Paulsen, Spectrochemical Analysis Section

G. W. Smith, Activation Analysis Section.

Emission Spectrographic Analysis.

By comparison of these results, it is seen that the

polarographic methods give very reliable results in such high

purity metal analysis

.

37
4. Determination of Copper and Iron in High Purity Gold

For the determination of iron in samples of high purity

gold rod and wire, extraction of iron was not considered since

gold is also extracted with most solvents. However, the ionexchange separation which removed platinum so effectively also

proved to be suitable for gold removal. Preliminary investigation of a method of analysis was made using the samples of

the gold rod. Considerable difficulties were experienced

because of the high iron blank coming probably from reagents

and the atmosphere. Two-gram samples were used and an iron

blank corresponding to about 2 ppm was obtained. This resulted in iron values for the rod ranging from 0.2 to 0.5 ppm

giving an average value of 0.33 ppm and a standard deviation

of 0.14 ppm. The experimental conditions were then altered

to use smaller amounts of reagents and also to utilize containers that would more effectively exclude atmospheric contamination. This resulted in a lowering of the blank to a

value corresponding to about 0.5 ppm of iron. The values

obtained for the wire as well as those obtained by spectrophotometry are shown in table 19.

Table 19. Iron in high-purity gold wire.

Iron found, ppm

Polarography

0.42

.45

.35

.41

Spect rophotometry

A

a Bb

0.45 0.36

.47 .44

.46

Avg 0.41 0.46 0.40

a

D. H. Christopher, Analytical Coordination Chemistry Section.

R. W. Burke, Analytical Coordination Chemistry Section.

38
Copper was later determined in the gold, polarographically

,

using a similar ion-exchange separation procedure. Blanks

still remained somewhat of a problem, being of the order of

0.1 - 0.2 ppm. On three aliquots of the rod, values ranging

from 0.1 to 0.2 ppm were obtained resulting in an average

value of 0.18 ppm. Results on the wire are shown in table 20.

Table 20. Copper in high purity gold wire.

Copper found, ppm

Polarography Spect rophotometry Activation Analysis

0.24 0.13 0.12

.23 .12 .11

.26 .14 .21

.12 .16

.18

.15

Avg 0.24 0.13 0.16

R. W . Burke, Analytical Coordination Chemistry Section.

W. D. Kinard, P. D. LaPleur, and D. A. Becker, Activation

Analysis Section.

5 . Analysis for Pollutants

One of the great potential areas of contribution for the

polarographic techniques and experience acquired here would

seem to be in the field of water and air pollution. As a result of some talks and publications describing polarographic

work done here, interest has been generated as to the possible

polarographic contribution to analysis of a number of trace

metals in materials such as atmospheric fallout, water, milk,

urine, and blood. At present, lack of agreement between different analysts and different techniques such as spectrophotometry, atomic absorption, and spectroscopy, leaves doubt as

39
to the true values in several important problems. The application of polarography in these analyses would certainly

result in improved methods in some cases . A preliminary

analysis has been made in this laboratory of a dust fallout

sample supplied by another laboratory. It was possible to

determine lead, cadmium, and zinc concurrently in the same

supporting electrolyte. The values obtained were consistent

with those expected for a sample of this type. A number of

other elements could have been determined at the same time

had they been of interest in this particular problem.

(E. J. Maienthal)

40
3. COULOMETRIC ANALYSIS

A. Introduction

The coulometric analysis program is concerned witn the

development of analytical methods of highest reliability and

their utilization in the analysis of standard reference materials as well as materials of importance to various research

programs of the National Bureau of Standards . During the

past year, considerable effort has been devoted to the development of a method for assay of boric acid and to numerous

determinations of boric acid for several purposes. Fundamental studies have resulted in the establishment of accurate

values for the electrochemical equivalents of two materials,

leading to a redetermination of the faraday . Methods already

developed have been employed in the determination of chromium

in several materials. These developments will be described

in the following sections

.

B. Research Activities

1. Development of a Method for Precise Analysis of

Boric Acid

The expanding use of boron and its compounds in nuclear

reactor technology and the NBS program concerned with the

issuance of the standard reference material for neutron flux

monitoring necessitated the development of methods for precise and accurate determination of this element. The most

widely used method for the determination of milligram amounts

of boron is titration of boric acid, complexed with some polyol

such as mannitol. These methods, however, are somewhat empirical in nature, particularly with respect to the amount of

polyol required for titration, and generally precise to only

a few parts per thousand. Le Duigou and Lauer recently reported a method for precise coulometric determination of boron

[15]. Their precision for 150-mg samples of boric acid was of

the order of 0.02%. However, they found a disagreement between

41
the coulometric value and the value obtained by conventional

acidimetric titration. This discrepancy was of the order of

0.1$. This fact alone was sufficient to intrigue our interest

in the coulometric behavior of this system.

In aqueous solutions, boric acid is a very weak acid

(pK - 9.2). Accordingly, titrations of boric acid must be

conducted in some complexing medium which increases its dissociation constant. Mannitol has been most widely used and

appeared to be most promising. The first two questions to

answer were: What concentration of mannitol is necessary and

sufficient to permit precise and accurate analysis of boric

acid, and does the concentration of mannitol have an effect

on the coulometric assay of boric acid? A number of samples

of boric acid were analyzed in the following electrolytes

:

1M KC1-0.25M mannitol; 1M KC1-0.75M mannitol; 1M KC1-1.5M

mannitol (sat'd). The analyses showed no significant difference (within 0.005%) between the results in the three media

for sample sizes of boric acid ranging from 1 to 6 meq.

Beyond 6 meq, the latter two electrolytes gave identical results but in 0.25M mannitol, the slope of the potentiometric

curve near the equivalence point was too small to permit accurate evaluation of the end point (i.e., the amount of mannitol

is insufficient to complex all of the boric acid)

.

Prom the standpoint of the magnitude of inflection, an

electrolyte containing 1.5M mannitol is superior, however,

its viscosity is rather high which presents some inconvenience

in forcing this solution through the fritted glass disks of

the coulometric cell as well as homogenization of the solution

during the course of analysis. Hence, as a matter of convenience, a concentration of 0.75M mannitol was used throughout

subsequent work. In addition, this duplicates the medium

used by Le Duigou and Lauer, thus its use permits investigation of the possible systematic sources of error noted by

these authors.

42
The accuracy of coulometric acidimetry conducted in 1M

KC1 solution has been verified previously; however, in these

boric acid analyses the supporting electrolyte is not just

1M KC1 but it is also 0.75M with respect to mannitol. To

investigate possible bias, HC1 solutions, single crystal

oxalic acid dihydrate, and acid potassium phthalate, respectively, were analyzed coulometrically in 1M KC1 both with and

without mannitol. This choice of acids was made to cover a large range of pK values which would include the pK of

a a mannitoboric acid (in 0.75M mannitol, the apparent K of

-5 a

boric acid is 4.17 x 10 ). The results of analyses of these

acids in mannitol medium were identical (within 0.003%) with

the results obtained in the absence of mannitol. Accordingly,

the accuracy of coulometric acidimetry is unaffected by the

addition of mannitol to 1M KC1. It was also noted that the

pH of the inflection points on the potentiometric titration

curves, obtained with the use of the glass-saturated calomel

electrode system, is virtually unaffected by the presence of

mannitol.

In further studies of bias, the boric acid sample size

was varied from 20 mg to 1.0 g. The assay values found were

identical. Thus, for sample sizes ranging over 1.5 orders of

magnitude, there is no apparent bia.s in the analytical method.

Boric acid of known purity is not available for evaluating the accuracy of the method. However, the absence of analytical bias due to composition of electrolyte and to sample

size support the conclusion that the method is highly

accurate

.

The precision of analysis of boric acid is illustrated

in figure 7 which represents the data for homogeneity studies

on boric acid Lot No. 92511- Open circles represent determinations with 600-mg samples, and dark circles - those with

200-mg samples. The numbers adjacent to the points represent

the sequence for each replicate analysis. Excluding sample

43
100.010

100.000

99.990

Figure 7. Homogeneity studies of boric acid.

No. 15 (which appears to be a material of somewhat different

composition) , the standard deviation of a single determination

is 0.0049%, which also includes any inhomogeneity of the

material.

2 . Determination of Strong Acid in Crystalline Boric

Acid

In analyzing boric acid solutions, such as solutions of

separated boron isotopes for use in the calibration of a mass

spectrometer, it is necessary to show that the titrated hydrogen ion is contributed totally by boric acid. In other words,

it is necessary to prove that there is no other acid in this

boric acid. Direct titration of strong acid, in the presence

of boric acid in 1M KC1 solution, was not found to be sufficiently sensitive due to buffering effect of boric acid.

Thus, it was impossible to resolve less than a few hundredths

of a percent of strong acid in the boric acid. Another method

44
needed to be developed and the obvious path was to resort to

preconcentration of strong acid. Removal of boric acid by

extraction into an organic layer, consisting of 5% solution

of 2-ethyl-l, 3-hexanediol in chloroform was attempted and

found unsatisfactory because a large amount of HC1 was lost

in the process.

The procedure finally developed for this purpose is based

on the 20-fold decrease of solubility of boric acid in water

between 100 and 0°C. A special sealed tube procedure was devised to recrystalize the boric acid from which the supernatant

liquid could be removed for determination of its strong acid

content. The results of analysis of SRM Boric Acid, Lot No.

92511 show that it contains 5-5 ppm of strong acid. Thus,

after applying the correction for the strong acid, the B/H

ratio in this material corresponds to 0.999991 ± 0.000013 on

the molar basis. The uncertainty of this ratio represents

the 95% confidence interval of the mean, based on 17 degrees

of freedom. This method requires large amounts of material

(1 to 2 g) , and thus is infeasible for the evaluation of the

stoichiometry of H^ BO.-, and H~ BO.-, isotopically "pure" samples due to considerations of cost and availability of material.

Consequently, a micro method had to be developed for the determination of strong acids in boric acid solution. The key

to this problem was to establish the amount of strong acid in

the SRM Boric Acid Lot 92511. This was done as described

above. Subsequently, solutions containing known, widely

varying concentrations of boric acid were prepared and their

pH was measured. A three-dimensional calibration graph was

constructed relating the following three parameters: pH,

concentration of boric acid, and the concentration of strong

acid (HC1) . Thus, knowing accurately the total acid concentration from coulometric analysis and the pH of the boric

acid solution, one can calculate the concentration of strong

acid by the method of successive approximations . The accuracy

45
of such determination is limited by the number of reiterations

that one wishes to make. The sensitivity of the three-dimensional calibration graph is such that 0.002$ of strong acid

in the original samples of boric acid can be easily determined

with an accuracy of a few relative percent.

3 . Electrochemical Equivalents of Benzoic and Oxalic

Acids

In the course of coulometric studies during the past

several years, a number of highly accurate assays have been

made of two materials, namely benzoic acid and oxalic acid

dihydrate . Since the purity of these materials has been

evaluated by independent methods, the coulometric assays may

be calculated to yield values for the electrochemical equivalents of these acids . These constants are not only interesting

in their own right but they permit a redetermination of the

faraday by a method not heretofore used, namely acidimetric

coulometry. The details of this work are discussed in a

recent publication [16] and are summarized in the following.

The acid was analyzed spectrochemically to determine the concentration levels of electrochemically active elements. Trace

levels of Cu were detected but the amount does not affect the

electrochemical equivalent of the acid by more than a few

7 parts in 10 . This, of course, is insignificant in comparison

with the other uncertainties of this determination.

Prom thermometric measurements, the purity of this acid

was estimated to be 99.997 mole percent, while calorimetric

evaluation indicated it to be 99.999 mole percent. Acidimetric

intercomparison of acids through sodium carbonate as a transfer material gave an assay of 99.9955 ± 0.0014$, where the

uncertainty represents the 95$ confidence interval for the

mean based on 7 degrees of freedom plus an allowance of

0.0008$ for the uncertainty in the purity of Na

2

C0- [17].

The oxalic acid dihydrate was single-crystal material

grown by J. L. Torgesen and J. Strassburger of the NBS

46
Crystal Chemistry Section from acetone-water mixtures by the

temperature dropping technique [18]. Optically clear fragments

of single crystals were selected for titration. Analysis of

this material revealed the impurities shown in table 21.

Table 21. Impurities found in oxalic acid dihydrate.

Element ppm by Weight Method of Analysis Possible Form

Li < 1 flame phot<Dmeter LiHCpCVH2

Na 39 » tt NaHCpO^-HpO

K < 1 emission

spectnDmetry

KHC O.-HpO

Rb < 1

» it RbHCpO^-HpO

Mg < 1

!! t! MgC

2 4

.2H

2

Pe < 1

tl t! Fe

2 (C2 4

) 3

.5H.

Si < 1

M It Si0 o

On the basis of the above analyses, taking sodium as 39

ppm and all other elements as 0.5 ppm and assuming that these

impurities exist in this material in some form equivalent to

the molecular compositions shown in column 4 of table 21, its

purity would be estimated as 99.9871$.

It is rather difficult to assign limits of uncertainty

to the assay of this material, but an attempt is made to place

reasonable bounds on the errors which might be involved. The

error due to an uncertainty in the sodium content of 2 ppm

would result in a correction uncertainty of 0.0006$. Taking

the middle of the range for the content of the rest of the

elements seems to be a reasonable approximation. This would

contribute a correction of 22 ± 9 ppm to the assay of the

material, where the uncertainty represents the 95% confidence

limit to the error in the correction, using Eisenhart's procedure [19] of assuming a binomial distribution for the actual

impurities. Thus, if the assumptions of the effective form

47
of the impurity are correct, the purity of this material is

uncertain by 0.0015$.

The coulometric method used is basically the same as described in ref. [20]. It consists of the reduction of hydrogen

ions derived from the weighed acid at the platinum cathode

according to the reaction

H

+

+ e" -» 1/2 H . The titration is carried out in 1M KC1 solution. A glass

electrode-saturated calomel electrode system is used for

measuring the change of hydrogen-ion concentration as a function of the passed charge to identify a differential potentiometric inflection point. The supporting electrolyte ( 1M KC1)

is initially acidified to facilitate the removal of COp, swept

with scrubbed nitrogen and then pretitrated to a pH of 7.00 by

passing small increments of charge. The charge consumed in

going from the end point of pretitration to the differential

pH inflection is taken as equivalent to the amount of hydrogen

ion which was introduced with the weighed acid.

The assembled coulometric cell is shown in figure 8.

The anode and the cathode compartments are l80-ml electrolytic

beakers connected horizontally by a 25-mm o.d. tube, approximately 6 cm in length, in which three sintered glass disks

of coarse, medium, and fine porosity, respectively, are sealed.

Each of the two intermediate compartments thus formed has a tube with a stopcock to enable filling and emptying by applying vacuum or nitrogen pressure. The volume of the compartment between the coarse and the medium frit is about 10 ml

and between the medium and the fine frit, about 20 ml.

The advantage of using a cell of relatively small volume

is two-fold. The sensitivity of the end-point detector system

is increased and impurities in the supporting electrolyte,

although remaining at the same concentration, are reduced

with respect to the total amount present by the inverse of

the ratio of volumes.

48
Figure 8. Coulometric titration cell for precise acidimetry.

The molded polyethylene cathode compartment cover is

held in place by a polyethylene lock ring. In it are mounted:

a combination glass-calomel electrode, an inlet for nitrogen

to be passed over the solution, a nitrogen outlet tube connected to a trap, a platinum cathode, and a 15 cm long x 3

mm o.d. polyethylene tube bent upward at the end (forming approximately a 30° angle with the main stem of the tube) and

connected on the outside to a polyethylene bottle. This

polyethylene system can be used for delivery of liquid samples

and for withdrawing some of the solution from the cell and

ejecting it at the walls and the top of the cell, thereby

rinsing any material which might have been deposited on the

top or the sides of the cell as a result of gas liberation

during the course of electrolysis

.

49
The nitrogen outlet tube is made from a cut-down 10-ml

pipet . Prior to titration, a drop of distilled water is introduced into the bulb of this pipet. After completion of

the titration, this drop is delivered into the cell. Thus,

any spray which might have been expelled into the tube is

returned to the cell.

A polyethylene cap is mounted about 1 cm above the top

edge of the cathode. The purpose of this cap is to catch most

of the spray from the cathode resulting from the liberation

of gaseous hydrogen.

An agar gel plug ( 3 g of agar per 100 ml of 0.1N KC1) is

cast into the bottom of the anode compartment to prevent liquid

from entering or leaving this compartment. A corrugated silver

sheet serves as the anode.

The whole cell assembly is mounted on a stage with a

magnetic stirrer under the cathode compartment. A 3/^-in

Teflon encapsulated stirring magnet is used in the cell for

agitation of the solution.

