xvEPA
United States
Environmental Protection
Agency
Environmental Monitoring and Support EPA 600 4-78-057
Laboratory September 1978
Research Triangle Park NC 27711
Research and Development
The Use of Tedlar
Bags to Contain
Gaseous Benzene
Samples at
Source-Level
Concentrations
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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THE USE OF TEDLAR BAGS TO CONTAIN GASEOUS BENZENE SAMPLES
AT SOURCE-LEVEL CONCENTRATIONS
by
Joseph E. Knoll, Wade H. Penny, and M. Rodney Midgett
Quality Assurance Branch
Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and
Support Laboratory, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina 27711, and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or recommenda-
tion for use.
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ABSTRACT
Tedlar bags have been evaluated as containers for gaseous benzene
samples at source-level concentrations. Sample stability over time periods
typically required in field work, "memory" effects, decontamination
procedures, and the temperature range over which the bags can be success-
fully used were subjects of this study. Benzene samples remained essentially
unchanged for up to 17 days. Cooling to -40° C or heating to 70° C did not
produce concentration changes. Above 105° C, decomposition of the bag seals
was observed. No evidence of permeation loss at room temperature was observed,
and absorptive loss could be observed only upon prolonged contact. Flushing
the bags with nitrogen was sufficient to remove all traces of previous samples.
Calibration mixtures were prepared in Tedlar bags by injecting measured
quantities of liquid benzene while metering-in nitrogen gas. These bag
standards were used to perform calibrations for the G.C. measurement of
benzene-containing cylinders. Corroboration of these results by three
other laboratories demonstrated that such bag samples are useful as
calibration standards.
ii
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CONTENTS ./,
Abstract 11
Figures . ' 1v
Tables v
Acknowledgments vi
1. Introduction 1
2. Conclusions 3
3. Experimental 4
4. Results and Discussion 6
References 21
Appendix A 22
m
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FIGURES
Number Page
1 Double Tedlar bag assembly 14
iv
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TABLES
Number Page
1 Freshly Filled Tedlar Bag Results as a Percent of
the Master Cylinder Concentration 8
2 The Effect of Temperature on Benzene Concentration of
Gas Mixtures Stored in Tedlar Bags 10
3 Variation of the Benzene Concentration of Gas Mixtures
Stored in Tedlar Bags at Ambient Temperatures 13
4 Benzene Concentration Changes in Double Tedlar Bag 16
5 Benzene Concentration Values of Aluminum Cylinders as
Determined by Various Corroborators 17
6 Interlaboratory Comparison of Benzene Concentration of
Various Analyzed Components 18
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ACKNOWLEDGMENTS
The authors acknowledge with thanks the help of Mr. William Lonneman
of this Agency and Mr. Robert Denyszyn of the Research Triangle Institute
for performing the corroborative analyses reported herein. They also
wish to thank Mr. Lonneman for permission to use his bag sealing machine
and Miss Susan Setzer for performing several analyses.
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SECTION 1
INTRODUCTION
A frequent problem in gas analysis involves the collection of a
representative and stable gas sample. Such problems are particularly
important in environmental studies since pollutants are, by their nature,
reactive materials that tend to undergo transformations with time. One
method that has frequently been employed utilizes nonrigid plastic con-
tainers (1). Many studies have been made of the ability of such bags to
preserve gas samples free from contamination and change. Schuette (2)
has reviewed much of the earlier work in this area, and Seila, et al. (3)
have discussed more recent studies and, in particular, the plastic Tedlar.
This latter investigation studies the effects of simulated sunlight and
radiation on the stability of hydrocarbon samples in Tedlar bags, in which
they observed a series of contamination peaks released by the radiation and
suggested that the origin of these peaks was manufacturing residues. Since
most investigators work in this area, the study was concerned with concen-
trations at ambient air levels.
On the other hand, plastic bags have also been used for stationary
source sampling. In this field, samples usually contain much higher con-
centrations and the major problems encountered result from sample cross-
contamination or "memory" effects and from the extremes of temperatures that
are encountered. Tedlar bags have been successfully employed in the source
sampling method for vinyl chloride (4). Also, Schuetzle, et al. (5) have
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compared various plastic materials and found Tedlar to be superior. This
material is a polyvinylfluoride that is relatively inert to many other
substances and that can be used to fabricate large containers. Flexibility
of container size is an important advantage in source emission analysis
where it may be necessary to collect gas over an extended period of time in
order to obtain a representative sample.
Recently, a method for the analysis of benzene has been proposed
that uses Tedlar bags for sample collection (see Appendix A). This method
has been developed in the Test Support Section of the Emission Measurement
Branch, ESED, EPA, and has been used to determine benzene concentrations in
the effluent streams from chemical process plants (6). In view of the
developing agency committments to control emissions of certain volatile
organic compounds, the present investigation was undertaken to study the
stability of benzene in Tedlar bags at source level concentrations. Specifi-
cally, it deals with time studies of the benzene concentrations in Tedlar
bags that were held at room temperature and that were heated and cooled.
Permeation and "memory" effects were investigated, and some information was
also obtained on the utility of bag samples as standards. This work was
carried out in the Source Section of the Quality Assurance Branch, EMSL, EPA,
which has a program to evaluate and standardize source emission test
methodology.
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SECTION 2
CONCLUSIONS
This study of Tedlar bags containing benzene/nitrogen gas mixtures that
were subjected to varying conditions yielded the following results:
When Tedlar bags were held at room temperature, the benzene concen-
tration remained within 94% of its initial value after 17 days.
When Tedlar bags were cooled to -40° C for one hour, no concentration
change could be detected.
