NBSIR 74-530

Preparation of Charcoal Sampling

Tubes Containing Known Quantities

of Adsorbed Solvents

B. C. Cadoff, E. E. Hughes, R. Alvarez and J. K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

July 1974

Final Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

NBSIR 74-530

PREPARATION OF CHARCOAL SAMPLING

TUBES CONTAINING KNOWN QUANTITIES

OF ADSORBED SOLVENTS

B. C. Cadoff, E. E. Hughes, R. Alvarez and J. K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

July 1974

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, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director

TABLE OF CONTENTS

Page

1.0 Introduction 1

2.0 Major Accomplishments 1

3.0 Preparation and Analysis of Charcoal Tubes for 2 NIOSH Collaborative Test

3.1 Preparation of Tanks Containing Known 2

Solvent- in-Air Mixtures

3.1.1 Primary Mixtures 2

3.1.2 Secondary Mixtures 4

3.2 Dilution of Tank Mixtures 4

3.2.1 Construction and Calibration of Gas 4

Dilution System

3.2.2 Use of Gas Dilution System to Fill 6

Charcoal Tubes

3.3 Charcoal Tubes 6

3.4 The Sampling System 7 3.4.1 Design and Calibration of Sampling 7

Orifices

3.4.2 Sampling System in Use 7

3.5 Analysis of Charcoal Tubes 7

3.5.1 Selection of Tubes for Analysis 7 3.5.2 Revised Values for Charcoal Tubes 11

4.0 Analytical Procedure 12

5.0 Suggested Modifications of the Standard Charcoal 13

Tube

6.0 New Gravimetric Procedure for the Analysis of 13

Solvent-in-Air Mixtures

7.0 Charcoal Tube SRM's 16

8.0 Papers to be Submitted for Publication 20

9.0 References 20

Appendix A. Revised Values Al

Appendix B. Consensus Values Bl
LIST OF TABLES

Page

3. 1 Orifice Flow Rates 10

7. 1 Concentration Levels for Organic Solvents 20

A. 1 Revised Values for Charcoal Tubes - Benzene Al

A. 2 Revised Values for Charcoal Tubes - Xylene A2

A. 3 Revised Values for Charcoal Tubes - p-Dioxane A3

A. 4 Revised Values for Charcoal Tubes - Ethylene A4

Bichloride

A. 5 Revised Values for Charcoal Tubes - Chloroform A5

A. 6 Revised Values for Charcoal Tubes - A6

Tr ichloroethylene

A. 7 Revised Values for Charcoal Tubes - Carbon A7

Tetrachloride

B. 1 Consensus Values - Benzene B2

B2 Consensus Values - Xylene B2

B. 3 Consensus Values - p-Dioxane B3

B. 4 Consensus Values - Ethylene Dichloride B3

B. 5 Consensus Values - Chloroform B4

B6 Consensus Values - Tr ichloroethylene B4

B. 7 Consensus Values - Carbon Tetrachloride B5

LIST OF FIGURES

3. 1 Outline of Procedure for Preparing Charcoal Tubes 3

3. 2 Diagram of Gas Dilution System 5

3. 3 Sampling System 8

3. 4 A Representation of the 35 Tubes Prepared at Each 9

Concentration Level

5. 1 Modified Charcoal Tube 14

7. 1 Diagram of SRM Sample Collection System 18

7. 2 Arrangement for Filling SRM Tubes 19
PREPARATION OF CHARCOAL SAMPLING TUBES

CONTAINING KNOWN QUANTITIES OF ADSORBED SOLVENTS

ABSTRACT

The method in widespread use for the determination

of the concentration of organic solvents in the work

atmosphere consists in collection of the solvent byadsorption on activated charcoal followed by desorption

with carbon disulfide and measurement by gas chromatography. This report describes techniques developed to

produce reference standards for this determination and

modifications in the analytical procedure to improve its

precision and accuracy.

1 . 0 Introduction

This is the final report on work performed under an

Interagency Agreement involving the preparation of charcoal

tubes containing known amounts of organic solvents. The

objective of this work was to develop techniques for the mass

production of charcoal tubes containing known amounts of

organic solvents, to serve as reference standards. A further

objective was to prepare a limited number of tubes for collaborative test of the NIOSH analytical method for measurement

of the concentration of organic solvents in air. The first

report, issued December 1, 1972, dealt with the preparation

of an initial batch of approximately 1000 tubes each containing known amounts of one of seven solvents, viz., benzene,

xylene, p-dioxane, ethylene dichloride, chloroform, trichloroethylene and carbon tetrachloride.

This report describes further activities of this project

and also summarizes the earlier work.

2 . 0 Major Accomplishments

1- Production of over 1000 charcoal tubes for NIOSH

collaborative studies, each containing one of seven solvents

at one of four or five concentration levels (benzene, xylene,

p-dioxane, ethylene dichloride, chloroform, t richloroethylene

,

and carbon tetrachloride) adsorbed on the charcoal. Each

tube was certified to contain a known amount of solvent

material (expressed in yg/tube) to within ±5 percent of the

assigned value. Replicate tubes did not vary from one another by more than ±2 percent.

2 - The development of a new accurate gravimetric procedure for determining both the concentrations and long term

stability of solvent-in-air mixtures, that gives promise of

general applicability not only to solvents but other materials

as well. (This work will be submitted for publication in the

technical literature.)

1
3- The design and fabrication of critical orifice sampling

assemblies that maintain unchanging sampling rates after manyhours of use. (This work will be submitted for publication

in the technical literature.)

