Dilute and shoot ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) analysis of psychoactive drugs in oral fluid

A fast and sensitive ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated for the measurement of the most common drugs of abuse and some new psychoactive substances in oral fluid. The target compounds were 6-monoacetylmorphine, morphine, codeine, cocaine, benzoylecgonine, amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine, Δ-9-tetrahydrocannabinol, cannabidiol, mephedrone, ketamine and synthetic cannabinoid 5F-AKB48 (5F-APINACA). Oral fluid (OF) samples were 1/3 diluted with water and separated by reversed phase chromatography with gradient elution of 0.1% formic acid in water and 0.1% formic acid in acetonitrile and detected with tandem mass spectrometry operated in positive multiple reaction monitoring mode. The method was linear for all analytes under investigation from limit of quantification (LOQ, range: 0.5-5 ng/ml) to 250 ng/mL OF. Recovery of analytes under investigation and matrix effect were always higher than 90% (recovery range: 90.6-105.5% and matrix effect range 90.6-101.3%) whereas intra-assay and inter-assay precision and accuracy were always better than 15%. The developed method was successfully applied to ten OF specimens obtained from a proficiency test program and previously analyzed by gas-chromatography mass spectrometry. Analytes concentration between the two methods presented an excellent agreement (r2 = 0.952) with overlapping values demonstrating method feasibility for high throughput laboratories needing indisputable results for clinical and/or forensic purposes.