United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-84-062 June 1984
Project Summary
Evaluation of Sampling
Methods for Gaseous
Atmospheric Samples
E. D. Pellizzari, W. F. Gutknecht, S. Cooper, and D. Hardison
Laboratory tests of air sampling meth-
ods were conducted with FEP Teflon
bags, Tedlar bags, five-layered polyeth-
ylene-aluminized bags, Pyrex glass
bulbs, stainless steel canisters electro-
polished by the Summa process and by
a Research Triangle Institute process,
Tenax-GC cartridges, charcoal tubes,
and nickel cryogenic traps. The sam-
pling methods were evaluated for collec-
tion and recovery efficiency; interfer-
ences from ozone, nitrogen oxides,
sulfur dioxide, and water vapor; sample
stability in storage; analytical accuracy.
reproducibility, and limits of detection:
simplicity; and convenience. Tests were
conducted with mixtures of 27 organic
compounds comprising a range of chem-
ical and physical properties. Mixtures of
the model compounds were prepared in
a specially designed permeation/dilu-
tion system. Mixtures were prepared in
clean ("zero") air at parts per billion and
parts per trillion concentration levels.
For the storage/stability studies, mix-
tures of the test compounds stored in
the various containers were sampled
and analyzed after storage for zero,
three, and seven days. Dynamically
flowing mixtures of the inorganic gases
and vapors and test compounds were
prepared for the interference studies.
Tests were conducted at two concen-
tration levels of the interference mix-
ture. A quality assurance program was
employed for all measured and analyzed
data.
An automatic air monitoring sampler
was designed and fabricated to collect
organic gases and vapors on sorbent
cartridges. The prototype sampler was
designed to collect duplicate samples
and up to 12 series samples for various
selectable sampling periods. A printer
automatically recorded sample identi-
fication and sample volume.
This Project Summary was developed
by EPA's Environmental Sciences Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering in-
formation at back).
Introduction
Because in situ measurement of or-
ganic vapors in the atmosphere is not
always feasible, samples are often col-
lected in the field and returned to the
laboratory for analysis. The quality of the
analyses of the various organic substanc-
es in the atmosphere directly depends on
the validity of the sample collection,
storage, and transfer methods employed.
Various methods have been used to
collect gaseous atmospheric samples.
These include collection in liquids, on
solid adsorbents, in plastic and rigid
containers, and in cryogenic traps. Seri-
ous limitations have been reported for all
methods, including adsorption of analyte
species on container walls, permeation of
vapors through the walls of plastic bags,
interference from water vapor, production
of artifact contamination, sample loss
through chemical reaction with the con-
tainer walls or other chemical species in
the sample, and inefficient collection and
transfer of analyte species.
This study was undertaken to test and
evaluate various methods of collecting
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and transferring gaseous atmospheric
samples for analysis of a variety of toxic
organic pollutants by gas chromatogra-
phy. In addition, in response to a need for
an automatic organic vapor sampler in
ambient air monitoring, a sampler to
collect sequential and replicate samples
on sorbent cartridges was designed and
fabricated.
The following types of sample contain-
ers were employed in the study:
1. Polymeric bags
2. Glass bottles
3. Stainless steel canisters
4. Tenax-GC sorbent cartridges
5. Charcoal sorbent cartridges
6. Cryogenic tubular traps
Sampling methods were tested with
synthetic mixtures of 27 organic com-
pounds comprising a range of chemical
and physical properties (see Table 1).
Table 1. Organic Compounds Tested
Chemical Group
The evaluation of the sample collection
and transfer methods included the follow-
ing considerations:
1. Limits of applicability
2. Collection efficiency
3. Recovery (transfer) efficiency for
gas chromatographic analysis
4. Analytical accuracy and detection
limits
5. Effect of potential interferences,
including ozone, NOX, SC"2, and
water vapor
6. Sample stability in storage
7. Quality of gas chromatograms
8. Simplicity and convenience
Synthetic mixtures of the model com-
pounds were prepared in a permeation/
dilution system designed to deliver the
compounds in the concentration range of
10 ppt to 100 ppb in clean ("zero") air.
