NBSIR 76-998

Development of a Solid

Sorption Tube and Analytical

Procedure for Hydrogen

Cyanide in the Workplace

Atmosphere

Barry C. Cadoff and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

April 1976

Final Report

Prepared for

National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202
/ 5 ^ * '
NBSIR 76-998

DEVELOPMENT OF A SOLID

SORPTION TUBE AND ANALYTICAL

PROCEDURE FOR HYDROGEN

CYANIDE IN THE WORKPLACE

ATMOSPHERE

Barry C. Cadoff and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

April 1976

Final Report

Prepared for

National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

U.S. DEPARTMENT OF COMMERCE, Elliot I. Richardson. S^»tmv

James A. Baker, III, Und9r Secretary

Dr. Betsy Ancker-Johnson. Assistant Secretary for Scianea and Taehnehgy

NATIONAL BUREAU OF STANDARDS, Emett Ambtor, Acting Director

I

TABLE OF CONTENTS

Page

1. INTRODUCTION 1

2. SCOPE OF THE INVESTIGATION 2

3. EXPERIMENTAL 2

3.1 Generation of HCN 2

3.2 Sampling System 2

3.3 Sampling Tube 2

3.4 Solution of Tube Contents . . 3

3.5 Impinger Procedure 4

3.6 Other Sampling Methods. . . 4

3.7 Analytical Procedure 4

4. RESULTS AND DISCUSSION 5

4.1 Generation of HCN 5

4.2 Sampling of HCN . 5

4.3 Sampling Tube Characteristics 5

4.4 Selection of Analytical Method 6

4.5 Comparison of Impingers and Tubes 7

4.6 Tube Analytical Results 8

4.7 Precision and Accuracy 8

4.8 Ascarite Tube and Filter Pad Methods. ..... 8

5. SUMMARY AND CONCLUSIONS 9

6. REFERENCES 9

APPENDIX

ANALYTICAL PROCEDURE: HYDROGEN CYANIDE IN THE ATMOSPHERE 15

i
TABLES

Page

1. Expected cyanide concentrations in solution under 10

varying sampling conditions

2. Comparison of tube and impinger collection methods 11

3. NaOH tube analytical results 11

FIGURES

1. Diagram of NaOH-filled tube 12

2. Typical calibration curve for cyanide in 0.1 M 13

NaOH

3. Typical calibration curve for cyanide in 2 M NaOH 14

ii
Development of a Solid Sorption Tube and Analytical

Procedure for Hydrogen Cyanide in the Workplace Atmosphere

B. C. Cadoff and J. K. Taylor

ABSTRACT

The development of a sampling tube for

collecting HCN in the workplace atmosphere is

described. The tube contains 4.0 g of flake

NaOH and can be readily fabricated in the

laboratory. Details are given concerning the

construction and use of the tube and data is

presented on collection of HCN at levels of

five times the TLV, one fifth the TLV, and

at the TLV. Analysis of the tube contents

using the cyanide ion selective electrode is

described. This method is simple, rapid, and

relatively free of interferences. Data on the

analyses of tubes containing cyanide is described and estimates of the precision and

accuracy of the method are given.

KEY WORDS: Air analysis; air sampling; gas

analysis; hydrogen cyanide; industrial hygiene;

ion selective electrode; sodium hydroxide; work

atmosphere

.

1. INTRODUCTION

This final report summarizes work on the development

of a method for collecting and analyzing HCN present in

workplace atmospheres. The approach to the problem has been

to devise a solid sorption device which, after the sample

has been collected, can be returned to the laboratory where

the analysis may be performed simply and rapidly. These

solid samplers represent an improvement in convenience and

versatility compared with liquid bubblers presently in use

since they can be used and handled without fear of spillage.

They are also directly applicable to personal sampling.

The sampling device described is a tube filled with

NaOH and the analytical procedure employs a cyanide ion

selective electrode. Previous work supported by the National

Institute for Occupational Safety and Health was reported

earlier (1) . .

