The vials containing the extracts were placed into gas chromatography (GC)
auto sampler trays that were continuously refrigerated by circulating 0 C glycol/
water through the trays. Extracts were analyzed by GC using a microelectron
capture detector (GC-ECD). Results were obtained on a Hewlett-Packard 6890
GC equipped with a microcell 63Ni detector at 280 C according to the general
procedure outlined in USEPA SW-846 Method 8095 (USEPA 1999). Direct
injection of 1 :L of soil extract was made into a purged packed inlet port, at
250 C, that was equipped with a deactivated Restek Uniliner (Restek, Belleforte,
PA). Primary analysis was conducted on a 6-m 0.32-mm-ID fused silica
column, with a 1.5-:m film thickness of 5 percent (phenyl)-methylsiloxane
(RTX-5 from Restek). The GC oven was temperature programmed as follows:
100 C for 2 min, 10 C min-1, ramp to 260 C, 2-min hold. The carrier gas was
helium at 10 mL min-1 (linear velocity of approximately 90 cm sec-1). The ECD
retention window for a specific signature compound, the extract was reanalyzed
on a confirmation column, 6 m 0.53 mm ID having 0.1-:m film thickness of
50 percent cyanopropylmethyl50 percent phenylmethyl-polysiloxane (RTX-225
from Restek). Further details of the procedure may be found in SW-846 Method
8095 (USEPA 1999). If analyte concentrations were within the linear range of
the ECD, concentrations were reported from the determination on the primary
column, unless coelution with another compound was apparent. In such cases,
concentrations were reported from the determination of the confirmation column.
Detection limits for the GC-ECD analysis were about 1 :g kg-1 for dinitro and
Extracts were also analyzed by reverse phase-high-performance liquid
chromatography (RP-HPLC) according to SW-846 Method 8330 (USEPA 1994).
When concentrations were above 500 :g kg-1, the reported concentrations were
taken from the HPLC analysis, which had a higher range of linearity. The
response of the GC-ECD was inadequate for the reduction products of 2,4DNT
(4-amino-2-nitrotoluene (4A2NT) and 2-amino-4-nitrotoluene (2A4NT)). Data
reported for these analytes were obtained by RP-HPLC. RP-HPLC analysis was
conducted on a modular system composed of a Spectra-Physics Model SP8800
ternary HPLC pump, a Spectra-Physics Spectra 100 variable-wavelength
ultraviolet (UV) detector set at 254 nm (cell path 1 cm), a Dynatech Model
LC241 auto sampler equipped with a Rheodyne Model 7125 sample loop
injector, and a Hewlett-Packard 3393A digital integrator set to measure peak
heights. Extracts were diluted with reagent grade water (one part extract and four
parts water). Separations were conducted on a 15-cm 3.9-mm NovaPak C-8
column (Waters Chromatography Division, Milford, MA) eluted with 85/15
water/isopropanol (v/v) at 1.4 mL min-1. Samples were introduced by overfilling
a 100-L sampling loop. Concentrations were estimated against standard
analytical reference material (SARM) multianalyte standards from peak heights.
Detection limits for 4A2NT, 2A4NT, and 3,5-dinitroaniline (3,5DNA) were
about 250 :g kg-1.
17
Chapter 2 Characterization of Explosives Contamination at Military Firing Ranges
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