The high precision electrical and timing circuits,

enabling measurements of charge passed through the cell to

within ± 0.0001% have been described previously [20,21].

Samples of both benzoic and oxalic acid were weighed by

substitution on a 20-g capacity microbalance . The standard

deviation of the weighing process was 0.003 mg. The weighings

were free of systematic errors except for the uncertainties

in the standard weights, which were less than 0.003 mg . The

weight of each sample was corrected for air buoyancy, based

on the density of the air which prevailed at the time of

weighing.

In general, the same titration procedure was followed

as described in ref. [20] except that the stirrer was operated

only during dissolution of the samples. The reason for turning off the stirrer during the titration is three-fold: (1)

to eliminate swirling of gas bubbles liberated at the cathode

50
into the bulk of the solution, thereby minimizing spray loss

of the analyzed material, (2) to minimize transfer of impurities in the supporting electrolyte to the electrode surface,

and (3) to minimize transfer of the investigated acid into

the intermediate compartments.

After electrolysis at about 101. 78 mA for a period of

time sufficient to react with about 99.95% of the sample, the

current was interrupted. The intermediate compartments were

flushed by applying nitrogen pressure or vacuum as needed and

the stirrer was turned on. The 6.43 mA current was then

passed incrementwise, where each increment corresponded to

about 0.02 C. The intermediate compartments were flushed

after passage of each increment of charge. The cell wall

and cell cover were rinsed by withdrawing and expelling

catholyte from the cell by means of the polyethylene rinse

system, as described earlier. Following the rinse, the pH

of the solution was measured to the nearest 0.001 pH unit and

recorded. At the end of the titration a differential plot

of ApH/AC was constructed to locate the inflection point.

Nineteen titrations of benzoic acid were carried out.

The data are summarized in table 22. Column 2 gives the

weight of benzoic acid corrected to the weight in a vacuum

and for an assay of 99.9955% based on the data of Bates and

Wichers [17]. Column 3 shows the number of coulombs which

were required to bring the pH of the solution to the inflection

point, determined graphically. Column 4 shows the value of

the electrochemical equivalent of benzoic acid, calculated

on the basis of columns 2 and 3. The mean value of the electrochemical equivalent of benzoic acid is 1.265715 ± 0.000036

mg/C , where the uncertainty includes 0.000014 mg/C as the

limits for a 9 5% confidence interval for the mean, based on

18 degrees of freedom and 0.000022 mg/C for effects of known

sources of possible systematic error.

51
Table 22. Electrochemical equivalent of benzoic acid.

Run No.

Wt of

benzoic

acid 3 g

a

1.000521

Coulombs

required

to titrate

790.4920

Electrochemical

equivalent

mg/C

1 1.265694

2 1.001966 791.6338 1.265693

3 1.001297 791.0651 1.265758

4 1.001155 790.9952 1.265690

5 1.002562 792.0710 1.265747

6 1.001457 791.2400 1.265680

7 1.000902 790.7553 1.265754

8 1.000968 790.8079 1.265753

9 0.999579 789.7362 1.265712

10 1.000006 790.0681 1.265721

11 1.000286 790.3129 1.265683

12 1.000543 790.5234 1.265671

13 0.999576 789.7482 1.265689

14 0.999337 789.5385 1.265723

15 0.999645 789.7800 1.265726

16 1.001315 791.1064 1.265714

17 0.999768 789.8663 1.265743

18 1.000402 790.3957 1.265697

19 1.001581 791.2968 1.265746

Mean 1.265715

Uncertainty (95% confidence limit for the mean) = 0.000014 mg/C.

aThe weight given in this column is corrected for the

buoyancy of the air and for purity of 99.9955$.

The results of coulometric titrations of 12 samples of

oxalic acid dihydrate are summarized in table 23. Column 2

gives the weight of oxalic acid, corrected to the weight in

a vacuum and corrected for impurities (see section on materials)

Column 3 shows the charge which was passed in bringing the

52
weighed amount of material in solution to the inflection

point of the pH titration curve. Column 4 is the value of

the electrochemical equivalent of oxalic acid dihydrate calculated on the basis of columns 3 and 4. The mean value of

the electrochemical equivalent of oxalic acid dihydrate was

found to be 0.653293 ± 0.000023 mg/C . The uncertainty figure

includes 0.000009 mg/C as the limit for a 95% confidence

interval for the mean based on 10 degrees of freedom and

0.000014 mg/C for effects of known sources of possible systematic error.

Table 23. Electroch(

dihydrate

smical equivale:nt of oxalic acid

Wt of Coulombs ElectrochemiCc3.1 Deviation

oxalic acid required equivalent from mean

Run No

.

dihydrate, g

0.395404

to titrate mg/C A x 105

1 605.2321 0.653310 1.7

2 0.396684 607.2161 0.653283 1.0

3 0.502996 769.9497 0.653284 0.9

4 0.381987 584.7072 0.653296 0.3

5 0.617067 944.5720 0.653277 1.6

6 0.484968 742.3577 0.653281 1.2

7 0.570579 873.4824 0.653223 7.0

8 0.490940 751.4959 0.653284 0.9

9 0.441219 675.3761 0.653294 0.1

10 0.626781 959.3928 0.653310 1.7

11 0.538062 823.6150 0.653293 0.0

12 0.509745 780.2558

Mean

0.653305 1.2

0.653293

Uncertaj-nty (95% confidence limit for the mean) = 0.000009 mg/C

aThe weight given in this column is corrected for the buoyancy

of the air and for purity of 99.9871%.

Note: The value obtained in Run No. 7 was excluded from the

calculations since it differs from the mean by more

than 3 times the standard deviation.

53
4. Redetermination of the Faraday

Values for the faraday have been calculated from the

electrochemical equivalents of benzoic acid and oxalic acid

dihydrate, described in section B.3., together with the accurately known equivalent weights of these materials. These

values are interesting because they were obtained by a method

not heretofore used for such a purpose, hence they contribute

an independent confirmation of the reliability of this constant.

Taking the equivalent weight of benzoic acid as 122.12467

and its electrochemical equivalent, determined in this investigation as 1.265715 x 10" 3 g/C, the faraday becomes 96,486.7 ± 2.5 C/g-equiv, and using 63.03326 as the equivalent weight of

oxalic acid dihydrate and 0.65329 2 x 10 g/C as its electrochemical equivalent, the faraday value is found to be 96,485.4

± 3.4 C/g-equiv.

Recently, Hamer [22] recalculated some of the faraday

values reported by earlier investigators. To focus attention

on the results obtained in this laboratory, Hamer' s table is

included here for comparison. The first eight entries of

table 24 are from Hamer' s table. The ninth entry is based

on work conducted in this laboratory and published earlier

this year [21]. Entries ten and eleven are based on the

electrochemical equivalents of benzoic and oxalic acid.

A practical problem concerned with units should be

pointed out. Although the National Academy of SciencesNational Research Council recommends 96487.0 ± 1.6 C/g-equiv

as the value of the faraday, this value is not consistent

with the electrical units as presently maintained by NBS and

thus throughout the USA [23]. The above faraday (96487.0 C/g

equiv) is expressed in terms of the absolute coulomb. Since

coulometry is an "absolute" method of analysis, one must use

a value for the faraday consistent with his electrical measurements. Electrical instruments and components in the USA

are calibrated in terms of the NBS volt, ohm and ampere.

54
Table 24. Summary of values for the faraday

.

Values

Method

Silver deposition

Q Iodide oxidation

Iodide oxidation

Oxalate

oxidation [26]

Omegatron [27]

Silver

dissolution [28]

Silver

dissolution

Silver

dissolutione,f

Iodide oxidation

Benzoic acid

reductioni

Oxalic acid

reductioni

h

NBS (legal)

basis

96476.9 ± 2.3

96487.7 ± 2.0

96488.7 ± 2.0

96481.6 ± 3.0

96487.3 ± 0.9

96485.4 ± 2.4

Absolute

basis l a

96478.1 ± 2.3

96488.9 ± 2.0

96488.9 ± 2.0

96482.8 ± 3.0

Absolute

basis 2b

96478.0 ± 2.3

96488.8 ± 2.0

96488.8 ± 2.0

96482.7 ± 3.0

96486.1 ± 0.9 96486.2 ± 0.9

96486.6 ± 2.4 96486.5 ± 2.4

96485.4 ± 1.6 96486.6 ± 1.6 96486.5 ± 1.6

96485.8 ± 1.6 96487.0 ± 1.6s 96486.9 ± 1.6

96485.5 ± 3.2

96486.7 ± 2.5

96486.7 ± 3.2 96486.6 ± 3.2

96487.9 ± 2.5 96487.8 ± 2.5

96485.4 ± 3.4 96486.6 ± 3.4 96486.5 ± 3.4

based on the relation 1 NBS ampere = 1.000012 absolute ampere

based on the relation 1 NBS ampere = 1.000011 absolute ampere

based on the silver/iodide weight ratio [24,25]

based on coulombs used to liberate iodine [24,25]

based only on the vacuum values of Craig, Hoffman, Law, and

Hamer [28]

fusing 107.8685 for the atomic weight of silver

svalue recommended by the National Academy of Sciences-National

Research Council [23]

calculated on the basis of the coulometric titration of ASpCU

with electrogenerated iodine reported in [21]

xvalues obtained in this work.

55
Accordingly, one must use the faraday on the "NBS" (legal)

basis (96485.8 NBS C/g-equiv) . Alternately, the use of the

"absolute" faraday must entail the introduction of corrections

to the NBS coulomb in order to convert it to the absolute

basis. The magnitude of this correction is still a subject

of some debate, nontheless it is between 11 and 12 ppm.

Returning to the faraday calculated in this work, it is

apparent that the overall agreement of faraday values obtained

in this laboratory with the accepted value is remarkably

good. This fact contributes to the confidence in the value

of the faraday, since the reduction of hydrogen ion has not

been thus far utilized for the determination of the faraday,

and this reaction offers another independent method for the

evaluation of this important physical constant.

Some corollaries may be drawn from this work. The data

obtained indicate that acidimetric coulometers can be made to

operate at a high level of precision. If the original acid

content is known accurately, they can also be made to provide

accurate measurement of the charge which passes through them.

Thus, to have an accurate coulometer for the purpose of coulometric analysis or any other current-time integrating purpose,

where current is neither constant nor a linear function of

time but varies in some complex manner, a sample of acid of

known purity or concentration can be conveniently utilized.

Even in the case of the unavailability of accurately assayed

acid, constant-current coulometric analysis of the available

material can provide the necessary assay. One of the practical advantages of such coulometers over the silver coulometer

is their simplicity and convenience of handling.

The results of this work, supported by other evidence on

the accuracy and precision of coulometric analysis [20,21,29,

30,31,32] pave the way for a change of philosophy in the field

of primary chemical standardization. The concept of absolute

purity, as defined by a perfect single crystal of a given

56
material, should be considered as criterion for the preparation

of high purity materials but not for the chemical analytical

determination of purity. In analytical chemistry, a much

more universal and unified concept correlating a common

property of a broad spectrum of materials through the use of

electrochemical equivalents is preferable. The conformance

of a given material to its theoretical electrochemical equivalent should define the absolute purity. The faraday, then,

would in fact be the primary chemical standard.

Although s similar proposal was made in 1958 by P . S.

Tutundzic [33]; objections were raised and the proposal was

not widely accepted. Perhaps the proposal was premature since

the state of the art of coulometry was far below that of conventional chemical analysis at that time. The efforts of

those in the field of precise coulometric analysis since that

time have advanced the technique to the point that most of

these previous objections are no longer valid. It is, therefore, the belief of the authors that for the unification of

primary chemical standardization, the approach of a material

to its theoretical electrochemical equivalent offers the most

rational criterion for purity wherever applicable. Having

the faraday as the standard, future efforts, not only of

chemists but also of physicists, would contribute to accurate

definition of this standard. Even now, however, the uncertainty of the faraday is about one order of magnitude smaller than

that of chemical standards commonly used.

5 . Effect of Photodecomposition of AgCl on Coulometric

Determination of Chloride

The photochemical reduction of silver chloride has long

been considered as a source of error in halide determinations

.

Because of the high precision of coulometric analysis, this

complication assumes added significance.

The photochemical reaction of interest may be represented

by the equations

57
2 AgCl + 2 hv -> 2 Ag + Cl

2

Clp + H

2

> H

+ + CI" + HC10

HCIO -»> H

+

+ Cl" + [0].

In coulometric chloridimitry , the indicator electrode system

(Ag-glass electrode) is reversible to silver ions and chloride

ions. It therefore offers a direct means for monitoring the

photo-reduction product (Cl~) and hence the rate of the photodecomposition, itself.

Experiments were conducted in which KC1 samples varying

in size from 20 to 130 mg were titrated with silver ion

electrogenerated in the dark. Following the completion of

titration, the fluorescent lights of the laboratory were

turned on and the emf of the indicator electrode was measured

as a function of time. On the basis of a previously constructed calibration curve, an equation was fitted to the data, representing the rate of decomposition of AgCl (more accurately,

the rate of production of Cl~) . The equation is of the form

R = at + bt 2 + ct 3

where R is the amount of Cl~ produced in u equiv . , t is time

in hours and a, b, and c are experimentally determined constants. For the conditions in this laboratory, the equation

was found to be

R = 0.490t - 0.090t 2 + O.OlOt 3

When the elapsed time required for a titration is substituted

in this equation, the amount of photodecomposition should be

calculable and applicable as a correction for over-titration

of a given sample.

To verify the accuracy of the equation, 3 samples of

KC1 were analyzed in the dark and 3 in the light. The results

of analysis are summarized in table 25. It can be seen that

58
the accuracy of the results is improved by almost an order of

magnitude when the correction is applied. Thus a difference

of 0.0160% between samples analyzed in the dark and in the

light, is reduced to only 0.0002% by use of the correction.

The standard deviation of a single determination is changed

only slightly from O.OO38 to 0.0035%.

Table 25. Effect of light on argentimetric titration of KC1.

In light

Number In dark In light (corrected)

1 99.9619

2 -

3 99-9640

4 -

5 99.9623

6 -

99.9831 (1 hr) 99.9653

99-9766 (0.5 hr) 99.4646

99-9764 (1 hr) 99-9589

Average 99-9627 99-9787 99-9629

s = 0.0012 s = 0.0038 s = 0.0035

C . Analysis of Standard Reference Materials

1 . Homogeneity Studies of Boric Acid

The boric acid to be issued as a standard reference material was received in a shipment consisting of 22 containers.

To determine the homogeneity of the material, samples were

taken from all bottles and analyzed by the previously developed

coulometric titration of mannitoboric acid, as described in

section B.l. The samples were weighed by substitution and

the true mass was computed by applying corrections for the

buoyancy of the air. The results of analysis are summarized

in table 26. With the exception of sample no. 15, all assay

values fall within ± 0.005% of the mean. Taking all values,

the average assay is 99-9997% and the standard deviation of a single determination is 0.0049%.

59
Table 26. Boric acid homogeneity studies.

Date of analysis

10-31-67

11-2-67

11-3-67

11-6-67

11-7-67

11-8-67

11-9-67

11-13-67

11-14-67

11-15-67

11-16-67

11-20-67

11-21-67

Sample no. Assay

17 99.9889

12 99.9999

1 100.0022

4 100.0024

9 99-9978

13 99.9997

2 100.0010

3 99.9983

22 99-9964

18 100.0032

16 99-9910

19 99.9975

7 100.0004

10 99.9896

20 99-9960

11 99-9993

21 99.9990

5 100.0028

15 100.0078

14 100.0005

8 100.0042

6 100.0037

10a 100.0020

15 a 100.0089

l6 a 99.9955

17 a 99.9975

15a 100.0055

Average 99.9997

aRepeat runs

From examination of the data it appears that errors are

random with respect to the sequence of analysis (neglecting

the three systematically high values for sample no. 15).

Since there is only a slight chance that the three samples

for the bottle number 15 would be high by more than one

standard deviation, we conclude that the results of analysis

of this bottle are high not due to random scatter, but more

likely because the material in it is significantly different

from the rest of the bottles. Excluding sample 15, the assay

60
of the remaining apparently homogeneous material is 99.9987

± 0.0018, where the uncertainty figure represents the 95%

confidence interval for the mean, based on 23 degrees of

freedom.

In the final evaluation of the stoichiometry of the SRM

boric acid, the 22 original samples were combined into four

composites. Composites containing equal amounts of samples

were made as follows: Composite I- 6, 8, 15, 18 and 5;

Composite II - 10, 16, 17, 20 and 22; Composite III - 3, 9,

19, 21, 11 and 13; Composite IV - 2, 7, 12, 14, 1 and 4.