1
2. SCOPE OF THE INVESTIGATION

The major portion of this work deals with the development of a NaOH-filled sampling tube capable of collecting

HCN under varying concentrations and sampling rates, and

the method of analysis employing a cyanide ion selective

electrode. Details such as fabrication of the sampling

tube, breakthrough capacities of the tube, reproducibility

of measurement and precision and accuracy of the analytical

method are given.

Also discussed are two other devices which were investigated. One is an Ascarite- filled tube which proved unsuitable and a cellulose filter pad wetted with NaOH solution

and supported in a plastic filter holder which while not

fully evaluated, nonetheless, appears promising.

3. EXPERIMENTAL

3 . 1 Generation of HCN

The HCN in nitrogen used in this work was contained in

a size lA cylinder at a pressure originally of 2000 psig.

This material was analyzed by the procedures outlined below

and was found to contain 120 ppm HCN. Concentrations of 50,

10 and 2 ppm were obtained with a dilution system (1) , consisting of a rotameter and flow controller each for the HCN

stream and for the diluent stream ("breathing air" contained

in a cylinder) , a chamber to mix the two gas streams and

finally a port, open to atmosphere, into which the sampling

device is placed. (Caution: All work with HCN should be

done in a laboratory hood.) Calibration of the rotameters

was done using either a 1 liter wet test meter or a bubble

flowmeter. The error associated with reproducing the same

mixture from day to day is estimated to be ±2 percent.

3 . 2 Sampling System

The sampling system has been described (1) . This

system can provide constant flow over a range of flow rates,

and for this work flows of 1 liter/min, 200 ml/min and

50 ml/min were used. The sampling rate was calibrated before

each series of runs and the flow rate error over a several

hour sampling period was no greater than ±2 percent.

3 . 3 Sampling Tube

The tube is constructed of an approximately 9 cm length

of polyethylene tubing, 3/8" I.D., 1/16" wall and 1/2" O.D.

A polyethylene tubing connector, 3/8" x 1/4" containing a

2
cotton wad placed inside the 3/8" diameter portion^, is

inserted into the bottom of the tube. The tube is filled

with 4.0 g of flake NaOH (Technical Grade, J. T. Baker

Chemical Co.^) by putting small portions on a spatula and

transferring the contents to the tube. The tube is tapped

after each increment to settle the contents. Flakes of

various sizes are used. The final increment of flakes is

made in the following manner. Several flakes are placed on

a small piece of absorbent cotton which is then rolled and

placed inside the tube. A second polyethylene tubing connector, 3/8" X 1/4" is inserted into the top of the tube.

To increase the breakthrough capacity water is added to the

tube in the following way. Water- saturated nitrogen is

sampled through the tube at a flow rate of 1 liter/min for

about 20 minutes which results in the addition of approximately 0.5 g water. Both ends of the tube are then capped

with 1/4" polyethylene caps. A diagram of the tube is shown

in Figure 1.

Pressure drops across the tubes are measured by connecting an open U-tube mercury manometer just below the tube

and sampling air through the tube at a 1 liter/min. Breakthrough capacity is determined by placing a second tube

downstream from the first and determining after a particular

sampling period the amount of cyanide collected in the

second tube. Breakthrough in this work is defined as occuring when the weight of cyanide in the second tube amounts to

1 percent or more of the total quantity of cyanide collected,

as determined using the cyanide ion-selective electrode.

3 . 4 Solution of Tube Contents

The connectors at both ends of the tube are removed,

and a stream of distilled water, from a washbottle, is used

to remove the flakes from the tube. The tube and both

connectors are throughly washed, and the washings are collected in a polyethylene beaker. The contents are stirred

to dissolve the NaOH. The cotton wad (from the top of the

tube) is then removed from the solution and rinsed several

times with water, and these rinsings are combined with the

solution: After cooling to room temperature the solution is

transferred to a 50 ml volumetric flask, diluted to mark

^One inch = 2.54 centimeters.

^Mention of a product here and elsewhere in the report does

not constitute endorsement by the National Bureau of

Standards, nor does it imply that the product is necessarily

the best available for the purpose.

