flowing at 1.4 mL/min. Retention times for the five
Table 1. Concentration ranges for the working
target analytes were RDX--2.9 min., TNT--5.3
standards of TNT, 2,4-DNT, RDX, 2ADNT, and
min, 2,4-DNT--10.3 min, 2ADNT--13.5 min, and
4ADNT prepared for the evaluation of the nitro-
4ADNT--15.4 min. Determination of HMX was
gen-phosphorus (NP) and electron capture (EC)
conducted using a 25-cm 4.6-mm CN column
(Supelco) using 50:50% water/methanol flowing
at 1.4 mL/min. The retention time for HMX was
Detector
Concentration range
(mg/L)
11.1 min.
NPD
0.2510.0
Sample preparation--soil
All soils were obtained from near-surface loca-
ECD
0.011.00
tions and air dried. While transferring subsamples
of soil to 40-mL amber VOA vials, pebbles larger
than 2 mm in diameter or any large pieces of veg-
injector (8690-0025) and two detectors, a NPD
etation were excluded. For the MDL study we used
(8690-0015) and ECD (8690-0020, Ni63), was used
an explosive-free soil obtained at Ft. Ord, Califor-
for this study. Separations were performed on a
nia. All other field soils analyzed were removed
Crossbond 100% dimethyl polysiloxane column,
from bulk samples in which detectable explosive
6 m 0.53 mm i.d., 1.5 m (Restek MXT-1). The
residues had been identified. These field-contami-
injection-port temperature was 250C and the ni-
nated samples had been obtained at firing ranges
trogen carrier gas was set at about 9.5 mL/min
and ammunition production plants.
(3640 psi). Injections (1 L) were made manually
Soil samples were prepared for the MDL study
with a 10-L glass syringe (Hamilton) equipped
by placing 20 g into seven separate amber 40-mL
with an extra long needle (7.5 cm).
VOA vials. These samples were each spiked by
When the NPD detector was used, the oven
adding 1.00 mL of an acetone solution containing
temperature was initially held at 100C for 2 min;
the five target analytes and HMX, using a glass
then the temperature was programmed at 20C per
pipette. This volume of spiking solution wetted
minute to 240C, and held at 240C for 0.5 min-
the top three-quarters of the soil and created a soil
utes. Air from the onboard purification system was
concentration of approximately 0.5 mg/kg, for
supplied at 6 psi (41 kPa) and zero grade hydro-
each analyte. After standing uncovered for 1 hour
gen was supplied at 7 psi (48 kPa) (flow rate was
inside an exhaust hood, 20 mL of acetone was
approximately 2 mL/min). The voltage setting for
transferred to each vessel using a graduated cyl-
the NPD was 350 V and this detector was un-
inder. Each bottle was capped and shaken several
heated.
times over a 5-minute period. The suspended soil
When the ECD was used, the nitrogen makeup
was allowed to settle for 30 minutes then a 3-mL
aliquot of the supernatant was pulled into a 5-cm3
gas was supplied at 3640 psi (248276 kPa) by
splitting the flow from the carrier gas supply line.
Luer-Lok syringe (Becton Dickinson & Co.) while
For ECD analyses the oven temperature was ini-
leaving a pocket of air between the plunger
tially held at 140C for 6 min, then temperature
and solvent extract. The air pocket prevented the
programmed at 20C per minute to 180C, while
acetone extract from coming into contact with
the detector was maintained at 250C.
the rubber plunger, which could compromise
the analysis. The extract was filtered through a
Millex-SR 0.5-m disposable filter unit (Millipore),
RP-HPLC analyses
Confirmation analyses, by reversed phase high
discarding the first 1-mL portion and collect-
ing the remainder into an amber 2-mL vial for
performance (RP-HPLC), were performed on the
subsequent instrumental analysis. Likewise, por-
working standards, stock aqueous solutions (used
tions of eight field-contaminated soils were ex-
for the aqueous method detection limit [MDL]
tracted with acetone and filtered in preparation
study), and field-contaminated soil samples. The
for analysis.
acetone-based standards and soil extracts were
diluted 1:5 (0.300 mL acetone + 1.200 mL water)
with reagent-grade water prior to analysis. Con-
Sample preparation--water
The MDL study for aqueous samples was per-
firmation analyses of the target analytes was con-
ducted on a C-8 column, 15 cm 3.9 mm (Nova
formed using a 1-L volume of reagent-grade wa-
ter fortified with the target analytes. An aqueous
Pak). The eluent was 85:15% water/isopropanol
4
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