McCulloch, G; (2017) The development of techniques for organic profiling of geoforensic trace evidence. Doctoral thesis , UCL (University College London).

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Abstract

There is a need to expand the range of analytical techniques which can be used to analyse the organic components of geoforensic trace evidence in order to allow the discrimination of more forensically relevant soils, situated at smaller distances from one another. Existing analytical techniques used in forensic geoscience are based on the analysis of the inorganic fraction of soil, which is often consistent across several kilometers, therefore a complementary analytical technique is required in order to maximise the evidential value of soils and sediments. HPLC has been proposed here as a suitable method, and during method development the most appropriate methods for handling and analysing soil evidence by HPLC were selected, producing a method that is significantly more sensitive, less costly, complicated and time consuming than the methods proposed by previous authors. The feasibility of reliably excluding soil samples from locations situated approximately 250m apart using the new HPLC method was demonstrated, and 100% accuracy (p=0.000) was obtained by performing canonical discriminant function analysis on the resulting HPLC data. The highly complex chromatograms obtained present challenges during data analysis which were resolved by selecting two subsets of markers, each containing a reduced number of peaks than the initial data set. This experiment was repeated at three UK sites, over 12-18 months, and at one site in the USA, and HPLC was shown to offer extremely high accuracy rates in discriminating samples at all four sites and therefore to be robust to changes in underlying geology, and to provide highly accurate discrimination at all time points, and to be robust to delays between sample collection and analysis. Collaborative experiments were undertaken, in which HPLC samples were re-analysed using quartz grain surface texture analysis, and wax marker profiling by GC, and HPLC was shown to offer better discrimination at this close-proximity spatial scale, in addition to offering potential benefits in regulated and commercialised forensic science laboratories due to its simplicity and efficiency.

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