3
(yielding a solution that is 2 M NaOH) and then analyzed.

If the solution has a higher concentration then 10"^ M

cyanide an aliquot is diluted with 2 M NaOH to bring the concentration below 10"^ M cyanide. This is important since

concentrations in excess of 10"^ M tend to rapidly destroy

the cyanide electrode (2)

.

3.5 Impinger Procedure

The tube method was compared with a standard sampling

procedure employing two midget impingers, in series. Each

impinger was filled with 15 ml of 0.1 M NaOH. After sampling, the contents of both impingers were combined, along

with the rinsings, and diluted with 0.1 M NaOH to 50 ml.

3 . 6 Other Sampling Methods

A glass sampling tube of a design described earlier (3)

was filled with 4 g. Ascarite, 20-30 mesh (A. H. Thomas

Co.). This tube was not suitable for reasons outlined in

the Results and Discussion section of this report.

A sampler consisting of a 1.5 inch (3.8 cm) diameter

cellulose filter pad, held in a plastic filter holder

(Millipore Co.) was used. The cellulose pad was treated

with one ml of 3 M NaOH solution.

3 . 7 Analytical Procedure

A cyanide ion- select ive electrode (Orion Model 94-06)

and a saturated calomel electrode are clamped in an electrode holder and connected to either a digital pH meter

(Orion Model 801) or a dial-type, expanded scale pH meter

(Corning Model 12). The electrodes are immersed in a 50 ml

polyethylene beaker containing 25 ml of the solution to be

analyzed. A small. Teflon-coated, magnetic stirring bar is

placed in the beaker and rotated at a constant speed.

Reproducibility of stirring speed and placement of electrodes

in the solution is necessary for reproducible readings. A

millivolt reading is recorded when there is little or no

change in millivolt readout, usually within a minute or two.

A calibration curve is drawn by plotting millivolt

reading vs. cyanide concentration (10"^ to 10"^ M) using

semilog graph paper. Cyanide standards are made by first

preparing 10"^ M NaCN in water (or 10"^ M KCN in water) and

serially diluting this solution with 2 M NaOH for the tube

analyses or 0.1 M NaOH for the midget impinger analyses.

4
4. RESULTS AND DISCUSSION

4.1 Generation of HCN

At the beginning o£ this investigation it was thought

that a humidifier in the generation system would be required

to simulate the various humidities that would be encountered

in actual field sampling since in some sampling procedures,

changes in humidity have an adverse effect on collection

efficiency. However, it was found that the most severe

condition for NaOH-tube sampling is a dry atmosphere, such

as is obtained in the generation system described. In fact,

the addition of water to the tube by the sampling of moist

atmospheres aids in capturing HCN by increasing the breakthrough capacity (see Section 4.3).

4.2 Sampling of HCN

The sampling system proved to be versatile and precise.

In duplicate runs, little or no difference was found in the

concentration of the pairs. Thus, the error of the combined

HCN generation and sampling systems was less than the error

associated with the cyanide electrode analytical procedure.

4 . 3 Sampling Tube Characteristics

Flake, technical grade NaOH was chosen rather than

pellet, reagent grade NaOH because the flakes packed more

evenly in the tube and there were fewer voids and channels.

No difference in cyanide electrode response was noted using

technical grade or reagent grade NaOH as the background

solution for the cyanide standards. It was necessary to

pretreat the tube with moisture as described in the Experimental Section since adequate capacity could not otherwise

be obtained. Thus, breakthrough occurred before 20 liters

of 50 ppm HCN had been sampled through a dry tube, while

with the moisture - treated tube breakthrough had not occurred

even after sampling 120 liters. The moisture treatment,

however, did tend to settle the tube contents, resulting in

occasional voids, but breakthrough was never observed with

these tubes. That the reagent is present in large excess

can be shown from the following example. If a tube collects

an 8 hour sample at a rate of 200 ml/min a total of 96 liters

passes through the tube. If the HCN concentration is 50 ppm

and the ambient level for CO2 is assummed, i.e. 300 ppm,

then the number of millimoles of HCN collected is 0.196

while 1.18 millimoles of CO2 is collected. NaOH reacts in a

1:1 molar ratio with HCN and in a 2:1 molar ratio with CO2.

