In this paper, researchers use gas chromatography/vacuum ultraviolet spectroscopy (GC/VUV) for spectroscopic and thermal analysis of explosive and related compounds.
To explore whether chromatography/vacuum ultraviolet spectroscopy (GC/VUV) can overcome limitations in differentiating explosive compounds that produces similar mass spectra, researchers undertook an analysis of explosive compounds using GC/VUV to establish its sensitivity, selectivity, and specificity for forensic explosive analysis. Nitrate ester and nitramine explosive compounds thermally decompose in the VUV flow cell, resulting in higher specificity due to fine structure in the VUV spectra. These fine structures originate as vibronic and Rydberg transitions in the small decomposition compounds and were analyzed computationally. The thermal decomposition process was further investigated for the determination of decomposition temperatures for the nitrate ester and nitramine compounds which range between 244 ºC and 277 ºC. Nitrated compounds were extensively investigated to understand the absorption characteristics of the nitro functional group in the VUV region. The nitro absorption maximum appeared over a wide range (170 - 270 nm) with the wavelength and intensity being highly dependent upon the structure of the rest of the molecule. Finally, the GC/VUV system was optimized for post-blast debris analysis. Parameters optimized include the final temperature of a ramped multimode inlet program (200 ºC), GC carrier gas flow rate (1.9 mL/min), and VUV make-up gas pressure (0.00 psi). The transfer line/flow cell temperature was determined not to be statistically significant. Analysis of explosives (intact and post-blast) is of interest to the forensic science community to qualitatively identify the explosive(s) in an improvised explosive device (IED). This requires high sensitivity, selectivity, and specificity. The development of a benchtop vacuum ultraviolet spectrometer coupled to a gas chromatography (GC/VUV) was developed in 2014 with a wavelength region of 120 nm to 430 nm.
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