Development of methods to determine analytes in a variety of matrices with applications to forensic science

Breidi, Salah Eddine (2014) Development of methods to determine analytes in a variety of matrices with applications to forensic science. (PhD thesis), Kingston University, .


This thesis comprises of studies based on the broad field of forensic analysis and the development of methods which can be applied to different matrices. The initial studies focus on the forensic determination of psychoactive drugs in hair matrix using newly deve1oped gas chromatography-mass spectrometry analytical methods. The second study focuses on the discrimination and matching of skid marks and rubber tyre analysis by using novel chemical analysis methods. This thesis reports the deve1opment and application of a series of innovative analytical methods: gas chromatography-mass spectrometry, inductively coupled plasma mass spectrometry, pyrolysis-gas chromatography-mass spectrometry and attenuated total reflection Fourier transform infrared spectroscopy. Gas Chromatography-Mass Spectrometric (GC-MS) methods for drug analysis routinely employ derivatising reagents. The aim of the first study was to develop a method for the analysis of two recreational drugs, delta-9-tetrahydrocannabinol (delta-9- THC) and cocaine in hair samples using GC-MS, without prior derivatisation, thus allowing the sample to be analysed in its original form. Ten hair samples, that were positive to ELISA analysis for either delta 9-THC and/or cocaine, were enzymatically digested, extracted and then analysed by gas chromatography-mass spectrometry. All samples measured contained delta 9-THC and one sample contained cocaine. The limits of detection (LOD) and quantification (LOQ) were 0.02 ng/mg & 0.05 rig/mg, respectively for cocaine and 0.015 ng/mg & 0.02 ng/mg, respectively for A9-THC. The wide detection window, ease of direct analysis by GC-MS, lower detection limits of un-derivatised samples and the stability of drugs using this technique offers an improved method of analysis. This experiment has been designed to develop an immunological screening test followed by a GC-MS confirmation method for the simultaneous analysis of delta 9- THC, THC-COOH, , OH-THC, cocaine, Benzoylecgonine (BZ), amphetamine (AP), methamphetamine (MA), in human hair, thus avoiding the significant factors responsible for drug degradation by acid and alkali hydrolysis and to obtain optimal recovery conditions. Enzymatic hair digestion was used to hydrolyse 18 Turkish samples using Proteinase K, Dithiothreitol and Tris HCl buffer. At the beginning, all 18 samples tested screened positive on ELISA, though analysis by GC-MS indicated that only 2 samples were positive for delta 9-THC and THC-COOH. Cross reaction lead to false positive results in the pre-screening step as a result of the degradation of the antibodies in the pre-coated ELISA microplate. Tyre rubber analysis Owing to an increase in the number of hit and run accidents, it is quite common for rubber traces to be left at the crime scene. The Forensic Scientist will have the task of analysing the tyre striation traces in order to identify the type of tyre involved in the accident. However, the tyre striations alone do not provide enough detail to show a high level of discrimination between different tyre manufacturers and individual models. In this study, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FI‘IR) and pyrolysis GC-MS methods were developed to enable greater discrimination between different tyre rubber samples. Seventy elements were screened for each sample by ICP-MS in both collision cell mode and reaction cell mode. ATR-FTIR analysis indicated a low intra-variability (analysis of similar tyres) which demonstrated high precision of the technique, and also showed a large inter-variability between different manufacturers and models, which supports their high potential as indicators to be used for discrimination between different tyres manufacturers and models. Principal Component Analysis (PCA) was utilised to distinguish between the different tyres.

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