4- Suggested improvements in the procedure for the analysis

of charcoal tubes, involving a means of preventing evaporation

of the carbon disulfide used as a desorber, and in the preparation of more accurate standard solutions for calibration of

the gas chromatograph

5- A suggestion for a design change in the charcoal tubes

to permit a simpler evaluation of the capacity or "breakthrough" characteristics of tubes in laboratory and field

s tudies

3 . 0 Preparation and Analysis of Charcoal Tubes for NIQSH

Collaborative Test

Figure 3.1 outlines the steps employed in the preparation

of charcoal tubes. The numbers 3.1 to 3.4 refer to the sections

of this report where each step is described.

3 . 1 Preparation of Tanks Containing Known Solvent - in-Air

Mixture's"

A major requirement of this project was to prepare

quantitative mixtures of each of the solvents in air so that

these could be used to deposit known quantities of solvent

on the charcoal tubes. Standard gas mixtures were of two

types: (a) primary mixtures prepared directly from the

liquid solvent, and (b) secondary mixtures prepared by

diluting the primary solvent-in-air mixture. For each solvent,

at least one primary and one secondary gas mixture were used

to cover the range of concentrations required.

3.1.1 Primary Mixtures

Basically, these mixtures were made by vacuum-distilling

a solvent into a size lA cylinder (43 liter capacity) and

subsequently pressurizing with air. Before filling these

tanks with solvent, the entire system was evacuated; the

solvent, contained in a small glass container, was then

allowed to distill until the vapor pressure in the system

reached a predetermined value which depended on the final

desired concentration in the tank and the volatility of the

solvent at room temperature. The tank was then pressurized

from a cylinder containing compressed air. Next, the tank
^9J to < I- 3Z Oz<r<

71^ 7K

2-o< A6<

V)OUao

c; •H

o,

<pO

<4-l u

<uuo^

a.o

•H

i-H P3O

to3

•H 3
was heated, using an infrared lamp, to effect complete mixing

by convection. A final pressure reading was taken after the

tank returned to room temperature.

The concentration of the resulting mixture was determined

in either of two ways. One involved the calculation of the

concentration based on the ideal gas law (at low concentrations

these solvents approach ideality); the second method involved

weighing the actual amount of solvent which distilled into the

tank [1].

3.1.2 Secondary Mixtures

These mixtures were prepared by transferring a portion

of the primary tank mixture to an evacuated second tank and

then pressurizing the second tank. These mixtures were

usually one tenth as concentrated as the primary ones. By

measuring the pressure after transfer of the primary mixture

and the final pressure after addition of the diluent gas,

the final concentration may be calculated. (This procedure

was later found to be uncertain and not suitable for the

quantitative preparation of solvent-in-air mixtures. See

Section 6.0.)

3 . 2 Dilution of Tank Mixtures

Further dilution of the tank mixtures was often necessary

and for this purpose a gas dilution system was used. This

consists of two separately controlled gas flow systems,

each containing a flowmeter to monitor the flow, a valve to

adjust the flow and a flow controller to keep the flow

constant. One stream contains the tank mixture while the

other contains the diluent gas (purified air). The two streams

are combined in a gas mixer and the resulting mixture then

flows to a gas manifold where the charcoal tubes may be filled.

3.2.1 Construction and Calibration of Gas Dilution System

Figure 3.2 shows a diagram of the main components of the

gas dilution system.

The following materials were used to construct the system:*

^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

4

For The Tank Mixture Flow:

Hastings Mass Flow Meter: 3 sizes used, 1000 cc/min,

5000 cc/min, 10000 cc/min

Moore Flow Controller (constant differential type) Model

63 BD

Whitey Valve (brass) 1RS4

For The Compressed Air Flow:

Air Purifier -- Granular charcoal and silica gel

, . . Brooks Rotameter (Sho-Rate) Type: 1355-00C9AAA

Moore Flow Controller (Constant differential type) Model

63 BD-L

, Whitey Valve (brass) 4RS4

A 3-liter wet-test meter was used to calibrate all of the

flowmeters used. The total system flow was kept at least 1.5

times the combined flow rates of the sampling orifices.

3.2.2 Use of Gas Dilution System to Fill Charcoal Tubes

The filling of tubes was accomplished by raising the

apparatus containing the tubes, until the tubes protruded

about half-way into the gas manifold. Vacuum was then applied

to the sampling system and continued for a total of exactly five

minutes. The tubes were constantly bathed by the gas mixture

during the sampling period. There are annular spaces between

the manifold ports and the sampling tubes that allow excess

gas mixture to flow out to atmosphere, thereby making it

possible to sample at atmospheric pressure without room air

being drawn into the apparatus.

3 . 3 Charcoal Tubes

The charooal tubes were manufactured by Mine Safety

Appliance Company in accordance with the recommendations of

NIOSH [2]. Several of the tubes were selected at random and

tested for resistance to air flow. The tubes so tested

varied over a range of less than 1 percent; that is the flow

through all these tubes, using a critical orifice, did not

vary as much as 1 percent. Thus, these sampling tubes were

considered to be interchangeable with respect to flow rate.

