Table 2. Soil sample concentrations established
relative to HS/GC analysis, the correlation shown
for discrete grab samples by the Gore-Sorber mod-
in Figure 3 suggests the opposite trend for recov-
ule and by in-vial sample collection and HS/GC
ery of this analyte from colocated field grab
analysis.
samples. That is, TD/GC/MS analysis of the Gore-
Sorber module typically resulted in greater con-
Gore-Sorber
centrations of TCE than established by HS/GC
In-vial HS/GC (g TCE/g)
(g TCE/g)
analysis. In reality too few comparison were made
Location
76 cm
91 cm
Mean
85 cm
to offer an explanation for this observation. How-
1
5.7
6.8
6.2
11.0
ever, in the presence of moisture (i.e., ample wa-
2
15
16
16
23.5
ter vapor), VOCs may not be as strongly retained
4
3.1
5.5
4.3
5.12
as by a desiccated soil; thus under field condi-
7
0.016
0.014
0.015
<0.02
tions Tenax-TA may have a greater apparent af-
13
1.5
1.6
1.6
2.19
finity.
14
2.1
5.2
3.6
2.31
Table 3 shows the TCE results obtained from
18 locations (Fig. 1), for both the two grab samples
and below, and analyzed by HS/GC. All values
taken for HS/GC analysis and the mass of TCE
are reported on a mass per mass basis by account-
sorbed by the passive soil vapor GORE SORBER
ing for the number of sorbent packs present (only
modules over the 16-day exposure period. In this
one of the three replicate packets present during
table (Table 3) the GORE SORBER results are re-
exposure was analyzed). A comparison between
ported only as the total amount of TCE deter-
these two methods was evaluated by plotting the
mined, since the mass of soil from which the va-
mean TCE concentration from the two grab
pors came is not known. Not included in Table 3
samples analyzed by HS/GC vs. the concentra-
is a single detection of cis-1,2-dichloroethylene,
tion estimated from analysis of the Gore-Sorber
and several for carbon tetrachloride and tetra-
module. This limited comparison (five out of the
six locations) has a correlation coefficient (r2) of
chloroethylene, established by the analysis of the
Gore-Sorber module. In every case where these
0.964, and slope of 1.62 (Fig. 3). Failure to detect
other analytes were detected, the mass established
TCE on the sorber module positioned at location
for TCE was at least 20 times greater (more often
no. 7 is consistent with the detection limit re-
>100).
ported for this technology (0.02 g TCE) and the
Looking first at the comparison between the
concentrations established by the colocated grab
colocated grab sample results, a strong linear re-
samples taken for HS/GC analysis (Table 2).
lationship is shown, with a correlation coefficient
Unlike the 57% recovery of TCE from the labo-
of 0.957 (Fig. 4). This correlation and slope of
ratory fortified soil as determined by TD/GC/
1.088 show that TCE was homogeneously distrib-
MS analysis of the Tenax-TA sorbent (Table 1)
25
Slope = 1.62
y-intercept = 0.9853
20
r 2 = 0.9645
15
Best
Fit
10
5
Figure 3. Comparison of the
mean TCE concentrations
(g/g) in grab samples estab-
lished by HS/GC and by
0
4
8
12
16
Gore-Sorber modules.
Grab Sample (g TCE/g)
6
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