Elemental Characterization of Leaded and Lead-Free Inorganic Primer Gunshot Residue Standards Using Single Particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry

Abstract

This study describes the use of single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) for the detection and classification of inorganic gunshot residue (IGSR) particles. To establish reliable multi-element criteria to classify IGSR particles, leaded and lead-free IGSR reference materials were analyzed, and the elemental compositions of the individual particles were quantified. The results suggest that expanded element compositions may be used to classify IGSR particles via spICP-TOFMS compared to those used in conventional IGSR analysis using scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS). For spICP-TOFMS analysis of leaded IGSR particles, classification may be based on the presence of lead (Pb), antimony (Sb), and barium (Ba) just as in SEM-EDS; however, additional particle types, such as lead-copper (Pb–Cu) particles, contribute significantly (∼30%) to the leaded IGSR particle population. In lead-free IGSR particles, the dominate multi-metal particle composition found is titanium–zinc (Ti–Zn) with a conserved Zn:Ti ratio of 1.4:1, but other elements, such as copper (Cu), are also characteristic. In mixtures of the two IGSR reference materials, we were able to classify over 80% of the multi-metal particles detected with no false-positive particle-type assignments. With spICP-TOFMS, particles smaller than those typically measured by SEM-EDS are detected, with estimated median diameters for leaded and lead-free IGSR of 180 and 320 nm, respectively. Through measuring these smaller particles, up to ∼two times more particles per mL are recorded by spICP-TOFMS compared to that found by SEM-EDS. Overall, high-sensitivity and high-throughput analysis using spICP-TOFMS enables quantitative, rapid multi-elemental characterization, and classification of individual IGSR particles.

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…A similar approach was adopted by Szakas et al who also used single particle ICP-TOF-MS to characterise gunshot residue. 302 These authors fired shots (having removed the bullet and propellant but leaving the cartridge and primer) and then collected the residue in a flask. Two primers were tested: one containing the classical mixture of Ba, Pb and Sb and the other being Pb-free.…”

Results of an interlaboratory comparison for characterization of Pt nanoparticles using single-particle ICP-TOFMS

“…The probability of such events can be determined by coincidence analysis and limited using adequate dilution. 25 The capabilities of sp-ICP-TOFMS have already been demonstrated through numerous different case studies, including multi-element NP characterization, 26,27 distinguishing between naturally occurring (NNPs) and engineered nanoparticles (ENPs), 16,28,29 analysis of surface water [30][31][32] and wastewater samples, 33 soil samples, [34][35][36] gunshot residues, 37,38 microplastics, 39,40 as well as more exotic samples such as polar ice dust 41 and space-station dust particles. 42 While all these works highlighted the benefits of TOFMS for multi-element NP analysis, the sp-ICP-TOFMS methodology has not yet been validated.…”