NBSIR 73-411

Development of Analytical Reference

Materials and Contaminant Generation

Systems - Work Completed During

Fiscal Year 1973

B. C. Cadoff, P. A. Pella, E. E. Hughes, E. P. Scheide,

A. A. Angotti, and J. K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

January 1973

Interim Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

NBSIR 73-411

DEVELOPMENT OF ANALYTICAL REFERENCE

MATERIALS AND CONTAMINANT GENERATION

SYSTEMS - WORK COMPLETED DURING

FISCAL YEAR 1973

B. C. Cadoff, P. A. Pella, E. E. Hughes, E. P. Scheide,

A. A. Angotti, and J. K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

January 1973

Interim Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

1 .

U. S. DEPARTMENT OF COMMERCE. Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director
i
DEVELOPMENT OF ANALYTICAL REFERENCE

MATERIALS AND CONTAMINANT GENERATION SYSTEMS - WORK COMPLETED DURING FISCAL YEAR 19 73

ABSTRACT

This report summarizes the research and development

activities performed by NBS for NIOSH, during Fiscal

Year 1973, under Interagency Agreement 123/3104459. Items

reviewed included: reference materials consisting of

filters containing hazardous metals and quartz-clay

mixtures; analytical standards for determination of

organic solvents; the development of air contaminant generator systems; reference samples consisting of blood and

urine with analyzed amounts of toxic elements.

INTRODUCTION

Work was completed or substantial progress was made on

all items identified in the Memorandum of Agreement. The activities carried out during Fiscal Year 1973 are outlined in

the following sections, identified to correspond to the

tasks described in the Memorandum of Agreement and reference

is given to NBS reports for full details on the tasks completed.

The progress on the remaining tasks is described in appendices

A through D.

A . Atmospheric Analysis Reference Materials

Techniques were developed for the preparation and certification analysis of filters containing the following

hazardous materials:

Series 1 Pb Cd Zn Sn

yg/filter

1-A 7.5 5 100 150

1-R 15 10 200 300

1-C 30 20 400 600
Series 2 Pb' Zn Mn

! yg/filter

2-A ' 7.5 100 250

I 2-B 15' 200 500

2- C 30 400 1000

Series 3 Be

pg/filter

3- A 0.1

3-B .0.2

3-C 0.4

One hundred sets of each series have been prepared,

analyzed, and delivered to NIOSH for their evaluation and use

Pull details are given in NBS Report NBSIR 73-256.

Techniques were developed for the preparation and certification analysis of filters on which mixtures of quartz and

clay were deposited.

Ser ies SiO

^

, pg Clay, mg Total, mg

000100-160 0 400 400

000200-260 30 370 400

000300-560 80 320 400

000400-460 200 200 400

Fifty filters of each series were prepared, analvzed and

delivered to NIOSP^ for evaluation and use as analytical

standards. Full details are given in NBS Report NBSIR 73-400

2
In each of the above cases, levels given are nominal

values. The reports give the recoiiunended analytical values.

B . Analytical Standards for Biological Materials

Work on blood samples containing biologically incorporated

lead was completed and analyzed samples were delivered to

NTOSH. The two sets of samples contained lead at "normal"

and "elevated" levels, respectively.

Work was completed on the development and analysis of

urine samples containing biologically incorporated mercury at

"normal" and "elevated" levels. A total of 200 samples

were delivered to NIOSH.

Techniques were developed and a number of freeze-dried

samples of normal urine and urine spiked with elevated levels

of selenium, arsenic, copper, nickel, and chromium were prepared and certified. A similar set of two samples containing

"normal" and "elevated" levels of fluoride was also prepared

and certified. These samples have been packaged in analytical

units and delivered to NIOSH.

NBS Report 73-406 gives full technical details of the

preparation and analysis of all of the biological samples

mentioned above.

C . Mercury Vapor in the Industrial Environment

Work was done on the development of techniques for production and certification analysis of reference materials for

the determination of mercury vapor in the occupational environ3
ment . A gas delivery system was constructed and performance

evaluated. A lot of prototype tubes containing mercury deposited

on iodized charcoal was prepared for method evaluation. Discussions shortly thereafter with the Project Officer indicated

alternate other approaches to collection of mercury vapor were

being considered. Accordingly, further production of charcoal

tubes was suspended, awaiting NIOSH's clarification of the

analytical technique.

The system for use in preparing the reference tubes is

essentially that described in NBS Report NBSIR 73-254.

The silver wool sampling technique appears to be very satisfactory for analytical purposes, but may not be feasible for

routine use, due to cost considerations. Charcoal is superior

as a collector, but there are analytical problems due to

desorbtion difficulties. A procedure in which charcoal is

used for collection, followed by desorbtion onto silver in

the analytical step seems to be a satisfactory one.

D. Analytical Standards for Determination of Organic Solvents

See Appendix A.

I: . Development of Generation Systems for Certification of Gas

and Vapor Sampling Instruments

Gas generation systems were developed, constructed, and

performance evaluated and reports have been prepared as indicated below. The modular concept was followed so that the

systems developed and delivered vary from complete independent

units, to gaseous mixtures for use with units already delivered.

4
Operational manuals have been prepared for each system. The

pertinent NBS reports are as follows:

NBSIR 75-254 - A Mercury Vapor Generation and Dilution System - E. P. Scheide, R. Alvarez, B. Greifer,

E. E. Hughes, and J. K. Taylor

NBSIR 73-255 - System for Preparation of Known Concentrations

of Methane in Air - E. E. Hughes, W. D. Dorko,

and J. K. Taylor

NBSIR 73-257 - Ion Selective Electrodes for Industrial Hygiene

Monitoring: Hydrogen Cyanide - E. P. Scheide,

E. E. Hughes and J. K. Taylor

NBSIR 73-258 - A Gas Dilution System for Acrolein - E. P. Scheide,

E. E. Hughes and J. K. Taylor

NBSIR 73-259 - A Gas Dilution System for Methyl Bromide - E. P. Scheide, E. E. Hughes and J. K. Taylor

NBSIR 73-260 - A Gas Dilution System for Arsine-Air Mixtures - P. A. Pella, E. E. Hughes and J. K. Taylor

NBSIR 73-261 - A Gas Dilution for Hydrogen Fluoride-Air Mixtures - P. A. Pella, E. E. Hughes and J. K. Taylor

NBSIR 73-292 - Gas Generating Systems for the Evaluation of

Gas Detecting Devices - E. E. Hughes, W. D. Dorko

and J. K. Taylor

In addition to the systems developed, considerable effort

was devoted to three additional systems. This work is

summarized in attachments to this report, as indicated below:

Sulfuric Acid Aerosol , see Appendix B

Phosgene , see Appendix C

TDI and MDI , see Appendix D

Formaldehydesee Appendix E

5
I
APPENDIX A

Progress Report

on

Development of Charcoal Tubes

as SRM's for Organic Vapor Analysis

Barry C. Cadoff

Air Pollution Analysis Section

Analytical Chemistry Division

National Bureau of Standards

Washington, D. C. 20234

1. INTRODUCTION

This is the second progress report on the preparation o£

charcoal tubes containing known amounts of organic solvents.