6
3 . 4 The Sampling System

3.4.1 Design and Calibration of Sampling Orifices

The sampling system, shown in Figure 3.3, is constructed

of 3/8" pipe with five evenly spaced ports (corresponding to

the ports of the gas manifold). In each of these ports,

a fitting is attached. Each fitting contains a 20 gauge

hypodermic needle, two inches long, which is brazed into the

fitting to form an air-tight seal. Atop the fitting is

installed a nominal 60 micron filter (Nupro Co.) to protect the

hypodermic needle from particulate contamination. Under

vacuum, hypodermic needles function as critical orifices

and the gage and length of these needles were chosen to

provide a flow of approximately 2 liters/minute [3] . These

critical orifices, even with the charcoal tubes attached,

function to provide a virtually constant flow. The flow

data (calibrated with a wet test meter) for these orifices

with tubes in place are given in Table 3.1.

3.4.2 Sampling System in Use

Five charcoal tubes are attached to the sampling system

with short sections of rubber tubing. The sampling system is

then raised and the tubes are inserted halfway into the gas

manifold in which the sample stream is flowing. The vacuum

is turned on and sampling is continued for exactly five

minutes. The vacuum is then shut off and the sampling

system is lowered. This procedure produces five sampling

tubes containing reproducible quantities of adsorbed solvents.

3 . 5 Analysis of Charcoal Tubes

3.5.1 Selection of Tubes for Analysis

A total of 35 tubes was initially prepared at each concentration level for each solvent. From these 35 tubes, five

were retained for analysis. Of these five, two were selected,

analyzed and reported in the December 1, 1972 report.

Figure 3.4 is a representation of the thirty five tubes

at each concentration level. The letters A through E refer

to the corresponding sampling orifices. The numbers 1 through

7 refer to the run number. Seven runs were necessary in order

to prepare 35 tubes at a given concentration level.

The shaded boxes represent those tubes selected for retention.

In all cases, tube "C" was chosen for analysis, along with

another tube from the remaining four shaded boxes. Thus, for

the five concentration levels in the benzene series, the

following tubes were analyzed and the results were listed in

the December 1, 1972 report.

7
8
Figure 3.4 A representation of the thirtyat each concentration level.

five tubes prepared
Table 3.1

Orifice Flow Rates

Orifice x Orifice Flow rate (1/min) Ratio: Orifice C

A 1.819 1.085

;B

^

1.624 0.9687

C ,.

- • : 1 . 676 1. 000

D 1.741 1.039

E 1.715 1.023

For Concentration Level 1

For Concentration Level 2 For Concentration Level 3

For Concentration Level 4

For Concentration Level 5

Tubes A and C

Tubes B and C

Tubes D and C

Tubes E and C

Tubes A and C

Since that time, some of the tubes originally sent to

NIOSH and unused have been returned to NBS for reanalysis.

10
3.5.2 Revised Values for Charcoal Tubes

The method of preparation of the charcoal tubes used

for the NIOSH collaborative tests should be capable of

producing tubes with a high degree of reproducibility.

Because the tubes were needed before all aspects of their

analysis could be verified, they were released with provisional values.

The provisional values were based upon the following

data. The tubes were analyzed by a gas chromatographic

method and these values were compared with those calculated

from gas flow and gas concentration data. This procedure

gave greater weight to the latter which was subsequently

found to be unjustified. Furthermore, the analytical

method, as originally used, introduced more error than

was tolerable. The source of this error was found to lie

in the manner of preparation of calibration standards.

Improvements described below overcame the analytical

deficiencies, and an improved gravimetric gas-analysis technique (see section 6.0) will give greater confidence in the

determined composition of tank mixtures in the future. However, since the gas mixtures were exhausted during preparation of the tubes, the only feasible means of establishing

the concentration levels for the original lot of tubes was

analysis of the remaining tubes by the improved chromatographic procedure, so this was done.

The revised analytical procedure uses calibration

solutions prepared by using micropipets to deliver the

solvent into volumetric flasks containing carbon disulfide.

A further modification consists in the use of 2 ml vials with

screw-top Teflon sliding-valve tops (Mininert Valves,

Precision Sampling Corp., Baton Rouge, Louisiana) for desorption of the solvent from the charcoal adsorbent. This type

of vial and closure is also useful for storage of standards,

to prevent differential evaporative losses. In fact,

standards have been stored in this manner for three weeks

without measurable changes in concentration. The modified

procedure is described more fully in section 5.0 of this

report

11
The revised values for the charcoal tubes prepared for

collaborative testing are given in Tables A.l to A. 7,

respectively, in Appendix A. These values are based on the

analysis of at least three tubes at each concentration level.

Six standards were prepared for each solvent and the gas

chromatographic response was plotted with respect to concentration, to yield linear calibration curves. Both gravimetric

and volumetric standards were prepared and differences between

duplicate standards did not exceed 3 percent.

Three tubes were analyzed for each concentration level,

using the procedure described in Section 4.0. At least two

injections were run for each tube and replication within 2 percent

of the G.C. signal was ordinarily observed. For purposes of

statistical comparison and convenience, all measurements were

normalized to values that would have been collected at the "C"

position. The values, so calculated, agreed, on the average,

within ±2 percent. From these considerations, it is believed

that the values assigned in the tables in this Appendix are

precise within ±2 percent. That is to say, all tubes in the

collaborative test lot are expected to have a relative agreement within ±2 percent of the tabulated values.

It is conservatively estimated that the tabulated values

are within ±5 percent of the "true" values. This reflects

the fact that different calibration solutions may vary by 3

percent, the agreement among tubes is 2 percent, and multiple

chromatographic injections give signals which have a range of

about 2 percent.

4 . 0 Analytical Procedure

The following is a brief description of the procedure

used for analyzing charcoal tubes.