Thus, 2.56 millimoles or 102 mg of NaOH are required for

complete reaction. This means that the tube contains NaOH

in a 40 fold excess. In view of this large capacity it was

5
considered unnecessary to either determine the mesh size of

a typical tube or to sieve the NaOH so that a known size

range of particles could be used for filling.

A typical tube, before use, has a pressure drop (at

1 liter/min flow) of less than 0.2 inches Hg . After sampling, the pressure drops increase but remain less than 1

inch Hg . However, before the filling procedure outlined in

the Experimental Section was adopted, tubes wer§ filled by

merely adding 4 g NaOH to the tube and inserting the top

cotton wad. Cotton was chosen as the separator rather than

glass wool, since it was felt that on storage the glass wool

could react with the moisture- treated NaOH. Some of these

tubes developed unacceptably high pressure drops due to the

crusting of the top layer of NaOH. The new tubes have not

crusted over due to the fact that the NaOH flakes in the

cotton wad intercept much of the HCN and CO2 that enter the

tube. The cotton fibers act as a separator for the flakes,

preventing them from crusting over. Acceptable pressure

drops have thus been obtained for 120, 50, 10 and 2 ppm HCN

at the following flow rates and sampling times:

1 liter/min for 15 minutes

200 ml/min for 2 hours

200 ml/min for 4 hours

Two tubes have been used to sample room air (55 percent

R.H.) at 50 ml/min for 8 hours with resulting pressure drops

less than 1 inch Hg

.

4 . 4 Selection of Analytical Method

A major consideration in selecting an analytical method

is that it be compatible with the sampling procedure. In

table 1 typical sampling rates and times are given along

with the amounts of cyanide collected and resulting concentrations, for 2 ppm and 50 ppm HCN. It is seen that the

concentrations of the resulting 50 ml solutions are within

the optimal operating range (2) of 10'^ to 10"^ M, with the

exception of the 1.96 x 10"^ M solution. This solution, of

course, can be readily diluted to put it in the range of the

calibration standards.

Another consideration in selecting an analytical method

is the accuracy and precision that can be expected. This

can be expressed for ion selective electrodes in the following way (4) . The potential of an electrode immersed in a

solution containing an ion to which it is reversible is given

by the Nernst equation,

E = E - ^

In fC (1)

o nF ^

6
i

Ignoring any variation of the activity coefficient f,

,c -RT dC

represents the variation of potential with concentration.

For a 1 percent variation in concentration at ordinary

temperature

,

_ 0.00026V dE C3)

For the case of the cyanide electrode, n = 1. Therefore,

a 1 mV change in reading is equal to about a 4 percent

change in concentration. This aspect is more fully discussed in the Precision and Accuracy Section of this report.

Finally, a suitable analytical method should be reasonably free of interferences. Chloride, iodide and bromide

can be tolerated if they are present in ratios with respect

to the cyanide concentration of less than 10^, 0.1 and

5 X 10^(2). Sulfide must be completely absent, and an

effective method of eliminating this interference has been

reported (5) . This involves the addition of lead nitrate to

precipitate the sulfide.

4 . 5 Comparison of Impingers and Tubes

In order to compare the results obtained with the

NaOH - filled tubes and the more conventional procedures for

collecting HCN, a series of runs were made using two midget

impingers in series, each containing 15 ml of 0.1 M NaOH.

At the same time and under the same conditions a series of

runs using tubes were made. Results are given in table 2,

which show the nominal concentrations (i.e. the concentrations based on the analyzed cylinder contents and the dilution ratios) and the actual concentrations analyzed. Good

agreement is found between the impinger and tube methods

except at the 2 ppm level where the impinger procedure gives

low results. This discrepancy was not investigated further.

