An evaluation of freezing and soil presence on volatile organic compounds emitted by decomposing pig tissues using SPME GC/MS
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The ability to quickly and efficiently locate concealed human remains is crucial in forensic investigations and when locating disaster victims. On occasions when human remains are recovered, correctly assigning a postmortem interval (PMI) may become necessary to corroborate statements or make an identification. While Human Remains Detection canines (HRD canines) provide rapid and sensitive searches, the mechanisms behind their sense of smell remain poorly understood. Over the past ten years, volatile organic compounds (VOCs) have been investigated in an effort to address questions concerning PMI, optimization of training aids, and portable 'sniffing' devices. The approaches taken for investigating VOCs emitted from decomposing tissues buried or otherwise have been diverse. They range from burying entire human bodies and sampling the above-ground volatiles using triple-sorbent traps (TSTs) to isolating small amounts of tissue into glass vials whereby the volatiles are sampled by Solid Phase Microextraction (SPME). The resulting studies have led to large quantities of data that are difficult to interpret and compare between studies. Furthermore, the restrictions surrounding access to human remains have caused many studies to use other animals, (pigs, chickens, cows, and deer) in particular the domestic pig, due to its similarities in hair coverage and tissue ratios. There have been several studies that attempt to address the effects that burial has on the resulting VOCs. However, the addition of a complex matrix to a process that already has many variables has caused difficulty in data interpretation. The purpose of this study was to identify how freezing and the presence of soil affect the VOC profiles of various tissue types (blood, bone, fat, small intestine, muscle, and skin) obtained over six weeks of decomposition. In order to accomplish this, the study was performed in three parts. The first part used fresh pig samples obtained only hours after euthanization, the second part utilized tissues from the same areas of the pig after the samples had been frozen for 6 weeks and the third part combined soil with three of the tissue types (blood, bone, muscle). SPME was employed at room temperature using a 65 µm PDMS/DVB coated fiber as the adsorbent material to extract the VOCs from the headspace. The use of SPME as the extraction method allowed for direct desorption and subsequent analysis into the injection port of the GC/MS. User-defined integration parameters were applied to each resulting chromatogram in an effort to identify what impact, if any, freezing and soil had on the resulting VOC profiles. The results obtained in this study suggest that the freezing and thawing of tissue samples have varying effects on the resulting chromatograms based on the complexity of the tissue-type. This implies that prolonged use and storage of some, commonly utilized, training aids may not be providing the most reliable scent profile for the HRD canines. Results obtained from the soil study were complex, but several overall trends were observed in the release and production of different compound classes. Comparisons to previous studies using similar extraction procedures demonstrate the need for a standardized protocol for future decomposition studies.