Cleanliness of Common Air Sampling Sorbents for
Application to Phenolic Compounds Measurement Using
Supercritical Fluid Extraction
ManTech Environmental Technology, Inc., Research Triangle Park, NC
Prepared for:
Environmental Protection Agency, Research Triangle Park, NC
1994
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
NIA

-------
EPA/600/A-94/163
CLEANLINESS OF COMMON AIR SAMPLING SORBENTS
FOR APPLICATION TO PHENOLIC COMPOUNDS MEASUREMENT
USING SUPERCRITICAL FLUID EXTRACTION
James R. Bowyer
ManTech Environmental Technology, Inc., Research Triangle Park, NC 27709
Joachim D. Pleil
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
ABSTRACT
The trace-level measurement of phenolic compounds in the ambient air is complicated
by the acidic and polar nature of the compounds especially dnring recovery from the sampling
medium. Recently, supercritical fluid extraction (SFE) has been proposed as an alternative
extraction method to Soxhlet extraction or thermal desorption to achieve more efficient
recoveries. For such methodology to become practical, the candidate sorbents must first be
tested for stability and cleanliness under SFE conditions. This paper describes exploratory
research results of background contamination tests and cleanup properties of some common air
sampling sorbent media with respect to future application to phenolic compounds monitoring.
INTRODUCTION
SFE offers the following advantages over more traditional extraction methods such as
Soxhlet: 1) less expensive in terms of solvent purchase and disposal, 2) less harmful to the
environment, 3) less time consuming in sample preparation, and 4) equivalent or better
recoveries to traditional methods. It is for these and other desirable characteristics that SFE has
become an increasingly popular alternative to other extraction techniques.1"5 It is also makes an
attractive alternative means of cleaning and extracting sorbents used in air monitoring.
This work describes preliminary results of clean up properties and contaminants in these
sorbents. Also investigated were the effects of storage and exposure to ozone67.
EXPERIMENTAL PROCEDURE
gprbent?
The sorbents used in this work were Tenax-GC, Tenax-GR (Alltech Assoc., Inc.,
Deerfield, IL), XAD-2, and Carboxen 563 (Supelco, Bellefonte, PA). For SFE extractions the
following amounts of each sorbent were used: Tenax-GC, 0.2g; Tenax-GR, 0.4g; XAD-2,0.4g;
Carboxen 563, 0.6g. For Soxhlet extractions the following amounts of sorbent were used:
Tenax-GC, 0.6g; Tenax-GR, l.Og; XAD-2, 2.0g; Carboxen 563, l.Og.
SFE conditions
Extractions were performed using a system that included two Isco pumps (models 260D
and 100D), a Lee Scientific oven (model 501), stainless steel tubing, and deactivated fused silica
restrictors (Polymicro Technologies, Phoenix, AZ). A sample of each sorbent was placed in a

