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

Experimental Tests on External and Terminal Ballistics of Different Types of Projectiles Fired From .38 SPL Caliber Cartridges and Study of Permanent Cavitation in Anatomical Modeling With 10% Ballistic Gelatin

ABSTRACT

The present study investigated the main morphological differences between the permanent cavities formed by 4 different types of projectiles fired from .38 SPL caliber cartridges in blocks of 10% ballistic gelatin with standardized formulation (Federal Bureau of Investigation Protocol), all fired from the same distance and from the same firearm, associated with its performances in external and terminal ballistics. The velocity or the mass presented by a firearm projectile will not always be solely responsible for the final configuration of the permanent cavity, in which the projectile design, for example, is an equally important element. Each type of projectile tested in the present work generated a different kind of permanent cavity, but they also varied in velocity (m/s) and energy (J). The use of 10% ballistic gelatin in scientific research that seeks to investigate the external and terminal ballistics of projectiles can contribute to the practice of professionals working either in forensic pathology or applied ballistics scenarios, as they can experimentally simulate the events that can occur in the tissues of victims inflicted by gunshot wounds, which also allows important applications in the medical, commercial, civil, and military sectors that deal with products and technologies related to the human body.

A simple voltammetric method to evaluate the firing distance through determination of nitrocellulose

Nitrocellulose (NC) is the main component of propellants for small firearm ammunitions. Even though NC particles are ejected from gun barrels together with bullets and they are often recovered on close-to-muzzle targets, quantitative analysis of nitrocellulose for forensic purposes has been neglected so far. Moreover, although the presence of the nitroester groups makes nitrocellulose electroactive, its electrochemical determination has been poorly considered in literature. In this paper, a quantitative differential pulse voltammetric method for the analysis of nitrocellulose in targets is suggested, with the aim of estimating its concentration decay on targets with increasing the shooting distance. The presented method works in acetonitrile/ethanol/lithium perchlorate, has a LOQ of 4 mg L-1 and linearity up to 2000 mg L-1. Ammunitions loaded with a nitrocellulose/nitroglycerine-based gunpowder were discharged to draw a calibration curve for shooting distance determination in the range from 5 cm to 120 cm. The effect of possible interfering substances (water, nitroglycerine, nitroguanidine, nitrites) was evaluated, and results are compared with literature methods.

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

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.

Chemical Analysis of Gunpowder and Gunshot Residues

The identification of firearms is of paramount importance for investigating crimes involving firearms, as it establishes the link between a particular firearm and firearm-related elements found at a crime scene, such as projectiles and cartridge cases. This identification relies on the visual comparison of such elements against reference samples from suspect firearms or those existing in databases. Whenever this approach is not possible, the chemical analysis of the gunpowder and gunshot residue can provide additional information that may assist in establishing a link between samples retrieved at a crime scene and those from a suspect or in the identification of the corresponding model and manufacturer of the ammunition used. The most commonly used method for the chemical analysis of gunshot residue is scanning electron microscopy with energy dispersive X-ray, which focuses on the inorganic elements present in ammunition formulation, particularly heavy metals. However, a change in the legal paradigm is pushing changes in these formulations to remove heavy metals due to their potential for environmental contamination and the health hazards they represent. For this reason, the importance of the analysis of organic compounds is leading to the adoption of a different set of analytical methodologies, mostly based on spectroscopy and chromatography. This manuscript reviews the constitution of primer and gunpowder formulations and the analytical methods currently used for detecting, characterising, and identifying their compounds. In addition, this contribution also explores how the information provided by these methodologies can be used in ammunition identification and how it is driving the development of novel applications within forensic ballistics.

Should inorganic or organic gunshot residues be analysed first?

Gunshot residues (GSR) collected during the investigation of firearm-related incidents can provide useful information for the reconstruction of the events. Two main types of GSR traces can be targeted by forensic scientists, the inorganic (IGSR) and the organic GSR (OGSR). Up to now, forensic laboratories have mainly focused on the detection of inorganic particles on the hands and clothes of a person of interest using carbon stubs analysed by scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM/EDS). Several approaches have been proposed to also analyse the organic compounds since they might bring additional information for the investigation. However, implementing such approaches might disrupt the detection of IGSR (and vice versa depending on the applied sequence of analysis). In this work, two sequences were compared for the combined detection of both types of residues. One carbon stub was used for collection, and the analysis was performed either by targeting the IGSR or the OGSR first. The aim was to evaluate which one allows maximum recovery of both types of GSR while minimising losses that might occur at different stages of the analysis process. SEM/EDS was used for the detection of IGSR particles while an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) was used for the analysis of OGSR compounds. Extracting OGSR first required the implementation of an extraction protocol that did not interfere with the IGSR particles present on the stub. Both sequences allowed good recovery of the inorganic particles since no significant difference was observed in the detected concentrations. However, OGSR concentrations were lower after IGSR analysis than before for two compounds (ethyl and methylcentralite). Thus, it is advised to extract rapidly the OGSR before or after IGSR analysis to avoid losses during the storage and analysis processes. The data also indicated that there was a low correlation between IGSR and OGSR highlighting the potential of a combined detection and analysis of both types of GSR.

