Semi-quantitative energy-dispersive X-ray spectroscopy (EDS) analysis are conventionally performed on the surface of one gunshot residue (GSR) particle. In comparison to EDS, total-reflection X-ray fluorescence spectroscopy (TXRF) can be used to identify and quantify more than a dozen elements in the presence of an internal standard, with high sensitivities for the elements commonly found in GSR. In our preliminary study, two different brands of bullets (Winchester and American Eagle) were each fired from two different types of firearms, a Colt Detective Special revolver and a Baretta semi-automatic handgun, at a piece of plain cotton fabric from a 4-inch distance. The entire GSR-on-fabric sample was digested in concentrated nitric acid for 24 hours to dissolve all the GSR prior to TXRF analysis. The firearms were shot either consecutively or allowed to cool between shots to determine if the heating of the gun affected the amount of residue collected. Distinct types of firearms and bullets were found to produce unique elemental profiles from digested total GSR, both qualitatively and quantitatively. The elemental analysis was focused on lead, barium, antimony, copper, and titanium, excluding the elements present in similar quantities in the blank solutions. Jacketed bullets produce GSR with higher concentrations of copper and lower concentration of lead. In contrast to SEM-EDS where only relative elemental percentages can be calculated from the spectrum, TXRF yields absolute quantitative information (presented in microgram of element per gram of bullet) when an internal standard such as Ga was used. It is possible to differentiate jacketed bullets from non-jacketed bullets shot from the same gun using TXRF fired from the same gun. The quantitative results from consecutive shots also suggested that the revolver and the semi-automatic handgun can be differentiated, confirming literature findings. While the pistol showed an increase in the amount of lead residue produced when fired consecutively, the amount of lead produced by the revolver decreased steadily from the first shot to the tenth shot. Our preliminary data demonstrated that TXRF can be used to differentiate the types of ammunition through the analysis of total GSR, which can be useful in crime scene investigation.

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

255th National Meeting (2018)

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