The first report, issued December 1, 1972, dealt with the

preparation of an initial batch of approximately 1,000 tubes,

each containing known amounts of one of seven solvents, viz.,

benzene, xylene, dioxane , chloroform, carbon tetrachloride,

ethylene dichloride, and t richloroethylene . Together, the

two reports contain descriptions of work done during FY 1973.

This report describes results obtained since December 1972

and includes plans for future work.

2. RE -EXAMINATION OF REPORTED VALUES FOR CHARCOAL TUBES

In the first report, values for the amount of adsorbed

solvent were given for each charcoal tube. These were calculated values from a computer-fitted straight line through

data points obtained from the analysis of the tubes and from

the flow-rates and concentrations of the gases used to prepare

the tubes. The predicted values, based on the gas concentrations-flow data, formed the X-axis, while the analyzed values

for the tubes formed the Y-axis. The reported results were

based on the fitted line through the points determined by

the predicted and analyzed values; this procedure gives greater

weight to the values based on the gas concentration.

Re -examination of the methods used to prepare the gas

mixtures has shown that errors may have been introduced in the
dilution steps. (This is discussed in detail in Section 4 of

this Appendix.) A few of the retained charcoal tubes containing

benzene have been analyzed recently, and the results from this

analysis are significantly different from the values reported

earlier -- in fact, these new data place the values for benzene

closer to the values reported by the participating laboratories.

To further clarify this situation, a number of tubes have

been re-analyzed and new values will be assigned. (A separate

report giving full details will be issued.)

However, even though the final values for the tubes may

be amended, the tubes themselves show little variability in the

quantity of adsorbed material. Thus, the tubes of a particular

concentration level, those labeled "E", for example, show a range of variation less than 2 percent. This is true, too,

for the tubes labeled A, B, C, and D. Similarly, the ratio of

the adsorbed material of any two tubes is essentially equal to

the ratio of the flow rates of the sampling orifices to which

they were attached during the filling operation. Accordingly,

their homogeneity does not appear to be in doubt. Therefore,

regardless of the absolute value of the contents contained in

the tubes, any variation in the analysis of the tubes at a given level that is greater than a few percent would indicate

variability in the analytical procedure.

The work to be performed for the Standard Reference

Material Charcoal Tubes (SRM's) will not, of course, depend

solely on analysis of the tubes, but will also be based on

2
the analysis of the gases used to fill the tubes. This will

be discussed in the following sections of this report.

3. DEVELOPMENT OF SAMPLING SYSTEM AND EXPERIMENTAL

DESIGN FOR THE PREPARATION OF CHARCOAL TUBE SRM'S

For the preparation of the original 1000 charcoal tubes,

a sampling system was used which provided cons tant flow at

each of five orifices -- but not identical flow. In fact, the

range of flow varied by about 10 percent. Thus, five different

values were listed for the charcoal tubes at each nominal

concentration level. For the SRM's, it was decided to prepare

tubes that can be certified to contain the same amount of

solvent, at each concentration level, within a certain known

error.

Since 4200 tubes are required to be filled for the SRM's

it was necessary to redesign the sampling manifold and to develop

a procedure which would provide matched orifices in sufficient

number to insure that the tubes could be filled in a reasonable

length of time. It was felt that a sampling manifold containing

about two dozen matched orifices would be suitable.

The final design has provision for 20 critical orifices.

'The orifices are mounted on a hollow brass base plate, 16.5 cm

(6.5 in.) in diameter and 1.9 cm (0.75 in.) in height. Each

critical orifice is a hypodermic needle (22 gauge) selected so

that the range of flow through all orifices varies by no more

than 1.5 percent. The selection of the needles necessitated

3
the testing of about 200 needles for flow characteristics.

The needles are fitted into Luer-loks''" (obtained from

hypodermic syringes) and were made vacuum- tight with the aid

of stopcock grease. The Luer-loks are soldered into the baseplate. This arrangement makes it possible to remove or

replace needles when necessary.

Atop the needles are placed Nupro"^ filters to protect the

needles from contamination by particulates . The tubes are

attached by short pieces of rubber tubing to the apparatus. In

use, the baseplate is connected to a vacuum source.

For the filling of the tubes at concentrations corresponding to 0.5, 1.0 and 2.5 times the OSHA level, a single gas

mixture will be employed. The use of a single gas mixture

should simplify the analysis of the gas and more importantly,

should produce tubes that have a definite known relationship to

each other. The tubes, for example, at the 1.0 OSHA level will

contain twice as much solvent vapor as the tubes at the 0.5

OSHA level. The amount collected will be determined by the

length of sampling time. These tubes will contain a quantity

of solvent equal to that which would have been adsorbed if a sample were collected at the rate of one liter per minute for

Certain commercial equipment, instruments, or materials are

identified in this paper in order to adequately specify the

experimental procedure. In no case does such identification

imply recommendation or endorsement by the NBS, nor does it imply

that the material or equipment identified is necessarily the

best ' available for the purpose.

4
ten minutes in an atmosphere containing solvent vapor at a concentration o£ 0.5, 1.0, and 2.5 times the OSHA level.

Thus, for the sampling orifices described above, which

have flow rates of about one liter per minute, the sampling

time needed to collect a sample equivalent to 2.5 times the

OSHA level would be ten minutes, if the gas concentration is

2.5 times the OSHA level. Similarly for tubes at the 0.5

and 1.0 levels, the sampling times would be two minutes and

four minutes.

4. DEVELOPMENT OF METHODOLOGY AND CRITERIA FOR PREPARATION AND ANALYSIS OF SOLVENT- IN-AI R MIXTURES

As pointed out earlier, the re -examination of the pressurized

tank mixtures of solvents -in-air has shown that errors in the

determination of the solvent concentrations may have been

introduced. This could occur when the assumption is

made that a dilution of a primary tank mixture to produce a second tank mixture will yield a concentration of solvent

vapor which is directly proportional to the dilution factor.

