TITLE
Supercritical Fluid Extraction as a Means of Cleaning and Desorbing
Common Air Sampling Sorbents


AUTHOR(S)
J.R. Bowyer, Mantech, RTP, NC 27709 and J.D. Pleil, U.S. EPA, (MD-
44), RTP, NC 27711

PERFORMING ORGANIZATION NAME AND ADDRESS
Mantech Environmental Technology, Inc.
Research Triangle Park, NC 27709

SPONSORING AGENCY NAME AND ADDRESS
National Exposure Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711

ABSTRACT
Supercritical fluid extraction (SFE) with carbon dioxide has become
an increasingly popular alternative method to Soxhlet extraction
for the measurement of organic compounds adsorbed on solid
matrices.  The application of SFE to air sampling materials for
recovery of adsorbed (collected) organic pollutants is an obvious
extension of this technology.  To develop appropriate methods, the
first practical steps are the determination of the physical and
chemical stability as well as the general cleanliness of the
candidate adsorbent materials under the demanding SFE conditions. 
Then the adsorbent behavior is compared to results from parallel
tests with commonly used Soxhlet extraction methods.  This paper
describes exploratory research with the common air sampling media
Tenax-GC, Tenax-GR, XAD-2, and Carboxen 563.   All were found to be
physically and chemically compatible with SFE.  XAD-2 and Carboxen
563 have an initial cleanup advantage over the two Tenax types and
Tenax-GC is subject to artifact formation from ozone exposure.  All
four sorbent types could, once cleaned, be stored for four weeks in
sealed cartridges without buildup of contaminants indicating that
the SFE cleanup procedure removes impurities from within the
sorbents.