Compound
Chloroalkanes
Chloroalkenes
Chlorinated aromatics
Aromatics
Alkanes
Nitro compounds
Phenols
Acrylo compounds
Ethers
Sulfur compound
Methyl chloride
1,2 -Dichloropropane
Chloroform
1,1,2,2-Tetrachloroethane
1,1,1 -Trichloroethane
Vinyl chloride
TetracMoroethylene
2-Chloro-1,3-butadiene
1,1-Dichloroethylene
Ally I chloride
Chlorobenzene
m -Dichlorobenzene
Benzyl chloride
Benzene
Toluene
1.2.3 - Trimeth ylbenzene
Ethylbenzene
o-Xylene
n-Decane
Nitrobenzene
o-Cresol
Acrylonitrile
Furan
Bis-(2-chloroethyl)ether
Propylene oxide
a-Epichlorohydrin
Methyl mercaptan
Boiling Point
-24.2
96.4
61.7
146.2
74.1
-13
121
59.4
37
45
132
173
215
80.1
110.6
176.1
136.2
139.1
174.1
210.8
190.9
77
31.4
178
34.3
116.5
6.2
In the study of potential interferences,
mixtures of ozone (Os), nitrogen oxides
(NO,), sulfur dioxide (SOa), and water
vapor were prepared in air and mixed
with the model compounds in a mixing
bulb within the permeation/dilution sys-
tem oven. Samples collected from the
permeation/dilution system were ana-
lyzed with gas chromatography by using
capillary columns and either flame ioniza-
tion or electron capture detectors.
Two experimental designs were devel-
oped. In one design the sampling volume
(«*30 L), sampling time, sampling rate,
and relative humidity (30%) were held
constant. No O3, NOX, or SO2 was added.
Model compound concentration and stor-
age time were variable parameters. Tests
were conducted at three concentration
levels: zero, low (> 10 ppt < 1 ppb), and
high (> 1 ppb < 100 ppb). Samples were
analyzed after being stored less than one
day, after three days, and after seven
days.
In the other experimental design, the
test mixture concentration (ppb level),
sample volume (30 L), sampling time, and
sampling rate were held constant. Con-
centrations of Oa, N0«, S02, and
water vapor were variable parameters.
Tests were conducted at two levels: low
(0 3* 75 ppb, NOx« 100 ppb, SO2 ~ 100
ppb, relative humidity = 30%) and high
(03« 500 ppb, NO, * 500 ppb, S02 « 200
ppb, and relative humidity » 90%). Tripli-
cate samples were collected with each
type of sampling device.
Procedures
Polymeric bags (FEP Teflon and Tedlar)
were cleaned before testing by flushing
them with clean air and exposing them to
ozone and direct sunlight irradiation.
Five-layered aluminized bags could not
be made reasonably clean and were
dropped from the study. Glass bulbs were
prepared from 2-L round-bottom Pyrex
glass flasks fitted with Teflon high-
vacuum stopcocks. They were filled with
clean air and evacuated at 150 °C. Two
types of steel canisters were tested. One
was fabricated in the laboratory of electro-
polished stainless steel and had a 2-L
capacity. The other was a 6-L stainless
steel container manufactured and sold by
D&S Instruments, Ltd. polished by the
Summa process. Both types of canisters
were cleaned by filling them with clean
air and evacuating them at 150°C. Virgin
Tenax-GC was extracted with methanol,
dried in a vacuum oven at 100°C, and
sieved through 30/60 mesh. Charcoal
tubes (from the National Institute of
Occupational Safety and Health) were
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purchased commercially and used as
they were received. Cryogenic traps were
made of coiled nickel tubing (0.25 in. o.d.
x 24 in. long) and were washed with
methanol and pentane, thermally condi-
tioned at 160°C with a helium gas purge,
and filled with clean glass beads.
