Fast detection and characterization of organic and inorganic gunshot residues on the hands of suspects by CMV-GC–MS and LIBS

• Fast detection and characterization of gunshot residues by LIBS and GC-MS
• New application of capillary microextraction of volatiles (CMV) for detection of volatiles associated with GSR presence
• Quantitation of inorganic and organic components present in GSR
• Evaluation of residues found on the hands of shooters and non-shooters
• The combination of both inorganic and organic analysis will allow better characterization and faster identification of GSR

A rapid method for the characterization of both organic and inorganic components of gunshot residues (GSR) is proposed as an alternative tool to facilitate the identification of a suspected shooter. In this study, two fast screening methods were developed and optimized for the detection of organic compounds and inorganic components indicative of GSR presence on the hands of shooters and non-shooters. The proposed methods consist of headspace extraction of volatile organic compounds using a capillary microextraction of volatiles (CMV) device previously reported as a high-efficiency sampler followed by detection by GC–MS. This novel sampling technique has the potential to yield fast results (< 2 min sampling) and high sensitivity capable of detecting 3 ng of diphenylamine (DPA) and 8 ng of nitroglycerine (NG). Direct analysis of the headspace of over 50 swabs collected from the hands of suspected shooters (and non-shooters) provides information regarding VOCs present on their hands. In addition, a fast laser induced breakdown spectroscopy (LIBS) screening method for the detection of the inorganic components indicative of the presence of GSR (Sb, Pb and Ba) is described. The sampling method for the inorganics consists of liquid extraction of the target elements from the same cotton swabs (previously analyzed for VOCs) and an additional 30 swab samples followed by spiking 1 μL of the extract solution onto a Teflon disk and then analyzed by LIBS. Advantages of LIBS include fast analysis (~ 12 s per sample) and high selectivity and sensitivity, with expected LODs 0.1–18 ng for each of the target elements after sampling. The analytical performance of the LIBS method is also compared to previously reported methods (inductively coupled plasma–optical emission spectroscopy). The combination of fast CMV sampling, unambiguous organic compound identification with GC–MS and fast LIBS analysis provides the basis for a new comprehensive screening method for GSR.