Liquid phase microextraction for the determination of 60 illicit drugs in oral fluid by HPLC-MS/MS analysis

The use of psychoactive substances is increasing worldwide and remains an important social concern. Even if instruments with high level of performances are available, the development of suitable methodologies to isolate the analytes are of interest [1]. The aim of this work was the development and validation of a liquid phase microextraction method for the determination of 60 illicit drugs belonging to different pharmacological classes in oral fluid (OF). The workflow of the present study consisted of four steps: sample collection through passive drool, centrifugation, parallel artificial liquid membrane extraction (PALME) clean-up and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis for the identification and quantification of the drugs. PALME is a liquid phase microextraction based on the use of a liquid support membrane which was first described and used in 2013 by Gjelstad et al. [2]. This technique uses a pH gradient to facilitate the mass transfer of uncharged analytes across a liquid membrane with organic support and this allows to extract, from an aqueous biological sample, acidic, basic or neutral molecules [3]. In this work, all the parameters that influence the extraction (extraction time, extraction pH, the composition of the extracting solvent and acceptor solution, the effect of adding salt) were evaluated; the method proved to be suitable for analytes of different classes using small quantities of organic solvent and biological sample and it is an example of green chemistry. The method was subsequently validated following the guidelines of Scientific Working Group for Forensic Toxicology by evaluating parameters such as precision and accuracy, LOD and LOQ, linear dynamic range, matrix effect, recoveries.