NBSIR 74-527

Development of Solid State Samplers

for Work Atmospheres

B. Greifer, B. C. Cadoff, J. Wing, J. K. Taylor

National Bureau of Standards

Department of Commerce

Wastiington, D. C. 20234

June 1974

Semiannual Report

Prepared for National institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

NBSiR 74-527

DEVELOPMENT OF SOLID STATE SAMPLERS

FOR WORK ATMOSPHERES

B. Greifer, B. C. Cadoff, J. Wing, J. K. Taylor

National Bureau of Standards

Department of Commerce

Wastiington, D. C. 20234

June 1974

Semiannual Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

CONTENTS

Page

1. INTRODUCTION

2. DEVELOPMENT OF METHODOLOGY 1 2.1 Contaminant Generation Systems 2 2.2 Gas Sampling Systems 4

2.3 Solid-State Sorbents 6

2.3.1 Solid-State Sorbent Requirements .... 8

2.3.2 Literature Survey of Solid Sorbents. . . 9

A. Fluorine and Hydrogen Fluoride. ... 9

B. Chlorine 10

C. Hydrogen Cyanide 11

D. Phosphine 12

2.3.3 Choice o£ Solid Sorbents and Devices . . 12

2.4 Gas Analysis 14

2.4.1 Determination of Contaminant Gases ... 14

A. Fluorine and Hydrogen Fluoride. ... 15

B. Chlorine 16

C. Hydrogen Cyanide 17

D. Phosphine 18

3. EXPERIMENTAL RESULTS 19

3.1 Hydrogen Fluoride 19

3.1.1 Gas Generating and Sampling Systems. . . 20

3.1.2 Solid Sorbents for Hydrogen Fluoride . . 20

3.1.3 Construction of Sorption Tubes 24

3.1.4 Analytical Method for Fluoride 26

3.1.5 Experimental Data 30

A. Collection Efficiencies of Sodium . . 30

Acetate

B. Capacity of Sorption Tubes 32

C. Effects of Elevated Temperature ... 32

D. Effects of Humidity 32

E. Precision, Bleed-out, Storage, Ship-. 34

ment

3.2 Hydrogen Cyanide 34

3.2.1 Determination of HCN Concentration ... 34

3.2.2 Screening of Solid-State Sorbents. ... 35

3.2.3 Discussion 36

3.2.4 Future Work 36

3.3 Phosphine 36

3.3.1 Experimental Method 36

3.3.2 Experimental Results 38

3.3.3 Conclusions and Future Plans 40

4. SUMMARY AND CONCLUSIONS 40

5. BIBLIOGRAPHY 42

i
CONTENTS (Continued)

Page

APPENDIXES

A. Precision and Accuracy Data for Residual A-1

Chlorine Methods

B. Precision and Accuracy Data for Phosphorous. . . . B-1

Methods

C. Summary of Data on Phosphate C-1

TABLES

1. Concentration Ranges of Reactive Gases 13

2. Collection Efficiencies of Various Sorbents for. . 23

HF

3. Collection Efficiencies of Sodium Acetate 31

for HF

4. Effects of Temperature on Collection of HF .... 33

5. Phosphine Sorption on Solid Materials. . . . . . .39

FIGURES

1. Block Diagram of Program Organization 3

2. Diagram of Gas Dilution System 5

3. Diagram of Gas Sampling System 7 4. Gas Generating and Sampling Systems for HF .... 21

5. Sorption Tube for HF 25

6. Pressure Drop Measurement Apparatus 27

7. Calibration Curve of Fluoride Standard Solutions . 29

i i
Development of Solid State Samplers for Work Atmospheres

ABSTRACT

A program is described for evaluating the efficiency

of solid sorbers for collecting trace quantities of hydrogen

fluoride, phosphine, hydrogen cyanide, chlorine, and

fluorine in work atmospheres for subsequent laboratory

analysis. The gas handling and sampling instrumentation

is described, and experimental results to date are presented.

Sodium acetate is a very efficient sorber for hydrogen

fluoride, and its solubility in water proves to be highly

advantageous for subsequent HF determination by ion selective electrode. Potassium permanganate impregnated silica

gel sorbs phosphine effectively, and Ascarite has been

found to sorb hydrogen cyanide, but quantitative experiments on the latter two systems are still in progress.

Work on chlorine and fluorine systems will be initiated

in the near future

.

1. INTRODUCTION

The report summarizes work on the development of sampling

procedures and devices for the collection of five toxic gases

in industrial atmospheres, viz. fluorine, hydrogen fluoride,

hydrogen cyanide, chlorine, and phosphine during the period

January 1 - June 30, 1974. The program is being carried out

under a Memorandum of Agreement between the National Bureau of

Standards and the National Institute for Occupational Safety

and Health.

The scope of the work includes investigation of various

sorbent materials and selection of appropriate sorbents

based on criteria of stability, cost, and effectiveness; and

development of suitable collection devices and analytical

methods for determining the contaminant levels collected.

To date, the experimental techniques have been developed

for sampling and analyzing the contaminant gases. Data have

been obtained on the sorption of hydrogen fluoride, phosphine,

and hydrogen cyanide on various solids and prototype sampling

tubes for hydrogen fluoride have been prepared and tested.

2. DEVELOPMENT OF METHODOLOGY

The project has been divided into several discreet categories, each of which is discussed in detail in the sections

that follow. In this section the technical parameters of the

1
problem are analyzed, various solutions to the problem are

considered, and finally decisions are made on at least one

approach that can be used for each area of concern. The

block diagram of Figure 1 illustrates the general approach

that was followed:

(a) By using a single analytical procedure for each

contaminant, the results from the solid-state sorbent

experiments may be easily compared to the results obtained

with standard wet collection procedures.

(b) Reliable flow controls for both the solid state and

the wet sampling assure that known amounts of contaminant

gases are trapped.

(c) The use of a compressed gas cylinder as a contaminant

source provides a sufficient quantity for a large number of

tests and experiments.

The procedures and considerations applied to this project

are general in nature and should be applicable to the development of solid-state sorbents for a wide range of contaminants.

2 . 1 Contaminant Generation Systems

To carry out the many tests required for the screening

and selection of solid-state sorbents, a reliable contaminant

source is required. The gases needed are all obtainable

commercially as the pure gases in compressed gas cylinders.

For this work, however, concentrations are required which in

some instances are less than one -millionth of the pure

gas, far too low a concentration to be reliably obtained by

diluting the pure gases in a dynamic flow system. However,

four of the gases are available commercially in the concentration ranges needed, and these were obtained from the

producer. The gases and nominal concentrations are listed

be low :

• HF 50 ppm

HCN 5 0 ppm

CI a 5 ppm

PH3 4.5 ppm

F2 U or 10"* ppm

The lowest fluorine concentration available is one percent

and this will require further dilution to achieve a level low

enough for this investigation.

The above concentrations were chosen for the following

reasons :
3
(a) The nominal concentrations equal or exceed the

highest levels required for this project.

(b) The gases can be used undiluted for rapid screening

of candidate sorption tubes.

(c) The entire range of needed concentrations can be

obtained simply by using a suitable gas dilution system.

The cylinders were supplied with nitrogen as the diluent

gas. For screening of tubes, the fact that nitrogen was the

background gas rather than air did not cause any observable

problems; for analysis at the lower concentration levels

breathing air or in-house compressed air was mixed with the

contaminant gas.

To obtain gas concentrations ranging from 1/5 to 5 times

the TLV (Threshold Limit Value), a gas dilution system as

illustrated in Figure 2 is required; several systems of this

type have been constructed and used successfully in earlier

projects involving dilution of gas mixtures [51], The mixing system illustrated uses air to dilute the contaminant

gas so that the composition of the matrix gas is effectively

air rather than nitrogen, especially at the lowest concentration levels. This dilution system can also be used to

study the effect of humidity on the sampling efficiency of

solid sorbents. By inserting a water saturator into the

diluent air stream, water-saturated diluent air can be

delivered to the mixing manifold. At a ratio of diluent air

to contaninant of 24:1, a final mixture of 1/5 TLV can be

achieved having 96 percent relative humidity. Other relative

humidities are obtained by varying the flow rates of the gas

streams

.

2 . 2 Gas Sampling System

In devising a gas sampling system, certain requirements

were necessary: flow rates as low as 50 nl/min and as high

as 1 liter/min were needed; constant flow at each of the flow

rates was required so that errors resulting from flow, and

hence volume, measurement could be kept to an absolute

minimum. Ordinarily, vacuum sampling using a critical orifice

is the preferred method. In this case, however, three critical

orifices would have been needed for the flow rates at 50 ml/min,

200 ml/min and 1 liter/min. Furthermore, a critical orifice

maintains constant flow only when the upstream pressure drop

is kept constant within a narrow range, and since the

experimental design required that one or more solid-state

sorbents and bubblers would be needed, the pressure drops would

thus change and periodic recalibration of system flow rates

would have been required.

4

To avoid these problems, a new sampling system, shown

in Figure 3, was designed. The system contains a downstream

flow controller and needle valve and is connected to a constant- vacuum source (in this case an air sampling pump).

The vacuum is kept constant at about 100 mm Hg and the

needle valve can be adjusted so that any flow rate between

50 ml/min and 1 liter/min can be selected. It has been found

that pressure drops up to approximately 400 mm Hg* are

tolerable and the flow will remain the same at a pressure

drop of 400 mm Hg as at zero mm Hg. This means that as

many as 10 sampling tubes and bubblers may be inserted in

the system without changing the flow rate.

This system maintains a preset flow to within ±2

percent for sampling periods ranging from minutes to

hours. Flow rate is easily set by using the 3-way valve

(Figure 3) to switch to a calibrated rotameter and

adjusting the needle valve to the desired flow rate. The

sampling of the contaminant gas is performed by loosely

inserting a sampling tube or impinger into the sampling

manifold. The sampling manifold receives the contaminant

gas from the gas dilution system where the flow rate is

adjusted so that it is at least 1.5 times the sampling rate,

thus assuring that no ambient air is drawn in by the

sampling system.