-------
clean 1 mL stainless steel extraction cartridge and extracted using 5% methanol (MeOH)/carbon
dioxide (COO (v/v) at 50 C and 6000 psi. Each sorbent was statically extracted for 30 minutes
then dynamically for 0.5 -1.5 hours with collection of extracted material over 30 minute
intervals during this time. Flowrates of the supercritical fluid were approximately 1 mL/min.
Collection was in vials containing 2-3 mL of methylene chloride (MeCy. These solutions were
then reduced to a final volume of approximately 1 mL with a N2 flow.
gpxhlet rendition?
Sorbent samples were weighed and placed in cleaned cellulose extraction thimbles. The
thimbles were then loaded in the Soxhiet extractors and the extractors were charged with 200
mL of extraction solvent. 5% ether/hexane (v/v) was used for the Tenax-GC and Tenax-GR
sorbents and MeCl2 was used for XAD-2 and Carboxen 563. The Soxhiet extractors were then
allowed to run for 16-18 hours; after which the solvent was rotary evaporated down to 3-4 mL
and then transferred to an evaporation vial for final reduction to 1 mL with a N2 flow.
Analysis by QC/MS
Once the samples were blown down to 1 mL, an internal standard of 4,4'-dibromo-
1,1'biphenyl was added at a concentration of 1 ng//iL. A 1-piL aliquot was then inject into a
Hewlett-Packard GC/MS (HP5890/HP5971A, respectively) equipped with an XTI-5 column
(Restek, Bellefonte, PA, 30 m, 0.25-mm i.d.,0.25-/xm d.f., catalog # 12223).
Temporal and chemical stability
Once the sorbents were cleaned, the SFE cartridges were sealed and allowed to remain
sealed for 4 weeks. This was done to determine if the sorbents remained clean once they were
extracted. At the end of this 4-week period the sorbents were once again extracted by SFE as
in the original clean up extraction above and the extract analyzed.
Chemical stability was investigated by exposing the sorbents to ozone and extracting them
using SFE as above. The ozone exposure was 115 ppb for 18.5 hours at a flowrate of 1.3
L/min. with a relative humidity of 48-52% for the Tenax-GC and Tenax-GR. For the XAD-2
and Carboxen 563, ozone exposure was 115 ppb for 16.0 hours at 1.5 L/min.with a relative
humidity of 40-50%. Again, the extracts were analyzed by GC/MS as above.
RESULTS
Initial "Clean-up" Extractions
As expected, analysis of the SFE and Soxhiet extracts from Tenax-GC, Tenax-GR, and
Carboxen 563 revealed significant amounts of impurities in the first sequential extracts.
However, the third sequential SFE extracts and the second sequential Soxhiet extracts showed
no detectable impurity except a consistent phthalate ester component. This compound was found
in all sorbents at varying levels but was greatly reduced with each subsequent extraction. It
should be noted that it was much easier and quicker to reach this level of "cleanliness" using
SFE (1.5-2 hours) than Soxhiet extraction (16-18 hours).
Analysis of the XAD-2 extracts revealed that this particular lot was surprisingly clean
given past experience with XAD-2. Previously, XAD-2 was repeatedly extracted but still
retained significant amounts of impurities. The impurities detected were the phthalate ester as

-------
in the other sorbents and an acid ester. The acid ester was only observed in the Soxhlet extract.
Subsequent extractions reduced the amount of these compounds in each extract.
During these initial clean-up extractions, it was noted that the hexane/ether mixture added
significantly to the background signal. Therefore, higher purity hexane was purchased and the
problem was eliminated.
The following observations were made after comparing the chromatograms of the
sequential SFE and Soxhlet extracts for the various sorbents.
Tenax-GC
	There were four primary contaminants associated with this sorbent. Two were
common to both the SFE and Soxhlet extracts and of the other two, one was found
in each.
Tenax-GR
	There were ten primary contaminants and they were components of both the SFE and
Soxhlet extracts at about the same relative levels.
XAD-2
	There were only two primary contaminants and one was associated with the SFE
extract and the other was associated with the Soxhlet extract.
Carboxen 563
 There were nine primary contaminants and only one was associated with the SFE
extract. The other eight were associated with the Soxhlet extract.
Temporal and Ozone Stability
Comments below pertain to chromatograms obtained from analysis of SFE extracts of
sorbent sealed for 4 weeks then extracted () and sorbent exposed to ozone then extracted (o).
Tenax-GC
	Comparison of the third sequential extract before sealing and the first extraction after
being sealed revealed that there was no residual contaminants except for the ever
present phthalate ester mentioned above. Also, after a second extraction this peak
also became negligible.
o Exposure to ozone did produce artifacts from the degradation of the Tenax-GC which
could be problematic if ambient measurements of compounds such as benzaldehyde
and acetophenone were being performed.
Tenax-GR
	Comparison of the third sequential extract before sealing and the first extraction after
being sealed revealed that there was no residual contaminants except the phthalate
ester. Again this was removed completely after the second extraction.