Recent analyses have shown that this error can be as large as

7 percent when, for example, t richloroe thylene at 1000 ppm is

diluted to 100 ppm. Accordingly, additional work on solventsin-air has been devoted to problems inherent in preparing and

analyzing these mixtures.

In the preparation of these mixtures, the solvent is '

introduced into evacuated size 1-A tanks either by distilling

the solvent or by injecting the solvent into the tank. The

tank is then pressurized to about 1000 psia. The concentration

5
may be calculated from (1) the weight of the solvent admitted,

the total volume of the tank and the final pressure; or (2)

the pressure of the solvent vapor and the final pressure.

In fact, measurements agree with calculated values within

about 2 percent when solvent-in-air mixtures in the range of

200-1000 ppm are prepared. The problem, then, occurs upon

dilution of these tank mixtures to levels near the OSHA range.

The dilution step, say from 600 ppm to 60 ppm is achieved

by withdrawing 10 percent of the original tank mixture and

transferring it to a second tank of the same size. This

second tank is then diluted with air to a final pressure of

10 times the pressure of the transferred gas. It is at this

step that anomalies present themselves -- i.e., the discrepancy

between concentration based on pressure - dilution data and

concentration based on gas chromatographic data. This can be

seen by comparing the figures given below, in which gas

dilution data are compared with gas chromatographic data

PPM PPM Percent Difference

Gas G. C. G. C. - Gas

Solvent Calculated Method Gas X 100

Benzene 202 202 0

31.7 28.8 - 9.1%

Ethylene 713 713 0

Dichloride 71.6 66.9 - 6.6%

Trichloro- 1016 1016 0

ethylene 98.1 90.9 - 7.3%

Chloroform 72 8 728 0

73.5 65.3 -11%
Gas chromatographic analysis of gases is performed by

transferring gas at known pressure and volume into the gas

chromatograph equipped with a flame ionization detector.

Response of the gas chromatograph measured in terms of area

of the resulting peak, is directly proportional to the amount

of compound contained in the sample. Therefore, a gas sample

which is one-tenth as concentrated as a second gas sample

should give a gas chromatographic response which is onetenth as large as the second sample. This response is shown to

be the case, for example, in tank mixtures of propane and

methane. Similarly, liquid solutions of each of the seven

solvents of interest (benzene, xylene, dioxane, chloroform,

carbon tetrachloride, ethylene dichloride, and trichloroe thylene)

give linear gas chromatographic responses vs. concentration.

However, in the gas mixtures of the seven solvents there are

significant differences between calculated concentrations

and concentrations obtained by gas chromatography. Although

it may be assumed, perhaps quite generally, that the gas

chromatographic data is correct, a confirmatory procedure is

required to prove this.

One procedure which can be used to calibrate the gas

chromatograph and thus determine the concentration of a solvent

vapor would involve the following steps: replumbing of the

gas chromatograph to enable alternate injection of liquid or

gnseous samples; determination, to within 1 or 2 percent, of

the volume of the gas sampling valve; accurately prepared

liquid solutions of the desired solvent in a material such as
carbon disulfide; calibration o£ the gas chromat ograph using

tlie liquid standards; and finally the determination of the

concentration of a gas mixture by comparing the gas response

to a calibration curve for the liquid solution of the solvent.

A direct method for measurement of solvent concentration,

which is now being used, involves collecting and weighing the

solvent contained in a known volume of the s olvent - in - ai

mixture. In this method, a calibrated orifice is used to

obtain a constant collection rate, the sampling time is carefully controlled, and a trapping medium -- a charcoal tube --

is carefully weighed before and after the sampling. The

concentration can then be easily calculated.

In this procedure the charcoal tube is connected to a sampling orifice and pure air is drawn through until the

tube registers a constant weight. The solvent-in-air mixture

is then drawn through the tube for a certain length of time.

The weight gain of the tube and the flow through the tube are

used to calculate the concentration of the gas mixture. The

collection is quantitative for reasonable flow rates and the

tubes have ample capacity to provide reliable measurements,

for example, a tank mixture of carbon tetrachloride prepared. at

a concentration of 680 ppm, yielded results of 688 and 683 ppm

by the charcoal tube method. Full details of this analytical

method will be described in a future report.
5. PRESENT STATUS OF SRM PRODUCTION

The technical details of the procedure to produce the

SRM tubes have now been developed to the point where production could be started. The tubes to be filled have been

received and the gas mixtures have been prepared and analyzed.

The production of the SRM's is being held temporarily

in abeyance, pending the NIOSH evaluation of the charcoal

tube analytical procedure. Once final approval has been

received, the work can be completed within a three-month

period.

9

APPENDIX B

Progress Report

on

The Generation of Known Concentrations

of Sulfuric Acid Aerosol

Peter A. Pella

Air Pollution Analysis Section

Analytical Chemistry Division

National Bureau of Standards

Washington, D. C. 20234

1. INTRODUCTION

This report describes some preliminary results obtained in the

generation of known concentrations of sulfuric acid aerosol. To

gain some familiarity with producing such aerosols, a generating

system was constructed which involved passing air at a known flow

rate through concentrated H2S0^ - fuming H2S0^ mixtures. The

entrained SO^ vapor was mixed with humid air in a mixing chamber

and then allowed to pass through a sample manifold. To monitor

the concentration of H2S0^ aerosol in the sampling manifold, one

port of the sampling manifold was fitted with a millipore filter

assembly and connected to a mechanical pump. Qualitative

determinations of the collected H^SO^ aerosol on the millipore

filter were made with BaCl^ . An alternate procedure for generating

H2S0^ aerosols was investigated w^hich obviates the need for acid

mixtures .

2. PREPARATION OF H^SO, AEROSOLS FROM ACID MIXTURES

2 —4

Historically, mixtures of concentrated - fuming acids

have been used to prepare aerosols in the tenth micron range (1,2).

The use of known amounts of fuming H2S0^ (i.e. oleum) will

produce known SO^ concentrations above the solution as calculated

from vapor pressure vs. temperature data. This procedure has

also been used to prepare H2S0^ aerosol particles for controlled

growth studies using light-scattering techniques (2). Therefore, this method of preparation served as a starting point

in the present study. Mixtures of the acids were prepared by

adding known volumes of 30 percent fuming H^SO. (i.e. containing
30-33 percent free SO^) to the concentrated (96 percent by weight)

acid. Solutions were prepared having SO^ partial vapor pressures

from 1 to 10 mm Hg at 25°C. Such solutions would theoretically

produce concentrations of H2S0^ aerosols in the range from 1,300

to 13,000 ppm.