When Tedlar bags were heated to 70° C for one hour, no concentration
change could be detected. When they were heated to temperatures above
105° C, a decrease of 6-20% was observed, along with decomposition of the
adapter and bag seals. The observed loss appeared to result from leakage.
There was no evidence of permeation loss at room temperature.
Flushing bags three times with nitrogen was sufficient to remove at least
99.9% of the previous samples, except when bags were held in contact with
benzene for prolonged periods of time. Then, desorption of benzene was
evident only after the bags were heated to 60° C for one hour.
Ten-liter bags had the same characteristics as 100-liter bags.
Tedlar bags are useful for preparing calibration gas mixtures from
measured quantities of liquid benzene and nitrogen.
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SECTION 3
EXPERIMENTAL
Tedlar bags were fabricated from 2-mil plastic sheets. The edges were
sealed with a Vertrod Thermal Impulse Heat Sealing Machine (Model 48 EPS 1/4
WC). Connections to the bag were made using an 0-Seal Straight Thread Adapt-
er having a 1/4 in. o.d. tube and a 7/16-20 thread (Swagelok 401-A-OR), which
was inserted through a 2 in. square piece of VisQueen polyethylene tape fixed
to the outside surface of the bag. The adapter was held in place with an
0.058 in. Teflon washer (1/2 i.d. by 1 in. o.d.) and a 7/16-20 nut. A
7115G4B Hoke ball valve was connected to the adapter.
A 65 ppm benzene in nitrogen reference mixture in an aluminum cylinder
was obtained from Airco, Inc. Two other such cylinders of benzene gas were
obtained from Scott Research Laboratories and were standardized at the Re-
search Triangle Institute. In one part of this study, benzene-nitrogen
mixtures in Tedlar bags were prepared by injecting in liquid benzene while
filling the bags with nitrogen. The nitrogen was measured using a No. 802
Singer dry gas meter; a No. 801, 10 microliter Hamilton syringe was used to
measure the benzene. In all other instances, Tedlar bags were filled directly
from the reference cylinder.
Benzene concentrations were determined using a Tracer Model 222 gas
chromatograph equipped with dual flame ionization detectors (No. 12016) and a
1.0 ml sampling loop. The output was recorded using an Autolab Systems IV
computing integrator. The chromatographic column consisted of an 8 ft. by
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1/8 in. stainless steel helix packed with 10% TCEP (1,2,3 tris-(2-cyanoethoxy)
propane) on 80/100 mesh Chromasorb P AW. The following operating conditions
were employed: inlet temp., 105° C; column, 75° C; detector, 165° C; carrier
gas, liquid air nitrogen at 20 ml/min. Under these conditions, benzene eluted
with a Kovats retention index of 1066. Only a single peak could be observed.
Tedlar bags were sampled by drawing the gas through the chromatographic
sampling loop using an Bell and Gossett LV 1/12 vacuum pump. The reference
gas was forced through the sampling system under its own pressure and was used
to normalize the gas chromatograph results.
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SECTION 4
RESULTS AND DISCUSSION
STABILITY OF BENZENE VAPOR WHEN STORED IN TEDLAR BAGS
In this phase of the investigation, a study was made of the stability of
benzene vapors that were contained in Tedlar bags for differing lengths of
time and under a variety of temperature conditions. Although much information
was available on the use of Tedlar bags in ambient air studies (3) and some
also had been obtained that related to stationary source sampling (5), much
data was missing that dealt with specific source problems. These problems not
only included questions of sample stability over time periods typically required
in field work, but also included "memory" effects, decontamination procedures
and the temperatup^^nge over which such bags can be successfully used. While
\
the conditions to which these bags were subjected are unlikely to occur in
laboratory studies, our findings do hold important ramifications for those
engaged in field work where extreme variations in temperature and concentration
do actually occur.
To initiate this study several tests were made to determine whether con-
tamination or "memory" effects,result when benzene vapor interacts with Tedlar.
Such effects could take place if benzene vapor is absorbed into the plastic
material and slowly released thereafter. This would be a problem if the bag
is refilled with another sample at a considerably lower benzene concen-
tration. Thus, this part of the study was carried out not only to assure that
"memory" effects did not cause errors in our results but also, because Tedlar
bags would be expected to be reused many times during field studies, to
6
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determine whether intercontamination of samples takes place. To determine
this, new Tedlar bags were filled with 65 ppm benzene/nitrogen gas mixture,
then the bag was flushed three times by repeatedly filling with nitrogen
and evacuating. The bag was filled with nitrogen and, when analyzed, benzene
could no longer be detected. (The detection limit of the GC system was less
than 0.1 ppm.) The bag was left to stand at room temperature for several days,
and, when reanalyzed, no detectable benzene could be observed. The experiment
was repeated using a Tedlar bag that had contained the benzene gas mixture at
room temperature for several days, one in which the bag containing the benzene
gas mixture was heated to 65° C for one hour, and one that was cooled to -40° C
for one hour. With only one exception, the flushing procedure described above
was adequate to remove all detectable traces of benzene from the container.
As stated above, the memory effect was actually observed in one instance.
A Tedlar bag that had contained 65 ppm benzene/nitrogen mixture for 17 days
was evacuated, flushed, filled with nitrogen, and measured. At first no
benzene could be detected in the bag's contents, but, when the bag was heated
to 60° C for one hour, a benzene concentration of 1.7 ppm was measured.
Apparently, benzene is slowly absorbed into the Tedlar plastic in amounts that
can become appreciable after an extended period of time. Therefore, these
results indicate that benzene-containing gas samples should not be left in
contact with the Tedlar plastic for any longer than necessary, if "memory"
effects are to be completely avoided.