The contents of the charcoal tube are transferred to a

2 ml vial fitted with a screw-cap Teflon Mininert valve. One

ml of CSz is added and the vial is capped. After desorption

is achieved, the valve is opened, which permits sampling

with a syringe without allowing evaporation of the solution.

An aliquot is then injected into the gas chromatograph

,

using the following modified syringe technique:

Two yl of CS2 are drawn into the syringe and the

plunger drawn back to leave a 2 yl air space. A 5 yl

aliquot of sample is then drawn into the syringe, and

the plunger is drawn back so that the entire aliquot is

12
visible in the barrel of the syringe. This enables the

analyst to read the exact volume of the aliquot and to

verify that no air bubble is present.

The gas chromatographic signal is then converted to yg/

tube by reference to a calibration curve. The calibration

standards are prepared by using micropipets to deliver a known volume of solvent into a 25 ml or 50 ml volumetric

flask. (Micropipets have been reported to be more accurate

than microsyringes (4)). These initial standards are then

diluted in the usual manner to produce a set of calibration

s tandards

Duplicate gas chromatographic determinations usually give

results that agree within 2 percent. For those cases where

the range is greater than 2 percent a third measurement is made.

5 . 0 Suggested Modifications of the Standard Charcoal Tube

The standard charcoal tube provides two sections of

absorber, separated with foam plugs. When both sections are

analyzed, the absence of solvent in the back section should

serve as an indication of efficiency of sample collection.

However, with certain organic solvents the solvent has been

observed to migrate from the front to the rear section during

storage, hence conclusions based on the two measurements are

not possible for these cases [5].

In figure 5.1, a modified charcoal tube is shown which

differs from the standard tube in that the two sections of

charcoal are separated. In the field, this tube is used to

sample atmospheres in the same manner as the standard tube,

but upon completion of the sampling, the tube is broken at the

construction between the two sections and both sections are

sealed with plastic caps. This prevents the apparent

migration of solvent vapors, upon storage, from the front to

the rear portion of the tube. When both portions of this

modified tube are analyzed it is possible to determine

whether breakthrough has occurred in the front section of the

tube

6 . 0 New Gravimetric Procedure for the Analysis of Solvent-iHAir Mixtures

As pointed out earlier in the report, errors were made

in determining the concentrations of some of the tanks used

for filling the charcoal tubes. The error occurs when the

assumption is made that a dilution of a primary tank mixture

to produce a secondary tank mixture will yield a concentration

of solvent vapor which is directly proportional to the dilution factor. The present work has shown that this error can

be as large as 11 percent when, for example, chloroform at

13
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•H

•po

0)u« 3oouo

Id

a; •Hm

•Ho

tnou

(50 •H

14
730 ppm is diluted tenfold. This phase of the work on solventsin-air has concentrated on problems inherent in preparing and

analyzing these mixtures.

In the preparation of these mixtures the solvent is introduced in the evacuated size 1 -A tanks either by distilling the

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

is then pressurized to about 1000 psia. The concentration may

be determined from (1) the weight of the solvent admitted, the

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

pressure of the solvent vapor and the final pressure. In fact,

these two measurements agree within about 2 percent when

solvent -in-air mixtures in the range of 200-1000 ppm are prepared. The problem, then, occurs upon dilution of these tank

mixtures to levels near the TLV range.

The dilution step, say from 600 ppm to 60 ppm may be achieved

by withdrawing 10 percent of the original tank mixture and

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

tank is then diluted with air to a final pressure of 10 times

the pressure of the transferred gas. It is at this step that

anomalies may present themselves -- i.e., the discrepancy

between concentration based on pressure and dilution data and

concentration based on gas chromatographic data. This can be

seen by comparing the figures given below, in which the gas

dilution data are compared with the gas chromatographic data.

PPM PPM Percent Difference

Solvent Gas Method G.C. Method G.C. - Gas— X 100 Gas

Benzene 202 202

31.7 28.8

Ethylene Bichloride 713 713

71.6 66.9 -6.61

Trichloroethylene 1016 1016

98.1 90.9 -7.3%

Chloroform 728 728

73.5 65.3 -11%

Gas chromatographic analysis of gases is performed by

transferring gas at known pressure and volume into the gas chromatograph equipped with a flame ionization detector. Response

15
of the gas chromatograph measured in terms of area of the

resulting peak, is directly proportional to the amount of

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

is one tenth as concentrated as a second gas sample should give

a gas chromatographic response which is one tenth as large as

the second sample. This response is shown to occur, for

example, in tank mixtures of propane and methane. Similarly,

liquid solutions of each of the seven solvents of interest

(benzene, xylene, dioxane, chloroform, carbon tetrachloride,

ethylene dichloride, and t richloroethylene ) give linear gas

chromatographic responses vs. concentration. However, in

the gas mixtures of the seven solvents there are significant

differences between calculated concentration ratios and

ratios obtained by gas chromatography. Although it may be

assumed, perhaps quite generally, that the gas chromatographic

data are correct, a confirmatory procedure is required to prove

this . A direct method, and one which is now being used,

involves collecting and weighing the solvent contained in a known volume of the mixture. In this method, a calibrated

orifice is used to obtain a constant flow, the sampling time

is carefully controlled, and a collection device -- a charcoal

tube -- is carefully weighed before and after the sampling.

The concentration can then be easily calculated.

