spiked by adding either 1 mL or 5 mL of a 50-g/
4.6-mm (5-m) cyano (Supelco LC-CN) column
L solution to 25-g soil samples to yield 2-g/kg
eluted with either 1.5 mL/min 1:1 methanol:water
and 10-g/kg samples for the nitroaromatics of
or 1.2 mL/min 12:13:62 methanol:aceto-
interest for mine detection (Table 1). The spike
nitrile:water. Injection volume for each separation
was 100 L. Following these HPLC separations,
solution also contained RDX at a concentration
four times greater than the nitroaromatics. The
absorbance was recorded at 254 nm on a Spectra
samples spiked with 1 mL were aged uncapped
Physics Spectra 100 variable wavelength UV de-
for one hour prior to extraction. The samples
tector.
spiked with 5 mL were aged 24 hours uncapped.
All samples were extracted with 50 mL of acetoni-
trile containing 3,4-DNT (25 g/L) as an internal
RESULTS
standard. These samples were also extracted for
18 hours in a cooled sonic bath.
Field-contaminated soils: Concentration
Similar spike recovery studies were performed
estimates by GC-ECD and HPLC-UV
with other matrices, including glass beads (25-
Wide concentration range
micron, 3M Company), silt (dry and wet), and AEC
To test the feasibility of using GC-ECD for the
soil.
analysis of soil extracts, we chose 24 archived field-
contaminated soils that contained several of the
analytes of interest over a wide range of concen-
tration (based on previous HPLC analysis) and a
GC-ECD
variety of sites across North America. Because
Initially we used an HP 5890 equipped with an
Ni63 ECD. Later, we used an HP 6890 equipped
some of these soils were analyzed by HPLC over
with a micro cell Ni63 ECD. For both GCs, we used
a decade ago, we repeated an HPLC analysis along
direct injection (250C) of 1-L samples. The in-
with the GC analysis using extract splits from 2-g
jection port liner was a deactivated Restek
soil aliquots extracted with 10 mL of acetonitrile.
Uniliner. The analytical columns were 6-m- by
We used the standard HPLC separation initially,
0.53-mm-ID fused-silica, 1.5-m film thickness of
then for those soils containing isomers of DNT and
either 100% polydimethylsiloxane (J and W DB-1)
Am-DNT, extracts were reanalyzed using one of
or (5%-phenyl)-methylsiloxane (HP-5). The GC
the alternative HPLC separations described above.
oven was temperature-programmed as follows:
For GC, extracts were analyzed on the HP 5890
100C for 2 min, 10C/min ramp to 200C, 20C/
where the ECD had a very limited linear range.
min ramp to 250C, 5 min hold. The carrier gas
All extracts were diluted by at least a factor of 10
was hydrogen or helium at 12 to 15 mL/min. The
makeup was nitrogen (30 to 40 mL/min). Con-
range. These large dilutions probably prevented
firmation columns were Restek RTX-200
the deposition of high boiling point residues in
(Crossbond trifluoropropyl methylpolysiloxane)
the injection port liner and on the head of the GC
and Restek RTX-225 (50% cyanopropylmethyl
column, a potential problem that concerns us
50% phenyl methylpolysiloxane). Details of the
when GC is used routinely for the analysis of soil
procedure may be found in SW-846 Method 8095
extracts.
(USEPA 1998).
Results of these analyses are shown in Table A1.
We correlated the GC concentration estimates with
HPLC-UV
those obtained by HPLC for those analytes that
Initial studies used the HPLC separation speci-
were detected 10 or more times out of the 24
fied in Method 8330. A 25-cm by 4.6-mm (5-m)
samples. The most frequently detected analytes
octadecyl (Supelco LC-18) column was eluted with
were TNT (18 times), RDX (11 times), 2,4-DNT (15
1.5 mL/min 1:1 methanol:water. Two alternative
times), TNB (19 times), DNB (12 times), and HMX
separations to achieve resolution of DNB, DNT,
(10 times). All correlation coefficients (Fig. 1) were
and Am-DNT isomers used either a 25-cm by 4.6-
greater than 0.97. However, with the exception of
mm (5-m) octadecyl (Burdick and Jackson OD5)
DNB, slopes of the least squares regression mod-
column eluted with 1.4 mL/min 33:13:54
els were significantly different from the expected
methanol:acetonitrile:water or a 15-cm by 3.9-mm
value of 1.00. For TNT, RDX, and 2,4-DNT, slopes
(4-m) Nova Pak C8 (Waters Millipore) column
were all greater than 1.00. Because concentrations
eluted with 1.4 mL/min 15:85 isopropanol:water.
for each of these analytes spanned over six orders
The confirmation separation was on a 25-cm by
of magnitude, this difference in slope may be an
4
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