Ketamine analysis: a study of enantioseparation on polysaccharide-based stationary phases

Ketamine (2-(2-chlorophenyl)-2-(methylamino)cyclohexanone) is a human and veterinary anaesthetic and analgesic with hallucinogenic properties. For this reason it is illegally used for recreational purposes and included in the controlled substance schedules of most countries. The compound possesses a stereogenic asymmetric carbon atom and can exist as a pair of enantiomers. Pharmacological studies have demonstrated that the S-(+)-enantiomer of ketamine is about three times more potent than the R-(–)-enantiomer as an analgesic. Currently, most ketamine formulations are racemic, however enantiopure S-ketamine is also available on the market under the brand name "Ketanest S". On the other hand, even if ketamine hallucinogenic potency is still largely unclear, some authors claim that the R-enantiomer is the most potent. Therefore it is interesting and useful to investigate the exact enantiomeric composition of ketamine, both when used as a conventional medicine and when abused as an illicit drug. Ketamine eudysmic ratio could be also studied as a marker of origin to discriminate between authorised industrial manufacturing and illicit “home made” synthesis. Moreover, ketamine chiral analysis in biological fluids can provide information on the intended use of the substance, considering that its racemisation in the body seems to be very low. The aim of this study is to test different polysaccharide-based stationary phases [1] and different chromatographic conditions to obtain a good ketamine enantioseparation by liquid chromatography with native fluorimetric detection (HPLC-FL). The method is under validation and promising to be applied for the chiral analysis of ketamine in different matrices, such as prescribed drugs, police confiscations and biological fluids, with the purpose of quality control analyses, detecting illicit use and contributing to the identification of the source of seized ketamine batches.