United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-82-052 Sept. 1982
Project Summary
Further Characterization of
Sorbents for Environmental
Sampling—II
J. C. Harris, E. V. Miseo, and J. F. Piecewicz
This report describes the continuation
of a systematic study of the behavior
of solid sorbents used to collect
organic vapors from gaseous media.
The studies were conducted using an
elution analysis chromatographic
method. The report deals with a series
of experiments. Sorbents not used in
earlier studies were examined to
determine their specific retention
volume and the percent recovery.
Organometallics, as a chemical class
not previously used, were studied to
determine their retention volumes on
some sorbents. The effect of methane
on the recovery and the effect of
mixed sorbents were also examined.
The resins used included Tenax-GC;
XAD-2 and -7; Ambersorb 340, 347,
and 348; and Florisil. One (Ambersorb
348) was found to be thermally
unstable and was not recommended.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Research Triangle
Park. NC, to announce key findings of
the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
This work involved the systematic
study of the use of solid sorbents to
collect organic vapors from gaseous
media. The use of an adsorbent-filled
cartridge has become increasingly
popular for sampling organic vapors.
The technique is used to sample source
emissions and for ambient air concen-
trations. The use of these sorbents for
environmental assessment studies has
been adopted by EPA/IERL-RTP's
Technical Support Staff by incorporating
a sorbent trap in the EPA Source
Assessment Sampling System (SASS)
train. To support this application and
gain a quantitative data base to guide in
applications of the method, Arthur D.
Little, Inc. has been carrying out
research for several years in this area.
This report is the fourth in a series
related to the use of sorbents for
environmental sampling. The aims here
were to:
• Determine the applicability of
other resins in terms of capacity,
effectiveness, and general use-
fulness.
• Investigate the recovery of several
chemical classes from various
resins.
• Investigate a mixture of sorbates
on a resin.
• Determine the behavior of organ-
ometallics (particularly tetraethyl-
lead and diethylmercury) on
various resins.
• Determine the effect of a mixed
atmosphere containing CI-U on
the specific retention.
These studies were conducted on
various resins to determine their
behavior using the elution analysis
chromatographic method described in
earlier reports.1'2'3
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Approach
Experimental Technique
The chromatographic method used in
this study was that of elution analysis.
In elution analysis, a small quantity of
adsorbate is injected onto the sorbate
cartridge in a very short time. The
specific retention volume, Vg, the
fundamental retention constant in gas
chromatography, can be determined for
a sorbate on a particular sorbent from
the resultant elution peak.
Knowledge of the value of Vg permits
an estimation of the retention volumeof
a solute at another temperature or for a
different sorbent cartridge size. Thus,
Vj, determined from conventional gas
chromatographic columns, can aid in
the design of sorbent sampling modules.
Experimental Apparatus
The basic apparatus used to determine
elution volumes, Vj, in this study was
reported earlier.2 Principal components
of the apparatus are: the sorbent
cartridge, gas chromatograph, and
pressure, flow, and temperature mea-
suring systems. The sorbent cartridges
were proportionally scaled down to 0.5
cm I.D. from the typical cross-section of
a SASS train sorbent resin canister. The
two gas chromatographs used in this
study were a Varian Model 1200 (a
single-column instrument employing a
flame ionization detector) and a Gow-
Mac 550 (a dual-column instrument
employing a thermal conductivity detec-
tor).
The sample introduction technique
used in the elution analysis studies
consisted of: taking up a small amount
(<0.5 //L) of liquid sorbate in a 10 /uL
syringe, expelling the liquid, and
pumping the syringe 50 or more times.
This allowed generation of a reproducible
dilute sorbate vapor concentration.
With the resulting low concentration
samples (<10 ppm), the experiments
could be conducted in the Henry's Law
region.
Three to five replicate elution experi-
ments were run for each set of chro-
matographic conditions.
Recovery Studies
As in previous studies, the break-
through volume was measured to
determine Vg20 values. Since the
sorbents are to be used for air sampling,
the percent recovery of sorbates from
the resins was determined for each
sorbate. Recovery experiments were
conducted using the sorbates, decane,
ethanol, and n-butanol on six solid
sorbents: XAD-2, Tenax-GC, charcoal,
Florisil, XE-340, and XAD-7. The
percent recovery of the sorbate from the
sorbent was determined by challenging
the sorbent with a known concentration
of sorbate in air for a given amount of
time. The sorbents were desorbed in
appropriate solvents which were analyzed
to determine the quantity of sorbate
recovered from the resin. The quantity
of the sorbate recovered from the resin
is compared to the quantity which
would have been collected (concentra-
tion in mg/m3 x sampling rate in
mVminx time in minutes). Vg data were
used to calculate the recommended
sampling volume to collect the sorbate
at 10 ppm on the various sorbents with
no breakthrough.
