Forensic analysis of explosives from water samples using solid phase microextraction-gas chromatography

Abstract

The forensic identification of bulk explosive and postexplosion residues is important in bombing investigation. The information can be used to determine the type of explosive, to link the suspect to the bombing case and ultimately to provide evidence in court. Many analytical techniques have been applied to the identification of explosives and explosive residues. In this study, a solid-phase microextraction (SPME) technique followed by gas chromatography (GC) was used to determine the explosive residues. Gas chromatography with electron capture detection (GC-ECD) is very sensitive towards post-blast residues and therefore useful for the determination of explosive molecules. Several parameters including adsorption time, desorption time and temperature, SPME fiber types, stirring effect and salting out effect were optimized to obtain reproducible data with good accuracy. Addition of 10 % w/v of NaCl in the aqueous medium and use of a Carboxen/Polydimethylsiloxane (CAR/PDMS) coating fiber led to optimal extraction efficiencies. LOD of studied explosive compounds for the optimized SPME method was quite low (0.02-0.10 ppm) except for PETN (0.67 ppm). SPME/GC-ECD was optimized and applied to the trace analysis of explosive residues in real pond water and water sample from collection trays. 2,6-DNT, TNT and PETN were successfully detected from water samples. For some sampling points, TNT and PETN were not detected due to the amount of explosives used and low concentration of the explosives in water samples. Direct Immersion SPME/GC-ECD was found to be applicable for qualitative and quantitative analysis of explosives in post blast water samples.