Odour profiling of blood training aids for blood-detection dogs using comprehensive two-dimensional gas chromatography (GCxGC)
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The use of blood-detection and cadaver-detection dogs as investigative screening tools to search for blood evidence is a contemporary addition to many law enforcement agencies around the world. The training protocols for these canines remain unstandardised and the specifics of the blood training aids implemented can vary between agencies. While there is a large field of research investigating the odour profiles of human remains, there has been very little research in a forensic context on specific tissue types such as blood, or that has linked variables in the blood odour with the response rate of these scent-detection dogs in the field. The aim of this thesis was to investigate the chemical odour profile of blood training aids utilised for the training of blood-detection and cadaver-detection dogs and compare this directly to responses in training, in order to assist in the development of more effective and standardised training protocols. As part of this thesis, headspace solid phase microextraction (HS-SPME) was coupled with comprehensive two-dimensional gas chromatography – time-of-flight mass spectrometry (GC×GC-TOFMS), a novel technique that is also only recently being introduced into this field, to analyse fresh and degraded blood samples, from single and multiple donors, as well as latent blood samples. Three studies were performed to investigate the chemical odour of blood under various conditions, which were compared with the responses of blood-detection and cadaver-detection dogs in scent line-ups conducted with local law enforcement. The first study examined the effect of ageing and analysed the volatile organic compound (VOC) profile of blood as it transitioned from fresh to degraded, over a 24-month period. Blood on two surfaces (non-porous aluminium tin and porous cotton) were compared and it was observed that fresh blood (collected within 24 hours) produced the most distinct profile irrespective of surface, and that as the blood degraded the odour became generalised across the two surfaces. However, comparing functional classes elucidated a common pattern between blood ages and surfaces. Similarly, results from the dog trials demonstrated that the blood-detection and cadaver-detection were more adept at locating fresh blood, with their efficacy becoming reduced as the blood aged. Notably, the samples on the non-porous surface posed a greater challenge for the canines to locate which is an important consideration for training protocols. The second study expanded on the effect of ageing by replicating the first study over a 6-month period using four different blood donors, to determine if inter-individual differences exist in the odour of blood. While the overall VOC profile of blood remained consistent across donors, some unique VOCs were identified between individuals as a result of variations in lifestyle, diet, health and environmental exposure. It was confirmed that the effect of ageing has a greater influence on the odour profile of blood and it was concluded that training aids should incorporate both fresh and degraded blood, with a single donor being sufficient. The blood-detection and cadaver-detection dog trials demonstrated the capability of the dogs to locate blood aged up to 6 months old regardless of the donor, but as the blood degraded, this efficacy reduced and displayed minor skewing for different donors. The third study evaluated the baseline detection limits of the blood-detection and cadaver-detection dogs to latent blood when compared with current analytical instrumentation and a common chemical presumptive test – i.e. luminol. The experiment replicated a scenario in which a suspect may attempt to wash away a victim’s blood on clothing to test anecdotal evidence of the sensitivity of scent-detection dogs. It was confirmed that the blood-detection and cadaver-detection dogs are much more sensitive than current analytical instrumentation, and are complementary screening tools to luminol for the detection of latent blood. The overall results of this thesis provide a greater understanding of the odour of blood as a training aid for blood-detection and cadaver-detection dogs, and will assist in providing scientific support for their deployment as investigative tools if their use becomes challenged in court.
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