Regioisomeric separation of ring-substituted cathinones by liquid chromatography–mass spectrometry with a naphthylethyl column

Recently, various new psychoactive substances (NPSs) have been detected as components of “legal high” products. Synthetic cathinones are one of the most popular classes of NPSs, and are structurally related to the stimulants amphetamine and methamphetamine. In this study, we investigated the differentiation of 2-, 3-, and 4-ring-substituted regioisomers for ethylmethcathinones, fluoromethcathinones, ethylethcathinones and fluoroethcathinones by liquid chromatography–mass spectrometry (/mass spectrometry). At the first step, it was difficult to differentiate the regioisomers by product ion spectra for each cathinone group. Therefore, we had to differentiate them by retention times. Under all tested conditions, the 3- and 4-ring-substituted cathinones were not separated by a conventional octadecylsilyl bonded silica gel column, but complete chromatographic separation of all regioisomers was achieved under optimized conditions using a column with a naphthylethyl-bonded stationary phase. Using these conditions, an authentic “legal high” product containing a fluoromethcathinone was analyzed, and the active ingredient was 4-fluoromethcathinone clearly differentiated from 2- and 3-fluoromethcathinone. The proposed method enables the separation of regioisomeric ring-substituted cathinones without the need for pretreatment steps, such as derivatization or purification. To our knowledge, this is the first trial to use the naphthylethyl-bonded column to separate ring-substituted cathinone regioisomers completely. This column seems to have potential to be successfully used for separation of other types of compounds with ring-substituted regioisomer structures.