SPME Holder
Plastic Screw Cap
Aluminum Foil
18 cm3
Vapor
SPME Fiber Collector
Headspace
Crystals of Military-Grade TNT
Soil
43 cm3 Amber Vial
Figure 1. Soil test device.
the vial opening and was secured in place using a
Design of experiment
plastic screw cap (Fig. 1). Two replicates for each
Replicates of each air-dried soil and each of the
combination of soil type and moisture level (18
two higher moisture level soils were placed in 40-
vials) were stored at room temperature (23C), at
mL , 27- 95-mm amber vials (six replicates of
4C, or at -12C. All vials were wrapped with a
each) to a depth of 2.5 cm. We used 40-mL (43 mL
sheet of aluminum foil to eliminate photocata-
total capacity) amber vials (Krackler Scientific)
lyzed reactions. Headspace samples were collected
with open-top screw caps, septa removed,
using solid phase microextraction (SPME) fibers
throughout the study. The vials were rinsed with
acetone and oven dried at 105C for several hours
at a number of time intervals from 11 to 173 days
as described below. After 63 days, we opened
prior to being used. We compacted the soil in
some replicates following headspace sampling,
each vial by dropping it several times onto a pad-
and sampled and analyzed the surface soil for
ded counter from a height of 5 cm. Previously
explosives-related compounds as described
ground and weighed (110-mg) portions of mili-
below. Other replicates were treated in an identi-
tary-grade TNT from Picatinny Arsenal were
cal manner at periods up to 173 days.
placed on top of the soil using a long-stemmed
polyethylene funnel. The TNT was spread into a
Soil sample collection, solvent extraction,
disk shape approximately 13 mm in diameter and
and analysis using RP-HPLC
1 mm deep, centered in the vial. Care was taken
After conducting the 63-day vapor analysis, we
to be sure no TNT touched the vial walls. An
decided to begin sampling the top 5 mm of soil in
additional 2.5 cm of soil was then carefully placed
one of the replicate vials (A) of the samples stored
in the vial, covering the TNT, and the soil was
at room temperature (23C). We did a similar
compacted as previously described. Bulk densi-
sampling on the 4C samples after 67 days and on
ties of the soils were determined by weighing two
the -12C samples after 69 days. Soils were sam-
representative vials of each soil, at each moisture
pled for replicate A, regardless of whether or not
level (Table 3). The vial weight was subtracted
signature chemicals were detectable in the vapor.
and the resulting soil weight was divided by the
The remaining replicate samples (B) continued
volume occupied by the 5 cm of soil (25 cm3).
their usual storage, with periodic analysis of the
Commercially available aluminum foil covered
3
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