A comparison of ultra high performance supercritical fluid chromatography, ultra high performance liquid chromatography, and gas chromatography for the separation of synthetic cathinones has been conducted. Nine different mixtures of bath salts were analyzed in this study. The three different chromatographic techniques were examined using a general set of controlled synthetic cathinones as well as a variety of other synthetic cathinones that exist as positional isomers. Overall 35 different synthetic cathinones were analyzed. A variety of column types and chromatographic modes were examined for developing each separation. For the ultra high performance supercritical fluid chromatography separations, analyses were performed using a series of Torus and Trefoil columns with either ammonium formate or ammonium hydroxide as additives, and methanol, ethanol or isopropanol organic solvents as modifiers. Ultra high performance liquid chromatographic separations were performed in both reversed phase and hydrophilic interaction chromatographic modes using SPP C18 and SPP HILIC columns. Gas chromatography separations were performed using an Elite-5MS capillary column. The orthogonality of ultra high performance supercritical fluid chromatography, ultra high performance liquid chromatography, and gas chromatography was examined using principal component analysis. For the best overall separation of synthetic cathinones, the use of ultra high performance supercritical fluid chromatography in combination with gas chromatography is recommended.

The utility of diode array ultraviolet (UV) detection for aiding in the identification of synthetic cathinones, including different sub-classes and positional isomers is presented. For 35 synthetic cathinones, unique UV spectra are obtained for seven sub-classes, including mostly beta ketones, where position and type of substitution on benzene rings give rise to differences in UV maxima and relative intensity of the spectral bands. This aspect is key to distinguishing positional isomers that contain differences in R substitution (mono and di) around the benzene ring, which provides complementary information to electron ionization mass spectrometry, where the latter technique cannot distinguish between these types of positional isomers. In addition, it is possible to ascertain the substitution position based on the UV spectra. For ten sets of positional isomers, it was possible to distinguish most of the positional isomers within a set. For ultra-high performance supercritical fluid chromatography (UHPSFC) versus reversed phase ultra-high performance liquid chromatography (UHPLC), there was at least a 10 nm blue shift in UV maximum (shift to shorter wavelengths). This highlights the importance of taking in account the effect of mobile phase on the UV maximum when performing method development in UHPSFC. Copyright © 2017 John Wiley & Sons, Ltd.

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