-------
o Only two artifacts were formed from exposure to ozone and at levels lower than for
Tenax-GC and did not include benzaldehyde nor acetophenone.
XAD-2 and Carboxen 563
o Comparison of the extracts before and after sealing showed no change in the sorbent.
o No effect on the sorbents was noted and uo artifacts were extracted.
CONCLUSIONS
The following conclusions can be drawn from this preliminary study:
O Since the two extraction methods can extract different components from the sorbents,
whichever method is used for clean up should also be used for the extraction of the
sample collected on the sorbent.
O Tenax-GR is preferable to Tenax-GC because of its greater stability in O,.
O XAD-2 and Carboxen 563 may be preferable to either Tenax type because of their
ease of cleaning and stability in Oj. Comparison of their collection and recovery
efficiencies to those of Tenax GC and GR will help determine this.
0 For preparation of small amounts of sorbents such as sorbent cartridges, SFE would
be preferable to Soxhlet extraction in terms of time and handling ease. A cartridge
could be filled, cleaned, used, extracted, and possibly reused, all without having to
remove and handle the sorbent thus minimizing the chance of contamination and
sample loss.
DISCLAIMER
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency under Contract No. 68-DO-0106 to ManTech Environmental
Technology, Inc. It has been subjected to Agency review and approved for publication.
Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
REFERENCES
1.	Hawthorne, S.B. 1990. Analytical-Scale Supercritical Fluid Extraction. Anal. Chem.
62:633A-642A.
2.	Hawthorne, S.B., Miller, D.J., Langenfeld, J.J., Burford, M.D. 1992. Analytical-Scale
Extraction of Environmental Samples Using Supercritical Fluids. ACS Symposium
Series 508. Washington, DC: American Chemical Society.
3. Wright, B.W., Wright, C.W., Gale, R.W., Smith, R.D. 1987. Anal. Chem. 59:38-44.

-------
4.	Chester, T.L., Pinkston, J.D., Raynie, D.E. 1992. Supercritical Fluid Chromatography
and Extraction, Anal. Chem. 64:153R-170R.
5.	Engelhardt, H.t Gross, A. 1991. Supercritical Fluid Extraction. Trends Anal. Chem.
10:64-71.
6.	Pellizzari, E., Demian, B., Krost, K. 1984. Sampling of Organic Compounds in the
Presence of Reactive Inorganic Gases with Tenax GC. Anal. Chem. 56:793-798.
7.	Bunch, J.E., Pellizzari, E.D. 1979. Evaluation of Chromatographic Sorbents Used in
Air Pollution Studies. J. Chromatography. 186:811-829.

-------
_ TECHNICAL REPORT DATA
(rte*st rmi/muvtti&u ok tht nrtnt btfatt comptrrinjl '

no. a.
EPA/600/A-94;i63
a. *ieit
4. TITLE *NO SulTlTLt
CLEANLINESS OF COMMON AIR SAMPLING SORBENTS
FOR APPLICATION TO PHENOLIC COMPOUNDS MEASUREMENT
USING SUPERCRITICAL FLUID EXTRACTION
DAT!
1.riRPOKMINB DKGANltATiDN COOt
j. yrOA[*l
~X P.. >^er- oA 3"v b >. \
l.ftMOAMIKB OHBANlXATIO* fti>0MT HO.
i rtnroiiuiNS ousaniiation mami ano ABOniss
HttrtTcc-U Gr>U""TO^ y T-viC-
R.eStM.t-c^v KG-
IB. PACSAAM iL-lut *1 6.
VV."C65.tkAt!/B*ANl kg).
Oo  O jOtS
2.I0Mf9MlNS AOINCT KAMI AND AODKIU
A wrb/m r.5 t>/ a m* l-
U.S, EPA
ft>ese^><.v"uJv i v-iotiA^le pc^rlCj JL?'?-!!
ia.T*M Of Al>*T4DH*ieOMVlAiO
 . fOHtOAlNB AOINCt cost
11. tumtUlNTARr MOTtS
u. autaact
ABSTRACT
The trace-level measurement of phenolic compounds in the ambient air is complicated
by the acidic and polar nature of the compounds especially during recovery from the sampling
medium. Recently, supercritical fluid extraction (SFE) has been proposed as an alternative
extraction method to Soxhlet extraction or thermal desorption to achieve more efficient
recoveries. For such methodology to become practical, the candidate sorbents must first be
tested for stability and cleanliness under SFE conditions. This paper describes exploratory
research results of background contamination tests and cleanup properties of some common air
sampling sorbent media with respect to future application to phenolic compounds monitoring.
17. KIT *OAM AKS DOCUMIWT AHALTit*
 DttenirroM
b.tDtHTIIItftt'O'tH IXDtD T!HUl
C. COS ATI rld'Ct0U|)



It CllTftllUTlO* tTATlMINT
RELEASE TO PUBLIC
1* lICUAiTt CLAIS (Tiut A(^on)
UNCLASSIFIED
21.mo. o
as (icuniTT ci.au(rim
UNCLASSIFIED
JJ MICl
(I>A Par* tVS-% (. 4-77) ac*iui csitibm it  unit*I

-------