United States
                  Environmental Protection
                  Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
                  Research and Development
EPA/600/S4-85/077 Jan. 1986
v°/EPA        Project Summary

                  Comparison  of  Solid
                  Adsorbent  Sampling
                  Techniques  for  Volatile
                  Organic  Compounds  in
                  Ambient Air
                  R. M. Riggin and R. A. Markle
                    The objective of this study was to
                  compare the performance of three solid
                  adsorbents (Tenax®, an experimental
                  polyimide resin, and Spherocarb®) as
                  well as whole air collection in canisters
                  followed by cryogenic trapping/gas
                  chromatography for sampling and anal-
                  ysis of a target list of volatile organic
                  compounds in ambient air.
                    A series of 14 experimental sampling
                  runs, wherein parallel samples were
                  collected using each of the techniques,
                  were conducted over a one-month pe-
                  riod. Several of the runs used audit or
                  other reference standards as a check on
                  method performance for known ana-
                  lyte concentrations.
                    Compared  to the three adsorbent
                  methods, whole air collection in canis-
                  ters followed by cryogenic trapping/gas
                  chromatography offered better preci-
                  sion and accuracy for the compounds of
                  interest, especially when a mass selec-
                  tive detection system was employed.
                  None of the three adsorbents gave opti-
                  mal performance for the entire list of
                  compounds, although in general
                  Tenax® gave the best results. Sphero-
                  carb® was the best adsorbent for
                  chloroethene (vinyl chloride),
                  dichloromethane, and 1,1,2-trichloro-
                  1,2,2-trif luoroethane.
                    The polyimide material suffered from
                  a number of operational problems
                  which weigh  heavily against its use in
                  ambient air sampling.
  This Project Summary was devel-
oped by EPA's Environmental Monitor-
ing Systems Laboratory, Research Tri-
angle 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
  The Methods Development and Anal-
ysis Division of the Environmental Mon-
itoring Systems Laboratory (EMSL) of
the  U.S. Environmental Protection
Agency (EPA) develops and evaluates
state-of-the-art and emerging analytical
techniques for determining organic
compounds in ambient air. Recently a
priority listing of volatile organics has
been established, and EMSL is focusing
on further development of analytical
methodology for the  determination of
these compounds.
  In general one of two approaches,
cryogenic trapping or gas/solid adsorp-
tion, is used to preconcentrate volatile
organics in ambient air. Each approach
has advantages and limitations. Cryo-
genic trapping has been demonstrated
to provide excellent recovery and preci-
sion for a number of volatile organic
compounds but is somewhat inconve-
nient when used in the field because of
the complexity and size of the appara-
tus.  Solid adsorbents can be conve-
niently transported to the field for sam-

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pling and returned to the laboratory for
analysis. Unfortunately none of the ex-
isting solid adsorbents show recoveries
comparable to cryogenic trapping tech-
niques for a wide range of components.
  By far the most widely employed ad-
sorbent for volatile organic compounds
is Tenax® GC. Tenax® has the advan-
tage of good thermal stability which al-
lows for efficient desorption of higher
boiling compounds (e.g.,  C-12 hydro-
carbons) during the analysis step. A pri-
mary limitation  of Tenax® is the low
retention volume of highly volatile
compounds (e.g.,  vinyl  chloride, 1,2-
dichloroethane, etc.). In order to extend
the applicability of solid adsorbent col-
lection to more volatile compounds,
EMSL has conducted development and
evaluation studies for various adsor-
bents which could be used in place of or
in combination with Tenax®.  The two
most promising  materials for this pro-
gram are a polyimide material formed
from pyromellitic anhydride and  4,4'-
diaminodiphenylsulfone,  and carbon
molecular sieves (CMS) sold under the
tradenames  Spherocarb®, and  Car-
bosieve®, or Carbosphere®.
  The objective of the work described in
the full report was to compare the per-
formance  of the three adsorbents
(Tenax®, polyimide, and  Spherocarb®)
as well as whole air collection in canis-
ters followed by cryogenic trapping for
sampling and analysis of representative
volatile organic compounds at realistic
concentrations in ambient  air. The
target compounds of concern are listed
in Table 1.