3. DESCRIPTION OF THE GENERATING SYSTEM

Figure 1 is a diagram illustrating the principle of operation.

Air is first dried and then passed through two bubblers containing

a mixture of the fuming and concentrated acids. The flow is

controlled by means of a differential flow rate controller DFC-1

and measured with a rotameter. The air saturated with SO^ enters

the mixing manifold and mixes with another stream of humid air.

The air is humidified by passing it through a bubbler

containing water. The flow is controlled by means of DFC-2 and

measured v\;ith a rotameter. The humid air mixes with the SO^

stream to form the H2S0^ aerosol. The aerosol passes to the

sample manifold where a sample is collected via a millipore filter

assembly for subsequent analysis. The presence of H2S0^

collected on the filter was confirmed qualitatively with BaCl2.

4. COMMENTS ON THE ACID MIXTURE METHOD OF PREPARING AEROSOLS

One of the major difficulties encountered in the above

procedure is the method of preparing the sulfur trioxide. The

preparation of hazardous acid mixtures on a routine basis would

seem to be undesirable in a calibration system of this type.

For this reason an alternate route was explored which if

successful would obviate the need for such acid mixtures. The
contact process for the manufacture of H2S0^ depends on the

conversion of to SO^ catalyt ically . The advantages of

using a catalytic conversion method here would be twofold.

First a working standard could be prepared which xvould consist

of a known concentration of in air or an SO^ permeation tube.

The could be then converted catalyt ically to SO^ and

mixed with humid air to produce a known concentration of the

aerosol. Secondly, if the conversion efficiency was 100 percent

or could be determined at each desired concentration level then

the aerosol concentration may not require monitoring in contrast

to the acid mixture method of preparation. For these reasons,

some initial studies were undertaken to gain more information

about this method.

5. PREPARATION OF CATALYTIC COm^ERTER

A catalytic converter was constructed and consisted of

finely dispersed Pt metal (5-10 percent) on asbestos fibers. The

fibers were loosely packed in a 12 in. long by 3/8 in. O.D. stainless steel tube as shoim in Figure 2. The tube was placed in a furnace as shown and held at 350-450 °C for catalytic conversion

of the SO2. The platinized asbestos was prepared by soaking fine

asbestos fibers in a saturated solution of E2^tCl^ in water.

The slurry was made basic with NaOH and then transferred to

a large procelain evaporating dish. Most of the water was

evaporated from the slurry by mild heating ina muffle furnace.

Then enough formic acid was added to completely cover the

3
slurry and the temperature was raised to 400°C. This

procedure produced Pt metal finely dispersed on the fihers.

Finally, the asbestos was thoroughly v/ashed with distilled water

and dried in a muffle furnace.

6. DETERMINATION OF THE CATALYTIC CONVERSION EFFICIENCY

The conversion efficiency of the converter was investigated

by passing an S02-air mixture through the converter and then

through a midget impinger containing a knoiAm concentration of I2

in a saturated KI solution.

The concentration of the SO2 was first measured by passing

it tlirough the unheated converter and then through the 12"^^

solution. Starch was added when the I2 solution v/as pale yellow.

The end-point was taken at the first disappearance of the

blue color of tlie starch-I^ complex. The volume of gas collected

was measured with a wet-test meter. Five measurements of

the SO^ concentration gave a mean result of 98 ppm with a relative standard deviation of 8 percent. The temperature

of the tube furnace was then maintained at 450°C as measured

with a thermocouple. Ten liters of the gas were passed

through the converter and collected in the ^2'^^ solution.

The I left was determined by adding a kno\\Ti amount of

AS2O2 solution and back titrating the excess As with

standard I2 solution using starch as an indicator. This

gave a result of 4.4 ppm of SO2 which indicates a conversion

yield of 93.5 percent SO^. Similar measurements on an

SO -air mixture containing 1900 ppm SO^ gave conversion

2

^

4
yields ranging from 82 to 90 percent but the conditions

were not necessarily optimum.

7. SUGGESTION FOR FUTURE WORK

The catalytic method has been shown to be a more desirable

and practical way of producing SO^ for H^SO^ aerosols. However,

furtlier study is warranted to determine conversion efficiency

yields at the 0.4 ppm level. Other important variables which m.ay

need to be considered for characterizing the performance of such

a system are listed as follows:

1. Characterization of part icle - s ize distribution via

light-scattering techniques.

2. Collection efficiency of H2S0^ aerosols on filters.

3. Development of analytical measured systems for

analysis H^SO. aerosols (e.g. acid-base titration, conductivity).

5
APPENDIX B

J REFERENCES

'^Mader, P. P., Hamming, W. J., and Bellin, A., Anal. Chem.

22_, 1181-1183 (1950).

2 Contarel, L., Matijevic^ E., Kerker, M. , and Huang Chao-Ming,

J. Colloid and Interface Science 24, 338-343 (1967).

6
SYSTEM

FIGURE I

FOR GENERATING SULFURIC ACID AEROSOL

AIR

IN

ROTAMETER

AIR : DFC

IN

ROTAMETER

DRYER DFC

fi

TO PUMP

rCID

S OLUTIONS

MIXING

MANIFOLD

SAMPLE

MANI FOLD

^MILLIPORE

<- ' FILTER

-^SAMPLE PORT

7
FIGURE 2

CATALYTIC CONVERTER

$.S« TIJBF - =;T|MSpSlll3=-> OUT

GLASS WOOL f PLATINIZED ASBESTOS

PLUGS

TUBE PLACED IN TUBE FURNACE

AND KEPT AT CONSTANT

TEMPERATURE I.E. (350-450)

8
APPENDIX C

Progress Report

on

A Gas-Blending System for Phosgene in Air

Peter A. Pella

Air Pollution Analysis Section

Analytical Chemistry Division

National Bureau of Standards

Washington, D. C. 20234

1. INTRODUCTION

This report summarizes the activity to date on a gas-blending

system for producing knovm concentrations of phosgene (COCI2) in

the range from 0.05 to 0.5 ppm. This work describes: (a) the preparation of phosgene-air and phosgene -nitrogen bulk mixtures in

the range from 5 to 1700 ppm, (b) the investigation of a number of

analytical methods for phosgene characterization and (c) the evaluation of a gas-blending system for producing phosgene concentrations

from 0.05 to 0.5 ppm. A study of the stability of the phosgenenitrogen bulk mixture is still in progress.

