APPENDIX I: GAS CHROMATOGRAPHY FIELD METHOD
Gas chromatography has not received wide use for quantitative explosives
analysis due to the thermal instability of several of the important analytes. How-
ever, Hable et al. (1991) demonstrated that by using a short-fused silica macro
bore column (0.53 mm) and a deactivated injection port, and setting high linear
velocities for the carrier gas, explosives analysis is possible. Recently a field-
transportable gas chromatograph that has many of these features and is equipped
with a thermionic ionization detector (TID) was found to be well suited for the
estimation of explosives (Hewitt et al. 2001a, b). This detector is selective for
compounds containing nitro functional groups, which are present in most
explosives. Indeed, all of the explosives cited in Method 8330 (Table 2), plus
NG, 3,5-DNA, and PETN, can be detected by GC-TID. The dynamic ranges of
detection are analyte-specific and extend over two to four orders of magnitude
(e.g., 100.01 mg/L) with detection limits often below 0.1 mg/kg (Table 2).
Lastly, because this detector is selective, hardware-store-grade acetone can be
used, eliminating the need to ship large quantities of this solvent to the field.
Water samples are prepared following the guidelines provided in Appendix
G, and soil sample preparation follows the guidelines presented in Appendix H.
Following extraction, an aliquot of the acetone is then drawn into a disposable
plastic syringe and filtered by passing through a 25-mm Millex FH (0.45-m)
filter that attaches via a Luer-Lok fitting. The filtered extract is directly trans-
ferred to a 2-mL amber deactivated glass vial.
A field-transportable SRI Model 8610C gas chromatograph equipped with a
heated (250C) TID detector, a heated (225C) on-column injection port, and an
internal air compressor can be used on-site for the detection of explosives
(Hewitt et al. 2001a, b). Separations were performed on a Crossbond 100%
dimethyl polysiloxane column (DB-1), 15 m 0.53 mm i.d., 0.5 df (coating
thickness). Injections of 1 L were made manually with a 10-L glass syringe
(SGE) equipped with cone pointed needle. The oven temperature program,
carrier gas and flow rate, detector voltage, and the use of a supply of air to the
detector are optimized for the explosives analytes of concern. When the analytes
of concern include nitroaromatics, nitramines, and nitrate esters explosives, ultra-
high purity nitrogen should be used for a carrier gas with the TID potential set at
3.40 V (Hewitt et al. 2000).