mL volumetric flask. The fortification solution and
Just before spiking, each soil-filled ampoule was
open ampoules of soil were left in the desiccator
placed in a metal tension clamp. Immediately af-
at room temperature (22 2C) for periods of 33
ter a 0.200-mL aqueous spike was introduced us-
ing a 0.500-mL glass syringe (Hamilton), the am-
and 44 days for experiments I and II respectively.
poule was heat-sealed with a propane torch. All
At the end of this period, the desiccator was
spike aliquots were taken from well below the wa-
opened and a 5-mm glass bead was placed on top
ter/air interface, and the stainless steel needle was
of each ampoule. Then, as quickly as possible, each
wiped before being inserted into the ampoule
was heat sealed with a propane torch.
neck. Depending on the soil, the aqueous spike
The sealed ampoules were then stored for 4 or
7 days in a refrigerator (4C) before triplicates were
wetted the surface of between 1/2 and 1/4 of the
grains.
removed for different sample preparation and
In addition to the soil subsamples, 0.200-mL ali-
analysis protocols. In experiment II, triplicates of
quots of the spiking solution were also placed into
each of the four soil types were transferred to VOA
three separate auto sampler Volatile Organic-com-
vials (44 mL) containing either 10 mL of MeOH or
pound Analysis (VOA) vials (22 mL, Tekmar) con-
tetraglyme. In experiment III, preparation of sam-
taining 10 mL of Type 1 water, which were imme-
ples for analysis was staggered over a 2-day period
diately given crimp-top caps and Teflon-faced bu-
so that analyte determinations could be made
tyl rubber septa (Wheaton). These vials were
within 2 hours of the ampoule being broken or
spiked at the beginning, middle, and end of the
when a 0.100-mL aliquot of the extraction solvent
soil sample preparation process (about 1 hour) to
was removed after 2 hours of contact with the spec-
assess whether there were changes in VOC con-
imen.
centration of the spiking solution.
The 60 sealed ampoules containing treated soil
Subsample preparation for analysis
were placed in a refrigerator at 4C for 2 days to
We evaluated six different sample preparation
allow the analytes to interact with the matrix. Then
procedures to determine how efficiently they
they were removed and triplicates of each soil type
recovered VOCs from the laboratory-treated soils.
(3 4) were randomly assigned to each of five dif-
With a HS equilibrium method, each sample could
ferent sample preparation and analysis protocols
only be analyzed once. In contrast, several aliquots
(Table 3). Each ampoule was then placed inside a
could be removed when samples were placed in
VOA vial and, after capping, the soil was dispersed
an extraction solvent, thus allowing for an assess-
by hand shaking, causing only the ampoule to
ment of extraction kinetics and holding time ana-
break. Once the soil had been completely removed
lyte concentration stability (Table 4).
from the broken ampoule, the VOA vials were
returned to the refrigerator for storage until anal-
ysis. The three auto sampler vials used to monitor
Table 4. Solvent extraction
spike concentration and solution homogeneity
periods and conditions.
were analyzed by HS/GC within 24 hours of
Extraction period
preparation.
Solvent
and conditions
I. Aqueous spike
Vapor fortification treatment--experiments II and III
MeOH
5 days
Two separate experiments were performed with
Tetraglyme
6 days
vapor-fortified soils. The first used six replicates
II. Vapor fortification treatment
of four soil types (Table 3). The second experiment
1) <2 hours
MeOH
used 18 replicates of the CR-B soil (Table 3). For
2) 2 days
both experiments, ampoules containing 2.00 0.01
3) 4 days
g of soil were placed in a desiccator with anhy-
4) 41 days
drous CaSO4 for 48 hours (Hewitt and Grant 1995).
5) 79 days
Tetragylme
Same as MeOH
After desiccation, the CaSO4 was replaced with a
small glass bottle containing 5 mL of tetraglyme
III. Vapor fortification treatment
1) <2 hours
and 0.5 mL of a MeOH-based stock standard. The
MeOH
2) 2 days
stock standard had been prepared by adding (and
3) 4 days
weighing) 0.100 mL of TDCE, CDCE, Ben, TCE,
4) 29 days
and PCE, and 0.150 mL of Tol, E-Ben, p-Xyl, and
Tetraglyme
Same as MeOH
o-Xyl to MeOH, then taking it to volume in a 25-
PPG
Same as MeOH
3
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