In this procedure the charcoal tube is first connected

to a sampling orifice and pure air is drawn through until the

tube registers a constant weight after which the solvent-inair mixture is drawn through the tube for a certain length of

time. The weight gain of the tube and the flow through the

tube are used to calculate the concentration of the gas

mixture. The method provides very reproducible results. An

extensive report on this procedure, including results obtained

with six solvents, will be published soon [6].

8. 0 Charcoal Tube SRM's

The investigations carried out under this Interagency Agreement have demonstrated the feasibility of producing SRM's

for the analysis of the organic vapor content of the industrial

atmosphere. By the preparation of reference tubes in large

lots, and the use of the improved techniques for analysis of

the gas mixtures and for verification analysis of the tubes,

certificate uncertainties of no more than ± 3 percent would

appear to then be possible.

For the preparation of the original 1000 charcoal tubes,

a sampling system was used which provided constant flow at

16
each of five orifices -- but not identical flow. In fact, the

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

values were listed for the charcoal tubes at each nominal

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

tubes, at each concentration level, that could be certified

to contain the same amount of solvent, within a more limited

range

Since several thousand tubes are required to be filled

for the SRM's, it was necessary to redesign the sampling manifold and to develop a procedure which would provide matched

orifices in sufficient number to insure that the tubes could

be filled in a reasonable length of time.

The final design, shown in Figure 7.1, has provision for

20 critical orifices. The orifices are mounted on a hollow

brass cylinder, 16.5 cm (6.5 in.) in diameter and 1.9 cm

(0.75 in.) tall. Each critical orifice is a hypodermic needle

(22 gauge) selected so that the range of flow through all

orifices vary by no more than 1.5 percent. The selection of

the needles necessitated the testing of about 200 needles for

flow characteristics. The needles were fitted into Luer-loks

(obtained from hypodermic syringes) and were made vacuum-tight

with the aid of stopcock grease. The Luer-loks were soldered

into the baseplate. This arrangement makes it possible to

remove or replace needles when necessary.

Atop the needles are placed Nupro filters to protect the

needles from contamination by particulates. The charcoal

tubes are attached by rubber tubing to the apparatus. In use,

the cylinder baseplate is connected to a vacuum source.

A sketch of the arrangement for filling the tubes is shown

in Figure 7.2.

The analytical work to verify the concentration levels

of the tubes will be simplified by the fact that matched

orifices will be used in their production. The modified procedure described in Section 4.0 of this report will be used

to analyze tubes statistically selected from the production

lot.

Table 7.1 lists the seven solvents and the ppm levels of

interest. The final charcoal tube SRM's will contain quantities

of solvent equivalent to that which would be collected in a 10

liter sample, at each of the concentration levels.

17
18
19
Table 7.1

Concentration Levels for Organic Solvents

Solvent Concentration (ppm)

Benzene

Xylene

p-Dioxane

Ethylene Bichloride

Chloroform

Trichloroethylene

Carbon Tetrachloride

0.5

1

2

74

10

10

20

2

8

50

30

40

40

80

8

30

300

200

150

150

300

30

0.5

2.5

2.5

5

0.5

8 . 0 Papers to be Submitted for Publication

It is expected that at least two publications will result

from this work. Tentative titles are given:

"A Simple and Precise Critical Orifice Sampling Assembly",

B. C. Cadoff, E. E. Hughes and J. K. Taylor

,; "A Gravimetric Procedure for the Determination of Solventin-Air Concentrations", B. C. Cadoff, B. Greifer,

P. A. Pella and J. K. Taylor

9 . 0 References

[1] Some of these gas mixtures were prepared by Prof.

L. C. Hall, visiting scientist at NBS.

[2] R. E. Kupel and L. D. White, "Report on a Modified

Charcoal Tube", Amer. Ind. Hyg. Assoc. J. 32., 456 (1971).

[3] J. P. Lodge, Jr., J. B. Pate, B. E. Ammons, and

G. A. Swanson, "The Use of Hypodermic Needles as Critical

Orifices in Air Sampling", J. Air Pollution Control

Assoc. 16, 197 (1966)

[4] C. F. Emanuel, "Delivery Precision of Micropipets", Anal.

Chem. 45, 1568 (1973).

[5] Personal Communication from Dr. Alexander Teass.

[6] B. C. Cadoff, B. Greifer, P. A. Pella and J. K. Taylor,

"Development of Contaminant Generation Systems for

Certification of Portable Air Sampling Instruments",

- NBSIR 74-573.

20
Appendix A

Tables A.l to A. 7 list the revised values for seven

sets of charcoal tubes containing organic solvents which

were prepared for NIOSH collaborative tests. These values

replace the preliminary values reported December 1, 1972.

Table A.l

REVISED VALUES - CHARCOAL TUBES

BENZENE

Concentration Level Tube Numbers yg/Tube

(Nominal 0.5 ppm)

II

(Nominal 6 ppm)

III

(Nominal 10 ppm)

IV

(Nominal 18 ppm)

V

(Nominal 50 ppm)

14A 2 OA 15.3

14B 20B 13.7

14C — 20C 14.1

14D — 20D 14 .

14E — 20E 14 .4

7A — 13A 132

7B 13B 118

7C 13C 122

7D 13D 127

7E 13E 125

21A 27A 318

21B 27B 284

21C 27C 293

21D 27D 304

21E 27E 300

28A 34A 548

28B 34B 489

28C 34C 505

28D 34D 525

28E 34E 517

OA 6A 153S

OB 6B 1371

OC 6C 1415

OD 6D 1470

OE 6E 1448

Al
Table A.

