Differential pulse anodic stripping voltammetry of lead and antimony in gunshot residues

Differential pulse anodic stripping voltammetry (DPASV) using a glassy carbon/mercury film electrode (GC/MFE) has been applied for characterization and quantitative detection of gunshot residues (GSR). This technique allows for simultaneous detection of Pb and Sb from GSR hand swabs that is simple, fast, and non-destructive. The use of a KNO₃/hydrazine sulfate matrix, instead of HCl, reduces possible interferences and allows for a small sample size to be used in analysis but yielding greater sensitivity.     

Gunpowder residues detection by anodic stripping voltammetry

Anodic stripping voltammetry has been applied to the quantitative detection of gunpowder residues. This technique allows a simple and fast simultaneous determination of Pb and Sb, with low cost instrumentation and avoids the necessity of highly specialized personnel. It can be extended to other problems of interest in the field of forensic laboratory work.     

The application of anodic stripping voltammetry to forensic science. II. Anodic stripping voltammetric analysis of gunshot residues

Non-destructive analysis of gunshot residues on hands was studied by anodic stripping voltammetry using a low-cost home-constructed polarograph. The washing solution was 0.5 M HCl. Antimony was first analyzed in 4 M HCl solution; and zinc, lead and copper were then simultaneously analyzed in 0.2 M acetate buffer (pH 5.9 ± 0.1).     

Distribution of lead and barium in gunshot residue particles derived from 0.22 caliber rimfire ammunition.

0.22 caliber rimfire ammunition is commonly encountered in firearms incidents in Australia. This paper reports on work which has confirmed the nonhomogeneous nature of gunshot residue (GSR) particles and that the lead and barium distribution within particles varies significantly with the particle size and structure. The outcome has been an improved understanding of how the particle formation influences the ability to determine the origin of GSR derived specifically from 0.22 caliber rim fire ammunition.     

The application of anodic stripping voltammetry to forensic science I. The construction of a low-cost polarograph

Intended for forensic gunshot residue analyses and other applications, a low-cost (about $250.00) polarograph was constructed. This instrument is essentially' an operational amplifier version of a three-electrode potentiostat containing a voltage ramp generator, a scan amplifier, an amplifier and a current-to-voltage converter, two voltage followers and an electrolysis cell. An anodic stripping procedure was developed for the simultaneous determination of a zinc, cadmium, lead, antimony and copper mixture, and used for testing the instrument. Effects of pre-electrolysis time, concentration changes, presence of other species and overlapping were also studied.     

Voltammetric analysis of luminescent markers in gunshot residues

Currently, SEM-EDS is used to detect gunshot residue (GSR) from the presence of Ba, Pb, and Sb in the sample. However, the development of new nontoxic ammunition (NTA) has prevented conventional metals from being found. In this work, we aim to determine the presence of an inorganic luminescent chemical marker based on rare earth in gunshot residues using the technique of squarewave voltammetry (SWV). After firing, the luminescent complex [(Eu₂Zr)(btc)₃(Hbtc)_0.5.6H₂O], which is used as a chemical marker, can be detected under a UV lamp. An aqueous solution with 0.1 mol L⁻¹ KCl as supporting electrolyte can be easily collected on carbon paste electrode surfaces for SWV analysis A = 100 mV, f = 10 Hz, and step potential of 5 mV are required. The luminescent marker incorporated into the carbon paste electrode showed two anodic peak currents in the region of 0.4 V (vs Ag/AgCl) and at 0.75 V (vs Ag/AgCl) and also a cathodic one in 0.4 V (vs Ag/AgCl). SEM-EDS was able to analyze the same voltammetric results for conventional and nontoxic ammunition containing the luminescent marker. Therefore, voltammetry and SEM-EDS are valid for detecting the new residue marker in GSR. Despite this, the electrochemical method is still more advantageous because of its low cost and lack of expensive equipment and supplies in forensic laboratories.     

Prevalence of organic gunshot residues in police vehicles

The present study investigated the organic gunshot residue (OGSR) background level of police vehicles in Switzerland. Specimens from 64 vehicles belonging to two regional police services were collected and analysed by LC-MS in positive mode. The driver’s and back seats were sampled separately to monitor potential differences between locations and to assess the risks of a suspect being contaminated by OGSR during transportation to a police station.The results showed that most of the 64 vehicles were uncontaminated (44 driver’s seats and 38 back seats respectively). Up to six of the seven targeted compounds were detected in a single sample, once on a driver’s seat and twice on back seats. The contamination frequency generally decreased as the number of compounds detected together increased. The amounts detected were in the low ng range and less than amounts generally detected just after discharge on a shooter. Our data indicated that detecting a combination of four or more compounds on a police vehicle seat appears to be a relatively rare occurrence. The background contamination observed was most probably due to secondary transfer from police officers (e.g. through recent participation in a shooting session or firearm manipulation) or from firearms stored in the vehicles. The present results might be used as a recommendation to minimize contact of a suspect with contaminated surfaces if OGSR is implemented in routine work in parallel to IGSR analysis.     