Procedure
  Three adsorbents—Tenax®, poly-
imide, and Spherocarb®—as  well as
cryogenic trapping/gas  chromatogra-
phy were operated in parallel to sample
ambient air, using  the sampling mani-
fold shown in Figure 1. The air stream
was spiked with 1-10  ng/liter  levels of
each target compound in order to en-
sure the presence of a detectable  con-
centration.
  Cryogenic sampling was accom-
plished  by collecting  integrated  sam-
ples, over the entire two-hour sampling
period, using specially treated stainless
steel canisters. The canister  samples
were then analyzed by cryogenic trap-
ping/gas chromatography using flame
ionization (FID),  electron capture, and
mass selective detectors.
  Duplicate ten-liter samples were col-
lected using each  of the three adsor-
bents. In addition five and twenty-liter
samples were collected for analysis by
EPA.
  All adsorbent samples were analyzed
by gas  chromatography/mass spec-
trometry. The analytes were thermally
desorbed from the cartridges onto a liq-
uid nitrogen-cooled trap and subse-
quently transferred onto a wide-bore
SE-30 capillary column. The individual
compounds were eluted using a tem-
perature program of -70°C to 150°C  at
8°/minute. Components were quantified
by comparing the integrated ion inten-
sity for a characteristic ion of each com-
pound to that  of standard injected on
the same day.

Results and  Discussion
  A series of experimental runs, listed
in Table 2, were conducted during July
and August of 1984.  As indicated  in
Table 2, Runs 4 and 11 were clean air
experiments using an audit cylinder
supplied by EPA and Run 5 was a simi-
lar experiment using the Battelle cali-
bration cylinder.
  In order to compare the performance
of the various methods for ambient air,
the apparent recovery of the adsorbent
samples for each  run, relative to the
cryogenic trapping value, was  calcu-
lated. Use of the  cryogenic trapping
value was considered to be most appro-
priate, since this technique generally
agreed best with the expected concen-
tration, and gave better precision than
did any of the adsorbent techniques.
Most of the values used for the  cryo-
genic trapping were obtained using the
mass selective detector, because this
detection system was less subject to po-

Table 1.    List of Target Compounds
              Compound
tential  interferences. However, the
toluene and  1,2-dimethylbenzene val-
ues were obtained using FID due to lim-
itations on the number of ions which
could be monitored using the mass se-
lective detector.
  Comparative data for the adsorbents
is summarized in Table 3. For poorly re-
tained compounds the  low volume
Tenax® sample (nominally 5 liters) was
used, whereas for better retained com-
pounds the duplicate 10 liter Tenax®
samples were used for these calcula-
tions.
  As expected, none of the adsorbents
performed best for all of the target com-
pounds. Tenax® performed  best  for
3-chloropropene (allyl chloride),
trichloromethane  (chloroform), 1,2-
dichloroethane,  1,1,1-trichloroethane,
benzene, tetrachloromethane  (carbon
tetrachloride), trichloroethene, tetra-
chloroethene (perchloroethylene), and
1,2-dimethylbenzene  (o-xylene).
Tenax® and polyimide gave essentially
identical results for toluene. As ex-
pected, on the basis of breakthrough
volume data, Tenax® gave  essentially
no  recovery for chloroethene (vinyl
chloride) and 1,1-dichloroethene (vinyli-
dene chloride).
  Polyimide performed better than both
Spherocarb® and Tenax® only for 1,1-
dichloroethene, although  only 55 per-
cent recovery and 28 percent standard
deviation were  obtained.  Polyimide
gave essentially no recovery for chloro-
ethene, despite the good  recovery ob-
tained for this compound in high purity
air sampling. Polyimide also gave dis-
appointingly low and variable recovery
for  1,1,2-trichloro-1,2,2-trif luoroethane
                        Concentration
                        in Calibration
                        Cylinder, \>.g/La
Chloroethene (Vinyl chloride)
Acrylonitrile
1,1-Dichloroethene (Vinylidene chloride)
Dichloromethane (Methylene chloride)
3-Chloropropene (Allyl chloride)
Trichlorotrifluoroethane (Freon 113)
Trichloromethane (Chloroform)
1,2-Dichloroethane
1,1,1-Trichloroethane (Methyl chloroform)
Benzene
Tetrachloromethane (Carbon tetrachloride)
Trichloroethene
Toluene
Tetrachloroethene (Perchloroethylene)
Chlorobenzene
1,2-Dimethylbenzene (o-xylene)
                            2.58
                            1.30
                            1.70
                            1.33
                            1.94
                            3.41
                            2.67
                            2.42
                            2.97
                            1.47
                            3.62
                            2.69
                            1.77
                            3.39
                            2.20
                            2.04
aAt 25°C and 1 atmosphere.

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                                                                                                     Exhaust
                                                                           Solid
                                                                        Adsorbent
                                                                         Sampling
                                                                          System
Calibration Cyl.
    Audit Cyl.
Figure 1.   Sampling manifold.

