IDENTIFICATION OF LOW EXPLOSIVES AND THEIR POST-BLAST RESIDUES VIA GAS CHROMATOGRAPHY (GC) COUPLED WITH VACUUM ULTRAVIOLET (VUV) SPECTROSCOPY

Analytical methods that are proposed for use in forensic science laboratories must possess three key attributes: sensitivity, selectivity, and specificity. These characteristics relate to the extent of an instrument’s response (sensitivity), the ability of the instrument to respond to analytes in mixtures (selectivity) and the ability to unambiguously identify the analyte (specificity). Given these requirements, one of the “gold standard” analytical techniques for the forensic analysis of low explosives has been gas chromatography/mass spectrometry (GC/MS). However, there are many explosives that yield similar or identical mass spectra, often with no molecular ion. A recent development with the potential to dramatically change this situation is a benchtop vacuum ultraviolet (VUV) detector for GC (GC/VUV). The data provided by GC/VUV is sensitive, selective, and has the potential to be more specific than mass spectrometry for several explosives. For example, in preliminary experiments we have demonstrated that GC/VUV can acquire highly complex and specific spectra of nitrate ester explosives such as EGDN, NG and PETN. Beyond this, however, there are no published accounts of using GC/VUV to analyze explosives such as black powder, smokeless powder, and black powder substitutes (either intact or as their post-blast residues). Therefore, the purpose of this proposal is to characterize various explosives in the VUV, understand the source of fine structure in the VUV, and design methods for GC/VUV for the most commonly encountered low explosives as well as realistic post-blast samples. We will achieve these goals in four stages: 1) assess the effects of photoionization on the VUV Spectra of explosives, 2) establish a set of optimized GC/VUV methods for intact explosives and their post-blast residues, 3) assess the specificity of VUV spectra for explosive structural isomers using chemometric methods, and 4) use GC/VUV to analyze a set of realistic forensic samples. "Note: This project contains a research and/or development component, as defined in applicable law," and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14). ca/ncf