Am-NT), 2-amino-4,6-dinitrotoluene (2-Am-DNT),
Table 2. RP-HPLC retention times (minutes)
and 4-amino-2,6-dinitrotoluene (4-Am-DNT). The
for the analytes of interest.
spiked samples were immediately placed into the ap-
propriate storage temperatures in the dark.
Analyte
Storage parameters and hold times
RDX
3.0
As mentioned, the soils were stored in the dark at
3-NA
3.5
three temperatures--room temperature (22 2C), re-
1,3-DNB
4.8
TNT
5.4
frigerator temperature (4 2C), and freezer tempera-
2-Am-6-NT
5.9
ture (4 2C). Triplicates stored under all three con-
4-Am-2-NT
6.5
ditions were extracted at time 0, after 4 hours, 1 day, 3
2-Am-4-NT
6.9
days, 7 days, 13 days, and 20 days, and the analyte con-
2,4-DNT
10.9
2,6-DNT
13.4
centration determined. An additional sampling and
4-Am-DNT
15.2
analysis was conducted at 9 days for samples stored at
2-Am-DNT
17.2
room temperature and at 30 days for samples stored at
4 and 4C. Because of the expected variability among
replicates, triplicate vials were analyzed for each stor-
age temperature for each storage time.
RESULTS AND DISCUSSION
Soil extraction
For soil extraction, the samples were warmed to
Concentrations of the spike analytes and transfor-
room temperature (which took approximately 15 min-
mation products obtained for each soil replicate are
utes) and extracted according to the procedure outlined
presented in Appendix A. Mean concentrations for each
in SW846 Method 8330 (USEPA 1994). Specifically, a
time period are presented in Table 3 for the samples
10.0-mL aliquot of acetonitrile (AcN) was added to each
stored at all three temperatures.
sample in a 22-mL scintillation vial. The vials were
Results for the time 0 samples at all temperatures
placed on a vortex mixer for 1 minute and placed in an
demonstrate that, at the start of the incubation, the con-
ultrasonic bath for 18 hours. The temperature of the
centrations of all four of the spike nitroaromatics were
bath was maintained at less than 25C with cooling
near 0.5 mg/kg. The results for the 4-hour samples at
22C (Table 3a) show that the degradation process at
water. The vials were then removed from the bath and
allowed to stand undisturbed for 30 minutes. A 2.0-mL
room temperature begins almost immediately and, for
aliquot of each extract was removed and combined with
some of the analytes, is very rapid. For example, the
8.0 mL of water. Each solution was then filtered through
mean concentration of TNT was reduced from 0.563
mg/kg to 0.461 mg/kg after only 4 hours at 22C.
a Millex SR (0.5-mm) disposable filter, with the first
milliliter discarded and the remainder collected in a
Figure 1 shows three chromatograms collected at
clean scintillation vial.
time 0 and days 1 and 7 for samples stored at room
temperature. This figure illustrates several dramatic
RP-HPLC analysis
changes in the sample composition over a relatively
All samples were analyzed by reversed-phase high
short time. First, the height of the peak corresponding
performance liquid chromatography (RP-HPLC) on a
to TNT is reduced by half in only 1 day and is only
modular system composed of the following: Spectra-
about one-forth its original height in just 7 days. The
Physics Model SP8800 ternary HPLC pump, a Spec-
peak for DNB was also reduced in height substantially
tra-Physics Spectra 100 variable wavelength UV de-
over this time, but to a lesser extent than TNT. In con-
tector set at 254 nm (cell path 1 cm), a Dynatech Model
trast, the peaks for 2,4- and 2,6-DNT dropped much
LC241 auto sampler equipped with a Rheodyne Model
less in the first 7 days, indicating that they are more
7125 sample loop injector, and a Hewlett-Packard
stable in this soil than TNT and DNB.
3393A digital integrator set to measure peak heights.
Evidence that the loss of TNT was partially attribut-
All extracts were analyzed on a 15-cm 3.9-mm
able to a degradation process, and not just poor recov-
LC-8 column (Waters) eluted with 85/15 water/isopro-
ery or irreversible sorption, was the increasing peak
panol (v/v) at 1.4 mL/min. Samples were introduced
height for the two amino reduction products of TNT:
by overfilling a 100-mL sampling loop. Retention times
2-Am-DNT and 4-Am-DNT. Likewise, 3-NA, the re-
of the analytes of interest are shown in Table 2. Con-
duction product of 1,3-DNB, is detectable in the chro-
centrations were estimated against SARM multianalyte
matogram as early as the day 1 sample. A plot of the
standards.
concentration of TNT with time (Fig. 2) shows that the
4
Previous Page
