A fast bioanalytical method based on microextraction by packed sorbent and UPLC–MS/MS for determining new psychoactive substances in oral fluid

Abstract

The emergence in recent years of potentially dangerous new psychoactive substances (NPS) that are not under international control has led to the development of multi-analyte procedures for their unequivocal quantification. A fast ultra-performance liquid chromatography–tandem mass spectrometry method (UPLC-MS/MS), in combination with a sample pretreatment based on microextraction by packed sorbent (MEPS), was for the first time used in this work for the simultaneous determination of NPS in oral fluid. This matrix is an effective alternative to typical biological samples for drug control in substitution therapy programs, and also for the prevention and reduction of traffic accidents. The proposed method allowed the separation and quantification of eleven synthetic cathinones, six opiates, scopolamine, cocaine and two metabolites in less than 3.0min by using appropriate isotope-labelled internal standards. The MEPS procedure, which is a miniaturized version of the SPE technique, is completed within 15min. The influence of variables such as the washing solution and eluent volumes, phase type, number of aspirate–dispense cycles and pH was investigated by using a 3441//16 asymmetric screening design and a response surface methodology based on a Doehlert design. The MEPS process performed optimally with a mixed-mode C8/SCX sorbent and a sample pH of 9. The proposed method was validated according to major guidelines and found to span the linear concentration range 0.5–500ngmL–1 (R2 ≥ 0.9903), and to be selective and precise (within- and between-day precision as %RSD were both lower than 13.7%). The accuracy, in terms of analyte extraction recovery, ranged from 75% to 125% for most of the analytes. The MEPS-UPLC–MS/MS method was successfully used to analyse twelve real samples from patients on a drug detoxification programme and proved an effective tool for drug monitoring.