Forensic Electrochemistry Applied to the Sensing of New Psychoactive Substances: Electroanalytical Sensing of Synthetic Cathinones and Analytical Validation in the Quantification of Seized Street Samples

Abstract

The electrochemical sensing of new psychoactive substance(s) (NPSs), synthetic cathinone derivatives also termed "legal highs", are explored with the use of metallic modified screen-printed electrochemical sensors (SPES). It is found that no significant electrochemical enhancement is evident with the use of either in situ bismuth or mercury film modified SPES compared to the bare underlying electrode substrate. In fact, the direct electrochemical reduction of the cathinone derivatives mephedrone (4-methylmethcathinone; 4-MMC) and 4'-methyl-N-ethylcathinone (4-methylethcathinone; 4-MEC) is found to be possible for the first time, without heavy metal catalysis, giving rise to useful voltammetric electroanalytical signatures in model aqueous buffer solutions. This novel electroanalytical methodology is validated toward the determination of cathinone derivatives (4-MMC and 4-MEC) in three seized street samples that are independently analyzed with high-performance liquid chromatography (HPLC) wherein excellent agreement between the two analytical protocols is found. Such an approach provides a validated laboratory tool for the quantification of synthetic cathinone derivatives and holds potential for the basis of a portable analytical sensor for the determination of synthetic cathinone derivatives in seized street samples.

An overview of recent developments in the analytical detection of new psychoactive substances (NPSs)

“…47 The authors scope for this work is to provide a rapid screening method to quickly respond to the rapid evolution of designer drugs and the consequent testing backlogs that develop. 50 This work demonstrated for the first time a rapid, accurate, and sensitive method for the quantification of synthetic cathinone components found in seized street "legal high" samples (NRG-2) via the use of an electrochemical protocol utilizing graphite screen-printed electrodes (GSPEs) which was also independently verified with HPLC. 48,49 Smith et al 50,51 provided an alternative to chromatography and proposed a novel sensing protocol based upon the electrochemical methods.…”

“…Further advancements in this methodology by the same authors 47 has seen the application of a time-of-flight (TOF) mass analyzer along with in-source collision-induced dissociation (CID) spectra to provide data for presumptive analysis of various synthetic cathinones in a similar fashion to GC-MS analysis. 50 Analysed in pH 4.3 acetate buffer, limits of detection were found to correspond to 11.80 μg mL −1 for 4-MMC and 11.60 μg mL −1 for 4-MEC. 46,47 Ion mobility spectrometry (IMS) has also been applied to the screening of an array of NPSs within the literature with acceptable results.…”

“…46 Solid synthetic cathinone samples (2-FMC, 2-MEC, 2-FEC and 2-EEC) were sampled directly without pre-treatment and positive ion mass spectra were acquired using a DART-SVP™ ion source interfaced to an AccuTOF mass spectrometer. 48,49 Smith et al 50,51 provided an alternative to chromatography and proposed a novel sensing protocol based upon the electrochemical methods. 47 The authors scope for this work is to provide a rapid screening method to quickly respond to the rapid evolution of designer drugs and the consequent testing backlogs that develop.…”

“…46,47 Ion mobility spectrometry (IMS) has also been applied to the screening of an array of NPSs within the literature with acceptable results. 50 Interesting developments in the detection of synthetic cathinone derivatives is the use of surface enhanced Ramanspectroscopy (SERS) have also been reported. Of note is the reduction of the cathinone substitutes; mephedrone and 4-MEC with a scope to provide an on-the-spot analytical screening tool with cyclic voltammetry.…”

Analysis of ‘legal high’ substances and common adulterants using handheld spectroscopic techniques

“…To this end, the use of a dropping mercury electrode was shown to detect mephedrone in urine, 32 and more recently Smith et al demonstrated the use of screen-printed electrochemical sensors for the detection of cathinone derivatives. 33,34 On the other hand, portable instruments are also available for several solid-state spectroscopic techniques such as ATR-FT-IR, near-infrared (NIR) and Raman. NIR and Raman spectroscopy are rapid and non-destructive, where several different samples can be measured within minutes.…”