REVISED VALUES - CHARCOAL TUBES

XYLENE

Concentration Level Tube Numbers ug/Tube

1 96A 202A 186

I 196B _ 202B 166

(Nominal 5 ppmj 1 9oC 202C 171

196D 202D 178

196E 202E 175

203A 209A 1911

II 203B 209B 1706

(Nominal 60 ppm) 203C 209C 1761

203D 209D 1830

203E 209E 1802

217A 223A 4246

III 217B 223B 3791

(Nominal 100 ppm) 217C 223C 3913

217D 223D 4066

217E 223E 4003

210A 216A 5535

IV 210B 216B 4941

(Nominal 150 ppm) 210C 216C 5101

210D 216D 5300

210E 216E 5218

A2
Table A.

REVISED VALUES - CHARCOAL TUBES

p-DIOXANE

Concentration Level Tube Numbers yg/Tube

18 9A 195A 141

I 189B 195B 126

(Nominal 5 ppm) 18 yc 195C 130

189D 195D 135

189E 195E 133

126A 132A 1638

II 126B 132B 1463

(Nominal 60 ppm) 126C 132C 1510

126D 132D 1569

126E 132E 1545

161A 167A 2978

III 161B 167B 2659

(Nominal 100 ppm) 161C 167C 2745

161D 167D 2852

161E 167E 2808

147A 153A 4378

IV 147B 153B 3909

(Nominal 150 ppm) 147C 153C 4035

147D 153D 4192

147E 153E 4128

A3
Table A.

REVISED VALUES - CHARCOAL TUBES

ETHYLENE BICHLORIDE

Concentration Level Tube Numbers yg/Tube

1 / 5A 181A 92.6

I 175B — 181B 82.6

(Nominal 2.5 ppm) 175C — 181C 85.3

1 / bD — 181D 88.6

1 7 bh 181E 87.3

1 33A 139A 1039

II 133B — 139B 928

(Nominal 30 ppm) 133C — 139C 958

133D — 139D 995

133E — 139E 980

1 8 2A 188A 1958

III 182B 188B 1749

(Nominal 50 ppm) 182C 188C 1805

182D 188D 1875

182E 188E 1847

154A 160A 3280

IV 154B 160B 2928

(Nominal 90 ppm) 154C 160C 3023

154D 160D 3141

154E 160E 3093

140A 146A 7213

V 140B 146B 6440

(Nominal 200 ppm 140C 146C 6648

140D 146D 6907

140E 146D 6801

A4
Table A.

REVISED VALUES - CHARCOAL TUBES

CHLOROFORM

Concentration Level Tube Numbers yg/ Tube

168A 174A 106

I 168B _ 174B 94

(Nominal 2.5 ppm) 168C 174C 97

168D 174D 102

168E 174E 100

105A lllA 1265

II 105B lllB 1130

(Nominal 30 ppm) 105C lllC 1166

105D HID 1212

105E HIE 1193

112A 118A 2027

III 112B 118B 1810

(Nominal 50 ppm) 112C 118C 1868

112D 118D 1941

112E 118E 1911

119A 125A 3992

IV 119B 125B 3564

(Nominal 90 ppm) 119C 125C 3679

119D 125D 3823

119E 125E 3764

A5
Table A.

REVISED VALUES - CHARCOAL TUBES

TRICHLOROETHYLENE

Concentration Level Tube Numbers yg/Tube

4 2A 48A 244

I 42B — 48B 218

(Nominal 5 ppm) 42C 48C 225

42D — 48D 234

42E 48E 230

Ilk 83A 3062

II 83B 2734

(Nominal 60 ppm) nc 83C 2822

77D _ 83D 2932

77E 83E 2887

35A 41A 5126

III 35B 41B 4576

(Nominal 100 ppm) 35C 41C 4724

35D 41D 4908

35E 41E 4833

91A 97A 9435

iv 91B 97B 8424

(Nominal 180 ppm) 91C 97C 8696

91D 97D 9035

91E 97E 8896

84A 90A 15369

V 84B 90B 13722

(Nominal 300 ppm) 84C 90C 14165

84D 90D 14717

84E 90E 14491

A6
Table A.

REVISED VALUES - CHARCOAL TUBES

CARBON TETRACHLORIDE

Concentration Level Tube Numbers yg/Tube

63A - 69A 38

I 63B - 69B 34

(Nominal 0.5 ppm) 63C - 69C 35

63D - 69D 36

63E - 69E 35

7 OA - 76A 308

II 70B - 76B 275

(Nominal 6 ppm) 70C - 76C 284

70D - 76D 295

70E - 76E 291

49A - 55A 671

III 49B - 55B 599

(Nominal 10 ppm) 49C - 55C 618

49D - 55D 642

49E - 55E 632

56A - 62A 1102

IV 56B - 62B 984

(Nominal 18 ppm) 56C - 62C 1016

56D - 62D 1056

56E - 62E 1039

98A -104A 11635

V 98B -104B 10387

(Nominal 200 ppm) 98C -104C 10723

98D -104D 11141

98E -104E 10970

A7

Q

Appendix B

Consensus Values

The initial lot of charcoal tubes described in the

report was analyzed by a number of collaborating laboratories.

The data reported by them has kindly been made available to

us by Dr. Alexander Teas s of NIOSH. For convenience of

intercompar ison , the values reported were first normalized

to what would have been expected if the tube used had been

prepared at the "C" orifice, by multiplying by the ratio of

the flow rates of the respective orifices. Tables B.l to B.7

summarize the reported values after normalization. The data,

so normalized, were used to arrive at consensus values for the

charcoal tubes.