Figures 2 and 3 show typical cyanide calibration curves

for 0.1 M NaOH and 2.0 M NaOH, respectively. It is seen

that the 0.1 M NaOH curve is linear over the 10"^ to 10"^ M

range. The 2 M NaOH curve is linear from 10"^ to about

5 X 10"^ M cyanide at which point a break in the curve occurs.

The remaining portion of the calibration curve, from

5 X 10"^ M to 10"^ M forms another straight line as shown in'

figure 3.

7
4 . 6 Tube Analytical Results

Table 3 summarizes results obtained at 50, 10, and 2 ppm

HCN (5 TLV, TLV and 0.2 TLV) sampled under two conditions of

flow rate and sampling time. Generally good agreement is

found between the 4 hour runs and the 15 minute runs, and

the analyzed concentration agrees well with the nominal or

predicted concentration.

4 . 7 Precision and Accuracy

It should be emphasized that reproducible measurements

with the cyanide electrode can only be obtained if details

such as electrode placement in the solution and rate of

stirring are kept uniform from sample to sample and are consistent with calibration conditions. Also, a sluggish

response, especially at low concentrations, may be a problem

caused by an etched electrode surface. This can be handled

by polishing the crystal surface with a mild abrasive paper.

With a properly operating system of pH meter, reference

electrode and cyanide electrode, the reproducibility of

three consecutive measurements on a single sample can be

expressed as an average value with a range of ±0.3 mV. Over

a period of an hour or more the variations in readings can

be as large as ±1.0 mV. Furthermore, the calibration line

itself has an uncertainty.

The most accurate measurements are made within a short

time of each other with calibration standards interspersed

among the samples. However, for routine analyses it is

estimated readings should not exceed ±7 percent of an

average value.

4 . 8 Ascarite Tube and Filter Pad Methods

The Ascarite tube was found to be an efficient collector

for HCN but cyanide was irreversibly adsorbed on the Ascarite

particles. Thus, the contents of an Ascarite tube, when

added to standard cyanide solutions at 10"^ and 10"** M

lowered the free cyanide concentrations to about 70 percent

of the original level. It was not possible to extract the

cyanide from the Ascarite, even after several washings.

Collection of HCN on cellulose filter pads containing

1 ml of 3 M NaOH appears promising based on the fact that no

breakthrough occurred during collection of 50 ppm HCN for 4

hours at the 200 ml/min collection rate. In addition, the

cellulose pad did not adsorb cyanide when placed in a

standard cyanide solution. Further work, however, is

necessary to fully appraise the potential of this sampling

method.

8
5. SUMMARY AND CONCLUSIONS

The NaOH sampling tube is a quantitative sorber for HCN

and has more than adequate capacity for sampling HCN at

levels as high as 50 ppm (5 x TLV) . Its design is simple

and can be fabricated easily using items commonly found in a

laboratory. The analytical procedure, employing a cyanide

ion selective electrode is also simple and rapid and lends

itself to the routine determination of large numbers of

samples.

6. REFERENCES

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

"Development of Solid State Samplers for Work

Atmospheres," NBSIR 74-527 (June 1974).

2. Instruction Manual for Cyanide Activity Electrode,

Model 94-06, Orion Research Incorporated (1972).

3. J. Wing and J. K. Taylor, "Development of a Solid

Sorption Tube for Sampling Hydrogen Fluoride in the

Work Atmosphere, NBSIR 74-581 (October 1974).

4. J. K. Taylor, E. J. Maienthal, and G. Marinenko,

"Electrochemical Methods," in "Trace Analysis, Physical

Methods," G. H. Morrison, ed., Interscience Publications,

New York, N.Y. , 1965.

5. 0. P. Bhargava, G. W. Deline and W. G. Hines, "Rapid

Determination of Cyanide in Waste Waters," in "Water

Quality Parameters," American Society for Testing and

Materials, Philadelphia, Pa., 1975.

9
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o

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pLD

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in

1 1 o o O O

LO I—

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I—

1

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to

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(J I—I OO

\j

(_) rH <Tt

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oJ in LO (D

+-> O >^ U

0

rH (Vl

<a > nH

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L) ^ U LO

<D CD LO (NJ put:! (NJ rH

•

Oi •H

I-H P

•H H e

•H

rH LO 00

P. rH

CO

4H

o

rH

•H
Table 2. Comparison of tube and impinger

collection methods

Nominal cone. Flow rate Sampling Tube or Analyzed cone.

