This study examined the results of using x-ray fluorescence (a portable instrument), ion mobility spectrometry (IMS), and mass spectrometry in attempting to detect gunshot residue (GSR) based on screening for organic materials in the residue.
X-ray fluorescence (XRF) was tested as a technique for screening hand swabs for the presence of metals associated with GSR (lead, barium, and antimony). Because XRF is a non-destructive analytical method, it can be combined with other methods in the field or laboratory in sequence to produce effective screening. Lead was found to be the most useful target element for XRF. Barium screening was ineffective, and antimony appeared in only a few positive samples. GSR detection based only on lead, however, may be subject to false positives. Although it is possible to perform IMS analyses in the research laboratory, significant work must be done before IMS can be used reliably in the field for organic GSR (OGSR) screening. The key development needed is a large population study and generalization of pattern-matching algorithms for differentiating shooters from non-shooters, along with an associated probability. Differential mobility spectrometry (DMS) is a promising alternative to IMS for OGSR detection. Additional work is needed before a full validation study can be conducted. This report notes that the ability to detect specific OGSR compounds collected from hands at some time post-firing depends on the time elapsed, evaporative loss, loss to skin permeation, sampling efficiency, storage conditions, sample preparation, and instrumental method. 2 tables, 1 figure, and 3 references