Rapid Detection and Quantification of Novel Psychoactive Substances (NPS) Using Raman Spectroscopy and Surface-Enhanced Raman Scattering.

Howbeer Muhamadali,Yun Xu,Alexandra Watt,Malama Chisanga,Abdu Subaihi,Carys Jones,Royston Goodacre,David I Ellis,Oliver B Sutcliffe

doi:10.3389/fchem.2019.00412

Abstract

With more than a million seizures of illegal drugs reported annually across Europe, the variety of psychoactive compounds available is vast and ever-growing. The multitude of risks associated with these compounds are well-known and can be life threatening. Hence the need for the development of new analytical techniques and approaches that allow for the rapid, sensitive, and specific quantitative detection and discrimination of such illicit materials, ultimately with portability for field testing, is of paramount importance. The aim of this study was to demonstrate the application of Raman spectroscopy and surface-enhanced Raman scattering (SERS) combined with chemometrics approaches, as rapid and portable techniques for the quantitative detection and discrimination of a wide range of novel psychoactive substances (methcathinone and aminoindane derivatives), both in powder form and in solution. The Raman spectra of the psychoactive compounds provided clear separation and classification of the compounds based on their core chemical structures; viz. methcathinones, aminoindanes, diphenidines, and synthetic cannabinoids. The SERS results also displayed similar clustering patterns, with improved limits of detections down to ~2 mM (0.41 g L−1). As mephedrone is currently very popular for recreational use we performed multiplexed quantitative detection of mephedrone (4-methylmethcathinone), and its two major metabolites (nor-mephedrone and 4-methylephedrine), as tertiary mixtures in water and healthy human urine. These findings readily illustrate the potential application of SERS for simultaneous detection of multiple NPS as mixtures without the need for lengthy prior chromatographic separation or enrichment methods.

Highlights

Novel Psychoactive Substances (NPS) are defined as any substance able to affect a person’s mental capability or emotional state (Welter-Luedeke and Maurer, 2016)
The Principal components analysis (PCA) scores plot of the pre-processed (AsLS and auto-scaled) Raman spectral data collected from the solid samples (Figure 3A) did display a clear separation of the samples according to their core structures
Whilst the diphenidines were separated from all other samples according to PC1 axis (Figure 3A) with a total explained variance (TEV) of 20.8%, the synthetic cannabinoids were clustered on the positive side of PC2, with a TEV of 16.4%, and away from all other samples

Summary

Introduction

Novel Psychoactive Substances (NPS) are defined as any substance able to affect a person’s mental capability or emotional state (Welter-Luedeke and Maurer, 2016). The use of vibrational techniques such as infrared (Schulz et al, 2004; Risoluti et al, 2016) and Raman spectroscopy (Penido et al, 2016), and surface-enhanced Raman scattering (SERS) (Yu et al, 2018, 2019), has attracted a lot of interest as a reliable alternative (D’Elia et al, 2015) as these physicochemical methods provide a portable (hand-held), rapid and cost-effective solution In addition to these advantages, these techniques enable on-site quantitative singular or multiplexed detection and identification of xenobiotic compounds such as NPS and their metabolites in human biofluids (Mabbott et al, 2015; Yu et al, 2019)

Objectives

Methods

Results

Conclusion