The forensic applications of chemical imaging

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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Chemical imaging utilises both molecular spectroscopy and digital imaging. Combining these analytical tools allows for spatial and spectral (chemical) information to be collected simultaneously. The availability of a rapid, non-destructive technique that provides highly discriminating results would be of significant advantage in forensic investigations. Chemical imaging has been identified as providing these and other benefits, and therefore warrants an in-depth assessment into the use of this technology for forensic applications. The overall objective of this research was to evaluate the use of visible and near- infrared chemical imaging for the analysis of forensic samples, including the development and optimisation of collection and data analysis procedures. Forensic evidence types examined in depth included writing inks, firearm propellants, and bruises on skin. Blue and black, ballpoint and rollerball pen inks were examined using absorbance and luminescence chemical imaging. Pre-processing and principal components analysis (PCA) was applied to the chemical imaging data to determine the effects on the resulting discriminating powers. The results were compared with those obtained using the Video Spectral Comparator (VSC). Chemical imaging was able to discriminate more blue and black ballpoint and rollerball inks than conventional examination using the VSC. The best results for all the ink types selected were achieved using the absorption mode and PCA treatment of the data after pre-processing steps. Further discrimination was made possible by combining the absorbance PCA data with PCA- treated luminescence data. Luminescence chemical imaging was used to examine a variety of propellant from .22 rimfire ammunition. Examinations were conducted on raw, unfired propellant, and on propellant collected after discharge from a weapon. Luminescence chemical imaging was able to visualise propellant residues on a cloth target and to discriminate propellant from different sources. Fired propellant could also be associated with an unfired sample. A searchable database containing physical and spectral characteristics was developed. The use of chemical imaging to assist in bruise age estimation was also investigated. Absorbance chemical imaging was used to discriminate between varying concentrations of bilirubin and hemoglobin on cloth and injected into pig skin. This technique provided superior results when compared with conventional photography and reflectance spectroscopy. Other evidence types that were successfully analysed using chemical imaging include textile fibres, latent fingermarks, thin-layer chromatography plates and oleoresin capsicum sprays. The successful application of visible and near-infrared chemical imaging to a range of forensic samples indicates that chemical imaging is an effective and reliable analytical tool for operational forensic laboratories.
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