2. PREPARATION OF PHOSGENE BULK MIXTURES

Initial gas mixtures were prepared by adding phosgene gas sampled

from above the liquid (Matheson Co.) at a partial pressure of 20 mm Hg

to a large cylinder and then filling it with air to 500 psi. This

yielded a concentration of 784 ppm. Similarly, a concentration of

17 00 ppm of phosgene - in-nitrogen was prepared by adding 110 mm of

phosgene to a cylinder and filling it to 1200 psi with "super-dry"

nitrogen. To confirm the purity of the phosgene gas used to prepare

these bulk mixtures, infra-red analysis of these mixtures was performed. A spectrum of the 784 ppm bulk mixture is shown in Figure 1.

This spectrum was compared with a reference spectrum of 1.5 mm partial

pressure of phosgene (99.5 + percent, redistilled from U. S. Naval

Ordnance Test Station, Chemical Division, China Lake, California).

The absorbances at A (5.5 ym) and B (12 vim) are prominent

phosgene lines. The CO2 at 4.3 ym and the H^O vapor 2.5-2.7

!
microns are believed to be present in the added air. IR analysis of

the phosgene -nitrogen mixture, however, showed no water vapor or HCl

absorbances. To remove the possibility of hydrolysis of the

phosgene in the phosgene-air bulk mixture because of the vapor

present, more dilute bulk mixtures were prepared by successive dilution of the 1700 ppm pho sgene -nit rogen mixture with "super-dry"

nitrogen. In table 1 is a comparison of the values obtained by

pressure measurements with the values obtained by chemical analysis.

These results show that a phosgene -nitrogen bulk mixture at the

5 ppm level can be prepared by successive dilution of a high

concentration bulk mixture with no apparent loss of phosgene.

TABLE 1

Preparation of a 5 ppm Bulk Mixture by Successive

Dilution of 1773 ppm Mixture

Cone. COCl

2 Percent Deviation

Calc'd Cone. COCl

(Press. Meas.)

Found (CI Meas.) Calc 'd-Found

X 100

(Mean) Calc 'd

1773

405

59

ppm

ppm

ppm

5.3 ppm

1683 ppm (3)*

381 ppm (6)

61 ppm (5)

4.9 ppm (4)

+ 5. 0

+ 5.9

-3.4

+ 7.5

*The number in parentheses represents the number of measurements made at each level.

3. DESCRIPTION OF ANALYTICAL PROCEDURES

One approach used in this work to analyze phosgene in mixtures

is to absorb the phosgene quantitatively in a solution containing

2
50 percent methanol (MeOH) and 0.1 M KOH. The phosgene is

completely hydrolyzed according to the ' react ion

COCI2 + 2K0H = 2KC1 + +

The resulting chloride concentration can then be measured using a

variety of methods. Three methods for measuring the chloride

concentration were investigated in this work and consisted of

potent iometry, coulometry, and titrimetry using m.ercuric nitrate.

3 . 1 Potent iometry

The chloride concentration was measured potentiometr ically

using either an ion-selective chloride electrode oranAg, AgCl

electrode prepared in our laboratory. The reference electrode was

a calomel electrode where contact with the analyte solution was

made with a potassium nitrate salt bridge. A calibration curve was

prepared by measuring known concentrations of KCl prepared in 50

-4

percent MeOH-0.1 M KOH solution. The curve was linear from 10

to lO"''' M Cl". A problem found in the application of this method

is that the electrode response was sluggish in this alcoholic

medium. The time required for the electrodes to reach equilibrium

varied from 1/2 to two hours and was considered impractical for

measuring phosgene in mixtures for this work.

3 . 2 Coulometry

A commercially available automatric coulometric titrator

was used to analyze the chloride concentration. The phosgene was

collected as already described in 50 percent, MeOH-O.lM KOH solution. This solution were titrated with electrogenerated silver ion.

The titrator was calibrated by plotting the time in seconds

3
required to titrate known concentrations of KCl in 50 percent MeOHO.IM KOH solution. A typical calibration curve is shoiAm in Figure 2 This method was used to determine the phosgene concentration o£ gas

mixtures from 5 to 1700 ppm. The concentration of phosgene in ppm

in the gas mixture was calculated as follov^s:

= 1/2

where

= concentration of phosgene in ppm in gas mixture.

M = moles of chloride x 10 ^ found in total volume of

absorbing solution.

; " E = molar volume of gas and is 24.5 liters/mole at 25 *>c.

V = volume of gas mixture collected in absorbing solution in

1 iter s

.

3 . 3 Titrimetry using Mercuric Nitrate

Chloride ion can also be titrated with a standard solution of

mercuric nitrate (0.005 N) in a 90 percent alcohol-10 percent

water solution (1). In this procedure, a mercuric nitrate solution

is standardized with kno^m chloride concentration in a 90 percent

alcohol-10 percent water solution at an apparent pH of 3.6 in the

presence of diphenylcarbazone as indicator. The mercuric nitrate

forms undissociated mercuric chloride, until an excess of mercuric

ions appear, which then combine with the indicator to form a violetcolored complex, thus marking the end-point in the titration. The

sensitivity of this method is sufficient for the determination of

a 5 ppm phosgene bulk mixture when 10 to 20 liters of the mixture

is collected in a 5-10 ml volume of 50 percent MeOH-0.1 M KOH

4
absorbing solution. The concentration of the phosgene in the bulk

mixture is obtained by using the equation:

r = T X V X E

2 MV

where

= concentration of phosgene in ppm in bTallc Tnixture.

T = titer of mercuric nitrate solution (i.e. \ig CI

equivalent to 1.0 ml of HgCNO^)^ solution).

V = volume of titrant used to titrate the CI in the

total volume of the absorbing solution in ml.

M = molecular weight of CI .

E = molar gas volume, which is 24.5 liters/mole at 25 °C.

V = volume of phosgene bulk mixture collected in liters.