2 , 3 Solid-State Sorbents

Solid-state sorbents have been in wide use for many

years in the detection of industrial contaminants and air

pollution. For the most part they have served to qualitatively

or semi-quanti tatively identify a contaminant or class of

contaminants and have most frequently been in the form of the

familiar detector tubes and the reagent- impregnated filter

paper. More recently solid sorbents have been used for

quantitative determinations of gaseous fluorides; in this

case, they have been either in the form of a coated tube [52]

or a treated filter paper [53], Of course, the most successful

application of solid-state sorbents to date has been in the

quantitative determination of organic vapors by adsorption

on charcoal tubes [57],

Capture of a volatile contaminant can be achieved by

the mechanisms of adsorption or reaction. Three general

routes are recognized. The first is the adsorption route in

which the solid-state sorbent captures the unchanged contaminant which can then be analyzed either directly or by chemical

conversion to a species which is then analyzed. The second

and third routes represent capture by chemical reaction, and

the product of this reaction can either be the final reaction

product for which an analytical method is available or an

*400 mm Hg = 3.00 Pa; 1 Pa = 1.333 x 10^ mm Hg

6
7
intermediate product which can be converted to the final

reaction product.

2.3.1. Solid-State Sorbent Requirements

In addition to some obvious requirements that a sorbent

device must possess, namely sufficient capacity to quantitatively capture a contaminant and, during the analysis phase,

to quantitatively desorb the contaminant, many other characteristics are required. Several are listed below and various

technical solutions are offered:

1. The resistance to air flow should not be greater

than 25.4 mm Hg at a flow rate of 1 liter/min

(as specified by NIOSH)

.

2. The device should be stable to the effects of

humidity, temperature and storage.

3. The device should indicate if breakthrough has

occurred,

4. The device should retain the contaminant of interest

in the presence of other substances in the air.

The air flow requirement can be met by a suitable choice

of sorbent tube geometry. An adsorbing medium such as charcoal or silica gel of, say, 20/40 mesh size could be used

in a sampling tube, which would then have flow characteristics

similar to the charcoal tubes now used for organic vapors.

Similarly, for tubes containing a reactive material, the mesh

size of this reactive material could be suitably chosen; or

alternately the reactive material could be coated onto selected

substrates such as glass beads, charcoal, or silica gel of

the proper mesh size. Devices other than packed tubes can

be fabricated to meet the flow requirement. For example, a treated filter paper or a tube packed loosely with treated

glass wool could also be designed to meet the flow requirement.

The effects of humidity, temperature and storage on

the tube containing the contaminant cannot easily be

predicted. In the case of HF and HCN , capture of the

acidic gases can be accomplished by reaction with basic

reagents, and the resulting fluoride and cyanide ions should

be stable. For F2, CI2 and PH3 stability will have to

be determined. (Further discussion of proposed ways of

capturing these gases is presented in the Gas Analysis

Sect ion)

.

A visual indication of breakthrough of the contaminant

gas can be achieved by placing downstream from the sampling

8
tube, either in a separate tube or as a back-up section, a color-change reagent which would signal breakthrough.

Alternately, a back-up section, isolated from the analysis

section o£ the tube by a separator, will permit indication

of breakthrough by laboratory analysis.

Finally, the requirement that the device retain the

contaminant of interest in the presence of other substances,

would appear to be easily met for the cases of HF and HCN,

since these gases are converted to the non-volatile anions.

Similarly, if the final choice of device for Fa, CI a and

PH_ employs a reaction to produce a non-volatile species,

then this requirement could also be met for these contaminants

Another practical requirement should be noted. As will

be shown in the Gas Analysis Section (2.4) most procedures

for capturing contaminant gases by chemical reaction

involve reactions in water. Hence, it may be necessary

for the trapping medium to contain enough water for reaction

to occur. If the humidity of the sampled air is high then

this may be sufficient; however, sampling in atmospheres of

low humidity may present problems. The use of a humectant,

such as glycerin, in the preparation of the sampling media

has been proposed as a solution to this problem [54].

2.3.2. Literature Survey of Solid Sorbents

Classical methods of trapping contaminant gases from the

atmosphere for subsequent chemical analysis recommend liquid

sorbers having nearly 100 percent efficiency. Solid sorbers

have been mentioned in the literature for trapping atmospheric

gases (e.g. sodium carbonate for sorbing HF) , but most often

they have been mentioned for specific applications such as color indicators for Draeger type tubes, or cigarette filters

for removing specific materials (such as solid particles or

HCN) from cigarette smoke. This section describes some solid

and liquid sorbers which have been mentioned in the literature

A. Fluorine and Hydrogen Fluoride Sorption

Most collections of fluorine and hydrogen fluoride have

been carried out in bubblers or midget impingers using water

or aqueous alkali solutions such as 0.1 N NaOH to trap the

acid gases. Solid sorbers impregnated with alkali have been

reported in recent citations; these have been of direct

interest

.

ASTM D 3269-73T mentions filter papers impregnated with

calcium-based fixative agents such as low-fluoride calcium

oxide or other soluble alkalies, and cautions that gaseous

fluorides collected on glass fiber filters cannot be quantitatively removed by leaching with water. Alkali impregnated

9
filter paper is mentioned also by Marshall and Wood [16],

and by Huygen [17] who have compared the efficiency of (a)

Whatman No. 1 paper impregnated with 20 percent KOH-10 percent

glycerol and (b) paper impregnated with 20 percent KOH-10

percent triethanolamine , with bubblers containing 0.1 N NaOH.

Huygen found essentially 100 percent collection efficiency

for freshly prepared filters at humidities greater than 25

percent; at 0 percent humidity the efficiency was 87 percent.

Hermann [10] used silver balls coated with a thin layer of

sodium carbonate in a quartz tube, comparing this sorber with

alkali-treated paper tape and sodium bicarbonate coated tubes.

Guilbault [19] has described paper tape impregnated with Mg-8-

hydroxyquinoline to give ppb detection capability by quenching

of fluorescence. Okita (1972) [23,24] has collected gaseous

hydrogen fluoride on filter papers impregnated with 1 percent

sodium carbonate and potassium carbonate using a permeation

tube to generate HF. Analysis using Alizarin complexone

spectrophotometry or specific ion selective electrodes at

concentrations of 0.05-1.0 ppm showed the filters to have

94 percent collection efficiency at 40 percent relative

humidity

.

Desbaumes [18] et al . have used a fluidized bed of silica

gel impregnated with 3 percent triethanolamine, eluting the

adsorbed gases with hot water. Salyamon and Popelkovskaya

(1973) [25] sorbed HF on silica gel for subsequent determination

of fluoride ions in air and water by twenty-five different

photocolorimetric methods. (They found that the criteria of

specificity, accuracy, and reproducibility were satisfied

best by the methods using reagents Zr-Eriochrome Cyanine; Zr

complex of 4-sulfophenylazo-l ,8-dioxynaphthalene-3,6-disulfonic

acid; and Ce-Alizarin complexone.) Tsuj imura et al. (1971) [26]

recovered about 90 percent of fluorine from a mixture of

fluorine, nitrogen, and oxygen on columns of silica gel and

activated alumina.

Some miscellaneous solid sorbers are membrane filters

impregnated with sodium formate [13] ; and polystyrene filters

impregnated with 10 percent sodium formate in 50 percent

ethanol, the latter being dissolved in buffered ethyl acetate

for direct determination of HF by an ion selective electrode [12]

.

B . Chlorine Sorption

As with fluorine and hydrogen fluoride, chlorine has been

collected in liquids such as water or 0.0125 N NaOH solutions;

or in acidified potassium iodide or methyl orange solutions

for direct colorimetric measurement. Elinson et al (1973) [34]

have described a chlorine-specific solid sorber consisting of

potassium boride and sodium carbonate soaked silica gel containing fluorescein indicator. The sorbent was chlorinespecific except for partial CO2 sorption.

10
A brief reference to the efficiency of activated charcoal

for retaining chlorine is given in ASTM D 1605-60. At 20°C

and 760 mm Hg , the maximum of chlorine that the carbon retains

when flushed with uncon taminated air is 15 percent. This

represents the practical sorption capacity for atmospheric

collection. For comparison, the retention is 8 percent for HF,

zero for water.

C. Hydrogen Cyanide Sorption

Classical methods of HCN sorption use bubblers or impingers

filled with water or aqueous alkali. Since cyanide can be

lost by volatilization, stabilization at a pH above 12 is

important (ASTM D 2036-72). Solid state sorbers mentioned

in ::he literature include filter paper impregnated with ferrous

sulfate and alkali (giving Prussian blue as a color detection

when subsequently submerged in dilute sulfuric acid) [14,41]

and silica gel impregnated with silver chloride, mercurous

chloride, or other metal salt to yield insoluble cyanide and free

HCl (the latter being detected with an indicator such as bromothymol blue or bromcresol green) according to a German

patent mentioned by Bark and Higson [37] Mercurous

diphenylcarbazide paper wetted with 3 percent NaHCOa has been

used by Tanaka and Yamamoto (1961) [12] who found a linear

relation between the length of the pink zone and the amount

of HCN, up to 6 yg/100 ml air.

Solid sorbents for HCN have been investigated by cigarette

filter manufacturers, because HCN is produced in tobacco

smoke. Filters of paper or cellulose acetate are used plain

or in.pregnated with, e.g. polye thyleneimine and/or zinc

acetate plus a humidifying section of encapsulated water [43]

to give about 83 percent trapping efficiency; or with zinc

oxide and triacetin, tri-or tet ra-e thylene glycol, triethyl

citrate or similar substance [44] to give a trapping efficiency

of 50-60 percent, passing 80 yg of HCN as compared with

210 yg for untipped cigarettes.

