Table 7. Average and standard deviations (n = 3) of analyte concentrations (mg/kg) for spikes
and samples after various holding periods in VOA vials under different storage conditions
(21 2C, 4 2C, and 12 3C).
Analyte concentrations (mg/kg)
D7
D14
D3
21C
21C
4C
12C
21C
4C
12C
Cmpd
Spike
D0
TDCE
3.82
3.48
3.27
3.00
3.11
3.35
2.32
3.04
3.34
.17
.10
.15
.12
.32
.04
.06
.12
.04
94%*
86%
89%
96%
67%
87%
96%
CDCE
3.88
3.73
3.16
2.25
3.33
3.52
1.56
3.30
3.65
.04
.03
.08
.09
.35
.08
.28
.06
.04
84%
60%
89%
94%
42%
89%
98%
Ben
2.95
2.77
1.45
ND†
2.50
2.69
ND
0.09
2.79
.04
.08
.19
.30
.01
.01
.02
52%
<1%
90%
97%
<1%
3.2%
101%
TCE
4.01
3.79
3.62
3.43
3.58
3.74
2.82
3.55
3.76
.08
.07
.13
.12
.33
.05
.12
.04
.04
95%
90%
94%
98%
74%
94%
99%
Tol
3.36
3.11
0.89
ND
2.72
2.99
ND
0.73
3.06
.10
.07
.13
.23
.06
.21
.03
29%
<1%
88%
96%
<1%
23%
98%
PCE
2.44
2.33
2.18
2.06
2.13
2.27
1.75
2.06
2.24
.04
.09
.06
.04
.15
.03
.08
.04
.04
94%
89%
92%
97%
75%
89%
96%
E-Ben
2.86
2.69
0.71
ND
2.29
2.59
ND
0.59
2.56
.04
.08
.39
.12
.04
.18
.04
26%
<1%
85%
96%
<1%
22%
95%
p-Xyl
2.94
2.72
0.98
ND
2.30
2.63
ND
1.02
2.65
.07
.08
.32
.13
.04
.12
.06
36%
<1%
84%
97%
<1%
38%
97%
o-Xyl
3.05
2.88
2.48
1.37
2.60
2.74
ND
2.68
2.85
.08
.10
.04
.10
.17
.04
.08
.08
86%
47%
90%
95%
<1%
93%
99%
* Percent recovery relative to D0 sample concentration.
† Not detected.
are for the most part composed of materials that
centration of VOCs was recovered following two
days of storage at 42C. Moreover, usually there
are inert with respect to VOCs. However, their re-
spective removable closures rely on formulations
was no further significant loss of VOCs when
of Teflon to produce a hermetic seal. The VOA vial
samples were transferred to a freezer and stored
at 12 3C for an additional 12 days. Therefore,
uses a 0.25-mm (10-mil) or thicker Teflon sheet
attached to a silicone septum, to serve as a com-
discrete samples could be collected and held for
pressible surface to seal against the glass rim. The
up to two days at a temperature that is compat-
En Core sampler uses Viton O-rings compressed
ible with the logistics of field operations. Then, if
against a rigid plastic surface (50% glass-filled
a longer holding time was necessary, they could
nylon) to create seals at both ends of the sample
be stored in a freezer on- or off-site, for up to an
coring/storage chamber (Fig. 4). These polymeric
additional 12 days, before being prepared and
materials have some limited adsorption proper-
analyzed.
ties and they also allow for the slow permeation
Freezing offers several advantages over the rec-
of VOCs. When used as chambers for discrete soil
ommended in-field chemical preservation option,
samples, typically 80% or better of the initial con-
e.g., no prior knowledge of the VOC concentra-
15
Previous Page
