Gunshot residues: screening analysis by laser-induced breakdown spectroscopy

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 non-shooters, 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.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.18871894Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Gunshot residues: screening analysis by laser-induced breakdown spectroscopy

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 non-shooters, 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