D. Phosphine Sorption

Liquid and solid sorbers have been described for the

direct reaction of phosphine with color- forming reagents.

Dechant et al . [47] have collected phosphine in a pyridine solution

of Ag-diethyldithiocarbamate and read the color of the

stable complex down to 0.05 ppm. The collection efficiency

of the sorber is 86 percent. Solid sorbers for phosphine

include impregnated papers and silica gel. Hughes and Jones

1^1963) [48]describe silver nitrate impregnated filter paper;

the visible spot can be compared with standard stains or

else removed with hot HNO3 and reacted with sodium sulfide

and boric acid for spect rophotome tri c determination at 470 nm.

11
Silica gel impregnated with AuClg is described by Kobayashi

and Meguro (1967) [49] as a detector tube where 0.03-150 ppm

phosphine can be determined by the length of the colored zone.

Muthu et al . (1973) [50]describe mercuric chloride papers

with methyl yellow indicator which turn from yellow to red

upon the liberation of HCl [by formation of P(HgCl)3J.

Nelson and Milun (19 5 7) [56] have determined phosphine in air

at ppb levels by metering known volumes of air through tubes

packed with silica gel impregnated with silver nitrate and

measuring the length of black stains.

2.3.3 Choice of Solid Sorbents and Devices

Two general types of sorbent devices that appeared promising were packed tubes and chemically treated filter paper.

Of the two, the packed tubes were considered to have greater

capacity for contaminant sorption, and were chosen for the

initial experiments. Table I presents calculations on the

volumes of contaminant gases required for the prescribed

sampling conditions. It shows that the sorber must be able

to retain 96 liters of contaminant gas at 5 times the TLV;

this comes to as high as 5.3 mg in the case of HCN

.

With respect to the merits of adsorption vs. chemical

reaction, it is considered that chemical reaction to form

a nonvolatile species would appear to be preferred unless

the adsorbed gases were retained very strongly, which is not

usually the case. With these considerations in mind, the

following solid state sorbents give promise of being efficient

trapping media.

For HF, formation of the fluoride ion by reaction with

a strong or weak base appears feasible. A procedure employing

sodium bicarbonate packed tubes has been reported [52] . Similar tubes may be useful for Fj

.

For HCN, reaction with a strong base to form cyanide ion

appears preferable, and a packed tube design should work.

For PH3 which is a strong reducing agent, an oxidizing

material could be used to form a nonvolatile phosphate.

Materials such as AgNOg , KMnO,, and other oxidants should

trap this gas, with subsequent determination of the stable

phosphate

.

For CI2 a reducing agent can be used as the trapping

medium. One possibility is the use of potassium iodide to

trap the chlorine, with resultant formation of iodine, a method that is used to determine ozone in air [55]. It might

be necessary to determine the total chloride concentration

also, to assure that the iodine was formed solely from the

CI2 and not some other oxidizer present.

12
Table 1. Concentration Ranges of Reactive Gases

GAS

HON

HG

Cl2

PH3

M.W. TLV

(g/mole) (ppm)

27.03

20.01

38.00

70.91

34.00

10

0.1

1.0

0.3

Conc'n^^

Range

(ppm)

2

50

0.6

15

0.02

0.5

0.2

5.0

0.06

1.5

Gases Collecteda/

4 hr at

50 ml/min

(12 liters)

(Mg)

27

663

6

147

0.4

9

7 174

1

25

1/4 hr at

1.0 1/min

(15 liters)

(Mg)

33

829

7 184

0.5

12

9

218

1

31

8 hr at

200 ml/min

(96 liters)

(Ug)

212

5,300

47

1,200

3

75

56

1,400

8

200

a/ M.W. — ^g = No. liters x ppm x ^^'^^

Range 1/5 to 5 times the TLV.

13
These choices, based on the literature review, were

considered only as a starting point in the experiments with

hydrogen fluoride, phosphine, and hydrogen cyanide. As will

be seen in Section 3, the sorber of choice for hydrogen

fluoride was sodium acetate, and for phosphine was charcoal

or KMnOi, dispersed on silica gel. None of these were mentioned

in the literature.

2 . 4 Gas Analysis

A brief literature review was undertaken to guide the

choice of analytical methods and solid sorbers for the gases

of interest. It was not intended to trace the history of

chemical analysis for these gases or to survey their applications to various different fields of interest. Rather,

the survey focused its attention mainly on textbooks and

reviews in order to learn which methods were considered so

reliable as to be designated "standard" methods. Because

of this limited objective the survey did not follow the

enormous body of available foreign literature other than to

call attention to specific Japanese, Russian, Polish, and

Romanian papers of immediate interest.

The collection and subsequent determination of hydrogen

fluoride, fluorine, hydrogen cyanide, chlorine, and phosphine

have been treated extensively in the literature of the past

ten years. An examination of recent review texts, Chemical

Abstracts , and Air Pollution Abstracts uncovered considerable

work on fluorine^ hydrogen fluoride aiTd hydrogen cyanide; and

somewhat less information on chlorine and phosphine.

2.4.1 Determination of Contaminant Gases

This review describes the most widely used methods of

gas detection and determination as well as the officially

recognized methods of analysis. The standard methods which

were a logical choice for use with this program, are here

defined as those listed in the 1973 Annual Book of ASTM

Standards Part 23, "Water; Atmospheric Analysis," [T] or in

" Standard Methods for the Evaluation of Water and Wastewater ,

[T] which will hereafter be referred to as "Standard Methods

..." In at least one case (i.e. phosphine) the standard

methods were judged to be awkward for determining contaminant

gas on solid sorbers. Less rigorous analytical methods were

preferred for their speed and simplicity in the initial

evaluations, reserving the standard methods for ultimate calibration and reference analyses later on. In all cases the

choices that were made of preferred analytical methods for

determining the contaminant gases were based on the information derived from the literature review.

14
Trace concentrations of gases have been determined mostly

by colorimetric techniques, but almost all conceivable methods

have been reported: titrations to turbidime trie , color, or

amperometric end points, coulometry, gravimetry, gas

chromatography, and atomic absorption spectrometry for

indirect determination of unreacted metals in solution.

Recently, potentiome trie determinations using ion selective

electrodes have been gaining in popularity [3] . Anion selective electrodes have been reported for fluorine and hydrogen

fluoride, cyanide ion, phosphorous (V) ion, and chlorine

(hypochlorite ion) ,- the latter not to be confused with

chloride [4 ] . A . Fluorine and Hydrogen Fluoride Determination

Fluorine and hydrogen fluoride are listed together

because they are frequently determined by similar procedures

since fluorine is changed to hydrogen fluoride in the presence

of moisture in neutral or acid media; also, they can be

separated easily by absorbing HF on NaHF2 if they appear

together.

ASTM D 3269-73T, available as a preprint of the 1974

edition of reference (1) describes the potentiometric determination of fluorides in the atmosphere by ion selective

electrodes using a combined total ionic strength adjuster

and buffer (TISAB) containing a complexing agent cyclohexylenedinitrilotetraace tic acid (CDTA) . Older methods such as that

described in ASTM D 1179-72 [1] or in "Standard Methods..."

[2a] have used citrate as the TISAB.

Colorimetric methods have been standard for fluoride

determinations; classically, these have depended on the

bleaching of highly colored metal complexes such as ZrEriochrome Cyanine R, or Zr-SPADNS as described in

ASTM D 1179-72 and ASTM D 3269-73T. The latter reference

describes also a relatively new color- forming reaction

usi:.g La-Alizarin complexone (also called Alizarin

Complexan a.id Alizarin Fluorine Blue).

Ion selective electrodes for fluoride are mentioned

favorably in reviews by Lambert (1968) [7a] and by Warner

(1973) [8a] as significant new developments in fluoride analysis,

Svoboda and Ixfeld (1971) [9] have used an ion selective

electrode with citrate buffer to analyze gaseous fluorine

compounds, and Hermann (1972) [10] recommends it in his review

of methods for measurement of gaseous fluorine compounds in

air environments, along with the Alizarin complexone and the

Zr-SPADNS spectrophotometric methods. Durst (1969) [11]

has used an ion selective electrode to determine fluoride in

dusts. Biheller and Resch (1971) [12] and Jahr (1972) [13]

15
have used fluoride ion selective electrodes for sensitive,

routine measurements with sodium formate impregnated solid

state absorbers.

Classical spectrophotome trie methods for fluorine and

hydrogen fluoride have depended on the bleaching of metalcomplex color lakes such as Zr-SPADNS or Zr-Alizarin where

the metals are removed as stable fluorides, thereby decreasing

the color of the solutions. A new standard method (in ASTM D

3269-73T) depends on the formation of the highly colored Laor Ce-Alizarin complexone. This appears to be the first

reported reaction in which fluoride ion forms a part of a colored complex. Leithe (1971) [14] discusses this method in

considerable detail, and it is also mentioned prominently

in Lambert's review chapter [7a] as being suitable down to

0.1 ppm of fluoride ion. West et al . [15] have used the method

for determining atmospheric fluorides, as have Marshall and

Wood [16], Huygen [17], Desbaumes et al [18], and Hermann [10].

Guilbault (1973) [19] has described fluorometric techniques

which measure the decrease of fluorescence of metal-complex

reagents such as Al-Acid Alizarin Garnet R, Al-Morin, Zr-3-

Hydroxy f lavone , and Mg-8-Hydroxyquinoline as the metals are

complexed by the fluoride; and also a direct-assay procedure

based on the increase of fluorescence of the Zr-Calcein Blue

complex

.

