oven temperature program for this application was
et al. 2000). For the simultaneous analysis of all three
165C for 1.5 min., ramp at 20C/min. to 190C, hold
types of explosives, the sensitivity is improved by us-
at 190C for 1.25 min., allowing sample injections to
ing ultra-high-purity nitrogen as the carrier gas and set-
be made about every 4.5 min. Figure 1 shows a typical
ting the TID potential at 3.40 V (Hewitt et al. 2000).
chromatogram for 2,4-DNT, TNT, 4AmDNT, and
The carrier gas pressure was set at 15 psi for an on-
2AmDNT under these conditions.
column flow rate of approximately 37 mL/min. Air was
At two other field trials the explosives analytes of
supplied to the detector from the onboard compressor
concern included both nitroaromatics and nitramine
at a flow rate of approximately 25 mL/min, with a pres-
explosives. The operating parameters for the analysis
sure setting of 5 psi. An oven temperature program of
105C, ramp at 10C/min. to 115C, ramp from 115C
of both of these classes of explosives and nitrate esters
to 240C at 25C/min., hold at 240C for 0.75 min.,
were based on the results of laboratory studies and a
allowed sample injections to be made about every 8.0
preliminary field trial (Hewitt and Jenkins 1999, Hewitt
min. Figure 2 shows a typical chromatogram for these
conditions.
Calibration standards
Analytical standards of 2,6-dinitrotoluene (2,6-
DNT), 2,4-DNT, TNT, pentaerythritol tetranitrate
(PETN), RDX, 4AmDNT, 2AmDNT, tetryl, and HMX
were prepared from standard analytical reference ma-
terials (SARMs) obtained from the U.S. Army Envi-
ronmental Center, Aberdeen Proving Ground, Mary-
land. The preparation and handling of mixed analyte
working standards has been reported elsewhere (Hewitt
and Jenkins 1999). In addition, all of the explosives
analytes listed in Table 1 for Method 8330 were pur-
chased as a mixed stock standard (each analyte 1.00
mg/mL), and nitroglycerin (NG) as a separate stock
standard (5.00 mg/mL), from AccuStandard, Inc. (New
Haven, CT). Both of these commercially prepared stock
standards were specially prepared using acetone as the
solvent.
Sample preparation
Sample collection, handling, and on-site preparation
for analysis varied for each trial based on the data qual-
ity objectives. The soil samples ranged from 0.5 to 40
g and were extracted with an equal-to-a-fivefold-greater
volume of acetone (i.e., 1:1 to 1:5). Extraction was per-
formed in either glass or plastic bottles by manually
shaking the soilsolvent slurry for 30 seconds or longer,
then allowing the soil to settle. The total extraction pe-
riod ranged from 5 to more than 30 minutes. The re-
duced ratio of sample weight to extraction solvent vol-
ume and short extraction period were used together
when the main objective was to rapidly establish the
presence of explosives residues. In general, field
extraction periods of 30 minutes or longer are recom-
mended for quantitative estimates of explosives resi-
dues in soils. Another general rule for quantitative ex-
plosives measurements is that, when extracting a moist
0
1
2
3
4
soil, the volume of acetone should be at least twice the
Figure 1. GC-TID chromatogram of 50 g/L 2,4-DNT,
moist sample weight. Following extraction, an aliquot
TNT, and 2AmDNT, and 200 g/L 4AmDNT.
of the acetone was then drawn into a disposable plastic
3
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