(ppm) (1/min) time (min) impinger (ppm)

ion 1 zu

1 n 1 rD lube 1 o r 1 Z 5

1lev9 n 101 J. . U X

c: 1 UU C

1 01 c

1 llip _L 1 1 ^ I 1 7 Q 1 ^ y

ion 1 Z U1 m cD imp mger 1 il

bU 1 01 1 7 Tub e

A

1 01 1 7 1 uoe D J

1 m 12X ^ 7

50 1.01 12 Impinger 58

10 1.01 12 Tube 10.2

10 1.01 12 Tube 10.2

10 1.01 12 Impinger 9.7

10 1.01 12 Impinger 9.7

2 1.01 30.5 Tube 1.91

2 1.01 30.5 Tube 1.95

2 1.01 30.5 Impinger 0.78

2 1.01 30.5 Impinger 0.89

Table 3. NaOH tube analytical results

Nominal cone. Flow rate Sampling Analyzed cone.

(ppm) (1/min) time

50 1.03 15 min 54

50 1.03 15 min 52

50 0.204 4 h 51

50 0. 204 4 h 48

10 1.01 15 min 10.3

10 1.01 15 min 10.2

10 0.198 4 h 9.8

10 0.198 4 h 9.6

2 1.01 15 min 1.89

2 1.01 15 min 1.92

2 0.200 4 h 1.95

2 0.200 4 h 2.01

11
3

2

////////////: wimiih

Figure 1. Diagram of NaOH-fillcd tube

1 - polyethylene

2 - polyethylene

3 - polyethylene

4 - NaOH flakes

5 - cotton wad

6 - cotton wad

tube

connectors

caps

12
MILLIVOLTS

Figure 2. Typical calibration curve for

cyanide in 0.1 M NaOH

13
MILLIVOLTS

Figure 3. Typical calibration curve for

cyanide in 2 M NaOH

14
APPENDIX

Analytical Procedure: Hydrogen Cyanide in the Atmosphere

Analyte: Cyanide Method No. P^CAM

Matrix: Air Range: 2-50 ppm or 13 yg

per sample

Procedure: Collection via

solid sorption Precision: ±7 percent

tube/ion selective

electrode analysis Classification:

Date issued:

Date revised:

1. Principle of the Method

1.1 Hydrogen cyanide in air is collected by a sorption

tube containing sodium hydroxide flakes.

1.2 Samples are dissolved in water.

1.3 The resulting solution is analyzed using the

cyanide ion selective electrode.

2. Range and Sensitivity

The recommended range for the method is 2-50 ppm HCN.

Recommended smallest sample size is approximately 13 yg.

3. Interferences:

3.1 Sulfide ion irreversibly poisons the cyanide ion

selective electrode and must be removed if found in the

sample. Check for presence of sulfide by touching a drop of

sample to a piece of lead acetate paper. The presence of

sulfide is indicated by darkening of the paper.

3.2 Sulfide is removed by the additon of a small amount

of lead nitrate. Check with lead acetate paper to determine

the completeness of sulfide removal. Avoid a large excess of

lead nitrate (2)

.

3.3 After precipitation of all sulfide, filter solution

through filter paper and proceed with the analysis.

15
4. Precision and Accuracy

The estimated precision and accuracy of the method is

±7 percent.

5. Advantages and Disadvantages of the Method

5.1 Advantages; The hydrogen cyanide is efficiently

collected and the analytical procedure is highly selective for

cyanide ions. The procedure involves few steps, is simple to

perform and the technique can be readily acquired. Commonly

available equipment and reagents are used.

5.2 Disadvantages: Close attention to operating details

such as uniform rate of stirring and placement of electrodes

in solution must be observed. An occasional slow or erratic

response of the electrode occurs, which can be corrected by

polishing the crystal surface with a mild abrasive paper.