The classical spectrophotometric methods for fluoride

are still to be found in recent compilations and reviews:

e.g. Boltz (1973) [8b] describes the Zr-Xylenol Orange, SrChlorani late , and Zr- and Th-Eriochrome Cyanine R procedures

and just mentions ion selective electrodes in passing. Other

methods for fluorine and hydrogen fluoride include titration

with thorium nitrate using alizarin or xylenol orange as

indicators as described in ASTM D 1606-60 and ASTM D 3269-

73T; gravimetric determination of lithium fluoride [20]; and

direct separation and determination by gas chromatography

[6b, 21,22].

B . Chlorine Determination

"Standard Methods..." calls iodometry the standard against

which other methods are judged, and amperometry as the most

accurate method for free chlorine [2b]. The starch- iodide

titration is described in ASTM D 1427-68 and the amperometric

method in ASTM D 1253-68 and in reference (2b).

A commercially available chlorine electrode (as opposed

to chloride) is available for determinations in the 0.01-10 ppm

range [4] . No literature references to potentiome trie determinations using this electrode were found.

16
The ortho-Tolidine colorimet ric method is the one most

frequently used [14], It is described in detail in ASTM D

1253-58 and in "Standard Methods" [2b]. The latter reference

describes other colorimetric methods including those using

reagents Ferrous DPD (i.e. N, N-die thyl -p-phenylenediamine)

,

leuco crystal violet; methyl orange; and SNORT (stabilized

neutral o-tolidine) ; and includes a table describing the precision and accuracy of these residual chlorine methods (Appendix

A). The table shows the SNORT method to have one of the lowest

relative errors among 15 laboratories for determining free

residual chlorine in water at the 0.8 ppm level. In contrast,

Sakai (1972) [27] says that ortho-Tolidine colorimetry is not

good for concentrations below several ppm.

The Methyl Orange method involving the quantitative

bleaching of methyl orange by chlorine is reported in recent

publications. Thompson et al, (1971) [28] determined 0. OSLO ppm CI2 by bubbling ambient air directly through the reagent

solution. Forwerq and Dopfer (1969) [29] describe an autoanalyzer for measuring chlorine emissions by the bleaching

of methyl orange; and two Russian articles, one by Vil'ner

(1972) [30] and the other anonymous (1972) [31] mention methyl

orange for determining chlorine in air.

Miscellaneous methods for chlorine include microcoulometry to ±2.5 percent accuracy and requiring no calibration,

reported by Dennison and Menichelli (1972) [32], and a Pt-Ag

galvanic cell with buffered KI electrolyte, described by Vasak

(1972) [33]. Guiochon and Pommier [6] describe gas chromatographic separations of chlorine from other gases on columns

of silica gel or Chromosorb wetted with fluorocarbon grease

or oil.

C . Hydrogen Cyanide Determination

ASTM D 2036-72 [1] describes a standard method for cyanide

ion by conversion to cyanogen chloride using Chloramine-T

,

and subsequent colorimetric determination with pyridine and

barbituric acid. Pyridine-pyrazolone colorimetry (after

Chloramine-T treatment) has also been listed as a standard

method [2c] . Po tentiome try using a cyanide ion selective

electrode has not been mentioned as a standard method although

cyanide electrodes have been available commeri cal ly . Mascini

(1971) [35] has used a cyanide electrode for measuring air

and water pollutants; his recent note on the pH and metal ion

sensitivity of this electrode (1973) [36] may explain the

absence of a standard potentiome trie method for cyanide ion.

In their comprehensive review of available methods for

determining cyanide. Bark and Higson (1963) [37] state that

colorimetric methods are best in the 0.1-1.0 ppm concentration range. They favor the Chloramine-T conversion of

17
cyanide to cyanogen chloride with subsequent color development

by either (1) pyridine-pyrazolone or (2) pyridine-benzidine

reagent which is banned now because of its carcinogenic nature.

Boltz reviews methods for cyanide (1973) [8b] and states that

the Konig reaction, on which the Chloramine-T pyridinepyrazolone method is based, is the most extensively used

method for HCN. The method is described in "Standard Methods"

[2c] and Epstein (1947) [38] is credited with its development.

Other sensitive methods for cyanide include the ChloramineT Nicotinamide method of Hanker et al. (1957) [39] which

yields a blue fluorescence that permits CN~ to be determined

between 0.30-5 ppm according to Guilbault [19]. The fluorescent reaction between CN and p-benzoquinone is specific for

cyanide and is sensitive to 0.2 yg in the total volume [8b,

19, 40].

Miscellaneous methods for cyanide that have been reported

include the demasking of colored or fluorescent metal

chelates by formation of stable cyanide complexes; amperometric

silver nitrate titration; po larography ; potent iometric titration with HgaCla; and gas chromatography.

D. Phosphine Determination

The direct determination of phosphine gas is not treated

in the descriptions of standard methods, but there are methods

for or thophosphate to which phosphine can be converted. The

standard colorimetric methods are based on the formation of

molybdophosphates or m.olybdovanadophosphates , differing in the

types of reducing agents employed, as stannous chloride,

ascorbic acid, etc. These are described in ASTM D 515-72 [1]

nd in "Standard Methods" [2d]. Inter laboratory tests [2d, 7b]

reporting on the precision and accuracy of various phosphorous

methods are shown in Appendixes B and C. The Stannous Chloride

method seems to give the smallest error.

Berck et al. [5] have described gas-liquid chromatography

of phosphine at the ppb level; Guiochon and Pommier [6] describe

the gas chromatographic separation of gaseous hydrides

including phosphine; and Dumas (1964) [45] has described the

determination of phosphine in air down to 0.5 ppm.

Phosphine has been determined as orthophosphate after

oxidation in a dilute KMnOi^ - sulfuric acid solution. If it

is possible to collect phosphine as orthophosphate using a suitable solid sorber, then the standard methods for

phosphate can be used. Most spect rophotome trie methods for

orthophosphate are based on the formation of phosphomolybdenum

blue or similar substances. The standard methods [l,2d] and

others are reviewed by Boltz [8b] , and by Burton (1973) [46] who

states that the Ascorbic Acid method now is used in probably

18
more than 90 percent of analyses. Dechant et al. (1966) [47]

use a colorime trie method based on silver diethyldi thiocarbamate

.

Fluorescence methods based on the formation of molybdophosphate

rhodamine B, quenching of Al-morin fluorescence, and an

enzyme reaction with glycogen to form NAPDH* have also been

mentioned [8b, 19].

Other methods for phosphate include potent iome trie and

conductome tr ic methods based on the release of HCl from

HgCl2; turbidimetric methods based on the reduction AgNOa

to Ag°, and the gravimetric determination of NHt, ) 3 POi+ • 1 2MoO 3 . A recently described ion selective electrode for

phosphorous (V) claims a measurement range of 0.1-95,000 ppm

for phosphoric (V) ion [4]. Potent iome trie methods using this

electrode have not yet been seen in the literature.

3. EXPERIMENTAL RESULTS

The efficiency of the solid state sorbers for trapping

and holding the contaminant gases for subsequent analysis was

evaluated by experiments involving passing known concentrations of gases through the solid sorbers into either a liquid

trap having essentially 100 percent trapping efficiency

(e.g. aqueous 0.1 N NaOH to retain HF) or a solid trap having

the same high trapping efficiency (e.g. AgNOs impregnated

silica gel to retain PH3). Three chemical analyses are of

importance here, and all must be carried out precisely and

accurately. These are: (1) determination of the steady-state

gas concentrations, (2) determination of the amount of gas

retained on the solid sorbers, and (3) determination of the

gases in the downstream bubbler or trap if any. The analytical

procedures were chosen from those deemed most suitable in the

literature review.

This section describes the experimental results obtained

in sorber studies with hydrogen fluoride, hydrogen cyanide,

and phosphine.

3 . 1 Hydrogen Fluoride

In this chapter, we describe the equipment for generating

h>'drogen fluoride gas mixtures and for air sampling, the

analytical method for fluoride determination, and the selection of solid sorbents. We present the experimental data on

collection efficiencies of the various sorbents, temperature

and humidity effects, breakthrough, and precision studies.

IVe also provide the specifications on construction of the

sorption tubes and a detailed procedure for the analysis of

fluoride

.

*NADPis hydrogenated NADP, the sodium salt of t r iphosphopyridine

nucleotide

.

19
3.1.1. Gas Generating and Sampling Systems

The experiments required hydrogen fluoride gas mixtures

of several concentration levels and sampling at various flow

rates. A gas generating system was constructed to produce

hydrogen fluoride-air mixtures of the desired concentration

levels, i.e., 1/5 TLV to 5 TLV levels, and also a sampling

system to withdraw gas samples at constant flow rates

ranging from 50 ml/min to 1 liter/min. Figure 4 is a schematic drawing of the systems.

The gas generating system consisted essentially of two

differential flow controllers (one had a stainless steel

diaphragm for hydrogen fluoride), two rotameters for measurement of flow rates of air and hydrogen fluoride gas, a stainless steel mixing manifold, and a stainless steel sampling

manifold. Either thick-wall Teflon or stainless steel hardware was used wherever hydrogen fluoride gas passed. A bulk

mixture of hydrogen fluoride in nitrogen supplied by a gas

cylinder was diluted with in-house compressed air in the

mixing manifold. Prior to mixing, the air was filtered through

glass wool only. Proper adjustment of the two rotameters

(valves V-2 and V-4 in Figure 4) produced hydrogen fluoride

gas mixtures of the desired concentration levels. The

sampling manifold was always open to the atmosphere.

The gas sampling system consisted of a 3-way valve, two

sorption tubes in series, a brass in-line filter, a differential flow controller, a rotameter, and a vacuum

pump. Gas samples were withdrawn under vacuum from the

sampling manifold in the gas generating system. When

adjusting valve V-6 (Figure 4) for the proper sample flow

rate, the 3-way valve V-5 was opened to the atmosphere. The

flow rates of the hydrogen fluoride -air mixtures in the

gas generating system were always maintained at three times

or more the flow rates of the gas samples in the sampling

system. The rotameters were calibrated by a wet test meter.

