AFTE Store - A Filtration Technique for Gunshot Residue Analysis by SEM and/or FAAS

At least three methods for the identification of gunshot residue are currently in use by various crime labs throughout the country. The methods involve analysis by SEM, AA, or NAA. There are advantages and disadvantages of each. While the AA methods provide good quantitative data, they suffer from inablility to definitely identify the sample as GSR. SEM techniques, on the other hand, offer absolute identification of particles as GSR; but suffers from time consuming analysis and difficult quantitation. NAA is not readily available for use and the cost is prohibitive. The present study allows for a decision to be made in the laboratory as to which technique to employ or whether to employ both SEM and FAAS. This is accomplished by the field collection of samples with isopropyl alcohol on swabs which are placed in tubes. Once in the lab, they can be treated by ultra-sonic shaking followed by filtration onto a .4 microns polycarbonate filter for direct SEM observation of particles, or handled conventionally for FAAS. The filter may be returned to the tube for subsequent analysis by FAAS. The advantages offered are versatility as to method of analysis, as well as the chance to take advantage of the excellent qualitative ability of SEM and the quantiative ability of FAAS simultaneously.