Differentiation of chloromethcathinone (CMC) isomers: The new kid on the block after methylmethcathinone (MMC) control in the Netherlands

Forensic drug-testing laboratories worldwide are faced with the challenge of identifying a diverse and continuously changing collection of psychoactive substances. In the Netherlands, cathinone-type drugs are frequently encountered by the police. Since the ban on 3-methylmethcathinone (3-MMC) in 2021, the chlorinated analogs 3-chloromethcathinone (3-CMC) and 4-chloromethcathinone (4-CMC) increased in occurrence. In line with many ring-isomeric drugs, their identification is cumbersome due to similarities in their mass spectrum and typically require additional spectroscopic analysis for unambiguous identification. Although only three different isomeric forms exist, spectroscopic analysis by FTIR and NIR revealed four different spectral signatures. The fourth spectrum was attributed to a hydrated form of 4-CMC HCl that existed in parallel with its anhydrous form. This was confirmed by transformation experiments and chemometric modelling of mass spectra. The isomer 3-CMC was only observed in its anhydrous form, while 2-CMC was never observed in actual casework. Finally, MS-based differentiation of the three CMC-isomers was achieved by both a PCA (principal component analysis) and an LDA (linear discriminant analysis) model built from the 70 eV electron ionization mass spectral data. The LDA model correctly predicted the isomeric form of 50 casework samples by retrospective analysis of the recorded mass spectra. These findings show that chemometric modelling is an important tool to extract additional information from laboratory data that already was generated for routine analysis.