Concentration Techniques for the Detection of Gunshot Residues by Scanning Electron Microscopy/Energy Dispersive X-Ray Analysis (SEM/EDX)

Abstract The efficiency of the filtration process for concentrating small populations of gunshot residue (GSR) particles (for detection by scanning electron microscopy/energy dispersive X-ray analysis [SEM/EDX]) was examined with a novel method using GSR particle suspensions. Methods of concentrating and segregating GSR particles on small areas (for example, 7 mm2) using both filtration and heavy liquid separations with centrifugation were examined from the practical point of view. It is shown that, in real cases, there may be an intrinsic difficulty in concentrating GSR particles as a result of a pile up of extraneous material or clogging of the collecting filter or both. Collection of GSR particles from clothes using a suction method was compared to the direct glue-lift technique. The suction method involved trapping the GSRs in an organic solvent and recovering them on a membrane filter. The method proved less efficient than using the glue-lift technique. From the findings in this study, it seems that the most efficient way of detecting GSR particles by SEM/EDX is by using the recently developed automated systems directly on glue-lift samples without any pretreatment.