Single shot, single sample, single instrument detection of IGSR and OGSR using LC/MS/MS

Abstract

Firearm discharge residue (FDR) contains organic and inorganic constituents that arise from the propellant; primer; and, to a lesser extent, the barrel, bullet, and casing. When a weapon is fired, residues are deposited on nearby surfaces with the hand being of primary forensic interest. Current methodology focuses on inorganic primer residues (IGSR) characterized using SEM/EDX. Advances in mass spectrometry have facilitated the detection of organic residues (OGSR) using variations of LC/MS and related ambient ionization methods. In the last few years, single sample collection has been used to characterize IGSR and OGSR via sample splitting and separate analysis by SEM and LC/MS. This paper presents an innovative approach in which IGSR and OGSR are collected on a single SEM stub sample, extracted in a two-step sequential process, and then characterized with a single instrument, LC coupled with triple quadrupole mass spectrometry. The key innovation is exploitation of host-guest and ligand chemistry to detect inorganic constituents. The precursor ion is the metal-ligand complex and the product ion is the metal cation. Identification is confirmed via isotopic ratios. A controlled shooting study using 1–3 shots from a 9mm and 0.38 revolver resulted in consistent detection of lead and EC down to a single shot discharge. Barium, calcium, and iron were also detected. The detection of antimony requires of use of tartaric acid, a multi-dentate ligand.