6. Apparatus

6.1 Sampling Apparatus

6.1.1 Sorption tube for hydrogen cyanide.

6.1.2 Personal sampling pump or other source of

vacuum.

6.1.3 A wet test meter or other suitable device for

measuring flow rates.

6.1.4 Thermometer.

6.1.5 Stopwatch.

6.1.6 Manometer.

6.2 Analytical Apparatus

6.2.1 Orion 94-06 Cyanide electrode or equivalent

6.2.2 Saturated colomel electrode or other suitable

reference electrode.

6.2.3 Expanded scale pH/millivolt meter.

6.2.4 Magnetic stirrer and stirring bars.

6.2.5 Polyethylene bottles. i

6.2.6 Polyethylene beakers, 50 ml.

16 I
t.2.1 Stainless steel forceps.

6.2.8 Volumetric flasks, 50 ml, for dilution of

sorption tube contents. Other sizes required

for preparation of standard solutions.

6.3 Sorption Tube Components.

6.3.1 Polyethylene tubing, 3/8" I.D., 1/2" O.D.

approximately 9 cm long.

6.3.2 Surgical cotton.

6.3.3 Polyethylene tubing connectors, 3/8" x 1/4".

6.3.4 Polyethylene caps, 1/4" I.D.

7. Reagents

7.1 Distilled water.

7.2 NaOH, flake, technical grade.

7.3 NaOH, 2 M. Dissolve 80 g NaOH, flake, technical

grade, in distilled water and dilute to 1 liter.

7.4 Sodium cyanide, reagent grade.

7.5 Lead acetate test paper.

7.6 Lead nitrate.

7.7 Sodium cyanide standards.

7.7.1 Prepare stock solution of 10"^M[CN"] by

dissolving 4.90 g NaCN in 1 liter of distilled water.

7.7.2 Dilute 1 ml of lO'^M [CN"] to 100 ml with

2 M NaOH for 10" [CN"] (26 yg/ml)

.

7.7.3 Dilute 25 ml of lO'^M [CN"] to 50 ml with

2 M NaOH for 5 x lO"**!^ [CN"] (13 yg/ml).

7.7.4 Dilute 10 ml of lO'^M [CN"] to 100 ml with

2M NaOH for lO-'^M [CN"] (2.6 yg/ml).

7.7.5 Dilute 25 ml of lO-'^M [CN'] to 50 ml with

2M NaOH for 5 x 10" [CN"] (1.3 yg/ml).

17
7.7.6 Dilute 10 ml of 10-'*M [CN"] to 100 ml with

2M NaOH for 10" [CN"] (0.26 yg/ml)

.

8. Procedure

8.1 Cleaning of Equipment. All glassware is washed in

detergent solution, rinsed in tap water and then rinsed with

distilled water.

8.2 Preparation of Sorption Tube.

A polyethylene tubing connector, containing a

cotton wad in the 3/8" diameter portion, is inserted into

the bottom of the polyethylene tube. The tube is filled

with 4.0 g of flake NaOH by placing small portions on a

spatula and transferring the contents to the tube. The tube

is tapped after each increment to settle the contents. Flakes

of various sizes are used. The final increment of flakes is

added in the following manner: several flakes are placed

on a small piece of absorbent cotton which is then rolled

and placed inside the tube. A second polyethylene connector

is inserted at the top of the tube. Water- saturated nitrogen

is sampled through the tube at a flow rate of 1 liter/min

for about 20 minutes which results in the addition of about

0.5 g water. Both ends of the tube are capped with polyethylene caps.

8.3 Collection of Samples.

8.3.1 The polyethylene caps are removed from the

sampling tube and the tube is attached with

flexible tubing to the sampling pump.

8.3.2 The pump is turned on to begin sample collection. Flow rate or volume measurements

should be made accurately. Flow rates ranging from 50 ml/min to 1 liter/min can be

selected.

8.3.3 After sampling, the tube is disconnected from

the pump and is capped with the polyethylene

caps

.

8.4 Analysis of Samples.

8.4.1 The caps are removed from the tube and the

top polyethylene connector is removed.

