Trimethylsilyl speciations of cathine, cathinone and norephedrine followed by gas chromatography mass spectrometry: Direct sample preparation and analysis of khatamines

Abstract

A literature criticism is given on methods using currently gas chromatography mass spectrometry (GC/MS) to determine cathine (CAT), cathinone (CTN) and norephedrine (NE), jointly khatamines. In this study, khatamines’ oximation, trimethylsilylation and mass fragmentation properties—applying N-Methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA), its trimethyliodosilane (TMIS) catalyst containing version (MSTFATMIS), N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and hexamethyldisilazane (HMDS)—was highlighted, at first. Derivatization, mass fragmentation and quantitation related, optimized model investigations have been carried out as a function of the reaction times and conditions. Special emphasis was put (i) on the stability of the primarily formed (CAT-2TMS, NE-2TMS, CTN-TMS(TMS-oximes)1,2), then transformed, fully derived (CAT-3TMS, NE-3MTS, CTN-2TMS(TMS-oximes)1,2) species, and, (ii) on the proportionally formed stable products, suitable to selective quantitation of all three natural amines, simultaneously. Results, as novelty to the field confirmed that (i) TMIS catalyzed trimethylsilyation triggers to form fully derivatized species unfortunately, in part only; while, (ii) khatamines’ simultaneous quantitation needs to be carried out in a two steps derivatization process consisting of oximation (1st step, hydroxylamine in pyridine) and trimethylsilylation (2nd step, MSTFA), to the CAT-2TMS, NE-2TMS, CTN-TMS(TMS-oximes)1,2. These species were characterized with their retention, mass fragmentation and analytical performance properties, in model solutions and in the presence of plant tissues, as well: R2, limit of quantitation (LOQ) data, expressed in pg/1μL injection basis, proved to be 62.5pg (CAT), 20pg (NE) and 62.5pg (CTN), respectively. The practical utility of proposal was enormously enhanced by the novel, direct sample preparation method. In this process, the freshly harvested, freeze-dried, then pulverized leaves of Catha edulis FORKS were directly derivatized, in the presence of the matrix. Reproducibility (in average 2.07 RSD% varying between 0.15 and 5.5 RSD%), linearity (0.9990–0.9994) and recovery (95.7–99.1%) values of the new sample preparation protocol was confirmed by the standard addition method for CAT, NE and CTN equally. From plant leaf, 0.061w/w% CAT and 0.014w/w% NE contents were obtained. In this tissue CTN was not found. Very likely attributable to the unfavorable climate for the plant: grown in Hungary of temperate zone and naturalized in the tropical Africa.