3.1.2. Selection of Solid Sorbents for Hydrogen Fluoride

Several substances for sorption of hydrogen fluoride

in air have been reported in the literature. These have included

sodium carbonate, sodium bicarbonate, sodium formate, sodium

hydroxide, and potassium hydroxide. In preliminary screening,

the collection efficiencies of sodium bicarbonate powders,

sodium citrate crystals, activated charcoal, activated charcoal

soaked with saturated sodium bicarbonate solution, firebricks

soaked with saturated sodium bicarbonate solution, and sodium

acetate crystals were determined. These substances were

packed in glass tubing of 6 mm outside diameter. The

resultant tubes had a maximum pressure drop of 2.54 cm

2 0
a.

a. o) Q. cu

i- -Q 1- -Q O 3 O 3

lO I—

.- o

r— t+- Q. -r- E C

-o

+-> O

0)c

lO

0) SS >> c Ol U1 > U

lO 01

0) +-> JZ SS

1/) +J o

LTi t.

s_ in +J

Ol 0) 1/5 Q. > Ol !_ o

Q- rO > QJ o O +-> U Ul > va me MO

U1 -a

O > a>

Ol 4-

fO 0)

C c 3 +-> <U

•r- I OJ S.

s- oj e Q>

OJ OJ <0 H-

+->!.+-><+-

<u o ••- s: t— q: Q ^ .— CM LT) r— <_>

=) I I I I u.

I— > =» > QC

Q

10EoM

>s

</>

0)

"5.Eaco

O)cocoooOoL.

Q

UJ

21
Hg at a flow rate of 1 liter/min. Table 2 shows the collection

efficiencies of these substances. The collection efficiency,

E, is defined as

(Ai - Bi)

: ' TK. - BO . (Aa - BJ - (1)

where Ai = amount of hydrogen fluoride collected in the first

^ sorption tube, in moles.

A2 = amount of hydrogen fluoride collected in the second

sorption tube, in moles.

Bi = blank for the first sorption tube,

B2 = blank for the second sorption tube.

The amount of hydrogen fluoride collected in the sorption tubes

was measured by the fluoride selective electrode method as described in Section 3.1.4. The blanks were determined using the

ambient air of the laboratory.

Table 2 is a summary of the collection efficiencies of

the solid sorbent system studied. Although sodium bicarbonate

showed relatively high collection efficiencies, it had the

disadvantage that it is available only in the powder form,

and the pressure drop of the sorption tube was over 25 cm Hg.

Its very low collection efficiency at the flow rate of

50 ml/min indicated that physical adsorption and desorption

might have taken place.

It was difficult to leach sodium fluoride from

activated charcoal and firebrick substrates. Fine particles

were found in the resultant solutions which required

filtration before analysis. No attempt was made to determine

the recovery of fluoride in the leaching process.

There is evidence that water is desirable for the

reactions of the solid sorbents with hydrogen fluoride, as shown by the higher collection efficiency (31.5 percent) of

sodium citrate plus 5 percent glycerine in water over the

dry salt. Activated charcoal soaked with saturated sodium

bicarbonate solution also gave higher collection efficiencies

when 5 percent glycerine was present.

The selection of sodium acetate crystals as the sorbent

for hydrogen fluoride was made on the following basis:

1. High collection efficiency for hydrogen fluoride.

22
Table 2. Collection Efficiencies of Various Sorbents for

3 ppm Hydrogen Fluoride Gas

Collection Flow rate Collection

Sorbent time (ml/min) eff (%)

NaHCOs 15

4

6

8

oo

min

nr

hr

hr

nr

1050

211

Z i 1

211

50

98

96

y b

99

73

.7-99.8

.8

o

. o .8

.3

a

Activated charcoal

20-40 mesh , (MSA, Pittsburgh, Pa.)

15

6

A8

min

hr

nr

hr

1050

211

41

5 0

93

90

82

5 7

.1, 97.

. 7 .8

4

Firebrick soaked with 1 c 1 J min 1050 70 .6

Charcoal soaked with

sat'd NaHCOs sol'n

15 min 1050 61 .0, 85. 0

Charcoal soaked with

sat'd NaHCOg sol'n +

5 percent glycerine

15 min 1050 89 .0, 90. 3

Na citrate crystals

(reagent grade) 20-40 mesh

15

4

min

hr

1050

211

12

11

.9

.8

Na citrate on polyurethane

+ 5 percent glycerine

sol'n

15 min 1050 31 .5

Na acetate crystals

(reagent grade) 20-40 mesh

15 min 1050 93 .9-97.5 c

^A total of 9 runs.

^See disclaimer on p 41.

^A total of 6 runs.

23
Acetate acts as a pH buffer in the fluoride ion

selective electrode method of analysis,

3. Ready availability as reagent grade in the 20-40 mesh

size ,

4. Relatively inexpensive,

5. Chemical stability of both sodium acetate and the

reaction product sodium fluoride under normal

condi t ions

,

6. Presence of three molecules of hydration per

formula weight highly desirable for the reaction

with hydrogen fluoride in air,

7. Non-toxic, non-irritating, non-corrosive,

8. High solubilities of both sodium acetate and

sodium fluoride in water.

3.1.3. Construction of Sorption Tubes

The sorption tubes were constructed according to the

procedure given below. The sodium acetate used in the experiments was pooled from the reagent bottles which were obtained

from three different chemical companies. The crystals of 20

to 40 mesh were separated from the bulk in the reagent bottles

by sieving. The only apparent difference among these three

sources of sodium acetate was in the distribution of particle

size. An average of 10 percent of the sodium acetate in the

bulk was of 20 to 40 mesh. No attempt was made to determine

the distribution of particle size of the 20 to 40 mesh crystals.

Figure 5 is a drawing of the sorption tube.

Specifications for Sorption Tubes

1. Join one piece of Pyrex glass tubing of 6 mm outside

diameter and 3 cm long to a Pyrex glass tubing of

13 mm outside diameter and 4 cm long. Make a very

slight constriction at the joint.

2. Join another piece of Pyrex glass tubing of 6 mm outside

diameter and 3 cm long to the other end of the 13 mm

tubing above. Make a very slight constriction at the

joint.

3. Introduce a wad of loose surgical cotton, about 5 mg

,

inside the tube.

4. Blow dry air inside the tube to arrest the cotton

at the "neck" of the tube.

2 4
TOP

igure 5. Sorption Tube for

25
5. With the aid of a small funnel and a piece of Tygon

tubing, fill the tube with 20 to 40 mesh reagent grade

sodium acetate crystals, NaCaHj O2 • 3H2O , up to the

"neck". Gently tap the tube to help the crystals

settle. Do not use crystals that are lumped together.

6. Insert a wad of loose surgical cotton, about 4 mg

,

on top of the sodium acetate crystals. Do not press

the cotton down.

7. Print an arrow on the outside walls of the tube to

indicate the air flow direction, i.e., the same

direction as the air that was used in seating the

cotton.

8. Connect the sorption tube to an orifice which has an

opening to pass air at 1 liter/min. Connect the

orifice to a manometer and vacuum with a tee. Figure 6

is a drawing of the pressure drop measurement apparatus.

9. Turn the vacuum on to check the pressure drop. Reject

the sorption tubes with a pressure drop of over 2.54 cm

Hg.

10. When not in use, place plastic caps on both ends of the

sorption tubes

.

3.1.4. Analytical Method for Fluoride

The ion selective electrode method for fluoride determination was chosen on the basis of its selectivity for fluoride

and simplicity in operation. The necessary equipment in this

method included a fluoride selective electrode, a calomel

reference electrode, a pH meter with millivolt mode, and a magnetic stirrer. The concentration of fluoride in a sample

solution was obtained from the millivolt reading and a calibration curve. The latter was established from a plot of

millivolt response versus fluoride concentrations of standard

sodium fluoride solutions. The standard solutions were

prepared from known weights of dried sodium fluoride

dissolved in 0.88 M sodium acetate solution. The procedure

for operation of the fluoride selective electrode instrument

is given below.

At the conclusion of gas sampling, the amount of fluoride

collected in the sorption tube was determined according to the

procedure given below. In the preliminary screening of solid

sorbents, the sorbents sodium bicarbonate and sodium citrate

were dissolved in sodium nitrate solution to give the same

ionic strength as the standard solutions. For charcoal and

firebrick, the sodium fluoride was leached out from the

substrates with 25 ml water.

26
SORPTION

TUBE

Jl

CRITICAL FLOW

ORIFICE

VACUUM

MANOMETER

Figure 6. Pressure Drop Measurement Apparatus

27
The amount, A, o£ fluoride collected, in moles of fluoride,

was calculated from the following equation:

where A = moles of fluoride in sorption tube

^ C = molar concentration of fluoride from analysis

of a 25 ml solution

The concentration of hydrogen fluoride, in parts per

million (ppm) , in the gas samples was calculated from the

following equation:

„^ Ax 24.5 X 10^

ppm HF - J ^ ^

(3)

where T = total collection time in minutes,

R = flow rate of gas sample in liters per minute at

standard temperature -pressure condition.

To study the effects of sodium acetate concentration

on millivolt response, a series of sodium fluoride standards

was prepared in 0.55 M sodium acetate solution. Figure 7

shows the calibration curves of the standard solutions in

both 0.88 M and 0.55 M sodium acetate solutions. The

effect of sodium acetate concentration was quite insignificant.

Operation of Fluoride Selective Electrode Instrument

1. Connect the fluoride and the reference electrodes

to the pH meter. Set the meter to "standby" position.

2. Transfer the sample solution to a 50 -ml polyethylene

beaker. Add 2 drops of 0.5 N" HNO3 to adjust the pH

of the solution to 6.8.

