Advanced spectroscopic techniques for the analysis of illicit drugs and explosives
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Law enforcement agencies are on a path to intelligence-led-policing, with an aim of gaining as much information as possible and interpreting that into actionable intelligence as quickly as possible. The focus on this information is not necessarily how accurate it is, but in what intelligence it can provide. In the illicit drugs environment, information about mixtures and purity could take months to obtain under current procedures. In the field of explosives analysis there is always a need for field- deployable methodologies that do not require the acquisition of expensive equipment. Currently available spectroscopic techniques used for the preliminary identification of illicit drugs are limited to “single point” spectroscopic methods. Samples that can prove particularly problematic for these methods include drug mixtures, especially those of low purity (e.g. tablets or powders with a range of diluents, adulterants and cutting agents) or new psychoactive substances (NPS) that have not previously been encountered. Furthermore, the information that these methods provide offers little value in the realm of intelligence to policing organisations. In a move to intelligence-led-policing and the desire for more data, ATR-FTIR hyperspectral imaging and Raman mapping are two techniques that have the potential to rapidly provide law enforcement with actionable intelligence on potential illicit drug samples. Both of these methods have been shown to have superior information content in comparison to their single point equivalents. This research compares the performance of the unsupervised chemometric techniques multivariate curve resolution (MCR) and simple-to-use interactive self-modelling mixture analysis (SIMPLISMA) in identifying components of mixtures (from hyperspectral image data) and estimating their purity, without the need for calibration. While all of the hyperspectral methods provided more information than current techniques, Raman mapping coupled with analysis by MCR was found to provide the most precise and accurate results. A feasibility study on the analysis of nitroaromatic explosives via fluorescence landscapes and PARAFAC was conducted. Although the initial aim of the project was to determine a field-deployable, ‘one-size-fits-all’ approach to nitro-containing explosives detection via reduction to amines, the reduction method was only found to be suitable for nitroaromatic explosives. Following the reduction to amines, derivatisation with 𝑜-phthalaldehyde (OPA) was performed to form fluorescent isoindoles. This two-step derivatisation process was demonstrated to take less than 60 minutes and was assessed to be field-deployable. However, fluorescence landscapes of the derivatised amines were found to be too similar for PARAFAC to separate and quantify.
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