Structure-related new approach in the gas chromatography/mass spectrometry analysis of cathinone type synthetic drugs

- Cathinone type synthetic drugs (CTSDs) were oximated then trimethylsilylated.
- Oximated then silylated CTSDs fragmentation patterns - based on GC/MS - are provided.
- The mechanism of CTDSs-trimethylsilyl oximes' quantitative formation was highlighted.
- Simple MSTFA derivatized products provide further transformed species, in equilibrium.
- Direct sample preparation from 10 to 40 μL centrifuged urine proved to be quantitative.

A novel, structure-related derivatization principle has been developed in order to quantify cathinone-type synthetic drugs (CTSDs), focusing on the most common pentedrone (PENT), including also 4-fluoromethcathinone (4-FMC), methcathinone (MCTN), 4-methylethcathinone (4-MEC), 3,4-dimethylmethcathinone (3,4-DMMC), and 4-ethylmethcathinone (4-EMC). Firstly, oximated and, secondly, trimethylsilylated CTSD derivatives were characterized by mass fragmentation patterns using GC/MS that led to the development of a harmonized, quantitative, two-steps derivatization methodology. The two-step process involved i) oximation with hydroxylamine hydrochloride; and ii) trimethylsilylation with N-methyl-N-(trimethylsilyl)-trifluoroacetamide (MSTFA). Next, the oximated-trimethylsilylated species were characterized by retention and mass fragmentation properties. Due to α-cleavage decomposition at their C1C2 bonds without exception, CTSDs uniformely exhibited a structure-related fragmentation pattern. The practical utility of this newly recognized mechanism was validated in urine samples employing an extraction-free and time-, work-, cost- and solvent-effective protocol in accordance with Green Chemistry. The centrifuged urines (10-40 μL) were evaporated to dryness, followed by derivatization. The analytical performance of the methodology was characterized by repeatability (RSD%, varying between 1.43% and 5.44%), limit of quantitation (LOQ, 15-24 μg/mL), linearity (R2, 0.9976-0.9998) and recovery (97-99%) values. The new principle was tested on drug users' urine: one specimen provided 56.8 μg/mL PENT (3.8 RSD%).Simple trimethylsilylation of CTSDs confirmed their special fragmentation patterns, not yet described. The instantenous combination of the primarily formed, characteristic fragments with the mass m/z 44, led to the special equilibrium of products: confirming that direct trimethylsilylation of CTSDs is not suitable for their quantitation.