These materials were used in subsequent studies.

The final evaluation of the assay of all four composites

is shown in figure 9 1 In the figure each circle represents

an individual titration plotted in the sequence in which it

was carried out. Shading of circles represents individual

composites: blend of all; Composite I; Composite II;

Composite III; Composite IV. It can be seen that there

is no systematic difference in the assay as a function of titration sequence . There is also no apparent difference between the four composites (within the precision of the method)

£ BLEND OF ALL COMPOSITE H

O COMPOSITE I

["J COMPOSITE HI

Q COMPOSITE IE

100.01 — —

385 100.00 • ,-, ^a© , PnD °» ®» -

to

CO< o

D

°

99.99

i

i I 1 I l 6 9 12 TITRATION SEQUENCE

15 18

Figure 9 Effect of titration sequence and composite

number on the assay of boric acid.

61
Table 27 summarizes this data for numerical evaluation

of the results. On the basis of this data, it can be concluded that the acidimetric assay of boric acid Lot No. 92511

is 99-9997 percent. This value is not corrected for the

strong acid in the boric acid, since from the standpoint of

an acidimetric standard the assay must reflect the total

available hydrogen ion. On the other hand, correction must

be applied when one is concerned with B/H ratio. After applying the correction for the strong acid, the B/H ratio in

this material corresponds to 0.999991 ± 0.000013 on the molar

basis where the uncertainty represents a 95% confidence interval of the mean, based on 17 degrees of freedom.

Table 27. Assay of b<Dric acid , LO:b No. 92511 . (Equi!Libra'ted a t 34$ re:Lative

humid:Lty f<or at least 30 min.

)

Sample No. Composit*3 No. Assciy; % a > PPm

1 Blend of all 100 .0008 12

2

it 99 .9978 19

3 I 99 .9990 7

4 I 99 .9941 56

5 II 99 .9983 14

6 II 99 .9992 5

7 III 99 .9998 1

8 III 100 .024 27

9 IV 99 .9987 10

10 IV 100 .0009 12

11 IV 100 .0002 5

12 IV 100..0012 15

13 IV 99..9961 36

14 I 100,.0042 55

15 II 100..0007 10

16 III 99 • 9973 24

17 III 100,.0025 28

18 II

Average

100,.0006 9

99..9997

s == 0,.0025

ts

77^ == 0,.0013

62
2 . Effect of Relative Humidity on the Stoichiometry of

Boric Acid, Lot No. 92511

'If he study of the behavior of this lot of boric acid indicates that this material is somewhat deficient in water,

i.e., apparently it was prepared under conditions which resulted in the formation of small amounts of B

? 0~. This conclusion is supported by the following evidence. Samples

weighed directly from the original boric acid containers and

permitted to sit in the room at 28 percent relative humidity

for 30 minutes gained weight, as illustrated in table 28.

The data in figure 10 show that at 28% RH, the time which

is required to weigh out a sample (approx. 15 min.) is insufficient for this material to absorb sufficient water to attain stoichiometry. At 34% RH, analyses of samples weighed

in the same period of time show that the stoichiometry of

this material corresponds exactly to H^BO^. Once the stoichiometric amount of water has been absorbed, the exposure of

the material, even to a very dry atmosphere, does not result

in the loss of water, and the composition of material corresponds to stoichiometric H~B0~.

Table 28. Absorption of water by boric acid.

Wt . of H BO

Sample

Number

Initial wt

of H BO

after 30-min

exposure to

2 8% RH 2x10 6

g

+ 136

Ch£

we

+

tnge in

:ight,

>rcent

1 1.351348-g 1.35l484g 0.010

2 1.3^0345 1.340394 + 49 + .004

3 0.934555 0.934655 + 100 + .011

4 1.685807 1.685968 + 161 + .010

5 2.249267 2.249379 + 112 + .005

6 1.343683 1.343823 + 140

Average

+ .010

+ 0.008%

63
Figure 10.

100.01 1 1 1 1

o

100.00 o

99.99

l I I 1 25 27 29 31 33 RELATIVE HUMIDITY IN THE BALANCE CASE ,%

35

Effect of relative humidity in the balance

case On the approach of boric acid to HoBCU

stoichiometry (15 min. exposure time).

Additional information on the effect of the relative

humidity of the environment on the stoichiometry of B 0„-H?

system at 25°C was obtained in controlled humidity experiments

Boric acid was initially exposed to room atmosphere (approx.

34$ RH) for several hours, in the course of which the material

absorbed water and achieved stoichiometric composition (as

illustrated in figure 7) . Subsequently, boric acid was placed

into controlled humidity environments. After at least a fourday exposure to a controlled atmosphere with an occasional

mixing of the crystals, samples were weighed out for analysis.

The results of these analyses are shown in figure 11. It

can be seen that in the 0-52$ relative humidity range, the

assay of boric acid remains constant and close to stoichiometric H BO . Beyond 52$ relative humidity, additional water

is sorbed by boric acid, reaching 0.02$ (referred to the

weight of stoichiometric boric acid) at 95$ relative humidity.

64
100.01

40 60

RELATIVE HUMIDITY,%

80 100

Figure 11. Effect of the humidity of the environment on

the assay of boric acid.

It is concluded that initial exposure of this lot of

boric acid to humid atmosphere is beneficial as it provides

moisture necessary to achieve stoichiometric H BO . Subsequently the material is stable and can be stored at any humidity below a/ 60%. Considering even drastic environmental conditions, such as variation of humidity between and 90%, the

material changes its stoichiometry by only 0.020%. This

probably occurs due to adsorption of water on the surface of

polycrystalline boric acid.

3 . Development of a Procedure for Precise and Accurate

Preparation and Aliquoting of Separated Boron-Isotope Boric

Acid Solutions

The following problems were investigated to develop techniques for the preparation of solution for calibration of a mass spectrometer: Evaluation of precision of aliquoting

relatively small amounts of boric acid solutions, to establish

the suitability for accurate mixing of desired ratios of sepa65
rated boron isotope solutions ( B and B) ; establishment

of suitable conditions for accurate preparation and storage

of boric acid solutions without significant changes in the

composition of the latter (storage for about 1 week); development of a reliable procedure for delivery of boric acid

solution aliquots into the coulometric titration cell; evaluation of any possible bias which might be associated with the

size of boric acid solution aliquots; development of a method

for the determination of small amounts of strong acids which

might be present in the separated isotope solutions, without

consuming large amounts of the costly solutions for this

purpose

.

Most of the solutions needed were prepared, stored and

aliquoted by Keith Sappenfield, 310.06. The material used

for the preparation of solutions was Composite II of the SRM

Boric Acid Lot No. 92511.

The procedure developed for the aliquoting of solutions

was similar to that described in ref. [1] with one exception:

instead of 1 ml syringes, 10 ml polyethylene syringes were

used as the weight burets. The solutions were prepared of

such concentrations that samples as large as 10 ml and as

small as 1 ml would bracket the sample sizes of separated

isotope solutions which would be required for accurate mixing

of known boron Isotope ratios (about 0.3 meq/g of solution).

From such a syringe, solutions were weighed by difference

into 4 oz polyethylene flasks . A closed syphon arrangement

(similar to the one described in ref. [34] was constructed

which fitted tightly over the 4 oz polyethylene flasks and

led into the coulometric titration cell. Using this arrangement, solution samples could be quantitatively transferred

into the titration cell without disassembling the coulometric

cell. Such an arrangement is highly desirable since in this

closed system nitrogen, flowing over the electrolyte in the

cell, keeps the atmospheric carbon dioxide out of the cell.

66
Two sets of experiments were initially conducted to

establish the precision of aliquoting, transfer and titration.

Equal size samples of boric acid solutions were aliquoted on

the same day and titrated soon thereafter (1 to 2 days after

aliquoting) . The results of these analyses are summarized in

table 29. It appears from these initial experiments that the

standard deviation of a single measurement (of the adopted

procedure for weighing, transfer, and coulometric process) is

about 0.00005 meq/g (on the percentile basis, the standard

deviation of a single determination is about 0.017$).

Subsequently the procedure was refined and investigation

was made of the effect of the sample size (aliquot size) on

the analytical determination of boric acid. The samples were

weighed out on the same day. The data obtained in these experiments are shown in table 30 . It can be seen from these

data that there is no systematic difference between analytical

results for the larger and the smaller aliquots (within 0.01$)

Table 29. Precision of aliquoting and analysis of

boric acid solutions.

Solution

Prepared & aliquoted

by K.

Sappenfield

II

Prepared &

aliquoted

by K.

Sappenfield

Aliquot

No.

1

2

3

4

Wt of aliquot, g meq found

10.95358

10.05553

10.45754

10.27975

19.63511

10.59936

2.988735

2.742278

2.852758

2.804252

Average

2.964446

2.926541

meq/g

0.272855

.272713

.272794

.272794

0.272789

0.276145

.276105

Estimated precision:

Average 0.276125

s = 0.000047 meq/g

67
Table 30. Effect of the size

aliquot on the coul

boric acid concentr

of boric acid solution

ometric determination

ation.

of

Solution

Aliquot

No.

Wt of

aliquot , g

10.20413

meq found

2.834423

meq/g

0.277772

A3Q06

b 3 6

Prepared & aliquoted

by K.

Sappenfield

4

5

6 a

2.02505

2.20348

l.l4274 a

0.562549

.612081

.324266 a

.277795

.277779

.283762 a

-

17

1

7 1.17222 .325603 .277766 + 12

0.277778

I 1 6.828209 1.193722 0.174822 + 24

Prepared & aliquoted by

G. Marlnenko

2

3

8.370246

8.755848

1.463594

1.531033

.174857

.174858 -

11

12

& C. Champion 0.174846

II 1 8.493900 1.281755 0.150903 + 1

Prepared & aliquoted by

G. Marinenko

& C. Champion

2

3

4

8.303518

21.30825

9.040497

1.253004

3.215547

1.364261

.150900

.150906

.150906

+ 4

2

2

0.150904

This sample is excluded from the consideration. A gross

error (2%) was apparently involved in handling it.

A very significant point needed clarification. What

are the most suitable conditions and containers for storing

boric acid solutions without any significant changes in concentration? Polyethylene bottles stoppered with rubber septa

and stored in room atmosphere were investigated first but

found to be unsuitable. This conclusion is supported by the

evidence shown in table 31. Solution "b" was prepared and

aliquoted on Dec. 7, 1967, then aliquoted again on Dec. 12

and finally on Dec. 15 . The data of table 31 show the average

68
concentration of solution on the various days of aliquoting.

It can be seen that the increase in concentration of solution

due to evaporation is non-linear. This is understandable

since even a constant rate of evaporation of water would produce greater effect toward the end, since samples are being

taken out for analysis from the bottle leaving a smaller and

smaller amount of residual solution. Therefore, a loss of a

given amount of water would produce a greater concentration

change in the smaller residual volume. Thus, concentration

changes with time become more significant as more and more

samples are taken out from the storage bottle.

Table 31- Concentration changes of solution (b) stored in

polyethylene bottle in room atmosphere.

Date of aliquoting Concentration, meq/g

Dec. 7 0.277666

Dec. 12 .277778

Dec. 15 .279337

Storage of solutions in glass at 90% and at 100% relative

humidity produces no noticeable concentration change over

significant periods of time. This is illustrated by the data

in table 32. It can be seen that solution "1", for example,

changed only 0.002% over a period of 20 days. This apparent

difference must be contributed by the random error component,

since the apparent concentration is decreasing and not increasing, while the concentration change of solution 2 (table

32) is in the opposite direction and of the order of 0.002%

in four days.

Referring to table 32, the last column shows percent

recovery. These values are based on the ratio of meq H-BOVg

of solution calculated from the weight of boric acid originally

used in preparation of the solution, to the meq H~B0_/g of

69
solution found by coulometric analysis. The average of this

column is 100.0025 with 0.0021$ as the 95$ confidence interval

for the mean, based on 7 degrees of freedom, while the assay

of the solid boric acid is 99-9997 with 0.0013$ as the 95$

confidence interval for the mean, based on 17 degrees of

freedom. It can be seen that the two means are within 0.0028$

of each other and their 95$ confidence intervals overlap.

Table 32. Stability of H^BCU solution stored in glass

bottles in 90-100$ RH atmosphere.

Date of

Aliquoting Sol ' n no . meq/g calc. meq/g found Recovery, $

1-3-68 1 0.277604 0.277609 100.0018

" " " - .277622 100.0067

1-23-68 tt ii .277617 100.0047

n it 1! .277603 99.9996

1-4-68 2 0.150901 0.150903 100.0013

1-5-68 ti II .150900 99-9996

ti h It .150906 100.0034

1-8-68 it 1! .150906

Averag

100.0029

e 100.0025

ts

7n"

~ 0.0021$

4. Determination of Chromium in Ferrous Alloys

The high precision coulometric method for titration of

hexavalent chromium developed in this laboratory consists of

the reduction of dichromate ion in sulfuric acid-ferric ammonium sulfate solution with electrogenerated ferrous ion. The

precision and accuracy of the method was verified and found

equal to a few parts in 10^ [30].

The method is exceptionally well suited for the determination of chromium in ferrous alloys, if the latter are treated

in an appropriate manner to convert all chromium to the hexa70
valent state. Of necessity, the other major constituent,

iron, would then be in the ferric state and would not interfere with the analysis.

Two methods of dissolution and oxidation of chromium

have been used in conjunction with the above coulometric titration procedure: (1) perchloric acid dissolution and oxidation and (2) sulfuric acid dissolution and ammonium persulfate oxidation of chromium.

Ferrochromium, SRM 196 , and cast irons, SRM 66 and SRM

51, were dissolved and oxidized by the first method. These

two materials illustrate the wide range of applicability of

the method since the chromium content in them ranges from 79%

in ferrochromium to 1/10 of a percent in cast iron 51

«

The use of perchloric acid dissolution in the analysis

of ferrochromium is very convenient as it eliminates the need

for a sodium peroxide fusion. One of the difficulties with

perchloric acid oxidation, however, is the formation of

chromyl chloride which may be lost by volatilization. This

difficulty, however, may be overcome by the use of a glass

refluxing apparatus with condenser, which permits recovery

of CrOpClp in the condensate (amounting to about 0.2% of the

total chromium) . The accuracy of the recovery of chromium

was verified by analyzing a known K„Cr sample, prereduced

with hydrogen peroxide and subjected to the same oxidation

procedure as the alloys . The recovery for 100 mg to 1 g samples of dichromate was 99-991%.

The results of analysis of 0.6 to 1.1 g-samples of

ferrochromium SRM 191 are summarized in table 33.

A similar material was used in the analysis of SRM cast

irons. The results of analysis are shown in table 34.

Since the dissolution of stainless steel is not a difficult problem, a different method of dissolution and oxidation was used in the analysis of SRM stainless steels lOlf and

lOlg.

71
Table 33. Determination of chromium in

ferrochromium, SRM 196.

Titration no. Chromium assay, percent

1 70.853

2 70.857

3 70.864

4 70.864

5 70.845

6 70.854

7 70.908

8 70.858

9 70.879

10 70.904

11 70.899

12 70.856

13 70.860

14 70.913

15 70.913

Average 70.875 s'/Vn = 0.007$

Table 34. Results of analysis of three randomly selected

bottles for each of the two SRM cast irons.

Chromium, wt . percent

6g (6) 6g (15) 6g (23)

0.3547 0.3630 0.3625

0.3560 0.3592 0.3573

0.3656 0.3597 0.3554

0.3653

0.3588 0.3606 0.3601

6g overall average 0.3599$ Cr, s = 0.0038

^ = 0.0029

51 (1) 51 (9) 5& (15)

0.1458

0.1422

0.1464

0.1448 0.1462 0.1490

51 overall average 0.1467$ Cr, s = 0.0027

.1419 .1463

.1465 .1502

.1502 .1504

ts

7H"

0.0021

72
The samples were dissolved in sulfuric acid, oxidized

with ammonium persulfate using silver nitrate as catalyst and

potassium permanganate as the indicator of the completeness

of oxidation, and removal of the latter with HC1. The

resulting solution was diluted and aliquoted by weight for

analysis

.

In order to establish the analytical precision in handling

the solution, aliquoting and titration of small samples, duplicate aliquots were analyzed for some of the solutions. The

differences of duplicate aliquots from their means (new mean

for each individual solution) were used to evaluate the solution handling and titration uncertainty. The standard deviation of a single determination was found to be 0.0022 absolute

percent (0.012 relative percent).