In. the stability study that is to be described below, the concentration
of benzene in gas within Tedlar bags was determined by comparing the bags
with a master cylinder from which the bags had been filled. Each time the
bags were measured, the cylinder was run and used to calibrate the chromatograph.
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The results in Table I show that this technique produced nearly identical
values. Later, measurements made with a Hewlett-Packard Model 5830 GC con-
firmed these findings.
The effect of temperature on bag stability was carried out as follows.
A bag was filled with the benzene/nitrogen mixture and measured. It was
then subjected to the temperature in question for one hour, after which
it was allowed to come to ambient temperature and was measured. The bag was
evacuated, refilled with the benzene/nitrogen mixture, and remeasured. It
was subjected to the temperature under consideration for an additional hour,
after which it was brought to ambient conditions and measured again. The GC
instrument was recalibrated using the master cylinder three times during each
such run (at the initial fill, at the end of the first conditioning, and at
the end of the second conditioning) to insure that the gas chromatograph was
giving stable responses. The results (Table 2) indicate no appreciable change
in benzene concentration over the range of temperatures studied, except that
some losses appear just above 110° C.
In order to establish an upper limit to the temperature conditions over
which Tedlar bags can be accurately employed in sampling procedures, bags
filled with 65 ppm benzene in nitrogen were heated for one hour at either
110° or 115° C. At this latter temperature, the Tedlar material softened,
became pliable, and the valve sealing tape melted, causing the valve fittings
to loosen and leak. These decompositions at 115° C made it impossible to
ascertain whether the drop in benzene concentration shown in Table 2 was the
result of vapor seepage through the valve and edge seals, or due to permeation
through the Tedlar material. As the results in Table 2 indicate, it is
4-~ „,,„„— u-_-. ..-_„.._ _«_4--j 1 .• _ T-.J-I-.- i o-_ - j .
i,w CS\plfOC L/CI I4.CI 1C VUpUlO WWII l»d IIICU III ICUIQI Ud^3 UU d LCIII^JC f'd UU ft
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Table 1. FRESHLY FILLED TEDLAR BAG RESULTS AS A. PERCENT OF THE MASTER
CYLINDER CONCENTRATION.
Run
1*
2*
3t
Number of
measurements
2
3
4
Percent
96.8
98.3
101.2
*Samples introduced using syringe.
•^Measurement made using Hewlett-Packard Model 5830.
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Table 2. THE EFFECT OF TEMPERATURE ON BENZENE CONCENTRATION OF GAS MIXTURES
STORED IN TEDLAR BAGS.
Benzene concentration in ppm
Run
1
2
3
4
5
6
7
Temp.
(C°)
-41
70
80
no
no
no
115
Initial
f i 1 1 i ng
65
65
65
65
65
65
65
After
first hour
64
64
63
61
61
60
52
After After
refilling second hour
67 66
65 65
64 64
66 60
—
__
—
-- Indicates that bags were not refilled.
10
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approaching 110° C for short durations without incurring significant loss of
sample, provided that the valve and bag seals remain intact. Above 110° C,
however, the bags deteriorate rapidly and exhibit sample loss, so use above
that temperature should be avoided.
It is important to emphasize here that the quality of the valve fittings
and bag construction is essential in obtaining sample stability. Care must
be taken that all three edges of the bag are heat-sealed withoi't gaps or
wrinkles. In some of our runs in the 1100-115° C range, double-sealed bags
with reinforced valve ports were substituted for the typical single-sealed
bags. This was done in an attempt to minimize sample loss at the higher
temperatures. Slight improvements were noted.
During the study cited above, we observed that heating Tedlar bags
produced several new peaks on the chromatograms. Such effects have been noted
by other investigators (3). To determine whether heating caused the release
of substances that would interfere with benzene measurements, a new Tedlar bag
was filled with nitrogen and heated to 90° C for one hour. A chromatogram of
the contents produced several peaks, but none of them fell within the integration
range of benzene. If any substances were emitted in that range, they were
below the 0.1-ppm detection sensitivity of our instrument. Thus, when making
measurements of benzene at source-level concentrations, heating Tedlar bags to
90° C for one hour does not cause the Tedlar to release substances that inter-
fere in the measurement of benzene, provided that the chromatographic column
and parameters used in this study are employed.
The studies cited above all dealt with stability and "memory" effects
that were observed over time periods of a few hours. We have also investigated
the stability of benzene/nitrogen mixtures in Tedlar bags for longer periods
11
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of time, for up to 408 hours. This work was done at ambient temperatures,
and the results are listed in Table 3. The measurements show that very little
change took place over the time periods that elapsed. They indicate that
Tedlar bags will be useful for the storage and transport of benzene-containing
samples.
Although these studies showed that benzene/nitrogen mixtures remain
relatively stable in Tedlar bags, all of the measurements were concerned with
demonstrating benzene loss by observing a concentration change. This is a
relatively insensitive method that would not have enabled us to detect small
changes if they had taken place. Further, it would not have given any in-
formation about the mechanism of such losses.
12
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Table 3. VARIATION OF THE BENZENE CONCENTRATION OF GAS MIXTURES
STORED IN TEDLAR BAGS AT AMBIENT TEMPERATURES.
