Development of new methods of detection and quantification of controlled and new psychoactive substances (NPS) using liquid chromatography-amperometric detection (LC-AD)

Zuway, Khaled Youssff (2018) Development of new methods of detection and quantification of controlled and new psychoactive substances (NPS) using liquid chromatography-amperometric detection (LC-AD). Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The global increase in the prevelance and abuse of new psychoactive substances (NPS) has required the development of new analytical methods for rapid, selective and inexpensive protocols for both their separation and detection. Electrochemical sensing of these compounds has been demonstrated to be an effective method for their in-field detection, either in their pure form or the presence of common adulterants. The electrochemical technique can differentiate between structurally-related phenethylamines (for example (±)-paramethoxyamphetamine and (±)-3,4-methylene dioxymethamphetamine, however it is limited in its ability to distinguish between structurally-related cathinone-derivatives, for example (±)-4-mephedrone and (±)-4-methyl-N-ethycathinone. The HPLC-AD protocol obtained a cost-effective, reproducible, and reliable sensor platform for detection of the target analytes by simultaneous HPLC-UV and amperometric detection protocol. Additionally, the simultaneous HPLC-UV and amperometric detection protocol detailed herein shows a marked improvement in selectively discriminating between structurally related compounds. This thesis demonstrates, for the first time, the combination of HPLC-UV with amperometric detection (HPLC-AD) for the detection and quantitative analysis of new psychoactive substances using a commercially available impinging jet (LC-FC-A system) or using a custom-made iCell channel flow-cell system (LC-FC-B), both incorporating embedded graphite screen-printed macroelectrodes. The method demonstrates the application of a cost-effective, reproducible, and reliable sensor platform for the simultaneous HPLC-UV and amperometric detection of target analytes. Although the amperometric detection (HPLC-AD) system that has been developed is not as sensitive as standard HPLC-UV detection,both LC-FC-A and LC-FC-B show a good agreement between the quantitative electroanalytical data. Therefore, they are suitable for the detection and quantification of new psychoactive substances, either in their pure form or within complex mixtures. Additionally, the simultaneous HPLC-AD protocol shows a marked improvement and advantage over previously reported electroanalytical methods. The electroanalytical methods were either unable to selectively differentiate between structurally related synthetic cathinones (e.g. (±)-mephedrone and (±)-4-MEC (Smith et al., 2014a), or utilised harmful and restrictive materials in their design by adding the illegal compounds in combination with the legal compounds.