Determination of nitroaromatic, nitramine, and nitrate ester explosives insoil by gas chromatography and an electron capture detector

Hazardous waste site characterization, forensic investigations, and land mi ne detection are scenarios where soils may be collected and analyzed for tr aces of nitroaromatic, nitramine, and nitrate ester explosives. These therm ally labile analytes are traditionally determined by high-performance liqui d chromatography (HPLC); however, commercially available deactivated inject ion port liners and wide-bore capillary columns have made routine analysis by gas chromatography (GC) possible. The electron-withdrawing nitro group c ommon to each of these explosives makes the electron capture detector (ECD) suitable for determination of low concentrations of explosives in soil, wa ter, and air. GC-ECD and HPLC-W concentration estimates of explosives resid ues in field-contaminated soils from hazardous waste sites were compared, a nd correlation (r > 0.97) was excellent between the two methods of analysis for each of the compounds most frequently detected: 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4-dinitrotoluene (2 ,4-DNT), 1,3-dinitrobenzene (1,3-DNB), 1,3,5-trinitrobenzene (TNB), and oct ahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The analytes were extr acted from soils with acetonitrile by 18 h of sonication in a cooled ultras onic bath. Two soil-to-solvent ratios were evaluated: 2.00 g:10.00 mi and 2 5.0 g:50.0 mi. GC-ECD method detection limits were similar for the two soil -to-solvent ratios and were about 1 mug kg(-1) for the di- and trinitroarom atics, about 10 mug kg(-1) for the mono-nitroaromatics, 3 mug kg(-1) for RD X, 25 mug kg(-1) for HMX, and between 10 and 40 mug kg(-1) for the nitrate esters (nitroglycerine [NG] and pentaerythritol tetranitrate [PETN]). Spike recovery studies revealed artifacts introduced by the spiking procedure. R ecoveries were low in some soils if the amount of soil spiked was large (25 .0 g) compared to the volume of spike solution added (1.00 ml). Recoveries were close to 100% when 2.00-g soil samples were spiked with 1.00 mi of sol ution. Analytes most frequently found in soils collected near buried land m ines were the microbial transformation products of TNT (2-amino-4,6-dinitro toluene [2-Am-DNT] and 4-amino-2,6-dinitrotoluene [4-Am-DNT]), manufacturin g impurities of TNT (2,4-DNT, 2,6-DNT, and 1,3-DNB), and TNT. The microbial reduction products of the isomers of DNT and of 1,3-DNB were also detected , but the ECD response to these compounds is poor. (C) 2001 Elsevier Scienc e B.V. All rights reserved.