3. Place the electrodes in the sample solution.

4. Place a magnetic stirrer in the beaker and turn on

the variable transformer to provide gentle stirring

of the solution.

5. At the end of 15 minutes, record the millivolt reading.

6. Set the meter back to "standby" position.

7. Empty the contents of the beaker. Rinse the electrodes

thoroughly with distilled water. Wipe the electrodes

28
Figure 7. Calibration Curve of Fluoride Standard Solutions

29
dry with soft tissue. The electrodes are now ready

for measurement of another sample. When not in use,

the electrodes should be submerged in distilled water.

Procedure for Measurement of Amount of Fluoride Collected in

Sorption Tubes'

1. Disconnect the sorption tube from the flow system.

2. Use a pair of straight corrugated forceps to remove

the top wad of cotton in the sorption tube and place

it in a polyethylene beaker.

3. Insert the top end of the sorption tube into the neck

of a 25-ml volumetric flask, and empty the sodium

acetate crystals into the flask. Gently tap the

tube against the flask to get the crystals into the

flask

.

4. With a stiff wire, break loose the bottom wad of

cotton. Let the cotton stay inside the sorption tube.

5. Rinse the inside walls of the sorption tube and the

cotton with 15-18 ml distilled water. Make sure all

the rinses go into the flask.

6. Remove the sorption tube.

7. Rinse the cotton in the polyethylene beaker with 5 ml

distilled water. Add the rinse to the 25-ml volumetric

flask

.

8. Dissolve the sodium salts completely.

9. Add enough distilled water to dilute to 25 ml. Mix

thoroughly. The solution is now ready for fluoride

concentration determination.

3.1.5. Experimental Data

A. Collection efficiencies of sodium acetate

Table 3 is a summary of the collection efficiencies of

sodium acetate crystals for hydrogen fluoride at room temperature (23.9° to 25.5°C). These runs were made in random order

and not in the order as given in Table 3. It was concluded

from these data that 3 gm of sodium acetate crystals of 20 to

40 mesh completely removed hydrogen fluoride from gaseous

mixtures having concentrations of hydrogen fluoride ranging

from 0.5 to 15 ppm, for collection time of 15 minutes at a flow rate of 1 liter/min, and for collection times of 4 to 8

hours at flow rates of 50 to 200 ml/min.

30
Table 3. Collection Efficiencies of Sodium Acetate for

Hydrogen Fluoride Gas

Collection Flow rate Collection

time ml/min ppm HF g NaAc eff (^)

15 min 916 4.90 1.87 94

15 min 916 5 . 08 1 .87 94

± 0 min Q 1 A 7. 7 0 J) . / U J . u 1innu u 15 min 916 - 4.64 3.0 100

15 min 916 5 .57 3.0 99

1 c ± J m T Ti JllJ-Xi X U X u Xinnu u

1 c ± J JUJ-ii X1 mU X nu U . O X J . u inn X u u

1 c ± D JUXil X U X u U.J/ J . u 1J- nnu u 15 min 1010 0.63 3.0 100

15 min 1010 0.70 3.0 100

1 t: X o JIL J. ii 1X mU X nu 3 1^4 3 n X1 nnu u

ill J.11 1X mU X nu X1 o ft . o o . u inn X u u

4 hr 52 0.69 3.0 100

4 hr 52 0. 74 3.0 100

At hn -rX U . o X J . u inn X U U

hn -rI D . u u J . u inn ± u u

/I nr K 7 It; 7 J . u inn i u u

4 hr 188 4.93 1.87 99

/I nr ± o o

Q 11 J . u inn 1 U U

/It nr 1 Q ft X y 0 nU.J/c: 7 J . u Xinnu U

11

1

X y 0 0 . u y o . u iinnu u nr 1 Q ft X y o

1 c: 4 o . u inn i U U

8 hr 52 0.74 3.0 100

8 hr 52 2.21 3.0 100

8 hr 52 4.64 3.0 100

8 hr 52 16.4 3.0 100

8 hr 188 5.43 3.0 100

8 hr 198 0.57 3.0 100

8 hr 198 4.37 3.0 100

8 hr 198 15 . 8 3.0 100

31
B. Breakthrough Study and Capacity of the Sorption Tubes

A gas mixture of 15 ppm hydrogen fluoride was passed

through two sorption tubes in series at a flow rate of 1,01

liter/min. Every 15 minutes, the second tube was replaced

by another sorption tube and its fluoride content analyzed.

No breakthrough was observed in 8 hours of collection. The

capacity of the sorption tube is therefore greater than 5.8 mg

hydrogen fluoride.

C. Effects of Elevated Temperatures

A Pyrex glass tube 13 mm outside diameter and 25 cm long

was placed in front of two sorption tubes, all in series and

wrapped with a heating tape. Heat was generated at a constant

rate using a variable transformer, and the temperature inside

the 25 cm tube was measured by a thermometer with air flowing

at 52 ml/min. A hydrogen fluoride gas sample was withdrawn

through this assembly at the same flow rate. The experiment

was repeated with the heating tape removed and with two new

sorption tubes.

Table 4 is a summary of the experimental results for

two different collection periods. Together with the experimental data presented in Table 3, it is concluded that the

collection efficiency of sodium acetate for hydrogen fluoride

was 100 percent at temperatures ranging from 23.9°C to 38.0°C.

However, there was a loss of 9 percent of hydrogen fluoride

at the elevated temperatures, as shown in the last column in

Table 4. Possibly, part of the hydrogen fluoride reacted

with the inside walls of the Pyrex tubes before it reached

the trapping reagent, resulting in lower absorption than

expected.

D . Effects of Humidity

A bubbler containing distilled water was used to saturate

the in-house compressed air with water at 25.0°C. The

hydrogen fluoride bulk mixture was mixed with this watersaturated air, and a sample was collected at 1.01 liter/min

for 15 minutes through two sorption tubes in series. The

experiment was repeated without the bubbler and with two new

sorption tubes. The concentration of hydrogen fluoride in

the sample was 34.8 ppm based on the dry mixture run.

The collection efficiency in both the water- saturated

and dry environments was 100 percent. However, the amount of

fluoride recovered in the water-saturated run was only 76.7

percent of that in the dry mixture run. Possibly, part of the

hydrogen fluoride reacted with the water vapor, and the

product (s) was adsorbed on the inside walls of the mixing and

sampling manifolds.

32
Table 4. Effects of Temperature on Collection

of Hydrogen Fluoride

Ratio of mol

Net mol fluo- fluoride colCollection Collection ppm ride collected lected (elev

Temp (°C) time (hr) eff (%) HF X 10"' temp/rm temp)

36. 0 1 100 5.2 0. 60 0.91

25. 0 1 100 5.2 0. 66

38. 0 3 100 22.9 7. 98 0. 914

25. 4 3 100 22.9 8. 73

33
E . Precision, Bleed-out, Storage, and Shipment Studies

A total of 20 sorption tubes was used to collect hydrogen

fluoride samples under identical experimental conditions, i.e.,

15 minutes of collection time at a flow rate of 1.01 liter/min

and hydrogen fluoride concentration of 3 ppm. These tubes

will be used for precision, bleed-out, storage, and shipment

s tudies

.

Four of these tubes were shipped to NIOSH. Of these four,

two are to be returned at once upon arrival at NIOSH, and the

other two are to be returned one week after arrival at NIOSH.

One of these 20 tubes was flushed with ambient laboratory

air at 25.2°C for 6 hours. Two were kept in a water-saturated

atmosphere at room temperature.

Of the remaining 13 tubes, five will be analyzed at one

time for precision, two will be analyzed one month later, two

will be analyzed one year later, and the last four will be

reserved as spares.

3 . 2 Hydrogen Cyanide

For the investigation of solid-state sorbents for HCN

it was decided to first determine the concentration of the

contaminant gas by a standard sampling procedure and analytical

method and then to compare these results with the results

obtained with candidate solid-state sorbents. In this way

accurate determinations could be made concerning the efficiency

of collection and the efficiency of desorption of HCN from

solid-state sorbents.

A pressurized cylinder containing 200 cu ft of HCN in

nitrogen with an analyzed concentration of 51 ppm, as received

from the manufacturer, was the contaminant source. For the

experiments described in this section the gas was not diluted

and was delivered to a gas manifold where sampling took place.

The sampling system was of the constant flow type described

in Section 2.2 of this report. For each determination a total of 15 liters of gas was sampled, at a flow rate of one

liter per minute for a period of 10 minutes.

3.2.1. Determination of HCN Concentration

For the determination of the HCN concentration, a standard sampling procedure was employed involving the capture of

HCN by bubbling the gas through a 0.1 M NaOH solution.

Several designs of bubblers were investigated and different

collection efficiencies were noted. The most efficient

procedure involved the arrangement of two midget impingers

34
in series, each containing 10 ml of 0.1 M NaOH. The first

impinger has a coarse fritted bubbler stem while the second

one was of the standard impinger type. After sampling at a rate of 1 liter/min for 15 minutes the contents of each

impinger were transferred to a 25 ml volumetric flask and

diluted to mark. The concentration of cyanide was determined

using the cyanide ion-selective electrode.

Calibration standards for this electrode were prepared

by diluting a stock solution of_NaCN with 0.1 M NaOH to give

solutions of 10 ^, 10 , and 10 cyanide. Millivolt readings were made using a pH meter with a digital readout. The

plot of millivolt readings vs. concentration on semilog graph

paper gave a straight line. The concentrations of the trapping

solutions were then determined by the use of this calibration

curve

.

It was found that about 95 percent of the total cyanide

captured was contained in the first impinger. However, it

was discovered that the concentration of the HCN was 1 ppm

instead of the expected 50 ppm, as the supplier had indicated*.

