Quantitative NMR as a tool for analysis of new psychoactive substances

Abstract

Several New Psychoactive Substances (NPS) have appeared on the drug market, following a new trend of drug consumption. Nuclear Magnetic Resonance (NMR) has been used, especially in the case of forensic analysis, as a tool for unambiguous structure determination of unknown NPS. The quantification of NPS in complex mixtures is, however, a very challenging task, especially in the absence of certified reference materials (CRM). In this work, we applied a quantitative 1H NMR (1H-qNMR) methodology performed without certified analytes for quantification of twelve NPS samples seized by the Brazilian Federal Police. The molecular structure of NPS samples were first confirmed by mono and bidimensional 1H and 13C NMR with unequivocally assigned signals, which allowed for the discrimination of constitutional isomers. A detailed compilation of NMR spectroscopic data showed that these NPS samples belong to cathinones, phenethylamines, and tryptamines groups. The quantitative analyses showed high precision (RSD = 2.67%) and low uncertainty (from 0.44% to 0.37%, with k = 2, 95% confidence). The NPS samples exhibited sufficient stability for a period of 48 h, which is longer than the experimental time frame and, therefore, assures the reliability and validity of the obtained results. Evaluation of some other figures of merit (selectivity, limits of quantification and detection) was also performed and confirmed the proposed method presents suitable and reproducible results. These achievements suggest the present methodology is highly adequate for forensic purposes, attaining excellent precision and accuracy, even in the absence of CRM.