RESULTS
pinkwater and the experiment was repeated at a differ-
ent freezing rate.
The ice cylinders were cut into disks (parallel to
Visual observations suggest that more contaminants
the freezing front) on a band saw located in a 30∞C
were excluded at the slower freezing rates. Slow freez-
coldroom. Each disk was about 2 cm thick and was
ing rates produced a clearer ice cylinder than fast freez-
placed in a previously weighed brown-glass, wide-
ing rates. This can be seen in Figure 3 by comparing
mouthed jar, which was then reweighed to obtain the
the color of the ice cylinders frozen in Runs #1 and #4.
exact volume of melt. The ice was allowed to melt and
The ice cylinder produced during Run #1, which was
the samples stored in a refrigerator until analyzed.
frozen at 11.7 mm/hr, is obviously darker than the cyl-
To determine whether or not explosives were ex-
inder produced during Run #4, which was frozen at
ceeding their solubility limit and precipitating out of
2.1 mm/hr. Average TNT concentrations in the ice cyl-
solution, we analyzed the water and the particles sepa-
inders were 18.10 mg/L and 0.88 mg/L for Runs #1
rately. To analyze the water, 4 mL of each sample were
and #4, respectively.
added to 1 mL of acetonitrile and the mixture filtered
The initial pinkwater was cloudy, but no particles
through a Millipore 0.45-mm cartridge into 2-mL
were visible. After freezing, the residue and some of
autosample vials. To analyze the particles, the remain-
the ice segments contained distinct particles. These
ing water sample (~ 35 mL) was filtered through an
varied from small, sub-millimeter, rounded particles
Alltech 0.45-mm nylon membrane filter and the filter
in the samples nearest the freezing plate to millimeter-
was then placed in a vial containing 10 mL of acetoni-
sized, elongated particles near the icewater bound-
trile. The vials were shaken for 30 minutes and then
ary. The ends of the cores in contact with the residual
allowed to sit in the dark for 48 hours. One mL of the
liquid were usually coated with precipitated material.
acetonitrile was added to 4 mL of distilled water and
Chemical analyses of the ice cylinders confirmed
the mixture filtered into autosample vials.
the visual observations. More of each constituent was
excluded from the ice cylinder as the freezing rate was
RP-HPLC analysis
decreased. The concentrations of TNT, RDX, HMX,
Reverse-phase high-performance liquid chromatog-
TNB, 2-Am-DNT, and 4-Am-DNT in each ice cylin-
raphy (RP-HPLC) was used for these analyses. Method
der are tabulated in Appendix A.
8330 (EPA 1994), the standard method for determin-
The effect of freeze concentration on TNT is shown
ing explosive residues in water and soil, was followed.
in Figure 4. As expected, the TNT concentration was
We used a C-18 column that allowed us to separate
highest in the ice cylinder produced at the fastest freez-
RDX, HMX, TNT, and their derivatives. Two com-
ing rate of 11.7 mm/hr. At 9.4 mm/hr, the TNT con-
mercially available standards, Mix 1 and Mix 2, which
centrations appear to be nearly the same as at 11.7 mm/
contained all the analytes of interest, were run with
hr. The plots at 6.7 and 5.4 mm/hr show a significant
the samples. The eluent used was a mixture of distilled
reduction in TNT concentration. The ice cylinders with
the lowest TNT concentrations were produced at freez-
water and isopropyl alcohol in an 85:15 mix.
a. Ice cylinder produced during Run #1.
b. Ice cylinder produced during Run #4.
Figure 3. Visual comparison of ice cylinder color and clarity. Freezing direction is left to right.
4
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