Development of procedures for casework specimen collection and processing for organic gunshot residue analysis
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The detection and interpretation of gunshot residues (GSR) plays a crucial role in the investigation of firearm related events. Specimens are commonly collected using GSR stubs with double sided adhesive carbon tape. After collection, the stubs can directly be analysed using scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX), which is widely used for the detection of inorganic gunshot residues (IGSR) as it provides simultaneous elemental and morphological information of discrete particles. Since SEM-EDX analysis focuses on the detection of characteristic GSR particles incorporating the elements lead, antimony and barium, the relatively recent introduction of lead free (LF) and heavy-metal free (HMF) ammunition challenges the current standard operating procedure (SOP) for GSR analysis. Other problems arise from the recent findings of GSR-like particles from environmental and occupational sources. The incorporation of organic gunshot residues (OGSR) into the current SOP can provide additional and complementary information that is alleged to overcome these limitations. This project focused on the detection and incorporation of OGSR to current GSR SOPs on different levels. A screening technique was developed for the in-field detection of compounds potentially present in smokeless powders and GSR. The technique was based on microfluidic paper-based analytical devices (μPAD) and fluorescence quenching of pyrene and showed promising results for detecting energetic compounds in OGSR. A portable μPAD reader was built and showed potential for in-field detection of GSR (and explosives). A second screening technique was developed based on solid phase extraction (SPE). This technique can allow pre-concentration and clean-up of samples before OGSR analysis, which might be necessary considering the low amounts of OGSR that are commonly detected on specimens directly collected after discharge. A proof-of-concept study using a completely automated on-line SPE robot, the RapidFire®, connected to a triple quadrupole mass spectrometer (QQQ-MS) was conducted showing promising results for the pre-concentration and/or screening of OGSR. To allow the detection of a broad range of OGSR, an ultra-high performance liquid chromatography (UHPLC) method with ultraviolet (UV) detection and mass spectrometric confirmation using a QQQ-MS was developed using a statistical approach (Artificial Neural Networks (ANN)). This approach was applied for the first time to GSR analysis. The network was trained and used for the prediction of retention times of the target compounds in relation to different gradients. The final UHPLC-UV method was fully validated and tested using simulated case specimens collected at an indoor firing range. It proved sufficiently sensitive and selective for the detection of OGSR from hands and the establishment of smokeless powder profiles. Three different collection protocols for the recovery of OGSR and IGSR from hands were conceptualised to enable both subsequent OGSR analysis by UHPLC-UV and IGSR analysis by SEM-EDX. Comparing the two superior protocols, the extraction efficiencies of OGSR from alcohol swabs and GSR stubs were found to be comparable, while GSR stubs proved to be more efficient in collecting OGSR. Testing the protocols using simulated case specimens taken at the shooting range confirmed that GSR stubs followed by liquid extraction are more suitable than wipes for a combined collection of OGSR and IGSR. Finally, the stability of OGSR on collection devices, i.e. alcohol swabs and GSR stubs, was investigated for a time period of 63 days. Interestingly, energetic compounds were found to be relatively stable, while stabilisers, often the target compounds for OGSR, degraded mostly following a negative logarithmic curve. This could be problematic for the developed SOP for the collection and analysis of both OGSR and IGSR, since SEM-EDX analysis is preceding OGSR analysis causing the degradation of compounds of interest. In summary, an SOP for GSR collection and analysis was developed that could potentially overcome problems arising from LF and HMF ammunitions. Further research studies into persistence and background are necessary to test the value of the developed SOP in a forensic framework.
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