3.2.2. Screening of Solid-State Sorbents

Although the HCN concentration was below the level needed

for this project, it was decided to use this gas to obtain

preliminary data on solid-state sorbents.

Two solid-state sorbents, activated charcoal and Ascarite

were tested for trapping efficiency. The charcoal tube was

of the type developed by NIOSH for trapping organic vapors

in air. The Ascarite tube was also of similar design, 6 mm OD

and containing a 40 mm length of 20-30 mesh Ascarite.

For these determinations the tube was positioned in the

stream of contaminant gas with a midget impinger (bubbler type)

downstream from the tube. After sampling, the tube contents

were extracted with NaOH, filtered, and diluted to 25 ml.

The contents of the impinger were also diluted to 25 ml.

Cyanide determinations were made on both solutions.

Activated Charcoal : The average of four determinations

[20-40 mesh) show the following:

1, Based on total cyanide recovered,

the charcoal trapped 80 percent

and the bubbler 20 percent.

2. The total cyanide recovered,

however, was 60 percent of the

predicted amount.

*See disclaimer on p 41

.

35
Ascarite : The average of four determinations show the

(20-30 mesh) following:

1. Based on total cyanide recovered, the

Ascarite trapped 100 percent.

2. The total cyanide recovered, however, was

85 percent of the predicted amount.

3.2.3. Discussion

It is seen that the charcoal tube shows breakthrough even

at the 1 ppm concentration level; hence, this particular tube

would not be suitable for HCN. However, it should be noted

that a larger charcoal tube may provide sufficient capacity

for HCN. Tubes of this type will be investigated. On the

other hand, the 6 mm Ascarite tube is an effective trapping

agent for HCN.

The recoveries of cyanide from both the charcoal and the

Ascarite tubes, however, were not quantitative. This may be

due to the fact that the extractions were done at room

temperature

.

3.2.4. Future Work

Further work will be done with the Ascarite tube and the

wider design charcoal tube. More vigorous extraction procedures will be tested. Other solid-state sorbents will also

be investigated. Arrangements have been made with the manufacturer to receive a replacement cylinder of HCN at the

required 50 ppm concentration level.

3 . 3 Phosphine

Phosphine supplied as 4.5 ppm in nitrogen in a compressed

gas cylinder was delivered to a vacuum sampling system in

an apparatus similar to that previously described for hydrogen

fluoride. The gas was fed through a rotameter into a plenum

from which it was sampled into solid state sorbers at atmospheric pressure by aspiration through a cons tant - flow

regulator; a sub -atmospheric reference pressure was supplied

by a rotary-vane pump. The strongly reducing nature of

phosphine imposed no limitations on materials of construction

which were glass, brass. Teflon, and neoprene. The flow

system is diagrammed schematically in Figures 2 and 3.

3.3.1. Experimental Method

Promising solid sorbers were screened rapidly to study

qualitatively the ease with which phosphine could be

36
immobilized in collection devices. The sorbents were packed

into two sizes of glass tubes: 6 mm OD as supplied in

commercially available charcoal - fi lied tubes used for

collection of organic vapors, and 13 mm OD tubes fabricated in this laboratory and described in the section on

Hydrogen Fluoride. The tubes were filled to a depth of 50 mm

except the 6 mm tubes which were used as received with 30 mm

of charcoal inside.

A plug of silver nitrate -impregnated silica gel was

inserted in the base of each tube to signal phosphine breakthrough, denoting the end of each experiment. This material

was prepared by slurrying 65 g of silica gel with 100 ml of

1.5 percent AgNOa solution, stirring manually on and off for

15 min, pouring off the excess liquid, and drying for 4 hr

at 90°C.

The sorber materials studied were:

1. Silica Gel (W. R. Grace Type 15, 30 - 60 mesh).*

2. Silica Gel impregnated with silver nitrate.

3. MSA Charcoal tubes (as used for organic vapors).

4. Activated Charcoal (Pittsburgh Type OL 20 - 50 mesh).'^

5. Potassium permanganate, reagent grade.

6. Silica gel impregnated with potassium permanganate.

Potassium permanganate impregnated silica gel was prepared in the same manner as silver nitrate silica gel using

1 g of KMnOit and 50 g silica gel (6 - 16 mesh).

The sorber tubes were either straight 6 mm OD tubes

constricted at one end, or 13 mm OD tubes 80-90 mm long with

6 mm OD end pieces to permit them to fit into the plenum and

the tubing connectors. When filled to a depth of 50 mm they

contained about 3 g of material. Glass wool plugs held the

sorber material and the silver ni trate -s ilica gel indicator

in place for most of the experiments but the 50 mm pressure

drop across the filled tubes exceeded the specifications which

called for no more than 25 mm pressure drop at a flow of

1 liter/min. When a thin polyester felt was substituted for

glass wool, the pressure drop across a filled charcoal tube

with silver nit rate -si lica gel indicator was only 20 mm of

mercury at 1 liter/min.

The sorber tubes were inserted into the plenum chamber

in which 4 . 5 ppm (nominal) phosphine in nitrogen flowed at

*See disclaimer on p 41. 37
a rate of 2.1 liter/min, and the gas was sampled at a controlled

rate of 1.0 - 1.4 liters/min. The time for the gas to break

through to the bottom of the sorber tubes, as signalled by

immediate blackening of the silver nitrate silica gel was an

indication of the ability of the sorber materials to immobilize

phosphine

.

3.3.2. Experimental Results

Table 5 summarizes the data obtained to date. The breakthrough experiments indicate that solid sorbers which depend

on physical adsorption have a limited but still useful capacity

for retaining phosphine. Silica gel is clearly unsuitable

by itself. On the other hand, activated charcoal in a 13 mm

dia. column containing about 2 g of material is capable of

retaining 34 liters of phosphine at 4.5 ppm (nominal), about

15 times TLV. This capacity is suitable for the 12-liter

collection at 50 ml/min and the 15-liter collection at 1.0

liter/min; and diluted 3:1 to make a 5 times TLV mixture the

capacity comes to 3 x 34 = 102 liters, just exceeding the

96-liter requirement for the 8-hr collection at 200 ml/min.

The immobilization of phosphine by reaction with a suitable reagent to yield a nonvolatile material appears to be

much more efficient than physical adsorption. Silver nitrate

impregnated silica gel used as the breakthrough indicator functioned very well as a sorber even in the small diameter 6 mm

tubes. The breakthrough time of 43 min. was estimated after

a 17-minute experiment by observing that the black band had

travelled 20 mm and had a total of 50 mm to go. The 43-liter

capacity of the 6 mm tube would be quadrupled by using a 13 mm

tube, but even the small tube exceeds the specified sorption

requirements considering that the phosphine gas concentration

is 15 times TLV.

The choice of potassium permanganate as a sorber was

based on its ability to form nonvolatile ortho-phosphates, so

it was expected that K^4nO 4 would be an excellent sorber. This

turned out to be true, but surprisingly it was not the

crystalline KMnO that functioned well, but the KMnO on

silica gel, present at a concentration of only about 16 mg

KMnO 4 per gram of silica gel. Apparently moisture is required

for the oxidation to proceed, and the roughly 30 percent

moisture content of the silica gel is necessary for the

reaction. No breakthrough was observed after 31 min flow at

1.3 liters/min.

Desorption experiments carried out on the permanganate

coated silica gel showed that the color could be removed

completely after several extractions with water. No desorption

experiments were carried out on charcoal, to date.

38
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39
3.3.3. Conclusions and Future Plans

The experimental work to date shows that activated charcoal and permanganate coated silica gel are the foremost

candidates for inclusion in solid sorption devices. The

choice between these, if a choice must be made, will depend

on the ease with which the phosphine may be desorbed and

determined quantitatively. This is the next step of the

experimental program.

Although the silver nitrate impregnated silica gel was

demonstrated to be an excellent sorber, the determination of

phosphine as metallic silver or as insoluble silver phosphate

appears to be very difficult. Consequently it is planned

to use this material only as a visual indicator and to

destroy excess phosphine.

Future plans include the quantitative determination of

phosphine on charcoal by desorption with pyridine and

spect rophotometric measurement of a suitable color reaction

in pyridine, e.g. silver diethyldithiocarbamate as described

by Dechant, Sanders, and Graul [47],

Phosphine on KMnOi^ may be present as the ortho -phosphate

,

by analogy with the known oxidation of phosphine with aqueous

acid permanganate [47]. If this turns out to be the case, phosphate

can be determined by a standard colorimetric phosphomolybdat

e

method after destruction of the excess KMnO(+.

It is anticipated that the phosphine experiments can be

concluded rapidly after the routine chemical analyses are set

up.

4 . SUMMARY AND CONCLUSIONS

A methodology has been developed for handling and sampling

contaminant gas mixtures at the rates and concentrations specified. Compressed gas cylinders containing the contaminant

gases at 5 to 15 times the TLV deliver the required gases (after

dilution if necessary) to a cons tan t - flow sampling system which

assures precise metering of the gases through tubes of solid

sorbent into liquid backup traps (if required) . Three complete

instrument assemblies have been designed and built for work

with hydrogen fluoride, hydrogen cyanide, and phosphine.

Analytical techniques for determining the amounts of contaminant sorbed by the tubes have been developed, based on

reliable methods described in the literature but modified for

the specific applications at hand. Hydrogen fluoride and

hydrogen cyanide are determined by ion selective electrodes.

Phosphine is detected at present with silver nitrate impreg40
nated silica gel, and spectrophotomet ric determination using

silver diethyldi thiocarbamate in pyridine is just now getting

under way.

Solid sorbents have been tested on filter paper and in

glass tubes 6 mm in diameter (the size used for charcoal

sorption of organic vapors in air), and 13 mm in diameter.

The latter size of tube proves to contain sufficient sorbent

for retaining the required quantities of hydrogen fluoride and

phosphine, packed so that the back pressure does not exceed

25 mm Hg at a flow of 1 1 i ter/minute

.