Comparison of four commercial solid-phase micro-extraction (SPME) fibres for the headspace characterisation and profiling of gunshot exhausts in spent cartridge casings

Headspace solid-phase micro-extraction (SPME) is a promising technique for the characterisation and profiling of gunshot exhausts in spent cartridge casings, especially for health and environmental risk assessments, as well as forensic purposes. To date, however, no comprehensive investigation has been carried out to objectively assess the kinds of compound released during a discharge that can be recovered by this approach, the selectivity of the main commercially available fibres, and their relative performances for the analysis of gunshot exhausts and the discrimination of different ammunition types. This study aimed to fill this gap. Gunshot exhausts in spent cartridge casings from four different ammunition types were analysed by GC–MS, after extraction with four different commercial fibres: 100 μm polydimethylsiloxane (PDMS), 85 μm polyacrylate (PA), 65 μm polydimethylsiloxane/divinylbenzene (DVB), and 85 μm carboxen/polydimethylsiloxane (CAR). Results showed that, overall, a total of 120 analytes could be observed across the cartridges, but the different tested fibres also displayed distinct performances, which were, to some extent, complementary for the characterisation of gunshot exhausts. DVB, in particular, recovered the most compounds simultaneously. On the other hand, the observed variability between measurements was also high, making it a poor candidate for (semi-)quantitative applications (e.g. estimation of time since discharge and/or source profiling). In this regard, PA demonstrated the highest potential for broad use and implementation in multi-purpose methods.

Efficacy study of non-lanthanide small luminescent molecules as gunshot residue indicators

The efficiency of using small, non-lanthanide and readily available molecules was tested as luminescent markers for gunshot residue (GSR) analysis. Three luminophores, namely pyrene (Py), fluorescein (Fl) and a Pt-CNN complex (Pt-C) were used in the present study by using their 5 wt% additives to gunpowder filled in a cartridge followed by firing with a 9 mm pistol. The easy visualization of GSR location, collection of GSR samples followed by their identification through various characterization techniques and the possibility of strategically using these markers as a cost-effective alternative compared to any lanthanide material were evaluated through this work. The comparison of physical mixture of marker and gunpowder and surface soaked gunpowder with the same marker (Py) was also evaluated. Spectroscopic (Optical, Luminescence and Raman), Microscopic, Spectrometric (Mass) and thermal analysis (Differential Scanning Calorimetry, DSC) of the marker, gunpowder and GSR residues implies that both the dyes and gunpowder retains their individual properties and those are merely a physical mixture. Overall, the present study clearly demonstrates that these small organic/metal complex based luminophores are cost effective luminescent marker as compared to lanthanide materials for GSR detection / collection and can be strategically use to track the illegal / unauthorized use of gunpowder.

Advances and limitations in the determination and assessment of gunshot residue in the environment

Gunshot residue (GSR) stemming from the discharge of firearms has been essential to advancements in the field of forensic science however the human and environmental health impacts from GSR are far less researched. GSR represents a multifaceted concern: it contains a complex mixture of inorganic and organic components and produces airborne particles with variable sizes, depositions, and fates. Herein we evaluate studies in the literature examining GSR collection, deposition, composition, environmental contamination, and potential remediation techniques within the last two decades (2000 - 2020). Throughout we reflect upon key findings and weaknesses in relation to environmental characterization of GSR and associated firearm contaminants. Research focused on techniques to analyze both inorganic and organic GSR simultaneously has begun, but requires additional effort. A vast majority of the available environmental characterization literature focuses on soil contamination at outdoor firing ranges for a select number of elements (Cu, Pb, Sb) with comparisons between ranges or at different collection distances and depths. There is limited ability for between study comparisons due to collection and analysis differences as well as a lack of background soil sampling. Notably, these studies lack direct quantification of the contribution of contaminants from GSR as well as analysis of organic compounds. Currently, there is a need for air monitoring to determine the composition, deposition, and fate of GSR, particularly in outdoor settings. This review summarizes the collection, characterization, and environmental studies related to GSR and highlights areas of research needed to establish the environmental health impacts.

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

The ability to manage, distil and disseminate the significant amount of information that is available from published literature is fast becoming a core and critical skill across all research domains, including that of forensic science. In this study, a simplified scientometric approach has been applied to available literature on gunshot residue (GSR) as a test evidence type aiming to evaluate publication trends and explore the interconnectivity between authors. A total of 731 publications were retrieved using the search engine ‘Scopus’ and come from 1589 known authors, of whom 401 contributed to more than one research output on this subject. Out of the total number of publications, only 35 (4.8%) were found to be Open Access (OA). The Compound Annual Growth Rate (CAGR) for years 2006 and 2016 reveals a much higher growth in publications relating to GSR (8.0%) than the benchmark annual growth rate of 3.9%. The distribution of a broad spectrum of keywords generated from the publications confirms a historical trend, in particular regarding the use of analytical techniques, in the study of gunshot residue. The results inform how relevant information extracted from a bibliometric search can be used to explore, analyse and define new research areas.