Benzene cone, (ppm)
Elapsed time Initial Final
Bag No. (hours) value value
1 48 65 63
2 336 65 61
3 48 65 65
4 48 65 63
5 192 65 65
5 336 65 64
5 408 65 61
13
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Therefore, in an attempt to determine whether small amounts of benzene were
passing through the plastic, we constructed a Tedlar bag system having
one bag within another (Figure 1). The inner bag was filled with the 65
ppm benzene/nitrogen gas mixture, and the outer bag was filled with an
equivalent amount of pure nitrogen. Thus, it would have been possible to
detect a much smaller loss of benzene from the inner bag, since our GC system
had a sensitivity of at least 0.1 ppm. However, as the results in Table 4
show, no benzene could be detected in the outer bag after 48 hours. Of
necessity, loss of benzene as a result of permeation through the plastic would
have been less than 0.1% per day.
USE OF TEDLAR BAGS TO PREPARE BENZENE CALIBRATION GAS MIXTURES
For this study, benzene/nitrogen mixtures were prepared in Tedlar bags
and employed as calibration standards. In one experiment, such bag standards
were used to calibrate our gas chromatograph while measuring the concentration
of benzene in aluminum cylinders. These results were checked by comparing
them with values obtained by three other laboratories. The cylinders in
question were prepared and measured by Scott Environmental Technology, Plum-
steadville, Pa. They were subsequently measured again at the Research Triangle
Institute (RTI), Research Triangle Park, N.C. and at the Environmental Sciences
Research Laboratory (ESRL) at this center.
The values reported by these three laboratories, along with our results
(QAB values), are listed in Table 5. They are consistent with respect to each
other and show no trend over the time period that elapsed. Although the
laboratories cited employed different methods of calibration and different
chromatographic columns, those details have not been included here since it
is not the purpose of this study to compare calibration and GC procedures.
14
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Figure 1. Double Tedlar bag assembly.
15
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Table 4. BENZENE CONCENTRATION CHANGES IN DOUBLE TEDLAR BAG.
Bag Benzene concentration in ppm
component Initial cone. Final cone*
Inner bag 65 63
Outer bag 0 <0.1
*Elapsed time, 48 hours
16
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Table 5. BENZENE CONCENTRATION VALUES OF ALUMINUM CYLINDERS AS
DETERMINED BY VARIOUS CORROBORATORS.
Benzene concentration (ppm)
Corroborator
Scott
RTI
QAB*
RTI
ESRL
Date of
analysis
7/1/77
7/27/77
11/23/77
12/9/77
12/12/77
Cyl i nder
BAL-107
65
79
76
74
80
Cylinder
BAL-111
324
374
365
336
355
*Tedlar bag standards used for calibration
17
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We feel that the consistency among the values obtained by the three labora-
tories is sufficient evidence for the accuracy of their results. QAB standards
were prepared by injecting liquid benzene into Tedlar bags with a calibrated
syringe while metering-in dry nitrogen gas. The quantity of nitrogen was
measured using a dry gas meter that had been calibrated with a spirometer.
Utilizing this procedure, two calibration standards were prepared that had
benzene concentrations of 31.8 and 133 ppm, respectively. However, only one
of the two cylinders under analysis fell within this calibration range; the
other one fell beyond it. Since GC system response was linear over the range
of the calibration standards employed, it was possible to carry out a linear
extrapolation to determine the value of the second cylinder. Measurements
made on both the high and the low concentration cylinders yielded results that
fell within the range of values obtained by the three laboratories cited above.
Additional tests were carried out using benzene in Tedlar bags as
standards. A series of four bags were prepared having benzene concentrations
of 33.5, 60, 108, and 135 ppm, respecti; y. The 33.5 and the 135 ppm bags
r f
were employed as standards and were u^/ in the analysis of the other two.
These latter bags were then measured at the Research Triangle Institute and
remeasured in our laboratory. All operations, including bag preparation
and measurements, were carried out on the same day. The results are listed
in Table 6. In another experiment, Tedlar bag standards were used for the
analysis of a cylinder containing approximately 9.5 ppm benzene in nitrogen.
Since the bag calibration standards were 31.8 and 133 ppm, it was necessary
to assume system linearity below the calibration range. These results are
also listed in Table 6.
18
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Table 6. INTERLABORATORY COMPARISON OF BENZENE CONCENTRATION VALUES
OF VARIOUS ANALYZED COMPONENTS.
Analyzed
component
Tedlar bag
Tedlar bag
Cylinder, RB
Benzene concentration
Prepared RTI
value value
60 62
108 109
9.5 10.1
in ppm
ESRL
value
—
--
9.5
QAB
value
57
105
9.7
19
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Tables 5 and 6 show that, for each component analyzed, measurements
made using Tedlar bag calibration standards fell within the range of values
obtained by the corroborating laboratories. The data is therefore evidence
that the calibrations were accurate and that useful standards may be prepared
in Tedlar bags. It should also be noted that such systems are not difficult
to prepare and are reasonably stable, as was shown elsewhere in this report.
Thus, when used in the source level concentration range being considered
here, benzene/nitrogen mixtures prepared in Tedlar bags make useful calib-
ration standards for gas chromatographic measurements.
In several of the instances cited above, measurements have been made
outside the range of the calibration standards that were employed. GC/FID
systems are linear in a very large range of sample sizes, and it is common
practice to assume that linearity persists below an established calibration
range over which linearity has been demonstrated. On the other hand, it is
risky to employ linear extrapolations in making measurements at sample
sizes much greater than the highest calibration standard employed. It is
not the purpose of this study to advocate that practice. Such results have
been included here only because they add additional weight to our findings.
20
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REFERENCES
1. Baker, R. A., and R. C. Doerr. Methods of Sampling and Storage of Air
Containing Vapors and Gases. Int. J. Air Poll., 2:142-158, 1959.