92式手枪射击距离与射击残留物分布密度相关性的研究

目的研究92式手枪射击距离与射击残留物分布密度的相关性,为射击距离的推断提供依据。方法选择92式手枪,在带皮的猪肉上覆盖白色棉布,设计了0m,0．1m,0．2m,0．5m,1．0m,1．5m,3．0m,5．0m,10m,15．0m,20．0m,25．0m共12个距离进行射击,提取白棉布上的弹孔圆周和距弹孔2cm的圆周上的射击残留物,利用扫描电镜／能谱仪对不同射击距离遗留在白棉布上的射击残留物进行检验。结果白棉布上射击残留物分布密度与射击距离呈负相关的关系。结论根据棉布上射击残留物的分布密度,能够推断射击距离,对涉枪案件中射击距离的判断有一定的参考价值。     

常见洗手方式对92式手枪射击残留物检出率的影响

目的研究常见洗手方式对92式手枪射击残留物检出率的影响,为确定犯罪嫌疑人射击与否的推断提供依据。方法实验人员使用92式手枪分别射击1枪和3枪,射击后0．5h内,射击人员的手分别用清水、肥皂和洗手液清洗3遍（对照组为未清洗）,对实验人员的手部进行射击残留物的提取,利用扫描电镜和能谱仪对射击残留物进行检验。结果持枪射击后,射击人的手部会附着大量的射击残留物,用常见的洗手方式进行清洗后,仍然能检测到射击残留物,且不同的洗手方式对射击残留物的检出率的影响差异显著。结论常见洗手方式不能完全清除手部的射击残留物,对涉枪案件犯罪嫌疑人的判定有一定的参考价值。     

An investigation on the secondary transfer of organic gunshot residues

Gunshot residues (GSR) are an important forensic trace in firearm-related events. Currently, routine GSR analyses focus on the detection and characterisation of the inorganic components (IGSR). The increasing prevalence of heavy metal-free ammunition challenges these current protocols and there is an increasing interest in how the organic components of GSR (OGSR) can provide complementary information. Similar to the situation with IGSR, OGSR compounds originally deposited on the shooter during the firing process may further be transferred onto another individual or surface. Hence, the aim of this study was to provide additional information regarding the risk of a secondary transfer of OGSR. Two scenarios were investigated, the first one related to the arrest process and the possibilities of a secondary transfer arising between a shooter onto a non-shooter (e.g. between a police officer and a person of interest (POI)). The second scenario concerned the transfer of OGSR onto the non-shooter after handling a firearm for few minutes without discharging it. One calibre was chosen, the .40 S&W calibre, used by several Australian State police forces. A secondary transfer was observed in all cases for the two scenarios investigated, for three compounds of interest: ethylcentralite (EC), diphenylamine (DPA), N-nitrosodiphenylamine (N-nDPA). The firearm handling scenario resulted in a larger secondary transfer to that of the arrest scenario. Overall, the amounts of OGSR detected on the non-shooter were generally lower than that detected on the shooter and controls after the arrest scenario. The results of this study provide complementary knowledge about OGSR, which can be further used to improve the current practice and the interpretation of OGSR evidence. In particular, it highlights that the secondary transfer proposition must be considered during the interpretation of forensic findings, especially when small amounts of OGSR target compounds are detected.     

A method for collection of gunshot residues from skin and other surfaces

A method of collecting gunshot residues from the skin of persons who have been injured by firearms has been developed. The method uses a commercially available, adhesive, transparent plastic film. This method is also useful for collecting gunshot residues from other objects, such as leather. The shooting distance is later estimated by ocular, microscopic or IR examination in combination with various chemographic tests.     

A simple method for collection of gunshot residues from clothing.

Simple equipment for the sampling of gunshot residue particles from clothing, inside of bags, pockets, etc, is described. Collection was achieved by vacuuming through a double filtration system constructed from a Nucleopore aerosol holder connected to an ordinary vacuum cleaner. The collected particles were examined by scanning electron microscopy. Good results were observed in functional tests of this equipment and the method has been introduced into casework in our laboratory. Various experiments on possible contamination of clothing by GSR particles were performed. The usefulness of clothing as evidence material in searching for GSR particles is discussed.     

