Initial evaluation of inlet thermal desorption GC–MS analysis for organic gunshot residue collected from the hands of known shooters

Abstract

The discharge of a firearm produces a wealth of physical and chemical evidence. Traditional forensic analysis has focused on inorganic particulates formed from the primer, referred to as gunshot residue (GSR). The last few years have seen interest in expanding the list of target compounds to include organic constituents of firearm discharge residue (OGSR). To facilitate adoption by the forensic community, new assays ideally should exploit instrumentation commonly found in forensic laboratories such as gas chromatography/mass spectrometry (GC/MS). Here, a commercially available thermal separation probe that fits directly into the injection port was evaluated as a means of sample introduction for GC/MS operated in a selected ion monitoring mode. A statistical approach utilizing bivariate plots linked retention time to ion ratio data to afford a probabilistic interpretation of the results. A total of 27 authentic shooter swabs were collected after firing of 1–5 rounds and were analyzed in halves or triplicates. Ethyl centralite was detected in 81% of the samples; diphenylamine in 56%, and 2-nitrodiphenylamine in 14%. Dimethyl and dibutyl phthalates were detected in a majority of the swabs but also in many of the hand swab blanks. The use of surrogate standards provided a measure of recovery and reproducibility for retention times and ion ratios.