Date of Graduation
Eberly College of Arts and Sciences
The use of firearm discharge residue (FDR) evidence has been on the decline as a result of instrumental and analytical limitations and the inability to evaluate and assign evidentiary value. To utilize FDR evidence to its fullest extent, detection methods exploiting modern advancements in instrumentation must be explored and developed. Research has been performed in an effort to modernize FDR analysis but to date nothing has been implemented or found widespread use in forensic laboratories. This research investigated three analytical techniques for the detection of FDR; (1) ion mobility spectrometry (IMS), (2) thermal desorption gas chromatography mass spectrometry (TD-GC/MS), and (3) electrospray ionization tandem mass spectrometry (ESI-MSn). An IMS method for organic gunshot residues was validated and then employed in a population study to determine shooter from non-shooters by analyzing samples taken from a subject's hands. Peaks corresponding to three organic gunshot residue (OGSR) compounds were detected in approximately 70% of shooter samples. Matrix issues associated with the swab material and the hands of subjects inherently complicated spectra. The results show a need of a pattern-based analysis rather than relying on peak identification for characterizing shooters vs. non-shooters hand swabs.;The next phase of this research was prompted by the need to develop confirmatory detection methods and reach lower limits of detection. A thermal separation probe was affixed to a GC/MS and allowed direct analysis of hand swabs without any prior sample preparation. A method was developed and authentic shooter swabs were analyzed. Although, three OGSR compounds were detected in 14-81% of authentic samples, additional work remains before the technique can begin to be implemented. Finally, experiments on detecting gunshot residue with ESI-MSn via complexing with a macrocyclic host were performed. The macrocyclic host, 15-crown-5, was evaluated for complexation with known GSR metals. Foundational parameters were established and single and double ligand complexes were identified using isotopic ratios and fragment ions. Mass spectral intensities were used to determine the binding selectivities of the metals to the crown ether and in turn the preferential binding of the target metals. Additionally, preliminary molecular modeling provided insight into some experimental observations. Overall, three methods were evaluated in an effort to modernize the analysis of firearm discharge residues and in doing so increase the evidentiary value. IMS and thermal desorption GC/MS proved adequate as screening methods for OGSR and while additional work is required, ESI-MSn proved promising for detecting complexed GSR metals. The advantage of coupling ESI-MSn and complexation is that it allows for the dual detection of OGSR and GSR. While modernizing analysis is key to increasing the evidentiary value it is apparent that coupling the detection of OGSR and GSR is the future of FDR analysis.
Stevens, Brittany Louise, "Comprehensive Modernization of Firearm Discharge Residue Analysis; Advanced Analytical Techniques, Complexing Agents, and Tandem Mass Spectrometry" (2017). Graduate Theses, Dissertations, and Problem Reports. 6726.