2. Schuette, F. J. Plastic Bags for the Collection of Gas Samples. Atmos.
Environ., 1:515-519, 1967.
3. Seila, R. L., W. A. Lonneman, and S. A. Meeks. Evaluation of Polyvinyl
Fluoride as a Container Material for Air Pollution Samples. J. Environ.
Sci., A-1K121-130), 1976.
4. Scheil, G. W. Standardization of Stationary Source Method for Vinyl
Chloride. Environmental Monitoring Series EPA-600/4-77-026, U.S. En-
vironmental Protection Agency, Research Triangle Park, North Carolina,
May 1977.
5. , Schuetzle, D., T. J. Prater, and S. R. Ruddell. Sampling and Analysis
of Emissions from Stationary Sources. J. Air Poll. Control Assoc.,
25:925-932, 1975.
6. Feairheller, W. R., A. M. Kemmer, B. J. Warner, and D. Q. Douglas.
Measurement of Gaseous Organic Compound Emissions by Gas Chromatography.
Monsanto Research Corporation CPA Contract 68-02-1404, Task 33, Dayton,
Ohio, May 1977-January 1978.
21
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APPENDIX. A
METHOD FOR THE DETERMINATION OF BENZENE FROM STATIONARY SOURCES
22
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1 AUG
METHOD 111. DETERMINATION OF BENZENE
FROM STATIONARY SOURCES
INTRODUCTION
Performance of this method should not be attempted
by persons unfamiliar with the operation of a gas
chromatograph, nor by those who are unfamiliar with
source sampling, as there are many details that are
beyond the scope of this presentation. Care must
be exercised to prevent exposure of sampling personnel
to benzene, a carcinogen.
1. Principle and Applicability
1.1 Principle. An integrated bag sample of stack gas containing
benzene and other organics is subjected to gas chromatographic (GC)
analysis, using a flame ionization detector (FID).
1.2 Applicability. The method is applicable to the measurement of
benzene in stack gases only from specified processes. It is not applicable
where the benzene is contained in particulate matter.
2. Range and Sensitivity
The procedure described herein is applicable to the measurement of
benzene in the 0.1 to 70 ppm range. The upper limit may be extended by
extending the calibration range or by dilution of the sample.
3. Interferences
The chromatograph columns and the corresponding operating parameters
herein described have been represented as being useful for producing an
adequate resolution of benzene. However, resolution interferences may
be encountered on some sources. Also, the chromatcgraph operator may
know of a column that will produce a superior resolution of benzene
without reducing the response to benzene as specified in Section 4.3.1.
23
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Stack Wall
ter (Glass Wool)
Probe
.y,-T { _ _ _ _ _ __ , _ _ _
Quick
Connects
Female
Teflon
Sample Line
Vacuum Line
Needle Valve
Flow Meter
Charcoal Tube
Pump
Rigid Leak-Proof
Container
Figure 111-1. Integrated-bag sampling train. (Mention
of trade names on specific products does not con-
stitute endorsement by the Environmental Protec-
tion Aeencv.")
24
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In any event, the chromatograph operator shall select a column
which is best suited to his particular analysis problem, subject to the
approval of the Administrator. Such approval shall be considered
automatic provided that confirming data produced through a demonstrably
adequate supplemental analytical technique, such as analysis with a
different column or G.C./mass spectroscopy, is available for review by
the Administrator.
4. Apparatus
4.1 Sampling (see Figure 111-1).
4.1.1 Probe. Stainless steel, Pyrex glass, or Teflon tubing
according to stack temperature, each equipped with a glass wool plug to
remove particulate matter.
4.1.2 Sample Line. Teflon, 6.4 mm outside diameter, of sufficient
length to connect probe to bag. A new unused piece is employed for each
series of bag samples that constitutes an emission test.
4.1.3 Male (2) and female (2) stainless steel quick connects, with
ball checks (one pair without) located as shown in Figure 111-1.
4.1.4 Tedlar or aluminized Mylar bags, 100 liter capacity. To
contain sample.
4.1.5 Rigid leakproof containers for 4.1.4, with covering to
protect contents from sunlight.
4.1.6 Needle Valve. To adjust sample flow rate.
4.1.7 Pump—Leak-free. Minimum capacity 2 liters per minute.
Mention of trade names or specific products does not constitute
endorsement by the Environmental Protection Agency.
25
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4.1.8 Charcoal Tube. To prevent admission of benzene and other
orgam'cs to the atmosphere in the vicinity of samplers.
4.1.9 Flow Meter. For observing sample flow rate; capable of
measuring a flow range from 0.10 to 1.00 liters per minute.
4.1.10 Connecting Tubing. Teflon, 6.4 mm outside diameter, to
assemble sample train (Figure 111-1).
4.2 Sample Recovery.
4.2.1 Tubing. Teflon, 6.4 mm outside diameter, to connect bag to
gas chromatograph sample loop. A new unused piece is employed for each
series of bag samples that constitutes an emission test, and is to be
discarded upon conclusion of analysis of those bags.
4.3 Analysis.
4.3.1 Gas Chromatograph. With FID, potentiometric strip chart
recorder and 1.0 to 2.0 ml heated sampling loop in automatic sample
valve. The chromatographic system shall be capable of producing a
response to 0.1 ppm benzene that is at least as great as the average
noise level. (Response is measured from the average value of the
baseline to the maximum of the waveform, while standard operating
conditions are in use.)
