FPSE–LC–MS/MS as a Reliable Tool for Quantifying Drugs of Abuse in Oral Fluid

The widespread use of drugs of abuse (DOA) constitutes a significant public health and social concern, highlighting the need for sensitive and reliable analytical methods particularly for alternative biological matrices. Oral fluid (OF) has emerged as a valuable matrix for the detection of recent drug intake and is extensively employed in forensic and toxicological investigations. Fabric phase sorptive extraction (FPSE) is a recently introduced sample preparation technique, characterized by simplicity, cost-effectiveness, rapidness, low solvent consumption and high analytical performance. A fully developed and validated FPSE-based method for oral fluid analysis will be presented, employing liquid chromatography–tandem mass spectrometry (LC–MS/MS) for the quantitative determination of ten commonly encountered DOA and metabolites including morphine, codeine, 6-monoacetylmorphine (6-MAM), methadone, amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine (MDA), cocaine, benzoylecgonine (BE), and ecgonine methyl ester (EME). The method demonstrated excellent linearity for all analytes (R² = 0.990–0.999), with absolute recoveries ranging from 10 to 93%, coefficients of variation between 2 and 17%. Limits of detection (LOD) and quantification (LOQ) ranged from 0.01 to 2 ng/mL and 0.03 to 6 ng/mL, respectively. Autosampler stability (24h) and short-term (one week) freeze stability exceeded 95 % and 90 % for all analytes. No significant matrix effects, interferences from the analytes or carryover were observed. Overall, the presented FPSE-LC–MS/MS method provides a sensitive, selective, and environmentally friendly analytical approach for the determination of DOA in oral fluid.