The analysis of organic and inorganic gunshot residue from a single sample

Abstract

The detection and interpretation of gunshot residue (GSR) can play an important role in the investigation of firearm related incidents. Recently, the potential of organic compounds to provide an additional means to discriminate between GSR and environmental particles, in particular in cases where lead-free ammunition is used, has been highlighted. This work describes a method for the extraction and detection of complementary organic and inorganic compounds from a single GSR sample, using a methodology that makes implementation in the current standard procedure feasible. GSR samples were collected from the shooter's hands following double and single discharges, using the traditional adhesive carbon aluminium stubs. Analysis of organic compounds was performed using solidphase microextraction gas chromatography mass spectrometry (SPME-GC-MS), followed by analysis of the traditional inorganic particles using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). Detection of both categorised organic GSR compounds (e.g. ethyl centralite, diphenylamine and 2-nitrodiphenylamine) and characteristic inorganic GSR has been achieved. Given the fact that the detected organic GSR compounds are relevant with respect to the confirmation of GSR materials, this method has successfully demonstrated the ability to obtain a total chemical profile from a single GSR sample, which has the potential to increase the probative value of GSR evidence.

Reviewing Research Trends—A Scientometric Approach Using Gunshot Residue (GSR) Literature as an Example

“…To address this question, with advancement in scientific knowledge, research has started to look at other techniques that may be complementary to the SEM-EDS analysis in order to understand more about the properties and composition of GSR particles. Recent studies included a wide range of techniques, such as powder x-ray diffraction (XRD) [54], x-ray spectrometry by total reflection (TXRF) [55], solid-phase microextraction (SPME) [56,57] or focussed ion beam (FIB) [58,59]. Some of these techniques are included in the INTERPOL Review Papers 2019 [60], and further information about the advantages and limitations of the techniques can be found in relevant literature.…”

“…The other aim of investigating the potential use of these techniques and methods is to address the growing availability of heavy metal free cartridges, even though without official figures being released from manufacturers, it is difficult to establish the current market share of lead-free ammunitions. SEM-EDS is facing some challenges in detecting particles from lead-free ammunition, but it is interesting to see studies have started to look at these heavy-metal free particles without any consideration of reference materials (see, for example, [56,61,62] and reference within). The detection limits of the techniques mentioned above are known from the information provided by the manufacturers.…”

Solid phase microextraction techniques used for gas chromatography: a review

“…A design similar to the SBSE/Twister W concept led to the development of Monolithic Material Sorptive Extraction (MonoTrap TM ) based on Merck DGaA monolithic technology (GL Science Inc., Tokyo, Japan). The monolithic-coated bars can be used for sampling liquids and volatile compounds by HS, prior to solvent desorption and GC analysis [28,29].…”

Combined Collection and Analysis of Inorganic and Organic Gunshot Residues

“…Several studies have also proposed a combined collection and/or analysis of IGSR and OGSR (19,(25)(26)(27)(28)(29)(30)(31)(32)(33) (Table 1). Each of these proposed protocols has advantages and drawbacks, as none of them allow the complete recovery of both IGSR and OGSR.…”

“…Moreover, it has to be decided what type of residue is collected first and where, as significant loss of the other GSR type might be sustained during this first collection step. Finally, some research suggests that only one specimen might be collected and analyzed sequentially using two instruments (27)(28)(29)(30)(31) or even simultaneously using one versatile technique (32,33). Sequential analysis can either be performed when the target molecules (IGSR and OGSR) are collected from a single specimen (generally a swab) separated during a sequential extraction (26,27) or when a specimen, generally a stub, is first analyzed for IGSR (potentially sustaining OGSR loss) before being analyzed for OGSR (27)(28)(29)(30).…”