Evaluation of Concentration Techniques For Small Populations of Gunshot Residue (GSR) Particles Using Calibrated GSR Suspensions

Abstract

It is generally accepted that the best method for the identification of GSR is by scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDX), a technique which utilizes not only the chemical composition of the particles but also their size and morphology. Nevertheless, there remain many problems in the effective use of this technique.The main problem is the length of time required to conduct a comprehensive search for GSR in the samples as presented to the SEM. Attempts to solve this problem have been made in two main directions: (1) Concentration of the GSR after sampling onto a small area concomittant with some sort of treatment to remove extraneous interfering matter, and (2) computer-aided mechanization of the searching procedure. The latter approach is still in its very early experimental stages, whilst the methods used in the second approach are in need of further improvement. In particular, there has been no quantitative work on the efficiency of various concentration processes when using very small populations of GSR.