The results of analysis of the two stainless steel samples

(lOlf and lOlg) are summarized in table 35. The first column

of the table shows the solution preparation number. The

second column indicates the bottle designation from which the

sample was weighed. The third column shows the size of the

solid sample taken for the preparation of that particular

solution. The fourth column shows the results of analysis

for the given solution or aliquot. The fifth column shows

the average of the results of two aliquots or the result of

a single titration for the given solution.

On the basis of these determinations, it can be concluded

that the two lots of stainless steel samples (lOlf and lOlg)

are homogeneous within the experimental uncertainty for sample

sizes ranging from 130 mg to 2.3 g. Taking the vanadium values

as 0.029 and 0.32 wt . percent for lOlg and lOlf, respectively,

their corrected chromium content is: lOlg - 18.435% and

lOlf - 18.474%.

73
Table 35- Analysis of SRM stainless steel for chromium.

101g

Sol'n Bottle Wt . of

No. No. sample, g Wt . % Cr 9- Ave wt_. % Cr

1 7 0.17 18.44

11 ti 18.440 18.442

2 7 0.15 18.463

18.456 18.460

3 1 0.13 18.451 18.451

4 3 0.19 18.443 18.443

5 7 0.24 18.439

" " 18.440 18.440

6 3 2.29 18.446 18.446

Average 18.447

= 0.008$ ts

7rT

lOlf

1 3 2.29

t! t! II

2 5 0.15

3 3 0.23

4 5 0.25

ti 11 ti

5 3 2.26

11 it 11

18.486

18.484 18.485

18.486 18.486

18.486 18.486

18.482

18.488 18.485

18.484

18.481 18.483

Average 18.485

ts

?n" = 0.002$

' uncorrected for vanadium

5 . Assay of EDTA by Acidimetric Coulometry

Acidimetric titration offers a simple and convenient

method for the coulometric assay of EDTA and related complexons . In principle, weighed samples of the complexon are added

to a supporting electrolyte of 1M CaCl ? which has been previously neutralized. This results in the liberation of hydrochloric acid (4 equiv. per mole in the case of EDTA and 2

74
equiv. per mole in the case of Na~ EDTA) . The acid so produced is titrated coulometrically as already described.

The performance of the method is illustrated by the assay

of a lot of reagent grade disodium salt of EDTA, shown in

table 36.

Table 36. Assay f Na

2

EDTA.

Sample No. Weight of salt i g Assay, %

1 0.987682 99.998

2 1.305296 99.998

3 0. 7^6620 100.005

Average 100.000,

6. Analyisis of Ion Exchange B eads

In connection with work conducted on ion exchange bead

microstandards (D. H. Freeman, 310. 09), it was necessary to

develop a method for precise determination of the ion exchange capacity of a cation exchange resin in the H form and

an anion exchange resin in the Cl~ form.

In the case of the RH resins, the supporting electrolyte

in the cell was 1M NaCl. Thus, when the ion exchange beads

were delivered into the cell, the following reaction took

place

:

RH + NaCl + RNa + HC1.

The liberated hydrochloric acid was determined by coulometric

acidimetric titration. The results of analysis obtained for

RH ion exchange beads are shown in table 37-

In the case of the RC1 resin, the supporting electrolyte

in the cell was 1M HClCv-lM NaClCv . The exchange reaction

was

RC1 + ClO^" -*• RCIC^ + CI".

The chloride ion produced by this exchange reaction was determined by argent imetric coulometric titration. The results

obtained for RC1 ion exchange beads are given in table 38.

75
Table 37- Analysis of RH ion exchange beads.

Sample No.

Approx. bead

diameter, y Wt of

resin, mg meq found

meq/g

of resin

Ionac C-240 250 270.44 1.30127 4.8117

400.61 1.92763

Average

4.8117

4.8117

lonac RH

(10-30y)

20 81.31

125.85

0.40210

0.62315

Average

4.945

4.952

4.948

Chromo RH

(10y+)

15 278.23

116.38

1.39271

0.58003

Average

5.006

4.984

4.995

Chromo RH

(10y-) 5 249.49 1.25760 5.041

117.76 0.59190

Average

5.027

5.034

Table 38. Analysis of RC1 ion exchange beads

Sample No. Wt of resin, mS meq found meq /g of resin

Ionac RC1 100.65 0.37083 3.445

37-36 0.12863

Average

3.443

3.444

Ionac A-540 101.276 0.364806 3.6021

160.139 0.576735 3.6015

190.767 0.687236

Average

3.6025

3.6020

76
In the case of RH resin, beads of several diameters were

submitted for analysis. For ease of plotting, capacity was

plotted with respect to the logarithm of diameter of the beads

(see figure 12). The results of analysis indicate that the

H capacity (meq H /g) depended upon the diameter of the

beads. It appears that, at some diameter of the exchange bead,

the H capacity reaches a limiting value, determined only by

the molecular configuration of the polymer. At this limiting

diameter of beads and below it, all of the side chains which

are involved in the ion exchange process are exposed to the

solution and can participate in the Ion exchange process

.

Above this limiting diameter, some of the active groups may

be isolated within the bulk of the beads and are thus effectively shielded from the reactants

.

5.04

COo

<

Ulm 5.00

u.O

4.96

O 4.92

i-<g 4.88

"" 4.84

4.80

T^ 11 I I I I I I 1

1 I I I I I I

l l l I 345 K> 20304050 100 200 DIAMETER OF ION EXCHANGE BEADS, /J.

400

Figure 12 . Loading factor of ion exchange beads as a function of bead diameter.

77
D. Analysis of Research Materials

The precise coulometric technique and procedures developed

in this laboratory are finding increasing applications to many

NBS program areas . Most materials submitted to this division

for analysis are now determined coulometrically when highly

accurate assays are required. Analyses of standard reference

materials were described in Section C. Several interesting

applications for analysis of research materials are mentioned

below.

Some calorimetric measurements made by the NBS Heat

Division required the analysis of HC1 solutions and HC1-HF

solutions resulting from the combustion of halogenated hydrocarbons . Accurate analyses were required to decide whether

simple acidimetric titrations, in the case of the former,

and whether an acidimetric and argentimetric determination,

in the case of the latter, would be definitive in determining

the amount of calorimetric reaction.

The HC1 solutions were analyzed coulometrically for both

H and Cl~ with the results shown in table 39. Both kinds of

determinations were made with an uncertainty of 0.0001 meq/g.

The systematic difference between the H and Cl~ values indicated that the acid had reacted to a small extent with the

metal of the calorimeter bomb. This unexpected conclusion

was confirmed by a spectrographic examination of the acid

which yielded impurities characteristic of the bomb. The

calorimetric measurements could be corrected for this source

of error.

In analyses of the HC1-HP solutions, all three elements

were determined, with the fluoride analysis being accomplished

by potentiometric titrimetry with a fluoride sensitive electrode (see Section 4.D.2. of this report). In these cases,

a satisfactory ionic material balance was achieved when consideration was made for the acid reaction noted above.
Table 39- Analysis of calorimetric reaction products.

r + H , meq/g of sol'n CI , meq/g of sol'n Ratio

H

CI

Solution I

0.7702 0.7704

0.7700 0.7700

Ave 0.7701 0.7702 0.99987

Solution II

0.3628 0.3630

0.3628 0.3628

Ave 0.3628 0.3629 0.99973

Solution III

0.3627 0.3629

0.3627 0.3629

Ave 0.3627 0.3629 0.99945

Coulometric acidimetry and argentimetry have been used

to establish the composition of a number of solutions used

in electrolytic solution research, when an accuracy of parts

in 10,000 or better was needed. Some of these have been hydrochloric acid in several non aqueous solvents such as Nmethyl proprionamide (NMP) , NMP-decalin, and NMP-cyclohexane

for NBS Section 310.03- Also, sodium carbonate, sodium bicarbonate, and potassium dihydrogen tartrate were carefully

assayed (to better than 1 part in 10,000) for use In establishment of the pD scale by Section 310.03-

(G. Marinenko and C. E. Champion)

79
4. ELECTROANALYTICAL MEASUREMENTS

A. Introduction

Research in the electroanalytical measurements program

has continued along lines initiated last year. Progress has

been made on the development of linear null-point potentiometry and the use of ion-selective electrodes in microanalysis

In addition, a number of SRM and service analyses were made,

and several limited research projects were undertaken and

completed.

B

.

Research Activities

1. Improved Microdetermination of Silver by Linear Null- Point Potentiometry [35]

Significant improvements in the results obtained for the

determination of submicrogram amounts of silver by linear

null-point potentiometry (LNPP) [36] have been achieved by

the use of several minor modifications of the technique.

Except for external pregeneration of the standard silver

solutions, the apparatus is identical to that previously

described [36]

.

a. Experimental . Instead of coulometrically generating silver incrementally in the titration half cell, a series of standard silver solutions are coulometrically prepared in separate 100-ml volumes of the inert electrolyte,

1 N HpSOj,. By the use of such pregenerated standard solutions

the analysis time for a set of test solutions is reduced by

a factor of about 4 or 5 to approximately 10 to 15 minutes

per determination.

The standard solutions are prepared in accordance with

the concentration of the unknown silver solution. The approximate concentration of the unknown is first determined

by a direct emf measurement or by a preliminary null-point

determination using standard solutions covering a wide concentration range. A test solution approximating the unknown

80
concentration and a minimum of two solutions above and below

this concentration are then coulometrically prepared. These

five standard solutions permit the determination of the equilibrium null-point potential and provide two data points before and after the equivalence point for a reliable graphical

or computer fit of the data to a straight line.

A . 1-ml aliquot of the end point solution is taken from

the standard solution (titrant) half cell (100 ml) and pipetted

into the null-point (test solution) half cell. The porous

Vycor null-point half cell is then immersed in the standard

solution, and the matched indicator electrodes are inserted

into each half cell. The cell potential is measured with a

high impedance recording system as before [36]. There is an

initial potential drift, caused by the dissolution of the

silver electrodes, which is more pronounced in the more dilute

silver solutions. After about five minutes, a limiting potential is reached which remains essentially constant for the

remainder of the time required for a complete determination.

This potential is used as the null point in subsequent determinations thereby compensating for the effect of silver

dissolution. Once this null-point potential is established

for the end point solution, the analyses of the unknown samples can be performed.

The . 1-ml sample of the unknown is pipetted into the

null-point cell, and the cell containing the standard silver

solution of lowest concentration is used as the titrant half

cell. After a stable emf is reached and recorded, the electrodes are rinsed, dried and the titrant half cell is replaced

by the cell containing the next higher silver concentration.

This substitution procedure is repeated until all of the

standard solutions have been used and the data points recorded.

The data are evaluated as before, using both a graphical

semilogarithmic plot and a linear least squares fit by computer

In the graphical analysis, the equivalence point is obtained

81
by a linear interpolation to the equilibrium null-point potential. The equivalence point is obtained by computer techniques from the null-point intercept of a linear least squares

fit of the data.

b. Results . Standard . 1-ml samples containing

0.054 to 54 micrograms of silver in 1 N H

?

SCK were analyzed.

Several determinations were made at each concentration level

and all showed good Nernstian behavior with the slopes of the

titration curves approaching the theoretical slope of 59.2

mV/pAg unit. Also, the deviation from linearity previously

observed at the lowest concentrations was not evident in this

work, presumably due to the establishment of the dissolution

equilibrium prior to the actual measurement of the cell emf

.

A summary of results is given in table 40 . An average

five-fold decrease in the error over the previous study is

observed between 0.05 and 2.7 ug of silver in a volume of

0.1 ml.

Table 40. Results of the LNPP determination of silver.

Ag

+ taken

yg/0.1 ml

53. 9

4

5. 39 4

0. 539 4

• 0539

4

Ag

+ found

yg/0.1 ml

54. °7

5. 4l

o

0. 5ll

2

0553 6

Error

n yg

0.13

.Olg

.001

8

.0014

2

7

9

9

7

c. Discussion . The advantages of greater linearity

of the titration curves, shorter analysis time, and improved

accuracy, are achieved by pregeneration of the standard solutions and the establishment of an equilibrium null-point potential to reduce the error caused by dissolution of the indicator electrode in the null-point cell. In this study, 54

nanograms of silver were determined with an error of less than

82
2 ng, while at higher concentrations (.above 10 uM) errors can

be reduced to 1% or less using the improvements in the LNPP

technique discussed.

2 . Fluoride Microanalysis by Linear Null-Point

Potentiometry [ 37

]

The determination of fluoride at subnanogram levels in

sample volumes of 10 ul has been achieved for the first time

using the modified fluoride activity electrode [38] in combination with the concentration cell technique of linear nullpoint potentiometry (LNPP) [36]. The fluoride sample in the

inverted fluoride electrode microcell is titrated by the addition of a standard fluoride solution to a second electrochemical half cell connected to the former by a salt bridge.

The emf vs. titrant concentration data are plotted semilogarithmically and the equivalence point is obtained by a

linear interpolation to the null-point potential.

The concentration cell employed is

LaF

3 |F"(CA

), KNO

3

(0.1M)||KNO

3 (0.1M)||KNO

3

(0.1M), F"(C

T )|LaF

3

10 y l salt bridge 100 ml

where LaF^ is the fluoride-specific membrane of the fluoride

activity electrode, C. is the concentration of the fluoride

solution being analyzed (i.e., analate solution), and CT

is

the concentration of fluoride in the titrant half cell. The

emf of this cell is given by the Nernst equation for a concentration cell:

(F~) RT A

E = AE - |i- in ^ + E

P (P") T

J

where AE is a bias potential between the two rxuori.de activity

electrodes due to differences in the inner reference solutions,

(F~)

fl and (F~) are the activities of fluoride in the analate

83
and titrant half cells, respectively, and E. is the liquid

j

junction potential. By the use of an excess of inert electrolyte (0.1 M KNCO throughout, the liquid junction potential

between half cells becomes negligible, and the activity coefficients of fluoride will be practically equal due to the

constant ionic strength maintained in the two half cells

.

Equation (1) thus simplifies to

RT In 1 -, CA

E = AE p log —

where the cell emf, corrected for the bias potential, is solely

dependent on the ratio of fluoride concentrations in the analate and the titration half cells (C. and CTM) when both half

cells are at the same temperature. Therefore at the nullpoint, where the cell emf is equal to zero, C. = CTM.

The 10-yl sample microcell is illustrated in figure 13

to show details of the assembly. This microcell comprises

the analate half cell. It consists of a fluoride activity

electrode which has been modified [38] to operate in an inverted position by conversion of the inner reference solution

(0.1 M NaF, 0.1 M KC1) to a gel (k% agar).

A 0.1 M KN0~ salt bridge connects the analate and titration half cells. The salt-bridge junction to the microcell

is made from a polyethylene tube drawn out to a fine capillary

and filled with a k% agar gel of 0.1 M KNO . The junction to

the titration half cell is made through a porous Vycor plug

[39].

The titration half cell consists of a l80-ml tall form

beaker in which are inserted a second fluoride activity

electrode (unmodified) , a stirrer, and a polyethylene capillary tube from the microburet. The microburet, readable to

0.01 ml, contains the standard fluoride titrant solution.

The titrant is prepared containing the 0.1 M KNO inert electrolyte background to prevent ionic strength changes when it

is added to the titration half cell.

84
SAMPLE SOLUTION

OOjil)

LaF3 MEMBRANE

TYGON SLEEVE

POLYETHYLENE CAPILLARY

SALT BRIDGE

POLYETHYLENE CAPS

POLYETHYLENE RING

lJ>J>JJ>>>JSf<

MODIFIED FLUORIDE ACTIVITY ELECTRODE

10mm

Figure 13. Fluoride electrode microcell

The cell emf may be conveniently measured by connecting

the electrode leads to an expanded scale pH meter (100 mV

full scale) which serves as a voltage follower amplifier for

a multirange potentiometric recorder. The cell emf can also

be read directly from the pH meter with only slightly reduced

precision, but the recorder facilitates continuous observation

of the emf equilibration and stability. The microelectrode

lead is connected to the glass electrode input jack of the pH

meter while the second fluoride electrode connects to the unshielded reference electrode input. The pickup of electrical

noise at this electrode does not constitute a serious problem

in the emf measurement because of the relatively low resistance of the fluoride electrode (approximately 500k ft) . The

emf is read from the recorder to the nearest 0.1 mV. The

complete assembly is shown in figure 14.

85
Figure 14. Apparatus for fluoride determination

by linear null-point potentiometry

.

In addition to evaluating the equivalence point graphically, data analysis is easily accomplished by computer techniques whereby the equivalence point is obtained from the

intercept of a linear least squares fit of the data. By this

technique, the computer is programmed to take the logarithm

of the X-value (CTM) before fitting the data and to print the

antilogarithm of the X-intercept (equivalence point concentration, C T

= C„) where the cell emf (or Y-value) is zero.

