Study of the fragmentation pattern of ketamine-heptafluorobutyramide by Gas Chromatography/Electron Ionization-Mass Spectrometry

Ketamine is an anaesthetic compound used in human and veterinary medicine with hallucinogen properties resulting in an increase illicit use by teenagers in rave parties. Although several gas chromatography/mass spectrometry (GC/MS) methods are reported for drug quantification both in urine and hair, the fragmentation pattern of analyte after derivatization with different reagents has been not yet fully investigated. The present work is aimed to fill this gap by reporting the study of the fragmentation pattern of ketamine, derivatized with heptafluorobutyric anhydride (HFBA-Ket), by using gas chromatography/electron ionization-mass spectrometry (GC/EI-MS). The complete characterization of the fragmentation pattern represented an intriguing exercise and required tandem mass spectrometry (MSn) experiments, high resolution accurate mass measurements and the use of deuterated d4-ketamine for corroborating the proposed structures and characterizing the fragmentation peaks carrying the unchanged aromatic moiety. An extensive fragmentation was recorded, mainly located at the cyclohexanonic ring followed by rearrangement processes of the product ions, as confirmed by superimposing mass spectra obtained from the deuterated molecule. The GC/EI-MS analysis of HFBA-Ket will represent a useful tool in forensic science, since high throughput analyses are ensured preserving both gas chromatographic stationary phase and mass spectrometer ion optics