Sampling was accomplished by con-
necting the sampling devices to the glass
sampling manifold of the permeation/
dilution system used to generate the test
gas mixtures. Bags, Tenax-GC cartridges,
charcoal tubes, and nickel cryogenic
traps were connected directly to the
manifold. The steel canisters and glass
bulbs were connected to the manifold
through a metal bellows pump. Bags
were filled with 10 or 20 L of sample.
Glass bulbs and steel canisters were
filled to about 15 psig. A 30-L sample
volume was used with the Tenax-GC
cartridges, charcoal tubes, and cryogenic
traps.
Samples in bags, glass bulbs, and steel
canisters were transferred to a gas chro-
matograph by a gas sampling valve
equipped with a stainless steel sampling
loop. Typically, 200 mL of sample was
passed through the sampling loop while it
was immersed in liquid oxygen. Bulbs
and canisters were placed in a heated box
(50° to 90°C) during sample transfer to
minimize loss of test compounds to the
container walls. Tenax-GC cartridge sam-
ples were transferred by a thermal de-
sorption chamber equipped with a nickel
capillary cryogenic trap. Cryogenic trap
samples were first transferred to Tenax-
GC cartridges by a thermal purge with
helium gas and then transferred to a gas
chromatograph via the thermal desorp-
tion chamber. Charcoal trap samples
were placed in a flask and desorbed with
a carbon disulfide/methanol solution.
Aliquots were injected into a gas chromat-
ograph equipped with an electron capture
detector
Results
Storage Stability Studies
Storage/stability studies of polymeric
bags, glass bulbs, and steel canisters
were not conducted at the low (ppt)
concentration level of test compounds. In
low-level tests of Tenax-GC cartridges,
charcoal tubes, and cryogenic traps, most
test compounds could not be detected or
could not be measured because of inter-
ferences in the gas chromatogram. Re-
sults for the high-level studies are re-
ported below.
Teflon and Tedlar bags developed high
levels of background contamination when
stored in lab air. Consequently, storage
tests were conducted with the bags
stored in sealed steel boxes which had
been flushed with clean dry air. In tests
conducted with 15 of the 27 model
compounds, Teflon bags showed large
losses after seven days of storage. In
Tedlar bags, the long-term losses (com-
parisons of Day 0 analyses with Day 7
analyses) were generally low. Recoveries
of test compounds on Day 0 were gen-
erally >70% However, propylene oxide,
a-epichlorohydrin, and o-cresol could not
be detected.
Long-term losses in the glass bulbs
were generally low. Recoveries of test
compounds were generally >75% for
compounds with boiling points below that
of ethylbenzene. Recovery of compounds
with higher boiling points was generally
lower. Propylene oxide, a-epichlorohy-
drm, and o-cresol could not be detected.
Long-term losses were generally low in
the steel containers electropolished by a
Research Triangle Institute process and
in the Summa-polished containers. Re-
coveries of test compounds with boiling
points below that of ethylbenzene were
generally slightly higher for the Summa-
polished canisters, and the recoveries of
compounds with higher boiling points
were even higher. Recoveries for the
Summa-polished canisters generally
were >72%. Propylene oxide, aepichloro-
hydrin, and o-cresol could not be detected.
No long-term losses of test compounds
were apparent in the results obtained
with Tenax-GC cartridges. For com-
pounds with breakthrough volumes great-
er than the sampling volume, recoveries
generally were >85%. Recovery was
highly variable for those compounds with
smaller breakthrough volumes, even after
applying corrections for breakthrough.
These compounds had breakthrough vol-
umes ranging from 1 to 18 L. All test
compounds could be detected with the
Tenax-GC cartridges.
Most test compounds could not be
detected in samples collected in charcoal
tubes. High recoveries were obtained
only for 1,2-dichloropropane and bis-(2-
chloroethyl)ether. Long-term losses of
these compounds were 14% and 23%,
respectively.
