The discharge of a firearm produces a wealth of physical and chemical evidence.  Current forensic analysis focuses on inorganic particulate residues originating from the primer and characterized by SEM/EDS.  Advances in mass spectrometry have afforded an opportunity to expand the potential analytical targets to include organic components such as stabilizers of energetics as well as ionic species.  Development of novel assays is contingent on definitive identification of viable target compounds in authentic firearm discharge residues.  In this study, mass spectral imaging (MSI) was coupled with time-of-flight mass spectrometry and secondary ion mass spectrometry (ToF-SIMS) for thorough characterization of firearms discharge residues from common small arm weapons and ammunition.  While the cost and complexity of current generation instrumentation precludes use in routine case work, MSI-ToF-SIMS can simultaneously collect, map, and display data obtained for organics, ionic, and organic compounds.   <br/>Samples were collected on fused silica wafers and on clean room wipes for imaging and analysis and data reduction was facilitated using principal component analysis.  Analysis of inorganic particulates (~50μm or smaller) showed the expected Pb-Cu-Sb in heterogeneous compositions such as Sb+/SbOH and Sr+/SrS. Elemental identification was confirmed via isotopic abundances.  Organic constituents identified included phthalates, dioctyl sulphosuccinate, nitroglycerine, and ethyl centralite.  Several compounds were identified as potential decomposition by-products of nitrocellulose.  Secondary ion and electron maps were produced to display individual mass fragments as well as composites that compared organic/inorganic residues.  Negative spectral mode scans revealed the presence of intriguing species such as SbC- and Pb-/PbOH-.  Details summaries and example images will be presented along with how results are being used to develop and validate new assays.

Exhaustive characterization of firearm discharge residue using mass spectral imaging and time-of flight secondary ion mass spectrometry

254th National Meeting (2017)

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