Gunshot residues: screening analysis by laser-induced breakdown spectroscopy

Abstract

A espectroscopia de emissão em plasma induzido por laser (LIBS) foi avaliada para a detecção de resíduos de disparo de arma de fogo (GSR) nas mãos de um suspeito. Para desenvolver o procedimento, 114 amostras foram obtidas pressionando um pequeno pedaço de fita adesiva contra a região dorsal das mãos de não-atiradores, atiradores após o disparo e de atiradores após terem lavado as mãos com sabão e água. As fitas foram analisadas diretamente em um equipamento LIBS baseado em um policromador echelle com resolução temporal construído em laboratório. Os espectros foram obtidos a partir da aplicação de um único pulso de laser em 20 locações diferentes, espalhadas uniformemente sobre a superfície da fita, para assegurar uma amostragem eficiente na detecção de resíduos de disparo. Os espectros mostram uma assinatura com linhas de emissão características de bário e chumbo. Quando os dados espectrais foram submetidos à técnica de reconhecimento de padrão SIMCA (Modelagem Independente e Flexível por Analogia de Classe), atiradores e não-atiradores foram corretamente classificados. O método baseado em LIBS e SIMCA demonstrou ser não-destrutivo da evidência do crime e permitiu discriminar as amostras coletadas de voluntários não-atiradores e atiradores, mesmo após a lavagem das mãos.Laser induced breakdown spectroscopy (LIBS) is further developed for the detection of gunshot residue (GSR) on the hands of a suspected shooter. To develop the procedure, 114 samples were obtained by pressing a small piece of adhesive tape against the dorsal region of the hands of nonshooters, of shooters just after firing a weapon, and of shooters after washing their hands with soap and water. The tapes were analyzed directly in a time-resolved echelle based LIBS system, assembled in the laboratory, and 20 single laser pulses, spread uniformly on the tape surface, were shown to be enough to ensure the detection of true positives. The spectra obtained by LIBS from the tape present a signature with emission lines that are attributed to barium and lead. After the spectral data was submitted to a pattern recognition method SIMCA (Soft Independent Modeling of Class Analogy), shooters and non-shooters were corrected classified. The method based on LIBS and SIMCA has been demonstrated to be non-destructive of crime evidence and enabled discrimination between the samples collected from non-shooter volunteers and shooter volunteers before and after washing their hands.Keywords: laser-induced breakdown spectroscopy, gunshot residues, SIMCA, screening analysis, LIBS IntroductionGunshot residues (GSR) evidence has been considered essential during recent decades in forensic science as it makes it possible to determine if a suspect has fired, been in crime location or come into contact with a firearm.Despite the recent advances in the production of the so called clean ammunitions and well sealed guns, the use of cheap and widespread standard fire arms and propulsive charge remains associated with the majority of hand-armed crimes.1 At the moment of shooting ...

Química forense: perspectivas sobre novos métodos analíticos aplicados à documentoscopia, balística e drogas de abuso

“…A utilização dessa munição em especial tem se mostrado extremamente problemática de ser evidenciada pelos GSR inorgânicos, mesmo utilizando SEM/ EDX. 31 Dessa forma, pesquisadores têm utilizado novas metodologias para a caracterização dos resíduos orgânicos (pólvora) e inorgânicos (Figura 1b), 32 utilizando técnicas de separação como eletroforese 13,33 e cromatografia líquida 34 ou espectrometria atômica (fluorescência de raios-X, XRF, [35][36][37] além da espectrometria de massas com plasma indutivamente acoplado, ICP-MS, 38,39 espectrometria de massas de íons secundários 40 e espectrometria de absorção atômica). 41 A análise de drogas de abuso é uma das áreas que desperta grande interesse da comunidade científica no que tange à química forense.…”

Multivariate treatment of LIBS data of prehistoric paintings

“…[17][18][19][20][21] The use of pattern recognition methods, such as PCA, in LIBS spectra has been described in the literature to discriminate different materials in archeological samples. 22 Duchêne et al 23 applied soft independent modeling of class analogy (SIMCA) and least-squares discriminant analysis (PLS-DA) in a cultural heritage application.…”

Fast Detection and Chemical Characterization of Gunshot Residues by CMV-GC-MS and LIBS

“…Disadvantages of color tests include high rate of false positive results as a result of positive reactions with other substances, and are dependent on each individual visual color perception [Silva et al, 2009;Vanini et al, 2014]. In addition, color tests react to the presence of target elements but cannot be used as a confirmation of GSR presence López-López et al, 2012].…”

“…Disadvantages of color tests include high rate of false positive results due to positive reactions with other substances, and are dependent on each individual visual color perception [Silva et al, 2009;Vanini et al, 2014]. Chromophoric tests that detect the presence of nitrites and nitrates are unreliable because there are multiple materials found to contain these functional groups, such as fertilizers [Hilton et al, 2010].…”

“…These color tests react to the presence of functional groups but cannot be used as a confirmation of GSR presence López-López et al, 2012]. Therefore, organic analysis is more reliable and is necessary to confirm the presence of target organic compounds in GSR [Burleson et al, 2009;Silva et al, 2009;Weyermann et al, 2009;Zeichner et al, 2009;Brożec-Mucha et al, 2011;Arndt et al 2012]. However, most of these techniques require time consuming sample preparation and are destructive;…”