For tests of a mixture of 14 test
compounds at the high concentration
level, unpacked cryogenictraps gave poor
recoveries, except for bis(2-chloro-
ethyl)ether. Traps packed with glass
beads and cooled with dry ice were used
for tests at the low concentration level.
However, most compounds either were
not detected or were obscured by inter-
ferences in the gas chromatogram.
Interference Studies
Teflon bags were not included in the
interference studies. Recoveries from
Tedlar bags were generally lower with
the high-level interference mixture of
Oa/NOx/SOe/water vapor than with the
low-level mixture. Recoveries of com-
pounds with low boiling points in the
presence of the low-level mixture were
generally lower than recoveries obtained
in the storage/stability study. Recoveries
with the low-level mixture generally were
>71%. Methyl mercaptan and the three
test compounds reported in the storage
studies were not detected.
Increasing the level of interference
produced mixed results from the glass
bulbs; the most prevalent effect was a
decrease in the recovery of test com-
pounds. For compounds with boiling
points >74°C, recoveries with the low-
level mixture generally were greater than
those obtained in the storage studies.
Recoveries of all compounds generally
were >72% The four test compounds
which were undetected in the polymeric
bags were also undetected in the glass
bulbs.
Increasing the level of interference in
the Summa-polished canisters resulted
in a decrease in recovery for the majority
of detectable test compounds. In compar-
ison with the results obtained in the
storage studies, recoveries at the low
level of interference were either de-
creased or unchanged for compounds
with boiling points <37°C and either
increased or unchanged for those with
boiling points >74°C (except for bis-
2(chloroethyl)ether and the four unde-
tected compounds). Recoveries of all
compounds generally were >74% with
the low-level mixture.
Generally, increasing the level of inter-
ference in Tenax-GC cartridges did not
produce a significant change in recoveries
of those test compounds with break-
through volumes greater than the sam-
pling volume. When a glass fiber filter
impregnated with sodium thiosulfate
was placed in the sampling line ahead of
the Tenax-GC cartridge, recoveries at
both interference levels were generally
improved. The filter, however, did not
remedy the problem of chromatographic
interferences that occurred for several
compounds Recoveries of the majority of
compounds that could be measured and
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had breakthrough volumes greater than
the sampling volume were lower than
those obtained in the storage studies.
The interference studies with charcoal
tubes were generally unproductive. Tetra-
chloroethylene and 1,1,2,2-tetrachloro-
ethane were the only compounds ob-
served with the electron capture detector.
Because of poor results obtained in the
storage/stability study, liquid oxygen
was used to cool the packed nickel
cryogenic traps. Excessive water, which
collected in the traps and was subse-
quently transferred to the Tenax-GC
cartridges a long with the test compounds,
was removed by storing the cartridges in
a culture tube that contained a quantity of
calcium sulfate. The presence of the low-
level interference mixture generally re-
sulted in lower recoveries of the test
compounds. However, even with the
liquid oxygen coolant, recoveries in the
absence of the interference mixtures
were generally poor. Comparison of high-
level results with low-level results was
precluded by the high variability in ob-
served recoveries.
Design and Construction of an
Automatic Air Sampler
A prototype sampler was designed and
constructed to collect ambient air samples
automatically in Tenax-GC cartridges
over a period of 72 h. The sampler
operates at 120 volts AC and consists of a
control unit connected to two independ-
ent sampling heads by flexible gas flow
lines, heater supply lines, and thermo-
couple wires. Each sampling head is
housed in a heated sample cover and
accommodates six sampling cartridges
plus one blank. The control unit incorpo-
rates a vacuum pump, a flow meter, a
flow integrator, fcnd a printer. Two sam-
pling heads allow for duplicate sampling
and the collection of up to 12 series
samples. Cartridges are transported in
the sampling head block, which is dis-
connected from the sampling lines and
sealed with cap plates on both ends.