Forceps are used to remove the cotton wad.

The contents of the tube, along with the

cotton wad are transferred to a beaker. The

bottom connector is removed. The tube and
connectors are then washed with a stream of

water £,rom a washed bottle into the beaker.

. The contents are stirred until all the NaOH

dissolves. The cotton wad is removed from

the solution with forceps and thoroughly

rinsed with water with the washings being

added to the beaker. The contents of the

beaker are then quantitatively transferred

to a 50 ml volumetric flask and diluted to

mark with water. The solution is then stored

in a polyethylene bottle.

8.4.2 Twenty-five ml of sample are transferred to

a 50 ml polyethylene beaker containing a

magnetic stirring bar. The cyanide electrode

and reference electrode are placed in the

solution and the millivolt reading is

recorded after the meter has stabilized.

Stirring rates are kept constant during

analysis of both samples and standards.

9. Calibration and Standards.

9.1 Obtain the millivolt readings from each cyanide

standard.

9.2 Plot the millivolt readings vs the cyanide ion

concentrations of the standards on semi-log paper. The

cyanide ion concentration in yg/ml is plotted on the log

axis.

10. Calculations.

10.1 The millivolt readings from the analysis of the

sample are converted to ygCN/ml of solution using the calibration curve.

10.2 The yg content of the sample is multipled by the

sample volume to obtain the total ygCN in the sample.

10.3 Convert the volume of air sampled to standard

conditions of 25°C and 760 mm Hg

:

V = V

P 298

^ ^ 7^0 ^ Tf773

where

:

= volume of air in liters at 25°C and 760 mm Hg

V = volume of air in liters as measured

19
P = Barometric Pressure in mm Hg

T = Temperature of air in degree centr igrade

.

10.4 The concentration of CN in the air sampled can be

expressed in yg CN per liter or mg CN per cubic meter.

mg/m^ = yg/liter

:a

T

mg/n,3 = total ug CN

s

10.5 The concentration of CN can also be expressed in

ppm, defined as yl of component per liter of air.

ppm = ylCN/Vg = R/MW ygCN/V^

= 0.94 X ygCN/Vg

where

:

R = 24.45 at 25°C, 760 mm Hg

.

MW = 2 6.02

11. References.

1. Instruction Manual for Cyanide Activity Electrode,

Model 94-06, Orion Research Incorporated (1972).

2. 0. P. Bhargava, G. W. Deline and W. G. Hines

,

"Rapid Determination of Cyanide in Waste Waters," in "Water

Quality Parameters," American Society for Testing and

Materials, Philadelphia, Pa., 1975.

USCOMM-NBS-DC

20
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-998

2. Gov't Accessioti

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Development of a Solid Sorption Tube and Analytical

Procedure for Hydrogen Cyanide in the Workplace

Atmosphere

5. Publication Date

January 1976

6. Performing Organization Code

^•WW^^C. Cadoff and John K. Taylor 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization 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 of Report & Period

Covered

Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or teas factual summery of most significant Information. If document includes a significant

bibliography or literature survey, mention it here.)

The development of a sampling tube for collecting HCN in the workplace

atmosphere is described. The tube contains 4.0 g of flake NaOH and

can be readily fabricated in the laboratory. Details are given concerning the construction and use of the tube and data is presented on

collection of HCN at levels of five times the TLV, one fifth the TLV,

and at the TLV. Analysis of the tube contents using the cyanide ion

selective electrode is described. This method is simple, rapid, and

relatively free of interferences. Data on the analyses of tubes containing cyanide is described and estimates of the precision and

accuracy of the method are given.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Air analysis; air sampling; gas analysis; hydrogen cyanide; industrial

hygiene; ion selective electrode; sodium hydroxide; work atmosphere.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

25

20. SEC;UR1TY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

$3.50

18. AVAILABILITY [x] Unlimited

I

' For Official Di stribution. Do Not Release to NTIS

Order From Sup. of Doc, U.S. Government Printing Office

Washington, D.C. 20402, SD Cat. No. CH

[x] Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

USCOMM-DC 29042-P74
Iii