The sorbents tested have included firebrick, glass beads,

charcoal, silica gel, sodium hydroxide, sodium citrate,

sodium bicarbonate, sodium acetate, Ascarite, potassium

permanganate, and silver nitrate both in bulk form and dispersed on substrates of filter paper and on silica gel. This

choice of sorbents to be tested was based on a literature

review of sorbents used in atmospheric analysis of the 5 contaminant gases of interest. To date, sodium acetate proves

to be a highly efficient sorber for hydrogen fluoride, while

potassium permanganate on silica gel shows considerable promise

for phosphine sorption, and Ascarite for hydrogen cyanide

sorption. The final selection of PH3 and HCN sorbers awaits

the completion of the quantitative analyses to show the

efficiency of the desorpt ion process.

The sorption efficiency of 3.0 g sodium acetate for

hydrogen fluoride is 100 percent at all specified flow rates

(1.0, 0.2, and 0.05 liters/min) , concentrations (1/5 to 5

times TLV) , and collection times (15 min to 8 hr) . The

efficiencies of charcoal and permanganate -coated silica gel

for phosphine, and of sodium hydroxide for hydrogen cyanide

are in process of measurement.

The feasibility of constructing small, efficient sampling

devices containing solid state sorbers to collect contaminant

gases for subsequent laboratory analysis has been demonstrated.

Future work will include the completion of accurate quantitative determinations of hydrogen cyanide and phosphine sorption,

and the evaluation of suitable sorbers for fluorine and

chlo ri ne

.

Disclaimer: Certain commercial materials are identified in

this report to adequately specify the experimental procedure. In no instance does such

identification imply recommendation or endorsement by the National Bureau of Standards, neither

does it imply that the material identified is

necessarily the best available for the purpose.

41
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Fluorides in the Atmosphere (Double Paper Tape Sampler

Method), ASTM Tentative Method (1973).

54. Natusch, D. F. S., Sewell, J. R. and Turner, R. L.,

Determination of Hydrogen Sulfide in Air - An Assessment

of Impregnated Paper Tape Methods, Anal. Chem. 46,

410 (1974)

.

55. Intersociety Methods of Air Sampling and Analysis:

Tentative Method for the Manual Analysis of Oxidizing

Substances in the Atmosphere, Health Lab. Sci. 7_, (3),

152 (1970).

56. Nelson, J. P. and Milun, A. J., Rapid Determination of

Phosphine in Air, Anal. Chem. 2_9 , 1665 (1957),

57. Cadoff, B.C., Greifer, B. , Pella, P. A., Taylor, J. K.

,

Development of Contaminant Generation Systems for

Certification of Portable Air Sampling Instruments, to

be published.

47
Appendix A

PKECK>iOS AND ACCURACY D\T\ FOR RESPDL'AL CuT-ORINE MeT>IOD

Method

Re^iduil Ch'orinc Concfntr Jlion

lodomctric

Ampcrometric

Orthotolidinc

OrthotoIiJine-arsenitc

Stabilized neutral orthotclidine

Ferrous DPD

Leuco cry stal violet

Methyl orange

Free

800

80O

800

800

800

800

800

Tot.^l

f g, 1

840

640

1.830

640

1,830

640

1.830

640

1.S30

640

1.S30

640

1.830

640

1.830

640

1,830

Number cf Labor jio.'ics

3230

32

2324

24

15

17

18 20

2123

1516

17

19

1919

17

1718 26

26

26

Relative

27.0

32.4

23.6

42.3

24.8

12.5 64 6 37.3

31.9

52.4

28.0

35.0

34.7

3.0

26.1

39.8

19.2 9.4

32.7

34.4

32.4

43.0

30. 1 19.9

A-1
Appendix B

Precision and Accurvcy Dktk for PiinsPHORUS Methods 2d/

Phosphorus Conccniraiion

Method Oriho- ph o^p h 0 rus phosph J ic

Pnlv- phosphnic Tot nl No. of Laboraicnc

Relative

O t J r; u .1 1 <j

s O

P. L 1 J 1 1 * C Error

"7 <

"> / J._ ^ 1 .o D. Vsnsdomol) bdatc A-t ^J inn

7.000 44 8.6 3.4

f inn Z J. 3 £• ottiDnous CtiloriLtJ IJ >

1 7,000 43 7.6 4.3

f inn Q 1

I*. in n _

r. Ascorbic acia

I 7.000 3

• 5.2 4.9

Hydrolysis •* 31 IvJtj.o / .4 vanadomol) bdatc JO DO.J 3.000 37 36.1 23.5

Hydrolysis • stannous

J jy DU, 1 chloride inn JO M / .D /.i.i 3.000 38 37.4 22.8

Persulfate +

f 210 32 55.8 1.6 vanadon:o!>bda*.: < 990 32 23.9 2.3 t

10,230 31 6.5 0.3

Sulfuric-nitrlc r^ciils *

f 210 23 65.6 20.9 vanadomoI> bdate < 990 22 0.6 t 10,230 20 7.0 0.4

Perchloric acid + f 210 4 33.5 45.2 vanadomol>bdjte •{ 990 5 20.3 2.6 [ 10.230 6 11.7 2.2

Persulfate + stannous f 210 29 28.1 9.2

chloride -j 990 30 14.9 12.3

[. 10,230 29 11_5 4.3

Sulfuric-nitric acids + f 210 20 20.8 1.2 stannous chloride •< 990 17 8.8 3.2

[ 10,230 19 7J 0.4

B-1
Appendix C

Summary of Data on Phosphate 7b/

Method

Stannous cliloi idc Aminon.iplitiuilsnlfonic .U Kt Stannous cliloi itle Willi extraction

Autoanalyzcr

Stannous chloride

AminGiKiphtho!-

sulfoiiic acid

Stannous cliloridc with extraction

Autoanalyzcr

Stannous chloride

Aminonaplitiio!-

sulfoiiic acid

Stannous chloride

with extraction

Autoanalyzcr

No. Mean Std. DiT.

Sample 1, IUOhil;. liter 33 9.50 O.HIG

Mean Hildliir Hihititc Error Sid. Pi t. Error

IS

4

5

9.10

9.19

9.50

0.374

0.44S

0.401

Sample 2, 5.0 tug., liter

.33 4.8 1 0.515

20

6

5

4.79

6.07

4.45

0.C35

2.S30

0.168

Sample 3, 0.5 nig. liter 32 0.52 0.099

20

8

5

0.65

0.76

0.51

0.314

0.258

0.195

0.50

0.84

0.81

0.50

0.19

0.21

1.07 0.55

0.02

0.15

0.26

0.01

8.5

4.0

4.8 4.2

10.7

13.2

46.6

3.7

48.3

33.9

38.3

5.0

8.4

8.2

5.0

3.8

4.2

21.2

11.2

4.0

30.0

52.0

2.0

C-1
BIBLIOGRAPHIC DATA

SHFET

1. !; hl.li \ ! (>l\ HI \-0\i \ \0.

NBSIR 74-527

2. C H)V 't /\C ( t S S 1 1,111

: No.

4. ri I I I ANP h i I 1 L Development of Solid State Samplers for Work

Atmospheres

3. R<i ;t)Uiu's Ac c <- s SI 1 1(1 N...

5. PubliL.iiion D.iti- June 1974

6. Pt'rforni I ( )r^an i / a[ i m i .ui'

7. Al I IKiR'Si B. Greifer, . C. Cadoff, J. Wing, J. K. Taylor

8. Ptrforniint; <)ri;jn. Kcpori Ni

9. PHKIORMINC OK',. AN i/.A i ION NAM!-; ANH AOPRI-.SS NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proice . Task, «\,rk Unii 3104150

11. Contract Cirant N'l

12. Spcnsoririj; On; an i/ at ion Name and Complete Address (Street, City. State, ZIP)

National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

13. Type (it Report & Period Covered

Semiannual Report

14. Sponsoring Agency C.odc

15. SLPPLHMhN TARI NOTi:S

16. A I* >'l R .AC. 1 (A 200-ivord or less factual summary ot most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here. ) A program is described for evaluating the efficiency of solid

sorbers for collecting trace quantities of hydrogen fluoride, phosphine, » hydrogen cyanide, chlorine, and fluorine in work atm.ospheres for subse- ; auent laboratory analysis. The gas handling and sampling instrumentation;

is described, and experimental results to date are presented. j Sodium acetate is a very efficient sorber for hydrogen fluoride, and!

its solubility in water proves to be highly advantageous for subsequent ! HF determination by ion selective electrode. Potassium permanganate | impregnated silica gel sorbs phosphine effectively, and Ascarite has beeni

found to sorb hydrogen cyanide, but quantitative experiments on the

latter two systems are still in progress.

Work on chlorine and fluorine systems will be initiated in the near

future

.

17. KhV 'Ai')RP)'^ f.s/v to f.i ive L-nrnes: alphab'^tic al order; capitalize only the first letter of the first key word unless a proper name, separated hv scmic olons ) Air analysis; air sampler; charcoal; chlorine; fluorine; gas analysis; hydrogen cyanide; hydrogen fluoride; industrial hygiene; phosphine;

sodium acet ate; sorber , s olid: work atmosp here

18. A\ All.AI-iLl'rV XX L n 1 1 IP. lied

For Oti'icia! Pi strihut i on. Do N'ot Relca.se ro NITS

''rder [ r.iiii Sup. ot Dcic. U.S. (ic.verr.ment i'rintinK Oificc

*ashin,cton, D.l . :.0 >>?., >V <

19. SECPRITV CLASS

(THIS RLPORT)

UNCL ASSiriF.D

21. NO. I '1 P \C,l.s

54

20. SKCLRH V ( l.AsS (THIS P AGL;

22.