4.3.2 Chromatographic Columns. Columns other than those listed
below can Le used, provided that the precision and accuracy of the
analysis of benzene standards are not impaired. Information confirming
that adequate resolution of the benzene peak is accomplished should be
available. Adequate resolution is defined as an area overlap of r.ct
more than 10 percent of the benzene peak. Calculation of area overlap
is explained in Appendix E, Supplement A: "Determination of Adequate
Chromotographic Peak Resolution."
26
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4.3.2.1 Benzene in the Presence of Aliphatics. Stainless Steel,
2.44 m x 3.2 mm, containing 10 percent TCEP on 80/100 Chromosorb P AW.
4.3.2.2 Benzene With Separation of the Isomers of Xylene. Stainless
steel, 1.83 m x 3.2 mm, containing 5 percent SP 1200/1.75 percent Bentone
34 on 100/120 Supelcoport.
4.3.3 Flow Meters (2). Rotameter type, 0 to 100 ml/min capacity.
4.3.4 Gas Regulators. For required gas cylinders.
4.3.5 Thermometer. Accurate to one degree centigrade, to measure
temperature of heated sample loop at time of sample injection.
4.3.6 Barometer. Accurate to 5 mm Hg, to measure atmospheric
pressure around gas chromatograph during sample analysis.
4.3.7 Pump—Leak-free. Minimum capacity 100 ml/min.
4.3.8 Recorder. Strip chart type, optionally equipped with disc
integrator or electronic integrator.
4.3.9 Planimeter. Optional, in place of disc or electronic
integrator, for 4.3.8 to measure chromatograph peak areas.
4.4 Calibration. 4.4.2 through 4.4.6 are for section 7.1 which is
optional.
4.4.1 Tubing. Teflon, 6.4 mm outside diameter, separate pieces
marked for each calibration .concentration.
4.4.2 Tedlar or Aluminized Mylar Bags. 50-liter capacity, with
valve; separate bag marked for each calibration concentration.
4.4.3 Syringe. 1.0 yl, gas tight, individually calibrated, to
dispense liquid benzene.
4.4.4 Syringe. 10 uml, gas tight, individually calibrated, to
dispense liquid benzene.
' 27
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4.4.5 Dry Gas Meter, With Temperature and Pressure Gauges.
Accurate to +2 percent, to meter nitrogen in preparation of standard
gas mixtures, calibrated at the flowrate used to prepare standards.
4.4.6 Midget Impinger/Hot Plate Assembly. To vaporize benzene.
5. Reagents
It is necessary that all reagents be of chromatographic grade.
5.1 Analysis.
5.1.1 Helium Gas or Nitrogen Gas. Zero grade, for chromatographic
carrier gas.
5.1.2 Hydrogen Gas. Zero grade.
5.1.3 Oxygen Gas or Air as Required by the Detector. Zero grade.
5.2 Calibration. Use one of the following options: either 5.2.1
and 5.2.2, or 5.2.3.
5.2.1 Benzene, 99 Mol percent pure benzene certified by the
manufacturer to contain a minimum of 99 Mol percent benzene; for use in
the preparation of standard gas mixtures as described in Section 7.1.
5.2.2 Nitrogen Gas. Zero grade, for preparation of standard gas
mixtures as described in Section 7.1.
5.2.3 Cylinder Standards (3). Gas mixture standards (50, 10, and
5 ppm benzene in nitrogen cylinders) for which the gas composition has
been certified with an accuracy of +_3 percent or- better by the manufacturer.
The manufacturer must have recommended a maximum shelf life for each .
cylinder so that the concentration does not change by greater than +5
percent from the certified value. The date nf gas cylinder preparation,
certified benzene concentration and recommended maximum shelf life must
have been affixed to the cylinder before shipment from the gas manufacturer
28
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to the buyer. These gas mixture standards may be directly used to
prepare a chromatograph calibration curve as described in Section 7.3.
5.2.3.1 Cylinder Standards Certification. The concentration of
benzene in nitrogen in each cylinder must have been certified by the
manufacturer by a direct analysis of each cylinder using an analytical
procedure that the manufacturer had calibrated on the day of cylinder
analysis. The calibration of the analytical procedure shall, as a
minimum, have utilized a threepoint calibration curve. It is recommended
that the manufacturer maintain two calibration standards and use these
standards in the following way: (1) a high concentration standard
(between 50 and 100 ppm) for preparation of a calibration curve by an
appropriate dilution technique; (2) a low concentration standard (between
5 and 10 ppm) for verification of the dilution technique used.
5.2.3.2 Establishment and Verification of Calibration Standards.
The concentration of each calibration standard must have been established
by the manufacturer using reliable procedures. Additionally, each
calibration standard must have been verified by the manufacturer by one
of the following procedures, and the agreement between the initially
determined concentration value and the verification concentration value
must be within +5 percent: (1) verification value determined by com-
parison with a gas mixture prepared in accordance with the procedure
described in Section 7.1 and using 99 Mol percent benzene, or (2) veri-
fication value obtained by having the calibration standard analyzed by
the National Bureau of Standards. All calibration standards must be
renewed on a time interval consistent with the shelf life of the cylinder
standards sold.
29
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5.2.4 Audit Cylinder Standards (2). Gas mixture standards identi-
cal in preparation to those in Section 5.2.3 (benzene in nitrogen cylinders),
except the concentrations are only known to the person supervising the
analysis of samples. The concentrations of the audit cylinders should
be:, one low concentration cylinder in. the range, of. 5 to 20 ppm benzene,
and one high concentration cylinder in the range of 100 to 300 ppm
benzene. Audit cylinders may be obtained by contacting: EPA, Environmental
Monitoring and Support Laboratory, Quality Assurance Branch (MD-77),
Research Triangle Park, North Carolina 27711. If audit cylinders are
not available at EPA, an alternate source must be secured.
