from the chamber, they were analyzed by head-
mL of water was included to serve as a source of
space gas chromatography (HS/GC). The analy-
moisture to the chamber atmosphere. Then the
chambers were capped and allowed to stand for
sis system used consisted of a HS autosampler
periods of 3 weeks or longer in an incubator held
(Tekmar 7000), coupled to a GC (SRI, model 8610-
at 11 1C. In all, eight chambers were prepared
0058) equipped with a 15-m DB-1 0.53-mm capil-
in this fashion. Table 3 lists the quantities and
lary column and photo and flame ionization se-
types of samples, length of exposure, and the con-
quential detectors. The settings used for both of
tents of the organic vapor fortification solution
these instruments have been reported elsewhere
used for each experiment.
(Hewitt 1995a). One exception was for the analy-
At the end of the exposure period, the chamber
sis of the chamber vapor samples, where a platen
temperature of 40C was used. In preparation for
was removed from the incubator and a 0.5-mL
gastight syringe (Hamilton) was used to immedi-
analysis the water and soil samples were gently
ately remove a 500-L headspace sample of the
hand shaken until all of the vial contents had
chamber gas. This sample, representative of the
been completely dispersed.
vapor concentration at the end of the exposure
Analyte concentrations were established rela-
period, was immediately transferred to a sealed
tive to working standards prepared by transfer-
ring small (<10 L) quantities from a methanol
22-mL autosampler volatile organic compound
analysis (VOA) vial (Wheaton). Because of the
stock solution. Working standards prepared for
limited volume of the analysis VOA vial, two nee-
the chamber gas samples were placed in empty
dles of the same gauge (22 gauge) were used for
autosampler VOA vials, while those for the soil
this transfer step. The tip of a second needle,
and water samples were added to 10 mL of Type 1
which served as a pressure vent, was positioned
water (Hewitt et al. 1992).
adjacent to the Teflon-lined septum (near the
cap), while the needle used to transfer the sample
RESULTS AND DISCUSSION
of chamber gas was positioned in the middle of
the VOA vial. Both needles were quickly removed
Although not presented, results from several
after the transfer was completed (≈3 seconds).
preliminary studies served as the basis for the ex-
Three separate headspace sample replicates were
perimental design. Some of the more important
prepared in this fashion, using two different syr-
findings of these initial studies were that
inges. This number of replicates and use of two
The hydrophobic membrane slowed the
movement of water vapor as compared to
syringes was necessary because the needles can
leaving sample vials uncovered, but did not
become partially clogged with pieces of septa
completely prevent this process from occur-
during the retrieval and transfer process.
ring,
After removing the vapor samples, the cham-
No analyte interactions were observed, that is,
ber was opened. For six of the eight experiments
the same approximate concentration ratios
the glass bottle containing 10 mL of groundwater
was sampled twice with a 1.00-mL pipette. These
among three different media were obtained
aliquots of water from the uncovered moisture
regardless if one or more analytes were
reservoir were transferred directly to a 22-mL
present,
autosampler VOA vial containing 10 mL of Type 1
Analyte concentrations in all three media
water. Similarly each of the 2-mL sample vials
were temporal (changed with length of
exposure).
were transferred to a VOA vial containing 10 mL
The concentrations established for the six anal-
of water after weighing and removing the cap
ytes studied, in the three different media, appear
and membrane. Immediately, after transferring
in Appendix A. There are eight tables in Appen-
these samples, a Teflon-lined gray butyl rubber
dix A, one for each chamber experiment. For both
and aluminum crimp top was used to seal the
the discrete soil samples and the water samples
headspace autosampler VOA vials. Special pre-
cautions were taken when transferring a sample
held in the membrane covered vials, the final
vial to an autosampler VOA vial containing 10 mL
weight (weight of moist soil or groundwater) was
of Type 1 water, so as not to disturb or spill,
used to compute the analyte concentrations. The
respectively, the contents of either vessel.
air-dried soils, which started with a moisture con-
tent of <1%, ended up with a 2 to 3% moisture
content, independent of exposure period length.
Analysis
On the same day the samples were removed
Samples with initial moisture contents of either 5
4
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