If all measurement errors are random, the average of all

values reported (consensus value) should be in good agreement

with the "true" value. A comparison of the average values

with the NBS values indicates large discrepancies, especially

for the lowest concentration levels.

A cursory inspection of the data presented in Tables B.l

to B.7 will identify a few values which are obviously outliers

and hence unduly influence the consensus values. While no

statistical rejection criteria were employed, the values

considered to be grossly in error were encircled, as indicated

in the tables, and these were eliminated before obtaining the

new average or consensus values given in each table, and

identified as "Avg (Adj.)". It is obvious that these values

are in much better agreement with the NBS values, and lend

additional confidence to their validity.

Bl
TABLE B.l Benzene

LAB 2 CL

20.

I 00

CL II

142.20

CL III

331.30

CL IV

488.30

CL V

1520.00

LAB 3 C65. 00^ C34 5.4 03 rB19.40J a269 . 2(t> Cr089, 70^

LAB 4A 14. 60 124.00 302.40 464. 50 1459.10

LAB 4B 13. 10 117.00 297.70 510. 10 1393. 20

LAB 5 17. 30 130. 50 307. 00 482.50 1467.40

LAB 6 12. 80 132.80 274. 50 474. 50 ao6o. oil)

LAB 7 17. 10 125. 90 312.80 469. 20 1491.80

LAB 8 15. 60 124.90 298. 60 450.70 1446.60

LAB 9 21. 20 110.80 292.30 451 .40 1616. 10

LAB 10 15. 00 129.00 308. 00 519. 10 1474. 00

LAB 11 17. 60 128.00 338. 00 541.80 1594.40

LAB 12 14. 30 115.20 276.60 447. 30 1315.40

LAB 13 14. 40 127.90 302.60 496.10 1459.30

Avg . (All) 19. 85 142.58 343.17 543.44 1722. 08

Avg . (Adj) 16. 08 125.68 303.48 482. 96 1353.11

NBS Values 14. 10 122.00 293. 00 505. 00 1415. 00

TABLE B.2 Xylene

CL I CL II CL III CL IV

LAB 1 196. 30 1796. 90 4187. 00 5014 .40

LAB 2 197. 30 1978. 00 4513. 70 5938 .70

LAB 3 128. 00 1856. 40 4420. 60 5633 . 50

LAB 4A 200. 20 2135. 50 4767 . 70 6161 . 00

LAB 4B 190. 90 1749. 80 4038. 10 5131 . 90

LAB 5 186. 40 1789. 30 4007. 80 5183 .70

LAB 6 253. 50 1655. 40 4220. 00 5611 .20

LAB 7 142. 70 1645. 80 3840. 20 5249 . 30

LAB 8 174. 40 1789. 20 3940. 30 5018 . 60

LAB 9 G62. 50"^ 1914. 00 3536. 00 4827 .70

LAB 10 143. 00 1767 . 40 3986. 50 5295 .80

LAB 12 197. 20 1893. 60 4098. 80 5451 .20

Avg . (All) 214. 37 1830. 94 4129. 73 5376 .42

Avg . (Adj) 182. 72 1830. 94 4129. 73 5376 .42

NBS Values 171. 00 1761. 00 3913. 00 5101 . 00

B2
TABLE B.3 p-Dioxane

CL I CL II CL III CL IV

LAB 2 135. 30 1570 . 50 2951 . 50 4250 . 30

LAB 3 138. 60 1546 .70 2676 .10 4063 . 00

LAB 4A 131

80 1510 . 00 2660 .80 4083 . 00

LAB 4B 141. 40 1525 .30 2840 . 00 4031 .00

LAB 5 142. 40 1493 .60 2705 .60 4035 .00

LAB 8 145. 70 1444 . 00 2763 . 00 3995 . 20

LAB 9 r258 . 8 0) 1585 . 60 2826 .20 4193 .80

LAB 10 1^2. 00 1664 .70 3019 .60 4382 .20

LAB 12 141. 90 1621 .40 2887 .20 4245 .20

Avg . (All) 154. 21 1551 .31 2814 .44 4142 . 08

Avg . (Adj) 141. 14 1551 .31 2814 .44 4142 . 08

NBS Values 130. 00 1510 . 00 2745 . 00 4035 . 00

TABLE B.4 Ethylene Dichloride

LAB 2 LAB 3

LAB 4A

LAB 5 LAB 6

LAB 7 LAB 9

LAB 10

LAB 12

Avg. (All)

Avg. (Adj)

NBS Values

CL I 94.80

93.60

112. 50

87.30

101. LQ, 44. Oj

.55.01.

