The cyclic nature of soil chemistry: Forensic analysis with the aid of ultra-high performance liquid chromatography

Despite its forensic importance as trace evidence, soil is under-utilised by forensic scientists due to a lack of research into the suitability of analytical approaches and a subsequent lack of understanding of the soil composition. Ultra-high performance liquid chromatography was used to analyse acetonitrile extractions from 210 soil samples taken from four locations across the Geelong and Surf Coast Shire areas of Victoria, Australia from March 2020 to January 2021. With the aid of principal components analysis of the UV-visible data chromatograms, it was found that this method could discriminate soil between locations, timepoints, and age points, and therefore, for the first time, shows that the method may offer a reliable method for forensic soil analysis. The approach used PCoA plots representing Bray-Curtis similarities comparing the UHPLC peak profiles which was able to show that the soil chemistry changes are cyclic, a factor that will help improve the utility of this approach for forensic analysis. As the separation was perfomred using a C₁₈ column, the LDA scores suggest that hydrophobicity based on methyl selectivity may be important in spatial discrimination using this method. Further this type of approach generates a simple visual representation of the data that will be of value for presentation within a courtroom.