3 . 4 Spectrophotometr ic Determination of Phosgene with 4-P-nitrobenzylpyr idine and N-benzylanil ine Reagent

The lack of specificity of methods which solely measure

chloride ion is a drawback in determining the stability of phosgenenitrogen bulk mixtures and in evaluating the performance of a gasblending system. For this reason a specific method for phosgene

analysis was sought to aid in these studies. Perusal of the literature revealed a number of spectrophotometric methods which have

been used to measure phosgene in air mixtures. However, almost all

of those reported indicate some interference of HCl (a common

hydrolysis product of phosgene) and other mineral acids. Recently,

Noweir and Pfitzen (2) have reported on the spectrophotometric

5
determination of phosgene in air below 0.1 ppm. The absorbing

reagent consisted of 0.25 percent 4 -p -nitrobenzylpyr idine (NBP) , and 0.5 percent N-benzylanil ine (BA) in diethylphthalate . These

authors found no affect of water vapor, HCl, CI2, ^0^, and other

vapors commonly found in industrial atmospheres on the color

development of this reagent with phosgene. Therefore, this method

was investigated in this work to detect any decomposition of phosgene

either in the bulk mixture or in the manifold of the gas blending

system.

4. EVALUATION OF A GAS-BLENDING SYSTEM FOR PRODUCING PHOSGENE

CONCENTRATIONS IN AIR FROM 0.05 to 0.5 PPM

A gas-blending system for producing phosgene concentrations by

dilution of a 4.6 ppm bulk mixture in the range from 0.05 to 0.5 ppm

was evaluated. The phosgene bulk mixture and diluent air were

admitted into the gas-blending system at precisely controlled flow

rates. The phosgene concentration of the diluted mixture in the

sampling manifold was determined by passing a known volume through

5-ml of the NBP-BA reagent at a rate of 0.5 1/min, waiting five

minutes for color development, and then measuring the absorbance

versus an NBP-BA reagent blank at 475 nm. A calibration plot was

prepared by collecting knoim volumes of the phosgene bulk mixture

in 5-ml of the NBP-BA reagent and measuring the absorbances. A

typical calibration plot is presented in Figure 3. Note that this

curve is non-linear above 4 yg C0Cl2/inl (i.e. A=0.4) and demonstrates

a negative deviation from the Lambert-Beer lax\^. The phosgene con6
centration of the bulk mixture was determined coulometr ically and

gave an average result of 4.6 ± 0.1 ppm. The results obtained

using the dilution system are plotted in Figure 4 and summarized

in Table 2,

TABLE 2 Calculated vs. Observed Phosgene Concentrations

in Sampl in^I Manifold

Flow Rate

Bulk Mixture

1/min

Flow Rate

Diluent

1/min

Dilution

Factor

Calc'd

Cone, ppm

Obs.

Cone, ppm

(Calc'd-Obs.)

Deviation

in ppm

0.237 0. 255 0.4817 2.2 2.2 0. 00

0.122 0.380 0.243 1.1 1.1 0. 00

0. 060 0.440 0.120 0.55 0.55 0.00

0.0329 0.491 0. 0628 0. 29 0.29 0. 00

0.101 3. 06 0.0320 0.15 0.13 • +0. 020

0.0329 3. 06 0.0107 0. 049 0. 046 +0. 003

These results indicate that dilutions of the phosgene bulk mixture

via the gas-blending system to produce concentrations from 0.05

to 0.5 ppm are accurate.

5. STABILITY OF THE PHOSGENE-NITROGEN BULK MIXTURE

The phosgene -nitrogen bulk mixture at the 5 ppm level was

measured coulometr ically over a period of three months and the results

are presented in Table 3. These results indicate no significant

decrease in the phosgene concentration over this time period. Because

of the non- specif icity of the coulometric method, the spec tropho to

metric technique using NBP-BA reagent was developed to investigate

any change in the phosgene concentration. One way to determine

7
whether any decomposition o£ phosgene has occurred is to absorb

a known volume of the bulk mixture in the NBP-BA reagent, and

then extract the phosgene from the complex quantitatively followed

by the coulometric measurement of chloride. This was accomplished

by the following procedure:

Forty liters of the bulk mixture was collected in 5-ml

of NBP-BA reagent. A 3.0 ml aliquot was placed in a separatory funnel and shaken with an equal volume of

;. methanol-KOH solution. This solution was allowed to

: stand for 1-2 hours to decompose the phosgene complex,

and 5-ml of distilled water was added. The mixture was

shaken and the diethyl phthalate was separated from the

alcohol -water phase. The organic layer was acidified

with a few drops of concentrated nitric acid and washed with | 5-ml of H2O. The wash water was then separated from the

organic layer and added to the alcohol-water phase from the

first extraction. The organic layer was checked for chloride I

ion by adding a few drops of CH^OH-AgNO^ solution. A

negative test was obtained. The alcohol -water phase containing the chloride ion was transferred to a 25.0 ml volumetric

flask and filled to the mark with 50 percent CH^OH-O.IN KOH

solution. A 6-ml aliquot of this solution was then titrated

coulometr ical ly . The average of two determinations was 4.2

ppm. This value compares favorably with the value of 4.6 ± .1

ppm obtained on the bulk mixture determined previously by

coulometry. Hence, these results indicate that the phosgene |

8
bulk mixture is sufficiently stable. Additional measurements

are still in progress to detect any change in the phosgene

concentration in the bulk mixture by following the absorbance

of the NBP-BA-phosgene complex with time.

TABLE 3

Study of the Stability of Phosgene-Nitrogen

Bulk Mixture

Time, Days Apparent COCl ^ Cone, ppm

4 4.9 ± .1

82 4.5

89 4.7

95 (3 months) « 4.6 ± .1

9
APPENDIX C

REFERENCES

^White, D. C. Mikrochim, Acta 3, 449 (1961).

2 Noweir, M. H. , and E. A. Pfitzer, American Industrial Hygiene

Association Journal 32, 163 (1971).

10
11
FIGURE 2

CALIBRATION FOR PHOSGENE

I

' 5

• -t

^

MICROMOLES CHLORIDE

12

FIGURE A

DILUTION OF PHOSGENE BULK MIXTURE

20

CALCULATED CONC.,PPM

14
APPENDIX D

Progress Pveport

on

TDI and MDI Vapor Generation and Dilution System

E. P. Scheide, E. E. Hughes and J. K. Taylor

Air Pollution Analysis Section

Analytical Chemistry Division

National Bureau of Standards

Washington, D. C. 20234
I

\
A. INTRODUCTION

This report describes experimentation performed in the

development of a generation system and method of analysis of

test atmospheres of toluene diisocyanate (TDI) and methylene

diphenyl isocyanate (HDI). Also, suggestions for future work

are included.

