(Received 28 December 1999; accepted 10 July 2000)
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Micellar electrokinetic capillary electrophoresis has been used to examine characteristic organic gunpowder compounds, including nitroglycerin, diphenylamine, ethylcentralite, and others. The purpose of this project was to develop MECE for implementation in gunshot residue casework. Studies were designed to provide data for evaluating casework samples. The first study compared the results of MECE analysis of organic gunshot residues (O-GSR) from firing range samples, to SEM results for inorganic GSR (I-GSR). MECE analysis found detectable O-GSR for each caliber of weapon examined except for the .22 caliber weapon. SEM analysis confirmed the presence of I-GSR in selected samples where O-GSR was identified by MECE, as well as vaporous lead for the .22 caliber sample. Repetitive firing experiments demonstrated that detectable O-GSR were not deposited each time the same weapon was fired under the same conditions. This leads to the conclusion that residue deposition mechanisms and collection efficiency significantly effect the outcome of O-GSR analyses. Another study found that detectable O-GSR do not persist for more than an hour after firing (under the conditions examined). Decomposition of O-GSR from environmental exposure occurs at a rate that is slow compared to residue persistence, thus, the value of O-GSR composition is not compromised by short term exposure. However, since time dependent changes do not occur, time of firing determinations cannot be made from this data. Finally, casework samples from the hands of suspected shooters and from victims' clothing were examined for O-GSR and I-GSR, O-GSR and I-GSR were identified on some of the samples. MECE has been found to be a potentially valuable tool in the examination of GSR evidence for characteristic organic gunpowder compounds.
Forensic chemist, Washington State Patrol Crime Laboratory, Marysville, WA
Stock #: JFS15003J