Fast and highly sensitive determination of tetrahydrocannabinol (THC) metabolites in hair using liquid chromatography-multistage mass spectrometry (LC-MS ).

In hair analysis, identification of 11-nor-9-carboxy-∆ -tetrahydrocannabinol (THC-COOH), one of the major endogenously formed metabolites of the psychoactive cannabinoid tetrahydrocannabinol (THC), is considered unambiguous proof of cannabis consumption. Due to the complex hair matrix and low target concentrations of THC-COOH in hair, this kind of investigation represents a great analytical challenge. The aim of this work was to establish a fast, simple, and reliable LC-MS routine method for sensitive detection of THC-COOH in hair samples. Furthermore, the LC-MS method developed also included the detection of derivatized 11-hydroxy-∆ -THC (11-OH-THC) as an additional marker of cannabis use. Hair sample preparation prior to detection of the two THC metabolites was based on digestion of the hair matrix under alkaline conditions followed by an optimized liquid-liquid extraction (LLE) procedure. Sample preparation by LLE proved to be more suitable than solid-phase extraction (SPE) due to less laborious and time-consuming steps while still yielding satisfactory results. A significant improvement in analytical detection was introduced by multistage fragmentation (MS ), which led to enhanced sensitivity and selectivity and thus low limits of quantification (0.1 pg/mg hair). The MS method included two transitions for THC-COOH (m/z 343 → 299 → 245 and m/z 343 → 299 → 191) encompassing the quantifier (m/z 245) and the qualifier ion (m/z 191). The method was fully validated, and successful application to authentic toxicology case samples was demonstrated by the analysis of more than 2000 hair samples from cannabis users with THC-COOH concentrations determined ranging from 0.1 to >15 pg/mg hair.