B. EXPERIMENTAL

1 . Analytical Systems

Several different analytical systems were considered for

use in the analysis of TDI and MDI vapors. These were: (1)

color imetric , (2) gas chromatography, and (3) infrared spectroscopy. The most common method in use is that originally pro4 posed by Marcali for the determination of TDI in air, and

subsequently modified by other v/orkers.^*^ This color imetric

method depends on the hydrolysis of the TDI to the corresponding

amine; the latter is diazotized and finally coupled with N-1-

naphthylethylenediamine to form a colored complex, which is

measured photometrically. This method was not used in our

experimentation because it does not differentiate between TDI

and the diamine that is formed upon the hydrolysis of TDI.

Infrared spectroscopy has also been used for the analysis

7 8 of isocyanates, ' but the sensitivity is too low for the proposed applications.

The analytical method finally chosen for this work was gas

chromatography using a flame ionization detector. Sampling

can be easily performed with this technique, it possesses
adequate sensitivity, and separation and identification of the

different isocyanates and their reaction products can be

acliieved. Even more sensitivity can be achieved if desired

using an electron capture detector. The most satisfactory

column was a 6 ft., 10 percent VC-W.98, 80-100 WHP column.

2. Generation Systems

• Several different types of generation systems were investigated and these are summarized below:

^ a. Pressurized Cylinders . Mixtures of TDI vapor in air,

nitrogen, and super dry nitrogen were made and placed in pressurized

steel cylinders. The TDI vapor from these cylinders was always

much less than the calculated concentration and contained

several reaction products. The TDI was apparently both adsorbing

onto the walls of the cylinder and decomposing. Experiments

were also performed using pre-conditioned cylinders with similar

results. Another problem associated with the use of pressurized

cylinders is that the bulk mixture needed of TDI is of extremely

low concentration. It might be possible to make stable cylinder

mixtures of TDI in nitrogen at higher TDI concentrations.

b. Liquid Saturators . The next generation technique

investigated was that of using a liquid saturation system. This

consists of an impinger containing TDI through which is passed a stream of clean, dry nitrogen. A diagram of this saturator is

shown in Figure 1.

The major difficulty in preparing TDI in air mixtures by

this method was contamination by volatile impurities. Even though

the impurity concentration in the liquid phase may be very low^,

2
problems are still encountered because of the extremelv low vapor

pressures of TDI and MDI. This causes the effective vapor phase

concentration of the volatile impurities to be much higher. If

these impurities interfere with the analytical determination,

then they must be completely removed. To illustrate this problem,

if a TDI sample contains 99.97 percent TDI and 0.03 percent

toluene in the liquid phase, the vapor phase will contain approximately equal concentrations of TDI and toluene because the vapor

pressure of toluene is 3000 times that of TDI.

Once the volatile impurities are removed, however, this

could be an effective method for generating TDI in air. This

method was set aside because of the hazard associated with

handling large quantities of TDI. It is felt that the TDI/silica

gel column presents far less of a hazard while being just as

effective as a generation system for TDI.

c. TDI/Silica Gel Column . To minimize the hazard in case

of accident, the liquid saturation technique was abandoned and

replaced by a TDI/silica gel "column". This "column" consists

of a piece of stainless steel tubing 3/8 inch in diameter and

25 inches in length. The "column" was packed with silica gel (6-

16 mesh, grade 05) which had been soaked in purified TDI for

30 minutes. The "column" was bent into a loop and on-off values

were attached at both ends. As dry air is passed through the

"column" the liquid phase (TDI) "bleeds" off of the column in

a constant and reproducible manner.

3
Prior to use, the "column" must be conditioned for

several hours by passing a slow stream of dry air through it.

This will remove any remaining volatile contaminants and

simultaneously coat the entire inside surface of the column

with TDI. After this conditioning process, the column will

emit a reproducible mixture of TDI in air. The reproducibility

of the system has been checked several times 1-2 weeks apart

resulting in daily reproducibility of ± 3 percent and weekly

reproducibility of ± 6 percent.

A study was made of the effect of the flow rate of air

through the column upon the concentration of TDI emitted. The

results of this study show that the concentration of TDI

remains constant (± 1 percent) using air flows between 1.5 and

5.5 liters per minute with increasing concentrations at lower

flow rates.

The column saturation technique was evaluated by chromatographic analysis, using liquid standards of various concentrations (TDI in toluene) , and was found to produce TDI concentrations of 4.6-5.0 ppm TDI. This concentration is less than

that produced by the liquid saturation technique (13 ppm) and

may be caused by an affinity of the TDI for silica gel thereby

lowering its effective vapor pressure, a pressure drop through

the column causing the concentration to decrease, or other

reasons

4 9-'

d. MDI . According to reports in the literature, '

and preliminary experimental investigations, MDI possesses too

4
low a vapor pressure to be generated in the gaseous state at

the concentrations of interest at room temperature. Its

danger occurs when it is in the form of an aerosol or a fine

dust particle. An MDI "column" similar to the TDI "column"

was constructed and evaluated but without success. Because

of these reasons, the development of an MDI gas generation

system has been delayed until more information can be obtained

and the decision made as whether or not to attempt the development of an apparatus for the generation of MDI aerosols and

dusts.

3 . The Dilution System

The TDI column has been used in conjunction with a dilution system to produce lower concentrations of TDI in air, but

with limited success. Several breadboard arrangements have

been tried, but more work is needed in this aspect of the

problem. The TDI coming out of the system is of much lower

concentration than calculated. Several suggestions are included

on the possible causes of this problem and directions for future

experiments.

4 . SUGGESTIONS FOR FUTURE WORK :

The following are suggestions for future experiments

to be performed.

1. New Dilution System i A new dilution system should be built to minimize the

internal surface area. Figure 2 shows a diagram of a mixing

manifold with low surface-to-volume ratio that would be

5
incorporated into the system.

2 . Longer Equilibration Time

The dilution system should be conditioned for much

4 9 longer times. It has been suggested, * that as long as 72

hours equilibration time is needed. Minimizing the internal

surface area of the dilution system should also shorten this

equilibration time.

3 . Dry Air

The use of super-dry air might also reduce losses

of TDI in the system.

4. Non -Adsorbing Materials

If the column and dilution system could be constructed

of materials that did not adsorb TDI the problem would be solved.

6
APPENDIX D

REFERENCES

Threshold Limit Values for 1965, American Conference of

Governmental Industrial Hygienists, 1014 Broadway, Cincinnati,

Ohio 45202.

Beatty, R. L., Beckert, A. J., and Bush, H. W. , Lab. Rept.,

U.S. Bur. Mines, p. 2 (May, 1962).

Woodbury, J. W. , Ind. Med. Surg., 25, 540 (1956).

Marcali, K. , Anal. Chem. , 29, 552 (1957).

