Elemental profiling of total gunshot residue using total reflection X-ray fluorescence spectrometry

Gunshot residue (GSR) is a composite of unburnt and partially burnt particles from various components of firearm ammunition cartridges. GSR is customarily sampled from small, localized spots and analyzed visually and elementally. The conventional analytical methods for localized GSR are most commonly done through a paired scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDS) to look for the presence of lead, barium, and antimony, the inorganic components of ammunition primer. Previous GSR analysis primarily focused on the material deposited on a shooter's hands and used swabbing or adhesive stubs to collect GSR. In this study, total gunshot residue (tGSR) from six types of ammunition was collected from fabric that was shot at a muzzle-to-target distance of 15 cm. Subsequently, each tGSR sample was digested in nitric acid and analyzed with total reflection X-ray fluorescence spectrometry (TXRF). The TXRF technique can simultaneously identify the individual elements in the tGSR and provide absolute elemental quantification. In contrast, EDS scans report the relative elemental compositions of localized GSR samples rather than giving absolute quantitation. This study reliably revealed distinct patterns in six key elements (lead, copper, barium, antimony, iron, and zinc) of tGSR among the ammunition investigated. Elemental profiles were developed from the analyses to represent each ammunition type and the elemental quantities obtained could be used to suggest the category of ammunition that was used.