89,00

85. 70

107. 00

94.86

85.30

CL II

975. 20

1009. 70

1042.40

950.90

1193. 50

1045. 90

1037. 70

985. 00

978.20

1024.28

1024. 28

958. 00

CL III

1759.40

2205. 00

1927.00

1712. 90

1871 . 00

1920.20

1795.70

1780.10

1984. 54

1871.41

1805. 00

CL

2964

IV

.20

C3595 . 803

3140 80

70

(3673792)

3066

3050

3018

3187

3059

3023

00

.60

. 00

.40

.60

.81

. 00

CL V

6430.40

7173.20

6836.80

62^9.8 0

(239032)

7050.00

7252.30

6483. 90

6441. 70

6928. 68

6746. 01

6648. 00

B3
TABLE B.5 Chloroform

CL I CL 1

XL III CL IV

LAB 1 88 . 60 1187.70 a 2 8 9 . 4 0 J

^ III ^ (254 6 . 5 0J

LAB 2 15500 1270.90 1941 . 90 3793.90

LAB 3 (261 . 90) r2295 .iaJ (34 80 . 5 07 C6864. 30^

LAB 4A 9580 1111.40 1736. 80 3339 . 20

LAB 4B 95

60 1200.40 1830.90 3579.00

LAB 5 (670. A668.10J ri3i0.50J> 4138. 20

LAB 6 117. 0(5 T^OO.O'O 1960.80 3271 . 90

LAB 7 101. 70 1210. 00 1935. 50 3792.80

LAB 8 103. 00 1228.10 1931.90 3605. 00

LAB 9 57. 80 1222.30 1677.40 3890. 60

LAB 10 94. 00 1215.70 1864. 00 3563.10

LAB 12 107. 30 1220.20 1900.60 3668. 50

Avg . (All) 162. 32 1335.83 1989. 18 3837. 75

Avg . (Adj) 101. 58 1206.67 1864.42 3664 . 22

NBS Values 97. 80 1166.00 1868.00 3679. 00

TABLE B.6 Tr ichloroethylene

LAB 2 LAB 3

LAB 4A

LAB 4B

LAB 5 LAB 6

LAB 7 LAB 8

LAB 9

LAB 10

LAB 12

Avg. (All)

Avg. (Adj)

NBS Values

CL I CL II CL III CL IV CL V

281. 10 2687.80 4594. 70 8664 . 00 14736. 50

206 . 90 (1935 . 50^ 3420.60 ao5oo. Qu;

257 . 10 2916. 30 4791. 70 8839 .70 14244. 00

262 . 10 2872. 90 4770.90 8813 .20 14122. 00

r979. 3Qj 03655 . 40^) 5692.80 9052 . 30 14626. 50

260. 80 5251. i'o 10360 . 00 15789. 00

248 . 00 2900.00 4829.70 8771 . 90 14300. 00

247 . 00 2883. 70 4656.40 8617 .50 14151. 00

C867. 20j) 2580. 00 4296. 20 7280 .30 14994. 00

245. 00 2885.00 4769.00 8475 .50 13817. 00

256. 00 2982.60 4867.80 8873 .20 15270. 00

373. 68 2870.94 4791.65 8461 . 69 14231. 82

251. 56 2887. 71 4668.98 8774 . 76 14605. 00

225 . 00 2822.00 4724. 00 8696 . 00 14165. 00

B4
TABLE B.7 Carbon Tetrachloride

CL I CL II CL Ill CL IV CL V

LAB 2 47. 30 281. 60 568. 60 943. 30 10972. 00

LAB 3 59.30 336. 70 694. 90 1128. 60 11751. 50

LAB 4A 32.70 289. 40 608. 90 1024 . 80 11136. 00

LAB 4B 54.80 263. 00 521. 00 961. 50 10978. 00

LAB 5 239. 40 550. 30 884 . 90 10370. 50

LAB 7 329. 00 649. 80 1016. 60 11550. 00

LAB 8 32.7(r 292. 30 608. 30 994. 80 11040. 00

LAB 9 18.30 211. 70 461. 90 710. 00 8570. 00

LAB 10 35. 00 295 . 20 600. 20 981. 40 10936. 00

LAB 12 378 . 80 778 . 80 1183. 50 11034. 00

LAB 13 44.00 311. 50 603. 70 962 . 50 11730. 00

(All) 54.97 293. 51 604. 22 981. 08 10915. 27

(Adj) 38. 01 293. 51 604. 22 981. 08 10915. 27

Values 35.10 284. 00 618. 00 1016. 00 10723. 00

B5
U S. DF: PT. OF COMM.

1 B'rLlOGRAPHIC DATA

1 SHEET

1. I'UHI.K A 1 ION OR Rl l'OK 1 NO.

NBSIR 74-530

2. Gov't Acce.s.sioii No.

3. R< c ipieni 's Acce.'i.sion No.

4. 1 1 1 Li: AM) siMvi 1 ri.i-; Preparation of Charcoal Sampling Tubes Containing

Known Quantities of Adsorbed Solvents

5. Publication Date July 1974

6. i^crl'orming Organization Code

7. AL: 1 IIOR(S)

B.C. Cadoff, E.E. Hughes, R. Alvarez, J.K. Taylor

8. Performing Organ. Report No.

9. pi:ki-okminc; organization name and address

national bureau of standards

- department of commerce

washington, d.c. 20234

10. Proiect/Ta.sk/Vtork Unit No. 3104150

11. Contract /Grant No.

1 2. Sponsoring C)rg .in i/.at ion Name and Complete Addres.s (Street, City, State, ZIP)

National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

13. Type oi Report & F^eriod Covered

Final Report

14. Sponsoring Agency Code

IS. SLPPLEMFfNTARY NOTES

16. AKSl RACn' (A 200-word or less factual summary of most si^idcant information. If document includes a significant

bibliography or literature survey, mention it here.)

The method in widespread use for the determination of the concentration

of organic solvents in the work atmosphere consists in collection of the

solvent by adsorption on activated charcoal followed by desorption with

carbon disulfide and measurement by gas chromatography. This report describes techniques developed to produce reference standards for this

determination and modifications in the analytical procedure to improve

its precision and accuracy.

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

)

Activated carbon; air sampling; gas standards; industrial hygiene

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