6. Procedure
6.1 Sampling. Assemble the sample train as in Figure 1. Perform a
bag leak check according to section 7.4. Determine that all connections
between the bag and the probe are tight. Place the end of the probe at -
the centroid of the stack and start the pump with the needle valve
adjusted to yield a flow of 0.5 1pm. After a period of time sufficient
to purge the line several times has elapsed, connect, the vacuum line to
the bag and evacuate the bag until the rotameter indicates no flow. Then
reposition the sample and vacuum lines and begin the actual sampling,
keeping the rate constant. Direct the gas exiting the rctarcotsr away
from sampling personnel. At the end of the sample period, shut off the
pump, disconnect the sample line from the bag, and disconnect the vacuum
line from the bag container. Protect the bag container from sunlight.
30
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6.2 Sample Storage. Sample bags must be kept out of direct sunlight.
Analysis must be performed within 24 hours of sample collection.
6.3 Sample Recovery. With a new piece of Teflon tubing identified
for that bag, connect a bag inlet valve to the gas chromatograph sample
valve. Switch the valve to withdraw gas from the bag through the sample
loop. Plumb the equipment so the sample gas passes from the sample valve
to the leak-free pump, and then to a charcoal tube, followed by a
0-100 ml/min rotameter with flow control valve.
6.4 Analysis. Set the column temperature to 80°C for column A or
75°C for column B, the detector temperature to 225°C, and the sample loop
temperature to 70°C. When optimum hydrogen and oxygen flow rates have
been determined, verify and maintain these flow rates during all
chromatograph operations. Using zero helium or nitrogen as the
carrier gas, establish a flow rate in the range consistent with the
manufacturer's requirements for satisfactory detector operation. A
flow rate of approximately 20 ml/min should produce adequate separations.
Observe the base line periodically and determine that the noise level
has stabilized and that base line drift has ceased. Purge the sample
loop for thirty seconds at the rate of 100 ml/min, then activate the
sample valve. Record the injection time (the position of the pen on
the chart at the time of sample injection), the sample number, the
sample loop temperature, the column temperature, carrier gas flow rate,
chart speed and the attenuator setting. Record the laboratory pressure.
From the chart, note the peak having the retention time corresponding to
31
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Nitrogen Cylinder
Boiling
Water
Bath
Dry Gas Meter
Capacity
50 Liters
Figure 111-2. Preparation of Benzene Standards.
(optional)
32
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benzene, as determined in Section 7.2. Measure the benzene peak area,
A , by use of a disc integrator or a planimeter. Record A and the
retention time. Repeat the injection at least two times or until two
consecutive values for the total area of the benzene peak do not vary
more than 5 percent. The average value for these two total areas will
be used to compute the bag concentration.
6.5 Measure the ambient temperature and barometric pressure near
the bag. From a water saturation vapor pressure table, determine and
record the water vapor content of the bag. (Assume the relative humidity
to be TOO percent unless a lesser value is known.)
7. Standards' Calibration and Quality Assurance
7.1 Standards.
7.1.1 Preparation of Benzene Standard Gas Mixtures. (Optional--
del ete if cylinder standards are used.) Assemble the apparatus shown in
Figure 111-2. Evacuate a 50-liter Tedlar or aluminized Mylar bag that
has passed a leak check (described in Section 7.4) and meter in about 50
liters of nitrogen. Measure the barometric pressure, the relative
pressure at the dry gas meter, and the temperature at the dry gas meter.
While the bag is filling use the 10 yl syringe to inject 10 yl of 99 +
percent benzene through the septum on top of the impinger. This gives a
concentration of approximately 50 ppm of benzene. In a like manner, use
the other syringe to prepare dilutions having approximately 10 and 5 ppm
benzene concentrations. To calculate the specific concentrations, refer
to section 8.1. These gas mixture standards may be used for four days
33
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from the date of preparation, after which time preparation of new gas
mixtures is required. (Caution: Contamination may be a problem when a
bag is reused if the new gas mixture standard is a lower concentration
than the previous gas mixture standard.)
7.2 Calibration.
7.2.1 Determination of Benzene Retention Time. This section can be
performed simultaneously with section 7.3. Establish chromatograph
conditions identical with those in section 6.3, above. Determine proper
attenuator position. Flush the sampling loop with zero helium or
nitrogen and activate the sample valve. Record the injection time, the
sample loop temperature, the column temperature, the carrier gas flow
rate, the chart speed and the attenuator setting. Record peaks and
detector responses that occur in the absence of benzene. Maintain con-
ditions, with the equipment plumbing arranged identially to section 6.3,
and flush the sample loop for 30 seconds at the rate of 100 ml/min with
one of the benzene calibration mixtures and activate the sample valve.
Record the injection time. Select the peak that corresponds to benzene.
Measure the distance on the chart from the injection time to the time at
which the peak maximum occurs. This quantity, divided by the chart
speed» is defined as the benzene peak retention time. Since it is quite
likely that there will be other organics present in the sample, it is
very important that positive identification of the benzene peak be made.
7.2.2 Preparation nf Chromatograph Calibration Curve. iyiake a gas
chromatographic measurement of each standard gas mixture (described in
section 5.2.3 or 7.1) using conditions identical with those listed in
34
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Sections 6.3 and 6.4. Flush the sampling loop for 30 seconds at the
rate of 100 ml/min with one of the standard gas mixtures and activate
the sample valve. Record C , the concentration of benzene injected, the
attenuator setting, chart speed, peak area, sample loop temperature,
column temperature, carrier gas flow rate, and retention time. Record
the laboratory pressure. Calculate A , the peak area multiplied by the
attenuator setting. Repeat until two consecutive injection areas are
within 5 percent, then plot the average of those two values vs C .
