The versatility of the XRPD for the drug detection

Abstract

The increasing prevalence of New Psychoactive Substances (NPS) on the drug market exerts considerable pressure on the development of novel detection techniques, especially those suitable for analyses directly on a crime scene. Raman and IR spectroscopy usually fulfil such needs; however, they have limitations (e.g. fluorescence in Raman and sometimes both Raman and IR have difficulties with identifying compounds in certain mixtures). For this reasons, we investigated the potential of X-ray powder diffraction (XRPD) for the identification of drug samples. Beyond identifying the actual controlled substances, this technique might also be very useful in identification of either organic or inorganic cutting agents. The sample crystals were crushed and flattened on the silicon pod to create a planar surface. Bruker D2 Phaser powder diffractometer with parafocusing Bragg–Brentano geometry using CuKα radiation (λ=1.5418 Å) was used for the measurement. The data were collected by an ultrafast LYNXEYE XE detector and subsequently evaluated using HighScore Plus 3.0e software. First, a series of 8 NPS standards was used to verify whether XRPD can distinguish between substances with similar chemical structures. The obtained XRPD patterns confirmed this ability. Subsequently, to verify the ability of XRPD to identify substances in real samples, a series of seized samples provided by Czech police was analysed by XRPD. The comparison of the obtained diffraction data with the patterns of the respective standards enabled their identification. Moreover, results from the analyses of cocaine street samples showed that XRPD might be able to detect not only the cocaine itself, but also the present cutting agents in a single run analysis. With respect to the physical basis of how the XRPD works, in case of mixtures, some signals in the diffraction pattern may overlap. However, if the overlap is only partial, identification of compounds in the unknown sample might still be possible with a proper database. XRPD was able to distinguish all the NPS despite their similar molecular structures and to identify each of the seized substances. Furthermore, XRPD was able to identify the main cutting agent in several samples of seized cocaine. These results show that XRPD could be a valuable analytical tool for the detection of both the unknown compounds and cutting agents in illicit drug samples.