A novel protocol for the combined detection of organic, inorganic gunshot residue

Abstract

This paper investigates three color tests, for a novel gunshot residue (GSR) detection protocol, which produces a color reaction to the organic gunshot residue (OGSR) components while preserving the inorganic gunshot residue (IGSR) for SEM-EDX analysis. The presence of both I/OGSR residues could potentially identify suspects in criminal investigations. Currently, two sampling devices are used to collect GSR: an aluminum stub with carbon adhesives to collect the IGSR particulates, and wipes to collect and test for OGSR. Field GSR detection tests are classified as presumptive, as the results are determined visually by color production. These tests are non-specific and are prone to false positives from environmental contaminants. Whereas, the main confirmatory GSR test is conducted via SEM-EDX which identifies morphology and lead-barium-antimony elemental composition generated from traditional primers. Sequential collection of I/OGSR residue can split the already miniscule sample, impacting downstream analytical techniques. An ideal presumptive OGSR color test would have increased specificity, would not interfere with the SEM-EDX analysis of IGSR, and allow for the analysis of the entire GSR sample on a single adhesive stub. The three organic color spot tests evaluated as candidates for this novel GSR detection protocol were nitrous acid, 4-nitrosophenol, and sodium borohydride. Each test was used to interrogate neat standards and mixtures in order to determine the sensitivity and specificity of each test, in addition to their application to real-world samples. As a result, the sodium borohydride test appeared to be the most specific and sensitive without hindering subsequent SEM-EDX analysis.