Combining attenuated total reflectance- infrared spectroscopy and chemometrics for the identification and the dosage estimation of MDMA tablets

Abstract

The principal objective of the Belgian Early Warning System on drugs (BEWSD) of the Reitox national focal point is to collect and disseminate information on the appearance of drugs circulating on the local drug market. To this end, one of the actions of BEWSD is to annually collect substances that are circulating on the Belgian summer festivals. Every year a high number of seized samples is collected and submitted to qualitative and quantitative analysis. The goal is twofold: next to the monitoring of the drug market, a surveillance on the quality of drugs is established with main focus on the evolution of MDMA dosages in ecstasy as well as the emergence of new psychoactive substances (NPS). The presented paper focusses on the characterization of ecstasy tablets, seized at summer festivals in the seasons 2016 and 2017. Samples were classically analysed with GC-MS and UV spectroscopy, representing a certain cost and time for analysis. In this paper, an approach is presented based on infrared spectroscopy to first differentiate ecstasy from other party drugs and further quantify MDMA in the tablets. To this end, a comparison was done between NIR and Mid-IR spectroscopy in combination with partial least squares-discriminant analysis (PLS-DA) and -regression (PLS). For the differentiation between MDMA positive and negative tablets, the best results were obtained by NIR and PLS-DA and resulted in a correct classification rate of 96% for an external test set. In addition, for the quantification of MDMA, the best results were also obtained with a PLS model based on NIR spectra. A RMSEP for the external test set of 3.86 was obtained and an R² value between real and predicted values of 0.88. This means that for the dosage MDMA per tablet, when taking into account the range of masses of the tablets in our sample set, the error varies between 8 mg for low mass tablets and 27.8 mg for high mass tablets. These are acceptable values for a first estimation and give a first indication of the risk the tablet may represent. The presented approach will be of use for on-site analysis. Moreover, when applied in a laboratory environment, it will reduce the workload for the analysis of MDMA tablets and thus liberating resources.

Keywords: ATR-(N)IR; Chemometrics; Illicit drugs; Mobile detection approaches.