Discrimination of SINTOX® GSR against environmental particles and its automated investigation by SEM/EDS

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A fundamental problem in gunshot residue (GSR) analysis by SEM/EDS is the distinction to environmental particles. The introduction of heavy metal free (HMF) primers such as SINTOX® enhanced this problem. According to the current ASTM E1588 Standard Practice, the identification of SINTOX® GSR by means of an automated classification scheme is based on the simultaneous presence of titanium and zinc in a particle, labelling them just as “consistent with GSR”. Since both elements often appear together in environmental particles, this leads to a certain number of false-positive findings. Therefore a large number of environmental particles originating from different sources such as waste incineration plants and volcanic ashes were analytically evaluated. In order to find possible distinctions between SINTOX® primer GSR and environmental particles, the components of SINTOX® ammunition and its generated residues resulting from the firing process were examined.A new classification scheme of high efficiency for SINTOX® GSR was developed extending the standard classification scheme based on the recommendations of the ASTM E1588 Standard Practice. The resulting new classes show a good selectivity and nearly no overlap with environmental particles. In casework, the new proposed classification process can reduce the total investigation time due to an improvement in the manual confirmation step of SINTOX® GSR.