Effects of Methane
Atmosphere on XAD-2
In the previous work,3 studies were
done to determine the effect of two
major gas components — H20 and CO2
— on the resin. The effect of methane,
found in stack gases at a concentration
of thousands of ppm, is investigated
here. Retention volumes were deter-
mined for four sorbates — n-pentanol,
n-butanol, n-octane, and n-hexane—on
XAD-2 at different column tempera-
tures and two different atmospheres,
with or without 1.1% methane in
helium. The sorbates were selected to
represent the classes of compounds
which had major differences in elution
behavior.
Effects on Vg of a Sorbate
Mixture on XAD-2
In additon to the effect of other gases
on the sorbate, it is useful to know the
resin's behavior in the presence of a
mixture of sorbates whose elution
behavior is considerably different from
each other. The sorbates used in this
experiment were n-heptane, ethylben-
zene, and n-butanol.
Retention Volumes of
Organome tallies
One of the Kiselev classes is organo-
metallics. Group C. To date, it was the
only group not investigated. Tetra-
ethyllead and diethyl mercury, both
stable in air, were used to investigate
this group. The retention volumes for
these two compounds were determined
on XAD-2.
Results and Conclusions
The work reported here was designed
to address several specific topics which
resulted from previous studies. In this
experimental investigation, twotothree
compounds each from a number of
compound categories were used as
models to investigate retention and
recovery phenomena in various sorbent:
sorbate systems. Several conclusions
can be developed on the basis of these
data.
Uncertainty in Vg Values
Review of cumulative sets of data on
Vj for the same sorbate: sorbent system
indicates that uncertainties in values of
Va20, extrapolated from measurements
at two or three elevated temperatures,
may be as high as a factor of five. This
uncertainty should be taken into account
when comparing data for different
sorbate: sorbent systems and in designing
sampling systems with appropriate
margins of safety to ensure quantitative
collection of a given sorbate.
Alternative Sorbents
Florisil is comparable to XAD-2 and
Tenax-GC in terms of its volumetric
capacity for collection of the alkanes,
alcohols and chlorinated aromatics
tested. Florisil showed very much
higher (about 10,000 times) capacity for
the chlorinated aliphatic species (di-
chloroethane, dichloropropane) tested
than either XAD-2 or Tenax-GC. It may
be the sorbent of choice for collection of
volatile chlorinated organics in applica-
tions, such as ambientair monitoring, in
which large volumes must be sampled
to meet detection limit constraints. The
low blank values obtainable by thermal
activation of Florisil are also an advantage
for such applications.
Limited data obtained for aliphatic
hydrocarbon sorbates suggest that
recovery from Florisil may be less than
quantitative. Also, the possible effects
of moisture on Florisil Vg's should be
investigated to determine its suitability
for stack sampling.
Ambersorb XE 3403, XE 347, and
Amberlite XAD-7 have substantially
greater capacity for collection of low
molecular weight alcohols than do
XAD-2 and Tenax-GC. Recovery of
alcohols from Ambersorb XE 340 was
also found to be satisfactory (75-88%);
recovery from charcoal and from XAD-7
was less than 50% in several tests.
Ambersorb XE 340 and 347 are therefore
suggested for applications involving
sampling specifically for volatile alcohols.
Organome tallies
The volumetric capacity of XAD-2 was
found to be adequate for collection of
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two organometallic compounds tested
— tetraethyllead and diethyl mercury.
Values of Vj for organometallics on
XAD-2 are very similar to those of
organic species with similar boiling
points, measured at the same tempera-
ture.
Effects of Methane
Atmospheres on Vl for XAD-
2
Data for aliphatic hydrocarbon and
alcohol sorbates indicate no effect of
1.1 % (11,000 part per million) methane
on the volumetric capacity of XAD-2.
Effects of Mixtures of
Sorbates
Data for an aliphatic, an aromatic
hydrocarbon, and an alcohol show no
evidence of competitive effects on vj
when several species are present at
parts per million concentrations in the
same sample.
References
1. Adams, J.W., K.T. Menzies, P.L.
Levins, "Selection and Evaluation of
Sorbent Resins for the Collection of
Organic Compounds," EPA-600/7-
77-044 (April 1977). PB-268 559.
2. Gallant, R.F., J.W. King, P.L. Levins,
J.F. Piecewicz, "Characterization of
Sorbent Resins for Use in Environ-
mental Sampling," EPA-600/7-78-
054 (March 1978). PB-284 347.
3. Piecewicz, J.F., J.C. Harris, P.L.
Levins, "Further Characterization of
Sorbents for Environmental Sam-
pling," EPA-600/7-79-216 (Sep-
tember 1979). PB-80-118763.
J. C. Harris, E. V. Miseo, and J. F. Piecewicz are with Arthur D. Little, Inc.,
Cambridge, MA 02140.
Larry D. Johnson is the EPA Project Officer (see below).
The complete report, entitled "Further Characterization of Sorbents for Environ-
mental Sampling—II," (Order No. PB 82-234 667; Cost: $7.50, 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:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
* US. OOVERNMtNTPHINTlNO OFFICE: 1WJ-559-017/0810
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