(Freon 113), 1,1,1-trichloroethane, and
tetrachloromethane. An operational
problem that weighs heavily against the
use of this material for ambient air sam-
pling is  the adsorption of a significant
amount of moisture onto the adsorbent.
The presence of water in the matrix led
to the chromatographic  column  plug-
ging during virtually all of the ambient
air sampling  runs (plugging of the
column was not observed for any dry air
runs using the audit or calibration cylin-
ders). A similar phenomenon is ob-
served for Spherocarb®. However, in
that case the cartridge is prepurged with
dry air,  at room temperature, prior to
analysis to remove adsorbed moisture.
A similar approach was not successful
in eliminating the problem for the poly-
imide material, indicating that the ad-
sorbed moisture is difficult to desorb
                  due to kirietic or thermodynamic fac-
                  tors.
                   Spherocarb® gave the best results of
                  the three resins  only for chloroethene,
                  dichloromethane,  and 1,1,2-trichloro-
                  1,2,2-trifluoroethane  and extremely
                  poor results for 1,1-dichloroethene,
                  3-chloropropene, 1,2-dimethylbenzene,
                  and tetrachloromethane. In the case of
                  1,1-dichloroethene artifactually high re-
                  covery, possibly due to dehydrohalo-
                  genation of 1,1,1-trichloroethane, was a
                  major problem.  Although low recover-
                  ies were anticipated for the other three
                  compounds, on the  basis of earlier
                  work, the low recovery of 1,1-
                  dichloroethene was not observed previ-
                  ously.
                   Despite the  problems  discussed
                  above, the data  set provides important
                  information for  ambient air sampling.
Inspection of the raw data reveals that,
except for the major problem areas dis-
cussed  above, the individual values
generally agree with the values ob-
tained by cryogenic trapping within a
factor of two or better (i.e., 50 to 150%
relative  recovery). In view of the large
temporal and  spatial variability of or-
ganic pollutant concentrations ob-
served  in ambient air, this extent of
agreement  between  methods is quite
good. Furthermore, the health effects
information  and mathematical models
used to assess the significance of the
data are subject to much greater uncer-
tainties.
  Another encouraging aspect  of the
data set is the very low blank levels ob-
served.  Our previous work with the
open-style Tenax® tubes commonly
employed in other laboratories resulted

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Table 2.   List of Sampling Runs
Run #
1
2
3
4
5
6
7
8
9
10
n
12
13
14
Sampling
Date
07/12/84
07/17/84
07/19/84
07/20/84
07/24/84
07/26/84
07/27/84
07/30/84
07/31/84
08/02/84
08/03/84
08/06/84
08/07/84
08/09/84
Description
Trial Run, Ambient Air
Ambient Air
Ambient Air
Audit Cylinder
Calibration Cylinder
Ambient Air
Ambient Air
Ambient Air
Ambient Air
Ambient Air
Audit Cylinder
Ambient Air
Ambient Air
Ambient Air
Table 3.    Performance Data for Solid Adsorbents Relative to Cryogenic Trapping
Compound
Chloroethene
1, 1-Dichloroethene
Dichloromethane
3-Chloropropenec
1,1,2-Trichloro-1,2,2-
Trifluoroethane
Trichloromethanec
1,2-Dichloroethane°
1, 1, 1-Trichloroethanec
Benzene
Tetrachloromethanec
Trichloroethene
Toluene
Tetrachloroethene
Chlorobenzene
1,2-Dimethylbenzene
Tenax
Breakthrough
Volume3,
Liters/Cartridge
0.8
Not Given
4
6

Not Given
13
18
9
27
13
28
122
106
249
334e
Average Recovery Relative
To Cryogenic Trapping, %
Tenax
	 t>
	 b
83(21)
87(35)

39(25)
100(36)
100(15)
130(42)
100(18)
1 10(37)
1 12(26)
70(19)
88(27)
78(35)
55(21)
Polyimide
	 b
52(28)
86(31)
140(68)

17(14)
75(25)
65(15)
51(14)
130(34)
53(19)
100(33)
70(17)
78(30)
57(21)
40(15)
Spherocarb
73(23)"
410(260)
85(12)
29(14)

