Isotope ratio mass spectrometry (IRMS) techniques have been used for decades to characterize chemical threat agents (CTAs), alongside a variety of more traditional chemical analyses. Here, we present a broadly applicable framework for methodologically applying different separation techniques to CTAs, specifically explosives (Figure 1). This framework allows an analyst to collect the most characteristic information possible from an explosive sample, through the separation and isotope ratio analysis of chemical constituents to produce multivariate datasets for sample discrimination and source attribution. A case illustration demonstrating the application of the framework focuses on plastic explosives C-4 and Semtex. Binder and plasticizer were extracted into cyclohexane, leaving the explosive components and other insoluble material. Plasticizers, oils, and additives were next extracted from the cyclohexane-soluble fraction into acetone, leaving the polymeric binder. Explosive components were extracted from the cyclohexane-insoluble fraction with acetone and then isolated via preparative HPLC. Isolated components were analyzed for component-specific stable isotope ratios. Control mixtures of previously characterized components were also separated and analyzed; they retained the isotope ratios prior to mixture. Two example C-4 explosives from different sources, with indistinguishable chemical composition and raw explosive 13C/12C and 15N/14N isotope ratios, were extracted and analyzed. The resultant binder and plasticizer 2H/1H and 13C/12C results were used to discriminate between the two C-4 samples that were otherwise apparently identical.

Applying isotope ratio mass spectrometry to characterize chemical threat agents: Case study on plastic explosives

253rd National Meeting (2017)

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