Performance evaluation of two Raman instruments for unknown forensic samples

Abdull Manap, Mohd Rashidi and Blagden, Nicholas and Munshi, Tasnim and Scowen, Ian (2015) Performance evaluation of two Raman instruments for unknown forensic samples. In: 7th Asian Forensic Sciences Network Annual Meeting & Symposium, 16-18 November 2015, Kuala Lumpur, Malaysia.

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Abstract

The Misuse of Drugs Act 1971 classifies Class A, B and C drugs as illegal and over 30000 Class A seizures were reported in England and Wales in 2013/14.1 The drug substance is typically formulated with an array of cutting agents, e.g. Benzocaine, Lidocaine and Phenacetin, leading to a complex mixture of organic species. Early attempts to automate identification of such materials were hampered by spectral overlap and interference. However, developments in computational deconvolution of a spectral data has led to the development of systems that potentially identify targeted components in complex mixtures.2 In this work, a Handheld Raman instrument (Thermo-TruNarc), incorporating an implementation of such an algorithms, was tested with an array of seized samples from UK forensic investigation. These ‘street’ samples were unmodified from seizure and presented as powders (43 samples) and oil (1 sample). The spectral output of the Handheld system was compared with spectra from a laboratory micro-Raman instrument obtained from at least three sites in each sample. Spectra from the laboratory system were assigned and the results compared to the identification reported from the portable system. In 39/44 of cases a valid identification was obtained although, of these, 12 required a sample treatment with an ethanol extraction followed by evaporation onto a proprietary SERS substrate (‘Test-Stick’ analysis). A detailed evaluation of spectral features was undertaken for all cases and where assignments were inconclusive after direct sampling these were mainly attributed to sample fluorescence. Hence, the TruNarc system was shown to be reliable and capable of identifying complex street sample and such identification are available to users with the minimum of spectroscopic expertise.

Keywords:Raman Spectroscopy, TruNarc, Benchtop, Narcotic drugs, Street Samples, Solid
Subjects:F Physical Sciences > F100 Chemistry
F Physical Sciences > F410 Forensic Science
Divisions:College of Science > School of Chemistry
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ID Code:22257
Deposited On:13 Feb 2016 19:53

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