Forensic Electrochemistry: The Electroanalytical Sensing of Mephedrone Metabolites

The constant and persistent synthesis and abuse of new psychoactive substances have sparked the requirement for rapid, on-site, sensitive analytical protocols for their sensing and quantification. Mephedrone (4-MMC) is currently one of the most popular legal highs among recreational drug abusers and imposes a serious public health problem. In this paper, the electrochemical sensing of two metabolites of 4-MMC, namely, nor-mephedrone (4-methylcathinone, 4-MC) and dihydromephedrone (4-methylephedrine, 4-MMC-R), utilizing screen-printed graphite electrodes is performed. The accessible linear ranges by cyclic voltammetry were found to correspond to 40–300 μg mL–1 for 4-MC in both phosphate buffer solution (PBS, pH 7.0) and spiked diluted human urine, whereas in the case of 4-MMC-R, the linearity ranges are 15–300 μg mL–1 (PBS, pH 3.0) and 25–300 μg mL–1 (spiked diluted human urine). To maximize the assay sensitivity, differential pulse voltammetry (DPV) was performed toward the sensing of 4-MC, which exhibited a linear response over the range 10–250 and 10–300 μg mL–1 in PBS pH 7.0 and spiked diluted human urine, respectively. However, 4-MMC-R demonstrated slightly higher sensitivity over the range 5–300 μg mL–1 in both PBS pH 3.0 and spiked diluted human urine. Using DPV, the limits of detection (3σ) were calculated and found to correspond to ca. 3.97 and 3.64 μg mL–1 for 4-MC and 4-MMC-R (PBS, pH 7.0 and 3.0), respectively, and ca. 6.34 and 3.87 μg mL–1 for 4-MC and 4-MMC-R (spiked diluted human urine), respectively. The potential interference of adulterants’ metabolites commonly found in NPS street samples was also explored (at both pH 7.0 and 3.0). The electrochemical approach reported herein provides a novel laboratory tool for the identification and quantification of synthetic cathinone metabolites and has potential for the basis of a portable analytical sensor for their fast, cheap, reliable, and accessible determination in the field.