Grim, K. E. and Linch, A^ L., Am. Ind. Hvg. Ass. J., 2

, 285 (1964).

^Reilly, D. A., Analyst, 88_, 732 (1963).

''oavid, D. J. and H. B. Staley, "Polyure thanes , Part III:

Analytical Chemistry," Interscience Publishers, New York

(1969)

g Snell, F. D. and L. S. Ettre, eds., "Encyc. of Industrial

Chemical Analysis," Vol. 15 (1972).

Stern, A. C, "Methods of Air Sampling and Analysis," Amer.

Publ. Health Serv., Wash., D.C. (1972).

Meddle, D. W. , R. W. Radford and R. Wood, Analyst, 94, 369

(1969)

Meddle, D. W. and R. Wood, Chemistry and Industry, 1635

(23 Nov. 1968)

Reilly, D. A., Analyst, 92, 513 (1967).

7
Figure 1. Liquid Saturator
6 in

diluent air

i

TDI (from column)

Figure 2. Proposed TDI Mixing Manifold

9
: '€
APPENDIX E

Progress Report

on

The Formaldehyde Generation and Dilution System

A. A. Angotti, E. P. Scheide, E. E. Hughes, and J. K. Taylor

Air Pollution Analysis Section

Analytical Chemistry Division

National Bureau of Standards

Washington, D. C. 20234

A. INTRODUCTION

This progress report describes experimentation performed in

the development of a generation and dilution system and method

of analysis of test atmospheres of formaldehyde. Also, suggestions for future work are included.

" B. EXPERIMENTAL

1 . Analytical Systems

The analytical systems considered for the analysis of

formaldehyde -air mixtures were gas chromatography'^ ^, and a 5-8 chromotropic acid colorimetric method. Gas chromatography

provided good selectivity but the sensitivity was not sufficient

for analysis of the lower concentration mixtures. For this

reason, the chromotropic acid colorimetric procedure was used.

The air sample was bubbled through the reagent and the resulting

color change was monitored by use of a spectrophotometer. A

probe colorimeter has been obtained and this will be used in the

analytical system in order to monitor the formaldehyde concentration output of the system continuously.

2 . Generation Systems

Several types of formaldehyde generation systems were

investigated and these are summarized below:

a. Pressurized Cylinders . Mixtures of formaldehyde

(obtained by passing a slow stream of the diluent over paraformaldehyde supported on asbestos) in air, nitrogen and superdry nitrogen were made and placed in pressurized steel cylinders.
These mixtures proved unsatisfactory because the analyzed concentration was always far less than calculated. Also, the mixtures

were not stable and decayed rapidly with time.

b. Liquid Saturator . Another way of generating mixtures

of formaldehyde in air is to bubble air through an impinger

containing formalin solution. This technique was abandoned

because of the large amounts of water, methanol and other

substances that accompanied the formaldehyde.

c. Paraformaldehyde . Two systems were used to produce

formaldehyde from paraformaldehyde. These are shown schematically

in Figure 1. They were about equal in efficiency and stability.

The output of the generator was fed directly into a mass spectrometer and while operating at room temperature only a formaldehyde

peak was observed. On the other hand, when the temperature was

increased, in order to increase the formaldehyde concentration,

other peaks appeared in the spectrum. Also, the paraformaldehyde

vaporized and later condensed downstream from the generator. For

these reasons, this generator system can only be used near room

temperature.

The range of formaldehyde concentrations obtainable with

this system is from 0.5 ppm to about 60 ppm. The major drawback,

however, is the increasing instability and unpredictability at the

higher formaldehyde concentrations. For example, the precision

at 1 ppm is ±1 percent, at 10 ppm ±4 percent, and at 50 ppm ±30

percent. The stability is good for 24 hours and longer at the

2
lower formaldehyde concentrations.

The time to reach equilibrium increases with increasing

formaldehyde concentration, and at the higher concentrations, the

system does not appear to reach equilibrium.

3 . The Dilution System

A standard dilution system was modified for use with the

formaldehyde generator. A schematic of this system is shown in

Figure 2.

C. SUGGESTIONS FOR FUTURE WORK

The following are suggestions for future experiments to be

performed.

1 . Effect of Flow Rate

Further experiments should be performed to investigate the

relationship between the formaldehyde and diluent flow rates.

It is possible that other flow combinations might increase the

precision of the generator output.

2 . Effect of Temperature

Further studies should be conducted on the effect of

temperature on the stability of the system, especially slightly

above and below ambient temperature.

3. Modified Dilution System

It might be possible to build a new dilution system of more

inert materials that would reduce the interaction between

formaldehyde and the walls of the system.

4 . Effect of Equilibration Times

Longer equilibration times at the higher formaldehyde

3
concentrations might produce a more stable output. This should

be investigated.

5 . Modified Analytical System

The new probe colorimeter will provide a tool to facilitate

the investigation of the system including the identification of

problem areas.

4
APPENDIX E

REFERENCES

•Mann, R. S. and K. W. Hahn, Anal. Chem. , 39 (11), 1314 (1967).

2 Onuska, F., J. Janak, S. Duras and M. Krcmarova, J. of

Chromatography, £0, 209 (1969).

^Bombaugh, K. J. and W. C. Bull, Anal. Chem., 34 (10), 1237

(1962)

^Otvos, I., G. Palyi, Z. Balthazar and B. Bartha, J. Chromatogr.,

6£, 422 (1971).

^West, P. W. and B. Sen, Z. anal, chem., 1_52, 177 (1956).

^Altshuller, A. P., D. L. Miller and S. F. Sleva, Anal. Chem.,

33 (4) , 621 (1961)

7Altshuller, A. P., L. J. Lang and A. F. Wartburg, Int. J. of

Air and Water Pollution, 6_, 381 (1962).

^Altshuller, A. P. and S. P. McPherson, JAPCA, 13 (3), 109 (1963).

5
COLUMN

IHPINCER

Figure 1. Formaldehyde Generation Systems

6


NBS-lUA (F<EV. 7-73)

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4. Ti ri.K AND SlUVVl l l.li

Tlo'v/'p^lr^T^Tn/^n'f' A'F An3l'\7"f"'ir"5jT T^f^'Pf^y^f^inr'^ ^Tii'f'fiT'ToTc onrl

Contaminant Generation Systems - Work Completed

During Fiscal Year 1973

5. Publication Date January 1973

6. Performing Organ i zat imi (JodiJohn K. Taylor

8. Performing Orpan. Report No. NBSIR 73-411.

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