69(30)
65(17)
75(14)
46(10)
140(63)
29(9)
90(33)
43(8)
72(30)
53(19)
20(7.9)
aData from Reference 2 at 90°F.
bNo meaningful data obtained.
°Low volume (nominally 5 liters) Tenax valued used for these compounds. Medium volume
 (nominally 10 liters) Tenax value used for all other compounds.
dValue in parentheses is standard deviation for all sampling runs, except for audit and calibra-
 tion cylinder sampling.
eValue for ethylbenzene.
in much larger blank levels being ob-
tained. In our hands the VOST-style
traps, which are positively sealed dur-
ing storage and analysis (desorption),
provide much lower bank levels.
  One must recognize that the composi-
tion of the atmosphere  being sampled
may have a significant impact on the
performance of any of the adsorbents,
due to chemical and physical effects
which are not fully understood. There-
fore, the results obtained in this study
may not be observed in all ambient air
sampling situations. Ideally one should
check the method performance using
the air sample of interest spiked with
known quantities of the compounds to
be determined. Since such experiments
are expensive to conduct, it is usually
not possible to obtain such data. For
this reason any ambient air sampling
data should be viewed as qualitative, or
at least semiquantitative, unless such
data are provided. The use of directly
spiked cartridges or spiked clean air
studies cannot substitute for such data.

Conclusions and Recommenda-
tions
  The significant conclusions  to be
drawn from this  study are presented
below:
  1) Compared to the three adsorbent
     methods tested, canister sampling
     followed  by cryogenic trapping/
     gas chromatography offers better
   precision and accuracy for the
   compounds of interest in this
   study, especially when a mass se-
   lective detection system  is em-
   ployed to overcome most poten-
   tial interferences.
2)  None of the three adsorbents eval-
   uated  gave the best performance
   for all  of the target compounds.
   Tenax® gave the best performance
   for 3-chloropropene, trichloro-
   methane (chloroform), 1,2-
   dichloroethane, 1,1,1-
   t rich I oroetha ne,  benzene,
   tetrachloromethane (carbon tetra-
   chloride), trichloroethene, tetra-
   chloroethene, and  1,2-dimethyl-
   benzene. Polyimide performed
   best only for 1,1-dichloroethene
   (vinylidene chloride). Spherocarb®
   performed  best only for
   chloroethene (vinyl chloride),
   dichloromethane, and 1,1,2-
   trichloro-1,2,2-trifluoroethane
   (Freon 113).  Toluene gave  com-
   parable results when Tenax® and
   polyimide were used, but lower re-
   coveries on Spherocarb®.

3)  The polyimide adsorbent has sev-
   eral operational difficulties which
   diminish its usefulness in ambient
   air sampling. A major artifact peak,
   acetonitrile,  is  generated when
   clean cartridges are stored longer
   than 24-48 hours before analysis.
   In addition, a significant amount of
   water is adsorbed during  sam-
   pling,  which  leads to plugging of
   the chromatographic column dur-
   ing analysis.
4)  Spherocarb® should be used only
   if highly volatile compounds such
   as chloroethene (vinyl chloride) or
   dichloromethane are of interest,
   since  several of the target com-
   pounds appear to be degraded in
   the sampling and analysis process
   for this adsorbent. High levels (ar-
   tifacts) of 1,1-dichloroethene
   (vinylidene chloride)  are formed
   on Spherocarb®  in many  in-
   stances.
5)  With a few exceptions, the recov-
   ery relative to cryogenic trapping/
   GC and precision obtained for the
   target compounds on solid adsor-
   bents is considered to be accept-
   able for most ambient air studies.
   Generally, individual data  points
   for the solid adsorbents agreed
   within a factor of two with the
   cryogenic sampling data.

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  6) The Volatile Organic Sampling
     Train (VOST) style cartridges gave
     low blank levels and are suggested
     as an alternative to the open style
     cartridge.
  On the basis of the results obtained in
this study, further evaluation  of  the
polyimide material for ambient air sam-
pling appears to be  unwarranted, since
a number  of operational difficulties
were encountered for which no obvious
solution exists. Furthermore, no  signifi-
cant advantages in terms of recovery of
highly volatile  compounds were  ob-
served, in comparison to Tenax®, when
sampling ambient air.
  The results of this study indicate that
the use of the VOST style cartridge of-
fers substantially better blank levels for
Tenax® than the conventional open-
style cartridges.  If this finding is inde-
pendently verified,  all  further studies
should use the VOST style cartridge.
Ralph M. Riggin and Richard A. Markleare with Battelle's Columbus Laboratories,
  Columbus, OH 43201.
James D. Mulik is the EPA Project Officer (see below).
The  complete report, entitled "Comparison of Solid Adsorbent Sampling
  Techniques for Volatile Organic Compounds in Ambient Air," (Order No. PB
  86-127 651 /AS; Cost: $11.95. 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 Monitoring Systems Laboratory
       U.S. Environmental Protection Agency
       Research  Triangle Park, NC27711
                                                                             U. S. GOVERNMENT PRINTING OFFICE-. 1986/646-116/20760

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