The computer readout also provides the slope of the best

straight line through the titration data points for comparison

with the theoretical Nernstian slope. The results reported

below are obtained in this way after an initial graphical inspection to determine any obvious anomalies in the titration

data.

Standard 10 yl sample solutions containing O.38 to 190

nanograms of fluoride in 0.1 M KNO were analyzed. The results of these determinations are tabulated in table 4l for

86
five measurements at each concentration level. At the lowest

concentrations, the initial titration points exhibit a deviation from linearity caused by the slight dissolution of the

lanthanum fluoride membrane not having reached equilibrium.

This effect is predictable from the solubility product of

LaF.-, and becomes a significant factor due to the extremely

small volume of solution employed. However, this effect does

not significantly affect the final results, as verified by the

very small error observed, because the emf value used as the

null point includes the same dissolution factor. That is, the

null-point potential is obtained from measurements on identical

half cell solutions over the entire concentration range studied

Since the measurements of these potentials are allowed to

reach equilibrium, the concentration of fluoride in the microcell increases due to the dissolution of LaF„ until the K is

3 sp

satisfied (this effect is negligible in the 100 -ml titration

half cell) . The response of these two electrodes therefore

only differs at very low concentrations.

Table Hi. Results of fluoride determinations by LNPP.

Fluoride taken Fluoride found

Error

s Cone. (M) /n, % % ng

1.01 x 10" 3 0.3 + 1.3 2.5

1.01 x 10~ 4

.5 + 1.0 0.1

g

1.01^ x 10~ 5 .6 + 1.4 .02

4.9

6 x 10" 6 .6 - 0.8 .00g

2.0 x 10 1.0 + .5 -00

2

The summary of results in table 4l gives the quantity of

fluoride present in the standard test samples, both in terms

of concentration- and in nanograms per 10 yl sample, the concentration of fluoride found (average of 5 determinations)

with the relative standard deviation of the mean, and the

87

Cone . (M) ng

1.00 x 10- 3 190

1.00 x io- 4 19.0

1.00 x lO- 5 1.90

5.0 x 10" 6 0.95

2.0 x io" b

.38
error expressed as a percentage and in nanograms. The error

of the method is nearly constant at about 1% over the entire

concentration range while the standard deviation of the mean

as a percent of the mean increases with decreasing concentration from 0.3% to 1% . At the lowest fluoride concentration

studied, 380 picograms of fluoride were determined with an

error of only 2 picograms . This clearly ranks this technique

as the most sensitive microanalytical method for the determination of fluoride.

3 . Electrochemical Generation of Fluoride Ion by SolidState Transference [40

]

Fluoride ion has been electrochemically generated by

means of the solid-state transport of fluoride ions through a

permselective membrane of europium-doped lanthanum fluoride.

The attainment of 100% current efficiency in such a system is

based on the assumptions that, in a crystal of this type, the

only mobile species is the fluoride ion (i.e., transference

number of fluoride ion is unity) , and no other sources of

current inefficiency, e.g., leakage currents, exist. Consequently, when an electric current is passed through the

crystal, the charge would be totally carried by the fluoride

ion

.

a. Apparatus . Using the very simple apparatus diagramed in figure 15 and shown in figure 16, a generation efficiency of 99.2 ± 0.5% (at the 95% confidence level) was

achieved for nine generations of 1.00 mM fluoride. The apparatus consists of a fluoride generation compartment, the

counter electrode compartment, a 90-volt d.c. source, two

variable current-limiting resistors, a 100 fi (0.01%) precision

resistor and recorder for current monitoring, and the electrolysis cell into which the fluoride is generated. The generation compartment consists of a membrane of lanthanum fluoride sealed with epoxy cement into a polyethylene tube. The

internal fluoride generation solution, 1 M NaF buffered at a

88
o

^-0.1 M KNOj (25ml) i-i^-z-pc^r-z-:?^- ---rrg^r^L---_T

ioo n RECORDER

90 VOLTS

-• ^v»——I W*J«VM ' «WW<WWrSWITCH

5Kil 330 KG

(FINE ADJ.) (COARSE ADJ.)

Figure 15. Electrochemical cell for fluoride generation.

Figure 16. Fluoride generation cell
pH of about 5.5 with HP, serves as the catholyte and supplies

fluoride ion to the inner surface of the LaF crystal to prevent fluoride depletion in the membrane. The cathode is a spiral of platinum wire, and the catholyte is continuously

stirred to prevent the formation of concentration gradients.

The resistance of the LaF~ membrane used ( 9 mm in diameter,

1.5 mm thick) is approximately 13k 0, . The double-junction

counter electrode compartment contains a spiral platinum

wire anode in a saturated KNO solution at an initial pH of

approximately 10 (with NHkOH) . Electrical contact to the

intermediate salt bridge is made through a porous Vycor-KN0_

liquid junction. The intermediate salt bridge contains

saturated KNO.-,, and contact with the electrolysis solution is

made through a second porous Vycor-KN0_ liquid junction.

b

.

Experimental . By applying a constant current

of 0.670 mA (current density = 1.05 mA/cm ) to the cell for a period of one hour, the passage of 2.412 coulombs of electricity should produce, at 100% current efficiency, 2.50 x 10

equivalents of fluoride or a final concentration of 1.00 mM

fluoride in the 25 ml of 0.1 M KN0_ electrolyte. The current

was manually controlled to better than ± 0.1% over the duration of the generation, and the time measurement was accurate

to within ± .05% . The efficiency of generation was calculated by analysis

of the resulting electrolysis solution. The analysis was

performed using the technique of "analate additions" potentiometry in which aliquots of the sample (analate) are delivered

into a known volume of a standardized fluoride solution, and

the analate concentration is calculated from the change in

emf of a fluoride activity electrode. The precision of this

technique at the millimolar level is 0.5% (expressed as the

95% confidence limits for the average of 20 determinations)

.

c. Results . The electrochemical generation of

fluoride was performed nine times with an average efficiency

90
of 99.2%. The 0.5% precision (95% confidence limits) corresponds to that for the measurement technique and therefore

cannot be used as an estimate of the generation reproducibility

The 0.8% inefficiency in the generation of fluoride by

this method is assumed due to an inefficiency in the transport of fluoride ions across, and/or an undetected leakage

around, the LaF_ membrane. In this preliminary study with a

relatively unsophisticated apparatus, the attainment of 99.2%

current efficiency reproducible to within 0.5% indicates the

potential use as a technique for the accurate generation of

fluoride ion in situ for coulometric analysis in the laboratory or for automated fluoridation of water supplies. In a practical sense, since the generation efficiency can be established for a particular set of operating conditions, the

current efficiency need not be 100% as long as it is reproducible .

4 . Analate Additions Potentiometry

While the standard additions technique has been used extensively in various analytical methods, the inverse technique,

herein called "analate additions", has apparently not received

any attention. In this procedure, aliquots of the solution

containing the species being determined (analate) are introduced into a known volume of a standard solution of that same

species. The amount of analate is then calculated from some

measureable change (depending on the method) produced by the

analate. In the potentiometric determination of fluoride by

this technique, the change in emf of a fluoride ion selective

electrode is related to the analate concentration by the

equation:

C = C a o

'V +V

' o a V

10 AE/S

a/_

91
where

:

C = concentration of analate

a

C = concentration of standard solution

o V = volume of standard solution

o V = analate volume

a

S = electrode response slope (mV/pP)

AE = emf (mV) change produced on addition of the analate

or, more simply, where:

a

C o [n-10 AE/S - (N-l)l

a

The precision of this technique is dependent upon the

precision in the measurement of AE. Under the present conditions, a standard deviation of about 0.2 mV is easily obtainable. The relative precision in measuring AE can be increased

by taking larger aliquots , thereby increasing the emf change,

but this introduces other complications such as changes in

the ionic strength and liquid junction potential as well as

the limitation set by the quantity of analate solution available . The sensitivity of this technique is dependent only on

the response slope, S, and is independent of the sample volume

Therefore, the aliquot added may be as small as necessary to

give a useable response since the volume requirement for

electrode immersion is already fulfilled by the standard solution. This technique is especially suited to small volumes

of concentrated sample solutions where it is not desired to

dilute as required for use in the standard additions method.

92
In this technique, the ionic strength will normally be established by the background electrolyte of the standard

solution.

For the determination of fluoride by analate additions

potentiometry , the following conditions were used: V in all

cases was 10 ml, V was varied from 5 to 20 ml in 5 ml steps

a

which resulted in AE ' s of 33 to 48 mV, and the response slope,

S, of the electrode was evaluated as 56.3c- ± 0.2- mV/pF. The

analate solutions analyzed contained 1.00 x 10" M and 1.00 x 10 M NaF in 0.1 M KN0„, and the respective concentration of

the standard solutions was one order of magnitude less . For

the two analate concentrations studied, a precision of 0.5%

(95% confidence level for an average of 20 determinations)

was obtained with this technique.

5 . Determination of Dissolved Oxygen using an Ampero - metric Oxygen Sensor

A limited study of a commercial amperometric oxygen

sensor was undertaken to evaluate its response over a wide

range of dissolved oxygen with its eventual application to

the determination of dissolved oxygen at trace levels. Briefly,

the sensor consists of a gold cathode and silver anode, electrically connected by a thin layer of KC1 gel. These sensor

elements are separated from the sample solution by a gaspermeable membrane of Teflon. The sensor also contains a temperature-compensating thermistor. External electronics

provide an . 8V polarizing voltage, signal amplification and

meter or recorder readout. In operation, oxygen gas diffuses

through the membrane and is reduced, causing a flow of current

proportional to the partial pressure of oxygen in the sample.

The apparatus developed and used in this study is shown

in figure 17. The oxygen sensor is mounted in the base of a 2-cm o.d. glass tube with a rubber stopper and sealed into

place with a coating of Glyptal. The bubbler is a medium

porosity glass frit connected to the sensor tube by a ground

93
Figure 17- Oxygen cell and analyzer.

glass joint, and the exit tube is connected to a second bubbler

to prevent the back-diffusion of atmospheric oxygen. The gas

samples are equilibrated with 5 ml of distilled water contained

in the tube above the oxygen sensor. Care was taken to prevent oxygen leaks by minimizing the number and length of rubber

connections

.

The analyses were performed by setting the readout meter

to 8.3 ppm dissolved oxygen for an air-saturated solution of

distilled water. The solution was then partially deaerated

using nitrogen of known oxygen content from 70,660 ppm to 2

ppm. The gas-solution equilibration was monitored with a

potentiometric recorder, and equilibrium was usually achieved

in 10 to 30 minutes. The response was linear down to a meter

reading of approximately 200 ppb dissolved oxygen (vs. the

gas standards) and rapidly leveled off at about 50 ppb. Below 50 ppb, the uncertainty in the measurements was of the

same order of magnitude (about 10 ppb) as the decrease to the

94
lowest level of dissolved, oxygen (^ 30 ppb )

, and the readings

were not a reliable estimate of the oxygen concentration.

Table 42 gives the dissolved oxygen concentration corresponding to the gas-phase oxygen. The data are also plotted

logarithmically in figure 18.

Table 42. Oxygen sensor response to dissolved oxygen,

ppm Op (gas in Np)

209,500 (air)

70,660

2,638

112

ppb Op (dissolved in HpO)

8,300 (calibration point)

2,800

150

35-50

25-40

10 ICf 10° ppm 2 (GAS IN N2 )

Figure 18. Oxygen sensor response to dissolved oxygen,

95
The lowest level to which a solution could be deoxygenated

with the 2 ppm oxygen was 24.5 ppb oxygen. This lower limit

may have been due to (1) the actual equilibrium oxygen concentration between the solution and gas phases, (2) equilibrium

with oxygen leaks in the system, and (3) a residual current

level in the sensing element itself.

The oxygen sensor provides a convenient and sensitive

method for the determination of dissolved oxygen above 50-100

ppb in distilled water. Below this value, increased sensitivity and stability are needed for this method to be of analytical usefullness.

C . Analysis of Standard Reference Materials

1. Analysis of Silver 2-Ethylhexanoate

Silver 2-ethylhexanoate is one of a series of stable,

oil-soluble organic compounds of metals certified for use in

the spectrographic analysis of trace elements in petroleum

products. This compound is being issued by the National

Bureau of Standards Office of Standard Reference Materials as

SRM # 1077a.

Silver determinations were performed by both gravimetric

and titrimetric methods on samples of the material taken from

the top of stock bottles 1, 2, 3, and 4, and from the bottom

of bottle 1. Samples consisting of 0.3 to 0.4 g of the material were ignited overnight in porcelain crucibles at 700°C.

The residues were weighed assuming complete combustion of the

organic material and conversion to metallic silver. The results are given in column 2 of table 43. The silver residues

were then dissolved in 2+1 nitric acid, diluted to about 70 ml

with distilled water, and titrated with standard NaCl. The

end points were located potentiometrically , and the results

are given in column 3. The results in columns 4 and 5 were

obtained by a microgravimetric method (by R. A. Paulson) in

which the silver was weighed as silver chloride after a

96
sealed tube (Carius) oxidation with nitric acid. A sample

weight of 10 mg was used.

The agreement of the analyses was excellent and indicates

a silver content of 42.60 ± 0.05$ (95$ confidence level) for

a stoichiometric purity of 99.0

Q

%.

Table 43. Silver content of silver 2-ethylhexanoate

.

Silver, percent

Sample Ignition Product Titrat:ion Carius

Tl 42..70 42,.76 42 .68

T2 42,.63 42..63 42,.74 42 .56

T3 42,.58 42,.58 42 .63

T4 42,.67 42,.67 42,.41 42 .54

Bl 42..57 42,.55 42 .37

Mean with

95% conf.

limit

42,,63 ± 0. 07 42,.64 ± 0. 10 42,.56 + o.:L3

Pooled mean. 42,,60 ± 0. 05

2. Analysis of o-Fluorobenzoic Acid

A sample of highly purified orthofluorobenzoic acid

(o-FBA) intended for use as a microchemical standard reference

material was carefully analyzed for evaluation of its purity

and also to verify its fluorine content for certification

purposes

.

The determination of fluorine in o-FBA was carried out

by decomposition of the organic material and the subsequent

determination of fluoride by potentiometric titration with

lanthanum (III) using a fluoride ion selective indicator

electrode

.

Several techniques were employed (by R. A. Paulson) to

decompose the samples, with varying degrees of success. An

apparent incomplete decomposition was observed with the sodium

fusion (Ni-bomb), catalytic combustion (in quartz and platinum

97
tubes), and Parr oxygen-bomb methods presumably due to the

formation of carbon tetraf luoride . However, the low results

observed could also be attributed to analytical error caused

by iron or silicate interferences . The oxygen-flask method

gave the most reliable and reproducible results. In this

method, the sample, wrapped in moistened (with water or methanol) filter paper, is combusted in a Pyrex flask containing

oxygen gas at approximately one atmosphere partial pressure

and an absorbant (water or dilute NaOH)

.

In general, the La(III) titrations produced classical

sigmoid-type titration curves in which the point of maximum

slope (inflection point) was taken as the end point. The

same point was taken in standardizing the lanthanum titrant

solution against standard sodium fluoride solutions . In

certain cases, the titration was abnormal in that a relatively

small potential change was observed until 10 to 20% beyond

the end point at which point a rapid emf change occurred which

leveled off at potentials significantly past the end point

potential. This effect is apparently due to either some type

of adsorption phenomenon or a slow kinetic step in the nucleation of the insoluble lanthanum fluoride. Since this abnormal

behavior was readily evident, the results of these titrations

were discarded and not included in the data below.

For 14 determinations, an average fluorine content of

13.57% was found with a standard deviation of the mean of

0.07%. This value compares favorably with the theoretical

value for o-FBA of 13.56% fluorine.

The material is being issued by the National Bureau of

Standards Office of Standard Reference Materials as SRM 1^9,

microchemical standard for fluorine determinations in organic

materials

.

3. Analysis of Au-Ag Metal Microprobe Standards

The composition of four Au-Ag alloys (20 mil wire form),

intended for use as electron microprobe standard reference

98
materials, was determined by a combination gravimetric/volumetric procedure in which preferential dissolution of one of

the constituents ("parting") was affected prior to analysis.

In the case of the higher-content silver alloys (60 and

80% Ag) , wire samples from the head, 1/4, 1/2, 3/4, and tail

portions of the spool were combined and treated with 1+1 HNO_

which preferentially dissolved the silver leaving a gold residue. The residue was filtered, ignited and weighed as metallic

gold. The silver solution was potentiometrically titrated

with a standard NaCl solution using a silver ion selective

indicator electrode.

