Pre-Screening for Explosives Residues in Soil
Prior to HPLC Analysis Utilizing Expray
KEVIN L. BJELLA
Characterization of the presence and amount of energetic residues on military
training ranges involves the sampling and analyzing of the surface and near-
surface soils. The concentration of energetic residues in samples collected at
firing points and impact locations can range from below instrumental detection
limits in parts per billion (ppb) to percent levels. Reverse-Phase High-
Performance Liquid Chromatography (RP-HPLC) is typically used for analysis
of these energetic residues. Extract concentrations of 10 parts per million (ppm)
TNT and 20 ppm RDX/HMX/NG are considered safe upper limits for RP-HPLC.
Higher analyte concentrations may carry over to subsequent samples, elevating
responses and yielding false positives. This requires reanalysis of the samples
possibly affected, and may require that corrective measures be taken to address
instrumental performance. To avoid interruptions to the analytical runs, a simple
screening technique was developed using a commercially available colorimetric
explosives detection kit.
Pre-screening utilizing the Expray Explosives Detection Kit prior to analysis
has proven to be useful for coarse determination of concentration values within a
factor of 10. Dilution can then be carried out to bring the sample concentration
down to an analytically acceptable level, and/or the placement within the
analyzing sequence can be designed to minimize the effects of the carryover.
This report describes the testing of the Expray Explosives Detection Kit for this