A probabilistic approach to the joint evaluation of firearm evidence and gunshot residues

The present paper addresses issues that affect both the separate as well as the joint evaluation of firearm evidence (i.e., marks) and gunshot residues (GSR). Mark evidence will be used as a basis to discriminate among barrels through which a bullet in question might have been shot whereas GSR will be used to draw inferences about the distance of firing. Particular attention is drawn to the coherent handling of uncertainties associated with the various parameters considered within each item of evidence. The proposed analysis relies on a probabilistic viewpoint that uses graphical models (i.e., Bayesian networks) as an aid to cope with the complexity induced by the number of variables considered. The paper discusses how an approach based on a probabilistic network environment can be used for the formal analysis and construction of arguments. Emphasis is made on the gain of insight into structural dependencies that may be uncovered when the evaluative process is extended beyond single items of scientific evidence.     

SEM/EDS analysis and characterization of gunshot residues from Brazilian lead-free ammunition

The exposition to heavy metal-rich airborne due to fire practicing has forced to the development of heavy metal-free environmental ammunition primers all over the world. Here we characterize the GSR elements present in the Brazilian lead-free ammunition produced by Companhia Brasileira de Cartuchos (CBC) and commercialized by MagTech in the U.S. and Europe under the name CleanRange centerfire cartridges. Both first and second generations of CleanRange in calibers 9 mm Luger, .40 S&W, .380 AUTO and .38 SPL were analyzed and compared to regular Brazilian CBC ammunition by scanning electron microscopy/energy dispersive spectroscopy. Differences in composition and morphology of GSR particles from the two generations of CleanRange were observed. The first generation ammunition (found in Europe) presented spherical particles, being strontium the only unique element detected. The second generation (found in the U.S.) produced irregular particles composed mostly by potassium, aluminum, silicon and calcium. We can conclude that identification of GSR derived from CBC second generation lead-free ammunition in suspects' hands may be impossible without the addition of a distinct metallic taggant in the primer composition by the manufacturer.     

Screening of gunshot residues using desorption electrospray ionisation-mass spectrometry (DESI-MS)

Several studies have indicated that there are potential environmental sources of particles resembling inorganic primer found in gunshot residues (GSR); as a consequence examiners are reluctant to unambiguously assign the origin of inorganic particles. If organic gunshot residues (OGSR) were found in combination with inorganic particles, the possibility of environmental sources could be potentially eliminated, thereby significantly enhancing the strength of the evidence. Methods have been previously described whereby GSR specimens can be analysed for the presence of OGSR or inorganic GRS (IGSR). However, no methods have been reported that allow the analysis of both OGSR and IGSR on the same specimen. Described in this article is a direct method using desorption electrospray ionisation-mass spectrometry (DESI-MS) for the detection of methyl centralite (MC), ethyl centralite (EC) and diphenylamine (DPA) on adhesive tape GSR stubs typically used for scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) analysis. The optimisation of numerous parameters was conducted using an experimental design. The results indicate that direct analysis of these organic components of GSR is possible although some limitations were also identified. This initial investigation has also indicated that subjecting stubs to DESI analysis does not interfere with subsequent SEM-EDX analysis of primer residues; therefore the technique described herein allows a comprehensive examination of GSR that would be highly probative in the event that both OGSR and IGSR are detected in the same specimen.     

A rapid microtechnique for the detection of trace metals from gunshot residues.

The most important facts and advantages of this method are as follows. 1. A simple separation and identification scheme for metals considered characteristic of gunshot residues was developed. 2. The apparatus used is inexpensive, simple, extremely versatile, and has moderate sensitivity. 3. Blanks of background ions present do not interfere with the test, but warrant consideration. 4. Few reagents are needed, and the results are preservable.     

A new method for collection and identification of gunshot residues from the hands of shooters

This work presents a novel collection method for gunshot residues (GSR) using a sampling procedure based on ethylenediaminetetraacetic acid (EDTA) solution as a complexing agent on moistened swabs. Detection was via a sector-field inductively coupled plasma mass spectrometry (HRICP-MS). The proposed collection and analytical method allowed detection of antimony (Sb), barium (Ba) and lead (Pb) after .38 shot tests. at detection limits of less than 1 microg L(-1) in four different areas of the hands of volunteers. This paper includes a discussion concerning hand areas near the thumb and forefinger as being more suitable for GSR collection as well as a comparison between differences observed using 2% diluted EDTA. 2% nitric acid solution, and simple deionized water as collecting solutions, proving the superior efficiency of EDTA in GSR recoveries.