The higher-content gold alloys (60 and 80% Au; HNO insoluble) were dissolved in aqua regia with considerable difficulty due to the formation of an impervious AgCl film on

the alloy which passivated the surface and prevented further

dissolution of the gold by aqua regia. To reduce this problem and facilitate dissolution, the 20, 40, and 60% Ag alloys

were first rolled into approximately 3 mil ribbon. In addition, the 60% Au-40% Ag alloy required alternate treatments

with NHkOH (to strip the AgCl from the ribbon surface) and

aqua regia over a period of several days to completely dissolve the gold from a 1-gram sample. In this method, the

gold is dissolved leaving the silver behind as the insoluble

chloride. This residue is filtered, dried, and weighed as

AgCl. The gold was precipitated as the metal by reduction

with SO followed by filtering, ignition, and weighing.

Due to the experimental difficulties encountered in the

dissolution of the lower silver content alloys (less than 75%

Ag) , the alloys containing 20 to 60% silver were redetermined

by an inquartation technique. In this technique, the alloys

are fused with enough high-purity silver to increase the

silver content of the alloys to between 75 and 80% . At this

level, the alloys are easily dissolved in 1+1 nitric acid

99
leaving a residue of metallic gold. The residue is filtered,

ignited 3 and weighed. The silver content is obtained bydifference . The data listed in table 44 are the combined results from

this technique and previous analyses with the reported values

for silver obtained by difference.

Table 44. Au-Ag content of microprobe standards.

Sample Gold, percent Silver, percent

1 23.1 76.9

2 40.1 59-9

3 60.2 39.8

4 80.3 19.7

D. Analysis of Research Materials

The development of a competence in the determination of

fluoride has resulted in its application to analytical problems

of interest to various research programs of the Bureau. Two

such service analyses are described below in which are illustrated the wide variance in sample matrices encountered.

1. Determination of Fluoride in Sodium Carbonate

Solutions

Sodium carbonate solutions containing fluoride from the

fusion of Na

2

LaoSir02i.F

2

with Na

2

C0 were analyzed by a double

standard additions technique using a fluoride ion specific

electrode. After adjusting all sample aliquots to pH 6 and

obtaining an electrode response curve by standard additions

to the blank sodium carbonate solution (response 54.5 mV/pF)

,

the fluoride concentration of the two sample solutions was

calculated from the emf changes produced by the addition of

two aliquots of a standard fluoride solution to each. The

results are summarized in table 44.

100
Table 45. Fluoride in sodium carbonate.

Fluoride found Av dev

Sample mg/ml mg (total) mM mM

1 0.040 6.3

2

2.1 0.1

2 .049 8.5o 2.6 .3

Average of two determinations.

2 . Determination of Fluoride in HF-HC1 Mixtures

Fluoride analyses were performed on two HF-HC1 solutions

resulting from the reaction of C1F~ and H p in a platinum-lined

Parr bomb. The determinations were carried out by the potentiometric titration of fluoride with 0.09578N La(NO^)^ using

a fluoride ion selective indicator electrode. A single aliquot of each sample solution was titrated after adjustment to

pH 6.5 ± 0.5- The results are given in table 46.

Table 46. Fluoride in HF-HC1 mixtures.

Sample Aliquot wt meq F~/g sample

1 0.62465 g 0.660

g

2 .44537 g •681

1

When combined with the coulometric results for hydrogen

ion and chloride (by G. Marinenko), these data account for a

material balance to an accuracy of about 2 parts in a thousand

(R. A. Durst)

101
5. MICROSCOPIC AND CLASSICAL MICROCHEMICAL ANALYSIS

A. Introduction

The activities of this laboratory include a number of

programs which are related in that they are concerned with

the analysis or characterization of very small amounts of

matter. These programs include:

1. The detection and identification of micro amounts

of materials

;

2. The development and preparation of ultramicrochemical

standards

;

3. The determination of trace elements in various

materials

;

4. The microchemical analysis of organic and inorganic

materials

.

A parallel activity consists in developing and improving

microscopic techniques and micromanipulative skills requisite

for providing such services to other programs of the Division.

B

.

The Detection and Identification of Microamounts of

Materials

A principal objective of the program is the development

of methodology and techniques for detection, handling, and

identification of contaminants of the atmosphere. The collection of contaminants is done by the methods usually employed in atmospheric pollution studies such as by the use

of impingers , filters, and tapes.

Frequently, only certain contaminants are of interest

and these must be removed from the filter media and sometimes

from a mass of other collected material. Ultrasonic vibration

is used to dislodge contaminants from the filter or, if possible, the filter is dissolved in suitable solvents. Centrifugation is used to concentrate the contaminants before transferring them to slides for microscopic examination. The unique

appearance and optical properties such as color, birefrengence

,

102
and index of refraction are used to help identify the actual

crystal, compound, or object present. The excellent illustrations contained in McCrone's Particle Atlas [41] are often

helpful in making identifications or in providing clues as to

the nature of contaminants present. In some cases, ultramicrochemical tests can be applied but usually the particle

is transferred so that an analysis may be made by various

instrumental techniques . Because the amount of sample is

ordinarily small, a high degree of manipulative skill is required for the handling and transferring of individual particles. It is also very necessary to have a clean environment.

The work which is presently being done In a laminar flow

clean bench will be moved soon to a laminar flow clean room

now under construction.

C . Ultramicrochemical Standards

Of special interest and importance is the preparation of

ultramicrochemical standards. These standards should have a

uniform known size and known composition so that measurement

of the size under a microscope will permit the calculation of

the amount of the element of interest present . Such standards

are useful for determination of detection limits as well as

for calibration of microchemical methods . They can also be

used as standards for instrumental methods such as mass spectrometry and electron probe microanalysis which use very small

amounts of material. While several other methods of preparation have been under consideration, the most promising is the

addition of metal ions to ion exchange resins of uniform size.

This technique was developed in cooperation with the Separation

and Purification Section which provided batches of beads in

the 1 to 10 ym size range.

There are several advantages to using ion exchange resins.

The beads are essentially spherical so that the volume can be

calculated from a measurement of the diameter. They are easily

loaded to either full or partial capacity by treatment with a

103
solution containing the desired ion. Since the loading

characteristics of the resins are known or may be determined,

the weight of the added ion can be calculated. The percentage

of the ion can .also be determined by chemical means using a

sufficient amount of beads

.

There are two problems which reduce the accuracy in determining the amount of ion present in the particle standard.

One is the difficulty in accurately measuring the diameter of

a bead, especially as it approaches 1 urn in size. Freeman

[42] has given the conditions for the most accurate measurement of bead diameters . The other is that the size of a bead

varies with its water content which is dependent on the humidity of the atmosphere to which it is exposed. By only working

in an atmosphere of 30 to 40% R.H. , this effect has been

minimized.

The mass m* of a particular element within a single resin

bead is given by [43]

* iTd pe* / , .px m* = -^- (1-f)

l

where the bead volume is —-r— , p is the density, e* is the

equivalent weight of the bound element of interest, and Ze.

is the equivalent weight of the resin including both the matrix

and attached ions. The matrix in this case is a homogeneously

sulphonated derivative of the copolymer of styrene and divinylbenzene with an equivalent weight of about 185. Some hydration

is allowed for by taking the variable f as the fractional water

content of the resin.

This laboratory has developed the technique for loading

beads with various elements and placing individual beads on

microscope slides for measurement of their diameters. Slide

mounting also provides a convenient means to transport individual beads for later use in analytical calibrations.

104
D. Determination of Trace Quantities of Uranium In Biological

Materials

1. Background

A recently initiated program of the NBS Office of Standard

Reference Materials to provide trace element standards in biological matrices has spurred an interest in development of

sensitive analytical methods especially adaptable to biological

analysis. Various materials such as dried blood, dried plasma,

and botanical matter such as dried alfalfa, dried kale, and

dried oak leaves have been proposed or are actually in preparation for this purpose. Accordingly, there is being pursued

within the Division an extensive program to characterize these

materials. During the past few years, a nuclear track technique has been developed for the detection of such fissile

elements as plutonium, thorium, and uranium and even for a

few nonfissile elements such as boron. The most extensive

use of this new technique has been for the detection of uranium

in inorganic materials for which purpose it has been found to

be highly sensitive and very versatile. There is no reason

to believe that it would not be useful for analysis of trace

elements in organic materials, although no studies of this

nature have been reported. Accordingly, it seems interesting

to investigate the applicability of this technique to the

analysis of biological materials, especially to the extent

that it might be advantageous for standard reference material

certification.

Fission occurs in natural uranium when it is exposed to

radiation of the proper type [44,45]. In general, this radiation for uranium is thermal neutrons and photons. If an insulating material is placed in intimate contact with the uranium, the recoiling fission fragments which enter the absorber

will leave along their paths atomically and electronically

disturbed regions. This type of radiation damage occurs because the ionization density produced along the fission-fragment

105
track is greater than the critical ionization density for the

absorber. The fission tracks can be made optically visible

by etching in a suitable solution. The tracking technique

has been described in a series of papers by Fleischer, Price,

Walker and other authors using several absorbing materials as

detectors [46-50]. These authors have used the technique in

a variety of studies for the purpose of dating of geological

samples, and for detecting trace quantities of uranium in

minerals, micas, and glass [51-53].

In the above-mentioned work, this technique was successfully employed in determining trace quantities of uranium in

geological and metallurgical samples [5^,55]- At NBS it was

thought that the method could be applied to determine the

uranium content of biological material. In the above-cited

work, uranium was either determined or detected only on the

surface of the materials without destroying the material.

However, with biological materials, surface analysis is not

feasible because of the porous nature of the organic matrix

and the odd shape and size of the sample. Accordingly, biological materials must be prepared in solution form for analysis, thus providing a more uniform geometry for irradiation

with the further advantage of reducing the bulk sample by

several orders of magnitude.

Any optically clear insulating material could be used,

in principle, to record fission fragment tracks, but because

10 7 interferring nuclear reactions are possible, e.g., B(n,a) Li,

selectivity of the recording medium is essential. For this

application, the material selected must be insensitive to

alpha particles, high energy protons and recoil neutrons and

record only fission fragment tracks . In a series of experiments, Fleischer, Price and Walker [51,52] found that Lexan

(a polycarbonate, c

1 f)

'ii 1 Q n) has the relatively high critical

ionization density required to act selectively in the manner

desired.

106
2 . Experimental

The prototype standard materials selected for analysis,

blood, plasma, and dried leaves were freeze-dried to remove

most of the water, then ashed at a low temperature in an

oxygen atmosphere using a low-temperature dry asher. Finally,

the residue was digested in nitric acid, filtered, and diluted

to a known volume. Carefully controlled drops of sample solution, delivered from a micropipette, were placed on Lexan

slides, 20 mm wide x 40 mm long x 25 mm thick. The solutions

were evaporated to dryness on a laminar flow clean bench.

(An infrared heat lamp was used in early experiments to evaporate the solutions but this technique was abandoned because

the heat lamp caused cracking of the Lexan.) Standard samples

containing known amounts of uranium were mounted on Lexan detectors in an identical manner, in order to establish for

specific irradiation conditions the relationship between the

number of tracks observed and the weight of uranium present.

In order to prevent external contamination, the slides

were packaged in polyethylene envelopes. After samples and

standards were wrapped in plastic, they were exposed to a thermal neutron flux at the Naval Research Laboratory's swiming pool-type reactor for five minutes in an approximate flux

11 -2 -1 of 3-5 x 10 n«cm -sec . After irradiation, the Lexan

slides were etched in 6 . 5N NaOH at 50° ± 2 °C for 45 minutes

[51]. Following the etching step, the fission tracks produced

2^5 from the U were counted with an optical microscope. The

tracks observed in the case of the actual samples were compared with the number of tracks produced by the standards,

irradiated under the same conditions, to determine the amount

of uranium present.

NBS certified 950-A Uranium Oxide, U~0o 3 was used as a

stock standard. The tUOn was digested in nitric acid to convert the oxide to U0p(NCOp, then the solution was diluted to

a specified volume with distilled water. Various known volumes

107
of the prepared stock solution were spotted on Lexan slides

in order to determine the relation of the number of tracks to

the amount of uranium irradiated. The relation was found to

be linear. Standards, samples and reagent blanks were irradiated simultaneously, then etched and counted. The purpose of

the reagent blanks was to determine the contribution of uranium

in the reagents which were used in the sample solutions. The

preparation of these slides was identical to that of the

standards and the samples. Prom the reagent blank it was

possible to determine the contamination level that the reagents

and Lexan slides contribute for each irradiation. The blank

slides were found to contain an average of eight fission tracks,

corresponding to 1.0 x 10 grams of uranium.

Trace amounts of uranium also can be determined by counting the fission tracks induced by photons. In this case, the

p o o fission fragments are produced from the U atoms. The samples and standards can be prepared in an analogous manner to

that utilized for thermal neutron irradiation. In a preliminary

study, standards were irradiated for five minutes in the

National Bureau of Standards Linear Accelerator (LINAC) . The

photons used to induce fission were produced from an accelerated electron beam with a maximum energy of 35 MeV that bombarded a tungsten converter. The LINAC was operated at an

integrated beam current of 20 uA. The fission tracks produced

p q Q

by the fragments from U were developed and counted. The

average weight of uranium per fission track was found to be

7.7 x 10 grams

.

3 . Results

The technique described has been used for the determination of uranium in several samples of biological materials

supplied by the Office of Standard Reference Materials, namely:

dried mammalian blood, mammalian blood plasma, and dried

leaves

.

108
Six independent analyses of dried blood gave an average

value of 0.55 ± 0.06 ppm for the uranium content. On the assumption that whole blood contains 15% "dried material" [56],

the uranium content of whole blood is calculated to be 83 ppb

.

Freeze-dried mammalian blood plasma was also analyzed.

Five independent determinations gave an average value of 1.09

± 0.25 ppm for its uranium content. On the assumption that

plasma contains 6% "dried material" [56], the uranium content

of plasma is calculated to be 66 ppb.

Determination of the uranium content of the dried leaves

gave results which varied between 1.7 and 14. 9 ppm. This

variation is attributed to the inhomogeneity of the material.

E . Analysis of Standard Reference Materials

1. Residual Fuel Oil

Of the many materials now classed as atmosphere pollutants, sulfur dioxide can be detected by human senses in lower

concentrations than any other common pollutant. Consequently,

it must be classed as one of the more objectionable pollutants,

at least from the point of view of the man-in-the-street . At

present, there are in force, or under consideration, regulations by various levels of government to control the amount

of sulfur dioxide in smoke and stack gas by means of various

scrubbing techniques, or of limiting the amount of sulfur in

the fuel.

Of the sulfur dioxide emitted to the air over the United

States in 1963 (greater than 23 million tons), about twothirds stemmed from coal-burning powerplants and another 16

percent from residual fuel oil. The Petroleum Products Survey

of the U. S. Bureau of Mines indicates that No. 6 fuel oil

Isold in the populous Northeastern area ranges from 0.52 percent to 2.9 percent in sulfur content. In the West, the maximum sulfur content exceeds 4 percent. In all probability,

after much debate pro and con, there will be limits placed on

the amount of sulfur in coal and fuel oil.

109
To provide a base for accurate analysis of fuel oil, the

National Bureau of Standards has certified two new standard

reference materials intended for use in the determination of

sulfur in residual fuel oil. Designated NBS SRM 1621 and

1622, the new standards were prepared from commercial fuel

oil supplied by the Esso Research and Engineering Co., Linden,

New Jersey.

The sulfur content of the fuel oils was determined by

combustion of one-gram samples in a Parr Oxygen Bomb, followed

by gravimetric determination as barium sulfate. The method

used differed from that designated as ASTM D129 in that any

iron present was removed with ammonium hydroxide and filtered

before the precipitation of the sulfate.

Two drums of oil were received containing oil with the

nominal sulfur contents of 1 and 2 percent, respectively.

Three samples were taken from each drum representing the top,

middle, and bottom portions. Approximately ten determinations

of sulfur were made from each portion of the 1 percent oil

and six determinations of each portion of the 2 percent oil.

Since there did not appear to be a significant difference between portions, the results for each oil were pooled.

To identify problems with respect to use or storage of

the sample, tests were made to determine the loss of volatile

constituents. Approximately six grams of oil were placed in

100-ml beakers and allowed to stand open at room temperature

for a period of time. The results are shown in table 47.

Table 47. Loss of volatile constituents from fuel oils.

Percent loss

Period of Exposure 1% Oil 2% Oil

1 day 0.39 0.40

2 days .61 .58

5 days .94 .91

7 days 1.11 1.10

110
From this study it is concluded that no problem should arise

during the routine weighing of analytical samples . Furthermore , no storage problem should develop, provided the sample

container is closed when not in use.