When the other standard gas mixtures have been similarly analyzed and
plotted, draw a straight line through the points. Perform calibration
daily, or before and after each set of bag samples, whichever is more
frequent.
7.3 Quality Assurance.
7.3.1 Analysis Audit. Immediately after the preparation of the
calibration curve and prior to the sample analyses, perform the analysis
audit described in Appendix E, Supplement B: "Procedure for Field
Auditing GC Analysis."
7.3.2 Bag Leak Checks. While performance of this section is
required subsequent to bag use, it is also advised that it be performed
prior to bag use. After each use, make sure a bag did not develop leaks
as follows: to leak check, connect a water manometer and pressurize the
bag to 5-10 cm h^Q (2-4 in. H,,0). Allow to stand for 10 minutes. Any
displacement in the water manometer indicates a leak. Also, check the
rigid container for leaks in this manner. (Note: an alternative leak
35
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check method is to pressurize the bag to 5-10 cm 1^0 or 2-4 in. H~0 and
allow to stand overnight. A deflated bag indicates a leak.) For each
sample bag in its rigid container, place a rotameter in line between the
bag and the pump inlet. Evacuate the bag. Failure of the rotameter to
register zero flow when the bag appears to be empty indicates a leak.
8. Calculations
8.1 Optional Benzene Standards Concentrations. Calculate each
benzene standard concentration prepared in accordance with Section 7.1
as follows:
B(.8787 mg)
c
c
10 yg yg mole
mg 78.11 yg
Y 106 yl 293
1 Tm
24.055 yl
yg mole
760
105
B (270.6) Equation 111-1
v v 293 Prc
vm Y Tm 760
Where:
C = Benzene standard concentration in ppm.
B = Number of yl of benzene injected.
V = Gas vclu,~e measured by dry gas meter in liters.
Y = Dry gas meter calibration factor.
P = Absolute pressure of the dry gas meter, mm Hg.
T • = Absolute temperature of the dry gas meter, °A.
.8787 ='Density of benzene at 293°A.
78.11 = Molecular weight of benzene.
24.055= Ideal gas at 293°A, 760 mm Hg.
10 = Conversion factor, ppm.
36
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8.2 Benzene Sample Concentrations. From the calibration curve
described in section 7.3, above, select the value of CG that corresponds
to AC. Calculate Cg as follows:
C P T.
Cs = p.T CM-S ) Equation 111-2
i r wb
where:
S , = The water vapor content of the bag sample, as analyzed.
C = The concentration of benzene in the sample in ppm.
C = The concentration of benzene indicated by the gas
chromatograph, in ppm.
P = The reference pressure, the laboratory pressure recorded
i t
during calibration, mm Hg.
T. = The sample loop temperature on the absolute scale at the
time of analysis, °A.
P- = The laboratory pressure at time of analysis, mm Hg.
Tr = The reference temperature, the sample loop temperature
recorded during calibration, °A.
9. References
1. Feairheller, W. R.; Kemmer, A. M.; Warner, B. J.; and
Douglas, D. Q. "Measurement of Gaseous Organic Compound Emissions by
Gas Chromatography," EPA Contract No. 68-02-1404. Task 33 and
68-02-2818, Work Assignment 3. Jan., 1978.
2. Knoll, Joseph E.; Penny, Wade H.; Midgett, Rodney M.;
Environmental Monitorfng Series Publication in preparation. Stability
of Benzene Containing Gases in Tedlar Bags. QA8/EMSL, (J. S. Environmental
Protection Agency.
37
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3. Bulletins 743A, 740C, and 740D. "Separation of Hydrocarbons"
1974. Supelco, Inc. Bellefonte, Pennsylvania 16823.
4. Volume 10, No. 1 "Current Peaks," 1977. Carle Instruments,
Inc., Fullerton, California 92631.
38
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse Lefore completing)
1. REPORT NO.
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
THE USE OF TEDLAR BAGS TO CONTAIN GASEOUS BENZENE SAMPLE
AT SOURCE-LEVEL CONCENTRATIONS.
5. REPORT DATE
August 1978
6. PERFORMING ORGANIZATION CODE
7.AUTHOR(S)
Joseph E. Knoll, Wade H. Penny and M. Rodney Midgett
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Quality Assurance Branch
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
1HD621
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA-ORD-600
15. SUPPLEMENTARY NOTES
To be published as an Environmental Monitoring Series Report.
16. ABSTRACT
Tedlar bags have been evaluated as containers for gaseous benzene samples for use
in EPA Method 111 - Determination of Benzene from Stationary Sources. When such bags
were used for storage, benzene samples remained essentially unchanged when held at
ambient temperatures for up to 17 days, wher. cooled to -40° C for one hour or when
heated to 70° C for one hour. At higher temperatures, some concentration changes were
observed and above 105° C decomposition of the bag seals resulted. At room tempera-
ture, there was no evidence of permeation loss and absorptive loss could only be
observed upon prolonged contact. Flushing bags three times with nitrogen was suffi-
cient to remove all traces of previous samples.
Tedlar bags were also used to prepare gaseous mixtures for calibration purposes
in gas chromatography. Such samples were prepared by injecting measured quantities of
liquid benzene into a bag while metering-in nitrogen gas.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. cos AT I Field/Group
Air pollution
Benzene
Calibration
13 B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
1INP1 AS SI FIFO
22. PRICE
EPA Form 2220-1 (9-73)
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