Sampling rates can be set from 7mL/min
to 1.5 L/min. Sampling periods are
available between 1 5 min and 12 h. The
printer prints time of day, date, and
sample volume, and it identifies the sam-
ple lines being used.
Short-term laboratory tests indicated
that the sampler operated properly, the
level of contamination developed in clean
cartridges stored in sealed sample heads
for seven days was approximately 2 times
the level developed in cartridges sealed in
culture tubes.
Conclusions
Teflon and Tedlar bags are subject to
leakage, permeation of gases through the
bag wall, and release of contaminants
from the wall by the interference mixture
employed in this study. Safe storage of
samples is limited to 24 h or less unless
bags are protected from dirty environ-
ments.
Glass bulbs break easily, which may
seriously limit the amount of sample
available for analysis. Although low re-
coveries were obtained in the storage
studies of compounds with high boiling
points, results from the interference
studies suggest that low levels of in-
organic gases and vapors present in
ambient air may improve recoveries of
these compounds.
Ruggedness and ease of cleaning are
two particular advantages of passivated
stainless steel canisters for field sampling.
However, even when pressured to two
atmospheres, the small volume of these
containers may seriously limit the amount
of sample available for analysis. Overall,
recoveries of test compounds at the low
level of interferences was comparable to
results obtained with Tedlar bags and
glass bulbs. These containers, as well as
the bags and bulbs, may not be suitable
for some compounds (e.g., methyl mer-
captan, propylene oxide, a-epichlorohy-
drin, and o-cresol).
For compounds with sufficiently high
breakthrough volumes, a relatively large
sample (all of which is available for
analysis) can be collected in a Tenax-GC
cartridge. The sampling cartridges are
light, small, and do not retain significant
amounts of carbon dioxide and water.
Low breakthrough volume is a problem
with some compounds. Also, great care is
required to avoid contamination of car-
tridges by contact with ambient air before
and after sampling. Low levels of inorgan-
ic gases and vapors present in ambient air
may result in poor recoveries of some
compounds and analytical interferences
that preclude analyses for certain other
compounds. Improved recoveries may be
obtained by using glass fiber filters im-
pregnated with sodium thiosulfate. The
filter also can be expected to produce
improvements in the recoveries of com-
pounds collected in the other types of
containers.
Results obtained with charcoal tubes
and nickel cryogenic traps were generally
poor. Neither sampling method, as em-
ployed in this study, showed sufficient
promise for use in ambient air sampling.
Recommendations
The three most promising types of
sampling devices (Pyrex glass bulbs,
Summa-polished stainless steel canis-
ters, and Tenax-GC cartridges) should be
further evaluated under field conditions.
The study should focus on gaseous
organic priority pollutants with the ob-
jective of establishing a generalized stand-
ard sampling protocol for priority pollut-
ants. Field testing should include the
following:
1. Indoor and outdoor sampling
2. Comparison of performances under
a variety of ambient conditions
3. Test compounds representative of
all types of gaseous organic priority
pollutants
4. Spiking samples quantitatively with
test compounds and labeled surro-
gate compounds
5. Evaluation of sodium thiosulfate-
impregnated filters with all sam-
pling devices
6. In situ comparisons with other
sampling methods being used in
other field studies
The automatic sampler requires further
testing before it can be judged acceptable
for ambient air monitoring. The
reliability, accuracy, and reproducibility
of the sampler need to be evaluated in the
laboratory and in the field under a variety
of ambient conditions. The sampler
should be modified sothat information on
power interruptions during sampling will
be recorded.
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E. D. Pellizzari, W. F. Gutknecht, S. Cooper, and D. Hardison are with Research
Triangle Institute, Research Triangle Park. NC 27709.
Stanley L. Kopczynski is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Sampling Methods for Gaseous
Atmospheric Samples." (Order No. PB 84-190 735; Cost: $23.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
b t'-v J K H.
b J u'.' -> L i
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G t <•-. C Y
U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/10604
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