In addition to the sulfur analysis, several routine determinations were made for descriptive characterization of the

oil. Carbon and hydrogen were determined by the conventional

micro-combustion method using 5-mg samples. Water was determined by the Dean-Stark distillation procedure (ASTM D-94)

.

Sediment was determined by a method similar to ASTM D-475

using 20-g samples. Ash was determined by ASTM Method D-482

using 5-g samples.

The results of all analyses are summarized in table 48.

Table 48. Analyses of residual fuel oils.

SRM 1621

Sulfur 1.048$

s = 0.058

n = 30

95$ Confidence Limit ± 0.021

Carbon 86.6%

Hydrogen 12.1$

Water Not detected (< 0.1$)

Sediment 0.01$

Ash 0.02$

SRM 1622

Sulfur 2.138$

s = 0.029

n = 17

95$ Confidence Limit ± 0.013

Carbon 85-3$

Hydrogen 11.3$

Water Not detected (< 0.1$)

Sediment 0.01$

Ash 0.05$

111
2 . Miscellaneous Analyses

The laboratory has provided a number of analytical

services incidental to the preparation, purification, and

certification of standard reference materials . Elemental

analysis for carbon, hydrogen, nitrogen, sulfur, and halogen

has been made on all of the organic materials now being prepared, purified and certified as standards. During the past

year, three organo-metallic compounds, cholesterol, urea,

creatinine, and uric acid, were extensively analyzed. Many

analyses have been made of the ion exchange beads already

mentioned, as well as intermediates prepared for the development of special exchange materials

.

(R. A. Paulson, B. S. Carpenter, W. P. Schmidt)

112
6. MISCELLANEOUS ANALYTICAL PROCEDURES

A. Determination of Sulfur in Plastic Clay

The certification of two lots of plastic clay as standard

reference materials (SRM 97a and 98a) required the determination of the sulfur content, estimated to be about 500 parts

per million. Because the conventional methods for the determination of this element in minerals is cumbersome [57], a new technique was developed.

The method devised consisted in the combustion of a mixture of the clay with a high silicon steel (SRM 125), using

conventional metallurgical analytical equipment . This latter

material has a low sulfur content of 0.003 percent, and provides a fluid melt . Mixtures of clay with the steel in the

ratios of 1:1, 1:2, and 1:3, respectively, were tried and the

latter proved to be the most satisfactory.

Samples of clay of 0.5g were mixed with 1.5g of the

steel, placed in combustion boats normally used for the determination of sulfur in metals, and burned in an ordinary resistance furnace at a temperature of at least 1440 °C. The

resulting sulfur dioxide was absorbed in starch-iodide solution

and titrated with potassium iodate according to the conventional

procedure. The results of the analysis are given in table 49.

Table 49. Determination of SO^ in clay.

S0_, percent Sample 3

SRM 98 (control) 0.077, .071

Certificate value 0.07

SRM 98a 0.315, -301, .320, .326

Average 0.315

SRM 97a 0.102, .104, .107, .104

Average 0.104

113
The sulfur content is calculated as S0~. A sample of

plastic clay SRM 98 was used as a control and the results

found were in good agreement with the certified value.

The method appears to be quite satisfactory for the determination of sulfur in clay and should be applicable to other

mineral products. It has the distinct advantage over the conventional method in being relatively rapid in that only about

8 minutes are required for each determination.

B . Determination of Carbon and Sulfur in Copper Foil

Some investigations of the mechanical and physical properties of electrodeposited copper required determinations of small

amounts (> 100 ppm) of carbon and sulfur in samples of foil,

stripped from stainless steel electrodes . Modifications of

conventional metallurgical analytical techniques proved to be

satisfactory for this purpose, as outlined below.

The copper foil (thickness approximately 1 mil) was cut

into 1/4-in. squares. For determination of carbon, samples

of 1.5 g were placed in combustion boats, covered with 1.0 g

of a low-carbon silicon steel (SRM 131) and ignited at 1300 °C

in a stream of oxygen. The carbon dioxide was absorbed in

ascarite-filled bulbs for gravimetric determination.

For determination of sulfur, direct combustion was satisfactory. Samples of the cut foil (1 to 2 g) were put in

covered combustion boats and ignited at 1440 °C. The sulfur

dioxide evolved was determined by starch-iodate titrimetry.

The results of analysis are given in table 50 and table 51.

Table 50. Determination of sulfur in copper foil.

Sample S, % Sample S,

197-A 0.0042

197-B .0043

197-C .0031

Average 0.0039

114

323-A 0.0014

323-B .0006

323-c

Avera?>;e

.0012

0.0011
Table 51. Determination of carbon in copper foil.

S amp le Carbon, percent

10-A 0.0054, .0072

10-B .005^, .0036

10-C .0036, .0072

Average 0.0054

193-A 0.0036, .0072

193-B .0054, .0054

193-C .0036, .0054

Average 0.0051

C . Analysis of Platinum-Chromium Alloys

The following procedure was devised and used for the

analysis of some platinum- chromium alloys prepared for metallurgical studies of this system.

The samples contained 3 to 30 percent chromium and the

remainder platinum. Approximately 160 mg of each alloy was

available for analysis . Those containing less than 15 percent

chromium could be dissolved completely in aqua regia. For

higher chromium concentrations, acid dissolution resulted in

residues which were fused with sodium pyrosulfate, followed

by solution in water. The combined solutions were evaporated

repeatedly with hydrochloric acid to remove the nitric acid.

Finally, the residues were dissolved in dilute acid and diluted to 300 ml so that the final solution contained 5 percent

hydrochloric acid.

The solution was heated to boiling and platinum was precipitated with hydrogen sulfide. The precipitate was filtered,

ignited, leached, and reignited in a porcelain crucible and

weighed as metallic platinum.

The filtrates from the above procedure were evaporated

twice to fuming with sulfuric acid. The salts were dissolved

in water and diluted to a volume of 300 ml. The chromium was

oxidized with ammonium persulfate, using silver nitrate as

115
catalyst, in the conventional manner, and titrated potentiometrically with ferrous ammonium sulfate.

The results of the analysis, reported in table 52, show

the procedure to give reliable results as evidenced by the

material balance achieved.

Table 52. Analysis of platinum- chromium alloys.

Sample Platinum, percent Chromium, percent Total

#1 (3% Cr) 97.1 2.8

#2 (6% Cr) 93.8 6.2

#3 (10J& Cr) 90.0 10.1

#4 (1556 Cr) 85.

1

14.8

#5 (21% Cr) 79-0 20.9

#6 {29% Cr) 71.8 28.1

(J. R. Baldwin)

99 .9

100 .0

100 .1

99 .9

99 .9

99 .9

116
7. INTERNATIONAL RESEARCH GRANTS PROGRAM

A. Introduction

The National Bureau of Standards awarded a grant to the

Technion Research and Development Foundation, Haifa, Israel,

on December 1, 1965 } to investigate "Trace Analysis by Anodic

Stripping Volt amine try" . Professor Magda Ariel, Chemistry

Department, Technion, Israel Institute of Technology, is

principal investigator. Dr. John K. Taylor, Chief, Microchemical Analysis Section, is the NBS project monitor. The

project was completed in March 1968. The results are summarized in the following sections

.

B. Trace Metal Determinations in Silicates

An anodic stripping voltammetric (a.s.v.) method has

been developed for the determination of zinc in silicates

[58]. The method is sensitive and is not affected by interferences resulting from varying sample composition.

The method has been evaluated by the determination of

zinc in NBS Standard Reference Material Opal Glass No. 91 and

U. S. Geological Survey samples G-l and W-l. This work shows

the method highly reliable for determinations at the ppm level

with standard deviations of 5 to 10 relative percent.

The determination of zinc in samples G-2, AQV-1, GSP-1,

BCR-1, and PCC-1 was carried out by this method. Five of

these standards have been analyzed by a neutron activation

method by Brunfelt et al [59] and the present results show

good agreement with those cited in Table II of their paper.

A report showing standard deviations and details of the problems encountered in the determination of copper and lead is

under preparation. The determination of copper by a.s.v.

combined with medium exchange is best carried out at a mercuryfilm electrode (see section C below).

117
C

.

Anodic Stripping Voltammetry with Superimposed A.C.

Potential

The combination of ac polarography with linear-scan

anodic stripping voltammetry has been investigated using a

phase-discriminating ac attachment [60]. The resolution

and sensitivity were compared with those obtainable under the

same conditions with conventional dc stripping techniques

.

Studies of resolution of neighboring peaks were conducted

For a species undergoing a two-electron reaction the error

resulting from overlapping of two consecutive peaks of equal

heights, differing in peak potential by 75 mV or more, does

not exceed 1 percent

.

For reversible reactants, a comparison of plain anodic

stripping with the ac anodic stripping combination shows

that the latter provides an increased sensitivity of about

one order of magnitude. This increase is retained, though to

a lesser degree, for slightly irreversible reactions.

The potentialities of the technique were demonstrated by

the determination of zinc in NBS SRM 91 (Opal Glass). The

results obtained agreed with those found using conventional

anodic stripping.

D. Studies of the Rotating-Film Electrode

This electrode, as described by de Vries [61], has been

evaluated experimentally for a.s.v. The expected advantages

were: improved sensitivity and resolution, adaptability to

medium exchange and diminished susceptibility to changes in

cell geometry. The main results showed:

1. The effective voltage range is narrower than that of

the hanging mercury drop electrode and depends on the thickness of the mercury-film;

2. Sensitivity is 10 to 20 fold that of an HMDE;

3. The electrode behavior is greatly influenced by

methods employed in coating, pretreatment and storage;

118
4. The theoretical assumption of an evenly spread film

is not upheld by Experiment; during electrolysis (rotation) a

thicker mercury film forms round the electrode rim, while

during stripping (electrode at rest) mercury tends to accumulate near the electrode center. Changes in electrode potential and/or the presence of surfactants also affect mercury

distribution. These effects need to be controlled before

good reproducibility is achieved;

5. For the determination of low copper concentrations

in samples requiring medium exchange between the pre-electrolysis and the stripping steps, the mercury-film electrode

gives good results.

E . Water Purification

The extremely low concentrations of trace metals determined require the consistently reliable purity of the water

employed. De-ionized water, while sufficiently free of ionic

contaminants, often introduces nonionic contamination (from

the ion exchange step); as a result, adsorption peaks may

appear in the voltagrams and the shape of the stripping peaks

of the metals (notably zinc) is affected.

Various purification methods were tried and the following

has been finally adapted:

De-ionized water is filtered and then passed through a column filled with activated charcoal (which has been kept in

an oven, at 950° in an inert atmosphere, for 2 hrs). The

effluent is distilled in a Pyrex still and finally redistilled

from a quartz still, by a non-boiling evaporation process.

The last stage is kept under constant recirculation so

that freshly distilled water only is employed. Water treated

by this method is practically free of interfering contaminants

:

after 30 min pre-electrolysis , hardly a trace of zinc stripping

peak may be obtained; its zinc content has been shown to be

less than 0.03 ppb

.

119
P. Theoretical Studies of Electrochemical Techniques

Theoretical Studies have been undertaken on several electrochemical techniques . A report dealing with potential-step

electrolysis followed by linear potential-sweep voltammetry

[62] was written, which was an extension of theory previously

developed [63]. The results are of importance for an experimental technique for trace analysis described by Yarnitzky [64]

and Ariel.

The problem of constant-current chronopotentiograms distorted by double-layer charging was attacked subsequently.

This led to four reports [65-68]. These investigations were

undertaken to clarify the usefulness of chronopotentiometry

to a.s.v. methods.

(M. Ariel and co-workers)

120
8. PERSONNEL AND ACTIVITIES

A. Personnel Listing

John K. Taylor, Section Chief

Carolyn E. Smith, Secretary

Gas Analysis —

Ernest E. Hughes

William D. Dorko

Julian M. Ives

Polarography —

E. June Maienthal

Coulometry —

George Marinenko

Charles E. Champion

Electroanalytical Measurements —

Richard A. Durst

Erick L. May (Summer Employee - 196 7)

Microscopy and Microchemistry —

Rolf A. Paulson

John R. Baldwin

B. Stephen Carpenter

William P. Schmidt

B. Publications

1. E. J. Maienthal and J. K. Taylor, "Improvement of

Polarographic Precision by a Comparative Technique", Microchimica Acta (Wien) 1967 , 939.

2. J. K. Taylor, "Measurement of Density and Specific

Gravity", Treatise on Analytical Chemistry _7, part 1, 4561-

4610 (1967).

3. R. A. Durst and J. K. Taylor, "Modified Linear NullPoint Potentiometry", Anal. Chem. 39, 13711-79 (1967).

4. R. A. Durst and J. K. Taylor, "Modification of the

Fluoride Activity Electrode for Microchemical Analysis", Anal

Chem. 39, 1483-1485 (1967).

5. G. Marinenko and J. K. Taylor, "High-Precision

Coulometric Iodimetry", Anal. Chem. 39, 1569 (1967).

121
6. J. K. Taylor, Editor, NBS Technical Note 425, "Microchemical Analysis Section: Summary of Activities, July 1966

to June 1967", U. S. Government Printing Office, October 1967.

7. R. A. Durst, Book review: Glass Electrodes for

Hydrogen and Other Cations , George Eisenman, Ed., Record of

Chem. Prog. 2_8, 4 (1967).

8. J. K. Taylor, Book review: Statistical Techniques

for Collaborative Tests , W. J. Youden, Capital Chemist 18 , 70 (1968).

9. R. A. Durst, "Fluoride Microanalysis by Linear NullPoint Potentiometry", Anal. Chem. 40, 931 (1968).

10. R. A. Durst, E. L. May, and J. K. Taylor, "Improved

Technique for the Microdetermination of Silver by Linear NullPoint Potentiometry", Anal. Chem. 40_, 977 (1968).

11. E. E. Hughes and W. D. Dorko, "Direct Mass Spe'aferometric Determination of Atmospheric Carbon Dioxide", Anal.

Chem. 40_, 866 (1968) . 12. E. J. Maienthal and J. K. Taylor, "Polarographic

Methods in Determination of Trace Inorganics in Water", in

Trace Inorganics in Water , Advances in Chemistry Series 73,

R. F. Gould, Ed., American Chemical Society, 1968.

13. E. E. Hughes, "A Simple Technique for the Absolute

Determination of Atmospheric Oxygen", Environ. Sci. Tech. 2_,

201 (1968).

14. E. E. Hughes and W. D. Dorko, "Accurate Mass Spectrometric Determination of Low Concentrations of Carbon Dioxide

in Nitrogen", Anal. Chem. 40_, 750 (1968).

15. E. E. Hughes, Book review: Gas Effluent Analysis , W. Lodding, Ed., Marcel Dekker, Inc., New York, 1967, J.

Am. Ceramic Soc. 5., No. 8, Ceramic Abstracts, p. 260 (1968).

16. D. F. Freeman and R. A. Paulson, "Chemical Microstandards from Ion Exchange Resins", Nature 218, 563 (1968).

122
C. Talks

1. J. K. Taylor, "Scientific Careers vs. Management

Careers", U. S. Civil Service Commission, Washington, D. C,

September 1967.

2. J. K. Taylor, "Electrochemical Methods of Trace

Analysis", Wilmington Section, American Chemical Society,

October 1967.

3. C. E. Champion and G. Marinenko, "Improved Methods

for Coulometric Determination of Halides", Chicago Meeting,

American Chemical Society, September 1967.

^ - R. A. Durst and J. K. Taylor, "Modification of the

Fluoride Activity Electrode for Microchemical Analysis",

Chicago Meeting, American Chemical Society, September 1967.

5. E. J. Maienthal , S. F. Cooper, and J. K. Taylor,

"Some Analytical Applications of Modern Polarographic

Techniques", ORNL Gatlinburg Conference, October 1967.

6. G. Marinenko , C. E. Champion, and J. K. Taylor,

"Coulometric High Precision Analysis", ORNL Gatlinburg

Conference, October 1967-

7. J. K. Taylor, "Recent Advances in High Precision

Chemical Analysis", University of Alberta, Edmonton, Alberta,

Canada, October 1967.

8. J. K. Taylor, "What is Chemistry?", DeChantal School,

Bethesda, Md. , November 1967.

9. B. S. Carpenter, "Nuclear Track Technique for Determination of Trace Elements", Howard University, Washington,

D. C. , December 1967.

10. J. K. Taylor, "Electrochemical Separations: Principles

and Practice", Analytical Chemistry Division Colloquium,

December 1967.

11. J . M . I ve

s

and E. E. Hughes, "Absolute Determination

of Low Concentrations of Oxygen in Inert Gases Using GalvanicType Cells", Third Middle Atlantic Regional Meeting, American

Chemical Society, Philadelphia, Pa., February 1968.

