Table 10. Average and standard deviation (n = 3) of analyte concentration (mg/kg)
stability in sample VOA vials with punctured septa vs. VOA vials with intact septa.
Intact septa
Punctured septa
spiking solutlion
samples
Cmpd
D0*
D7
D14
D21
D0
D7
D14
D21
TDCE
3.82
3.78
3.71
3.65
3.48
2.93
2.57
2.04
.17
.21
.18
.26
.10
.27
.38
.50
99%*
97%
96%
84%
74%
59%
CDCE
3.88
3.78
3.82
3.82
3.73
3.35
3.22
2.89
.04
.19
.10
.22
.03
.14
.20
.29
97%
98%
98%
90%
86%
77%
Ben
2.95
2.89
2.92
2.88
2.77
2.51
2.34
2.03
.04
.10
.11
.17
.08
.10
.18
.27
98%
99%
98%
91%
84%
73%
TCE
4.01
3.89
4.02
3.95
3.79
3.46
3.20
2.71
.08
.10
.11
.14
.07
.14
.29
.39
97%
100%
99%
91%
84%
72%
Tol
3.36
3.24
3.31
3.24
3.11
2.76
2.60
2.28
.10
.10
.16
.22
.07
.13
.25
.28
96%
99%
96%
89%
84%
73%
PCE
2.44
2.43
2.46
2.41
2.33
2.04
1.84
1.55
.04
.07
.09
.12
.09
.13
.20
.28
100%
101%
99%
88%
79%
67%
E-Ben
2.86
2.80
2.87
2.74
2.69
2.44
2.28
1.99
.04
.17
.04
.14
.08
.10
.20
.20
98%
100%
96%
90%
85%
74%
p-Xyl
2.94
2.87
2.97
2.85
2.72
2.43
2.33
1.99
.07
.10
.12
.18
.08
.14
.18
.25
98%
101%
97%
89%
86%
73%
o-Xyl
3.05
2.90
3.07
3.02
2.88
2.60
2.56
2.14
.08
.08
.12
.19
.10
.12
.16
.22
95%
101%
99%
90%
89%
74%
*Percent recovery relative to D0 sample concentration.
ability to recover sorbed analytes by direct vapor
when using the lower level of analysis in Method
partitioning methods of analysis may also decrease
5035, i.e., direct purge-and-trap.
with the length of storage, is why most studies
Additional findings unique to the empty VOA
rely on a MeOH extraction for sample prepara-
vial experiments were that
tion. Experiments designed to assess sample pres-
Samples analyzed directly by a vapor parti-
ervation are likely to be confounded by matrix ef-
tion method of analysis failed to achieve
fects when a vapor partitioning method of analysis
quantitative recoveries (Table 8).
is used. Therefore the interpretation of the results
The rate biological degradation appears to in-
would be ambiguous, with the possible exception
crease at lower analyte concentrations (Tables
of a study performed with a matrix similar to Ot-
7 and 8).
tawa sand (Hewitt 1998b).
Biological degradation of VOCs appears to
Concerning only spiked samples prepared by
be stopped when a soil/water slurry is fro-
zen (Table 8).
MeOH extraction, the decreases in analyte concen-
trations shown for Ben, Tol, E-Ben, and p-Xyl in
Soil/MeOH slurries show decreasing analyte
Tables 7 and 8 show that losses were apparently
concentrations with time when held in a VOA
more rapid at lower analyte concentrations when
vial with a punctured septum (Table 10).
held at 4 2C. These compounds decreased by
The first observation, and the possibility that the
18
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