Groundwater Sampling Devices
15
A combined explosives standard (8330 Calibration Mix #1) (Analytical
Reference Materials Ultra Scientific) (1000 g/mL in acetonitrile) was diluted in
HPLC-grade acetonitrile to yield 100 g/mL. These standards were stored in the
dark in a freezer. Working standards were made each sampling day by adding the
diluted standard to deionized water to yield 2.5 and 0.25 mg/L.
Pesticides
Samples were collected in 43-mL glass vials with Teflon-lined plastic caps.
Thirteen mL of sample were removed from each vial and discarded. The pesti-
cides in the remaining 30 mL were extracted using pesticide-grade hexane
according to a modified EPA Method #505 (US EPA 1991) as described by
Parker and Ranney (1997b). After the hexane layer was carefully drawn off with
a Pasteur pipet, any remaining water was removed by passing the hexane through
a Pasteur pipet filled with glass wool and anhydrous sodium sulfate that had been
washed with hexane. The dried hexane samples were then placed in 1.8-mL
amber glass autosampler vials and stored at 4C until they were analyzed.
Analyses were performed on a HewlettPackard (HP) 5890 series II gas
chromatograph (GC) with an electron capture detector (ECD) equipped with an
HP 6890 series autosamplerinjector, all under the control of HPChemstation
software. The GC was operated in splitless mode with 1-L injections. The
instrument was set with the following operating parameters: an injector temper-
ature of 225C, oven temperature of 200C, detector temperature of 300C, purge
time 1 min. The column was a megabore multi-capillary SE-54 (Alltech), 1 m
2 m film. The flow rate for the hydrogen carrier gas was 58 mL/min and 37 mL/
min for the nitrogen makeup gas.
Each of the primary certified pesticide standards (Ultra Scientific) (1000 g/
mL in hexane) was diluted with pesticide-grade hexane to yield 100 g/mL. A
combined standard of aldrin and dieldrin was made by adding 1 mL of each of
the diluted standards into a 10-mL volumetric flask with hexane to yield 10 g/
mL. A combined standard containing all three pesticides was then made by
adding 5 mL of the diluted dieldrin and aldrin standard and 5 mL of the more
concentrated lindane standard to a 100-mL flask to yield 500 ng/mL dieldrin and
aldrin and 5 g/mL lindane in hexane. Lower concentration standards were made
by serially diluting the combined standard in hexane to yield 200 and 100 ng/mL
of aldrin and dieldrin and 2 g/mL and 1 g/mL lindane. All the standards were
kept in the dark in a freezer. The method detection limit (MDL) was obtained
according to the EPA protocol as described in the Federal Register (1984).
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