123
12. R. A. Durst, "Microanalysis of Fluoride at Subnanogram

Levels by Linear Null-Point Potentiometry", Third Middle

Atlantic Regional Meeting, American Chemical Society,

Philadelphia, Pa., February 1968.

13. J. K. Taylor, "Electricity and Chemistry", T. C.

Williams High School, Alexandria, Virginia, February 1968.

Ik. J. K. Taylor, "Electrochemical Methods", American

Chemical Society, San Francisco, Calif., April 1968.

15. R. A. Durst, "Equilibria in Electrochemical Cells",

National Institutes of Health, Bethesda, Md. , February 1968.

16. R. A. Durst, "Fluoride Microanalysis by Linear NullPoint Potentiometry", American Chemical Society, San Francisco,

Calif., April 1968.

17. R. A. Durst, "Electrochemical Generation of Fluoride

Ion by Solid-State Transference", Chemical Society of

Washington, May 1968.

18. J. K. Taylor and G. Marinenko, "Applications of

Coulometry to High Precision Analysis", American Chemical

Society, Akron, Ohio, May 1968.

19. B. S. Carpenter, "Applications of the Quantimet

Analyzing Computer in Chemical Microscopy, Howard University,

Washington, D. C, May 1968.

D. Committee Activities

J. K. Taylor

Service Analysis Coordinator, Analytical Chemistry Division

Member, Review Board, Science Book List, American Association

for the Advancement of Science

Member, Board of Managers, Washington Academy of Sciences (WAS)

Elected member, Council of the American Chemical Society (ACS)

Member, Council Committee on Chemical Education, American

Chemical Society

Member, Panel on Chemistry, Civil Service Board of Examiners

Member, Board of Managers, Chemical Society of Washington

Member of Council, The Polarographic Society of London

124
Member , Advisory Committee, Laboratory Guide, American Chemical

Society

.

R. A. Durst

Treasurer, The Capital Chemist, Chemical Society of Washington

Chairman, Auditing Committee, ACS Division of Analytical

Chemistry

Member, Member Services Committee, Chemical Society of

Washington

Chairman, Local Dinner Arrangements Committee (NBS meeting),

Chemical Society of Washington

Safety Representative, Microchemical Analysis Section

E. J. Maienthal

NBS Reporter for Capital Chemist, Chemical Society of

Washington

Elected member, Board of Managers, Chemical Society of

Washington

Editor, Analytical Chemistry Division NewsLetter.

R. A. Paulson

Member, Services Analysis Committee, Analytical Chemistry

Division

Collaborator, Committee for Study of Microchemical Methods,

Association of Official Agricultural Chemists.

E . Award

J. K. Taylor

American Institute of Chemists, Washington Section, Honor

Scroll Award.

125
F . Standard Reference Material Analyses

Material

Cast Iron 6g

Cast Iron 51

Cast Iron 51

Cast Iron 342a

Analyst

JRB

EJM

GM & CEC

JRB

Steel 125b

Stainless Steel lOlf

Stainless Steel lOlg

Ductile Iron 1140,

1141, 1142, 1140a,

1141a, 1142a

Cast Steel 1138, 1139

1138a, 1139a

Ferrosilicon 59a

Perrochromium 196

Solder 127b

Solder 1131

Au-Ag Microprobe

JRB

JRB

Determination

S,C (total), P, Si

C (graphitic)

Ti

Cr

S,C (total), C

(graphitic) , P,

Si

C,S,P,Si,Mn

C,S,P

JRB Mn

GM & CEC Cr

JRB C,S,P

EJM Bi,Cu,Ni

EJM Bi,Cu,Ni

RAD Au,Ag

Technique

C,G,S

P

F

C,S,G

EJM Ti P

GM & CEC Cr P

JRB C (total), C

(graphitic )

,

S, P, Si

C,G,S

EJM Ti P

JRB S,C,P c,s

JRB C,S,P,Si,Mn,V C,S,Pot

GM & CEC Cr F

JRB C,S,P,Si,Mn,V C,S,Pot

GM & CEC Cr F

C,G,S

C,S

S

F

C,S

P

P

G,Pot

126
Material Analyst Determination Technique

Au-Cu Microprobe JRB Au,Cu G

Intermediate purityzinc 683

EJM Cu,Pb,Cd,Fe,Al P

Intermediate purityzinc 728

EJM Cu,Pb,Cd,Fe,Al P

High purity zinc 682

H.P. platinum 680

Doped platinum 68l

High purity gold 685

Cobalt Glass

Clay 97a, 98a

EJM Cu,Pb,Cd P

EJM Pe P

EJM Fe,Cu,Pb P

EJM Fe,Cu P

RAP Water, COp, loss

on ignition

G

JRB SO.

Boric Acid GM & CEC Assay for purity F

Na

2

EDTA GM Assay for purity F

Sucrose 17 RAP Moisture, ash G

BSC Reducing sugars G

Dextrose 4l RAP Moisture, ash G

BSC Reducing sugars G

Cholesterol 911 RAP C,H M

Urea BSC & WPS Insol, ign. loss

C,H,N

G,M

Fluorine micro RAP & RAD F Pot

standard 149

Lead organic 1059b RAP C,H M

EJM Pb P

Zinc organic 1073b RAP C,H M

EJM Zn P

127
Material Analyst Determination Technique

Magnesium organic

106lb

JRB

WPS

Mg

C,H

G

M

Silver organic 1059b RAP C,H M

RAD Ag Pot

Tin organic 1057b JRB Sn G

WPS C,H M

Fuel oil 1621 RAP,WPS,BSC s,c\ H C,G,M

Fuel oil 1622 RAP,WPS,BSC s,c\ H C,G,M

COp in nitrogen EEH & WDD COp Ms, G

1601, 1602, 1603

Op in nitrogen EEH & JMI °2 Gal

1604, 1605, 1606,

1607, 1608

Key to Analyst

JRB - John R. Baldwin

BSC - B. Stephen Carpenter

CEC - Charles E. Champion

RAD - Richard A. Durst

WDD - William D. Dorko

EEH - Ernest E. Hughes

JMI - Julian M. Ives

EJM - E. June Maienthal

GM - George Marinenko

RAP - Rolf A. Paulson

WPS - William P. Schmidt

Key to Technique

C - Combustion

F - Coulometric

G - Gravimetric

Gal - Galvanic cell

M - Microchemical

Ms - Mass spectrometric

P - Polarographic

Pot - Potentiometric

S - Spectrophotometric

128
9 . REFERENCES

[1] J. K. Taylor, Editor, NBS Technical Note 425, October

1967.

[2] E. E. Hughes, Environ. Sci. Tech. 2, 201-3 (1968).

[3] E. Glueckauf, "Compendium of Meteorology", T. P. Malone,

Ed., Chap. 1, p. 4, American Meteoroligical Society,

Boston, Massachusetts, 1951.

[4] P. G. Benedict, "The Composition of the Atmosphere with

Special Reference to Its Oxygen Content", Carnegie

Institute of Washington, Washington, D. C, 1912.

[5] P. Hersch, Anal. Chem. 32, 1030 (I960).

[6] J. M. Ives, E. E. Hughes, J. K. Taylor, Anal. Chem. 40_,

1853 (1968).

[7] E. E. Hughes, W. D. Dorko , Anal. Chem. 40, 750-5 (1968).

[8] C. D. Keeling, Scripps Institute of Oceanography (private

communication)

.

[9] E. E. Hughes, W. D. Dorko, Anal. Chem. 4_0, 866-8 (1968).

[10] H. Moissan, Paris, C. R. Acad. Sci. 137., 600 (1903).

[11] Shinya Oana, J. Earth Sci., Nayoga Univ. 5, 103-24 (1957).

[12] M. B. Jacobs, "The Chemical Analysis of Air Pollutants",

Interscience, New York, pp. 170-172, i960.

[13] E. J. Maienthal and J. K. Taylor, Microchem. Acta 1967 , 939.

[14] J. K. Taylor, Editor, NBS Technical Note 403, October

1966.

[15] Y. LeDuigou and K. F. Lauer, Proc. Conf. High-Precision

Anal. Substances of Interest to Nuclear Energy, Bureau

Central de Mesures Nuclaires, Brussells, Jan. 18-22, 1965.

[16] G. Marinenko and J. K. Taylor, Anal. Chem. 40_, 1645 (1968)

[17] R. G. Bates and E. Wichers, J. Res. NBS 59, 9 (1957).

[18] J. L. Torgesen and J. Strassburger, Science 146 , 53 (1964)

[19] C. Eisenhart, J. Res. NBS 67C, l6l (1963).

[20] J. K. Taylor and S. W. Smith, J. Res. NBS 63A, 153 (1959).

129
[21] G. Marinenko and J. K. Taylor, Anal. Chem. 3£, No. 13,

1569 (1967).

[22] W. J. Hamer (J. Res. NBS, in press), private communication . [23] NBS Tech. News Bull. 47, No. 10 (1963).

[24] G. W. Vinal and S. J. Bates, Sci. Papers Bur. Standards,

No. 218 (1914).

[25] S. J. Bates and G. W. Vinal, J. Am. Chem. Soc. 36., 316

(1914).

[26] D. N. Craig and J. I. Hoffman, NBS Circ . 524, 13 (1953).

[27] H. Sommer and J. A. Hippie, NBS Circ. 524, 21 (1953).

[28] D. N. Craig, J. I. Hoffman, C. A. Law, and W. J. Hamer,

J. Res. NBS 64A, 381 (i960).

[29] G. Marinenko and J. K. Taylor, J. Res. NBS 67A, 31 (1963).

[30] G. Marinenko and J. K. Taylor, ibid 67A , 453 (1963).

[31] F. A. Cooper and J. C. Quayle, Analyst 91, 363 (1966).

[32] G. C. Goode, J. Herrington and W. T. Jones, Anal. Chim.

Acta 37, 445 (1967) . [33] P. S. Tutundzic, Anal. Chim. Acta 18, 60 (1958).

[34] J. K. Taylor, Editor, NBS Technical Note 273, October

1965.

[35] R. A. Durst, E. L. May, and J. K. Taylor, Anal. Chem. 40,

977 (1968).

[36] R. A. Durst and J. K. Taylor, Anal. Chem. 39, 1374 (1967).

[37] R. A. Durst, Anal. Chem. 40_, 931 (1968).

[38] R. A. Durst and J. K. Taylor, Anal. Chem. 39, 1483 (1967).

[39] R. A. Durst, J. Chem. Educ. 43., 437 (1966).

[40] R. A. Durst and J. W. Ross, Anal. Chem. 4p_, 1343 (1968).

[41] W. C. McCrone, R. G. Draftz, and J. G. Delly, The Particle

Atlas , Ann Arbor Science Publishers, Inc., Ann Arbor,

Michigan (1967)

•

[42] D. P. Freeman, Applied Optics 3, 1005 (1964).

[43] D. F. Freeman and R. A. Paulson, Nature 218, 563 (1968) .

130
R. L. Fleischer, P. B. Price, R. M. Walker, Science 1*19 , 383 (1965)

.

P. B. Price and R. M. Walker, J. Appl. Phys . 33, 3407

(1962).

R. L. Fleischer and P. B. Price, Geochimica et Cosmochimica Acta 28, 1704 (1964).

R. L. Fleischer and P. B. Price, J. Appl. Phys. 34, 2903

(1963).

R. L. Fleischer and P. B. Price, Science l40 , 1221 (1963)

R. M. Walker, P. B. Price and R. L. Fleischer, Appl.

Phys. Letters 3, 28 (1963).

M. Debeauvais, M. Maurette, J. Mory and R. Walker, Int.

J. Appl. Radiation and Isotopes 15, 289 (1964).

R. L. Fleischer, P. B. Price, R. M. Walker and E. L.

Hubbard, Phys. Rev. 133, A1443 (1964).

R. L. Fleischer, P. B. Price and R. M. Walker, New

Scientist 3 78 , 406 (1964).

E. C. H. Silk and R. S. Barnes, Phil. Mag. 4_, 970 (1959).

R. L. Fleischer, P. B. Price and R. M. Walker, Nuclear

Science and Engineering 2_2, 153 (1965).

[55] P. B. Price and R. M. Walker, Appl. Phys. Letters 2, 23

(1963).

[56] H. J. M. Bowen, United Kingdom Atomic Energy Authority

Research Group Report, AERE-24196 (1963).

[57] W. F. Hillebrand, G. E. F. Lundell, and J.I. Hoffman,

"Applied Inorganic Analysis", p. 711, John Wiley and

Sons, New York, N. Y., 1953.

[58] G. Koster, U. Eisner and M. Ariel, Z. Anal. Chem. 224 , 269-279 (1967).

[59] A. 0. Brunfelt, 0. Johansen, and E. Steinness, Anal.

Chim. Acta 37, 172 (1967).

[60] U. Eisner, C. Yarnitzky, Y. Nemirovsky and M. Ariel,

Israel J. Chem. 4, 215-223 (1966).

131

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

[52]

[53]

[54]
[6l] W. T. de Vries, "Anodic Stripping Voltammetry with a

Mercury Film Electrode", Thesis, Free University,

Amsterdam, 1967-

[62] W. T. de Vries, "Potential-step electrolysis followed

by linear-sweep voltammetry at a plane mercury- film

electrode", J. Electroanal. Chem. (in press).

[63] W. T. de Vries, J. Electroanal. Chem. 14, 75 (196-7).

[64] C. Yarnitzky and M. Ariel, J. Electroanal. Chem. 10_, 110

(1965).

[65] W. T. de Vries, "Distortion of const ant -current chronopotentiograms by double-layer charging, J. Electroanal.

Chem. (in press )

.

[66] W. T. de Vries, "Correction of constant-current chronopotentiograms distorted by double-layer charging" 3 submitted for publication.

[67] W. T. de Vries, "Influence of double-layer charging in

Programmed-Current chronopotentiometry" , submitted for

publication.

[68] W. T. de Vries, "Double-layer charging in constantcurrent chronopotentiometry at a mercury-film electrode",

submitted for publication.

132
NBS TECHNICAL PUBLICATIONS

en

PERIODICALS

JOURNAL OF RESEARCH reports National

Bureau of Standards research and development in physics, mathematics, chemistry, and engineering.

Comprehensive scientific papers give complete details of the work, including laboratory data, experimental

procedures, and theoretical and mathematical analyses. Illustrated with photographs, drawings, and

charts.

Published in three sections, available separately: • Physics and Chemistry

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times

a year. Annual subscription: Domestic,

$6.00; foreign, $7.25*.

• Mathematical Sciences

Studies and compilations designed mainly for the

mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

numerical analysis, theoretical physics and chemistry, logical design and programming of computers

and computer systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic,

32.25; foreign, 22.75*.

• Engineering and Instrumentation

Reporting results of interest chiefly to the engineer

and the applied scientist. This section includes many

of the new developments in instrumentation resulting

from the Bureau's work in physical measurement,

data processing, and development of test methods.

It will also cover some of the work in acoustics,

applied mechanics, building research, and cryogenic

ngineering. Issued quarterly. Annual subscription:

omestic, $2.75; foreign, $3.50*.

NONPERIODICALS

Applied Mathematics Series.

tables, manuals, and studies. Mathematical

TECHNICAL NEWS BULLETIN

The best single source of information concerning

he Bureau's research, developmental, cooperative

nd publication activities, this monthly publication

is designed for the industry-oriented individual whose

daily work involves intimate contact with science

and technology

for engineers, chemists, physicists, research managers, product-development managers, and

company executives. Annual subscription: Domestic,

$3.00; foreign, $4.00*.

•Difference 'Dinerence in price is due to extra cost of foreign mailing.

Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) developed in cooperation with interested industries,

professional organizations, and regulatory bodies.

Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts,

pamphlets, etc. Monographs. Major contributions to the technical literature on various subjects related to the Bureau's scientific and technical activities.

National Standard Reference Data Series.

NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated.

Product Standards. Provide requirements for

sizes, types, quality and methods for testing various

industrial products. These standards are developed

cooperatively with interested Government and in- dustry groups and provide the basis for common

understanding of product characteristics for both

buyers and sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other agency

and NBS-sponsored work) of limited or transitory

interest. CLEARINGHOUSE

The Clearinghouse for Federal Scientific and

Technical Information, operated by NBS, supplies

unclassified information related to Governmentgenerated science and technology in defense, space, atomic energy, and other national programs. For

further information on Clearinghouse services, write:

Clearinghouse

U.S. Department of Commerce

Springfield, Virginia 22151

Order NBS publications from:

Superintendent of Documents

Government Printing Office Washington, D.C. 20402
U.S. DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20230

OFFICIAL BUSINESS

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE