Oral fluid (OF) is a new biological matrix for clinical and forensic drug testing, offering easy and non-invasive sample collection mainly accomplished with commercial disposable devices. Due to a stronger correlation than urine with blood concentrations, screening based on OF is greatly gaining value in DUID (Driving under the influence of drugs) programs worldwide (Strano-Rossi et al., 2012). Furthermore, cannabinoids are usually the most prevalent analytes in illicit drug testing and for this reason application of OF testing requires sufficient reliable data to support sensitive and specific cannabinoid detection for forensic purposes (Lee et al., 2013). Cannabinoids analysis has been historically performed using GC-MS technology, either with single quadrupole or triple quadrupole systems. However, in the last decade the role of LC-MS/MS in modern forensic toxicology laboratories has gained more relevance because of less extensive sample preparation, reliable results and versatility.

The present work describes a simple fully validated method for the determination of THC and THC-COOH in oral fluid by using liquid chromatography coupled to triple quad mass detection (LC-ESI-MS/MS). Chromatographic separations were carried out with a ZORBAX Eclipse Plus C18 RRHT (2,1mm x 100mm x 1,8μm) column in less than 8 minutes. Chromatography and mass spectrometric instrumental conditions were optimized in order to keep minimal sample preparation. Oral fluid samples were centrifuged and diluted prior to LC-MS analysis.

The lower limit of quantifications (LLOQ), defined as the lowest concentration with an intraday and inter-day accuracy RSD < 20 %, was 0.1ng/mL in OF (0.0625pg on column) for THC and 0.25ng/mL in OF (0.156pg on column) for THC-COOH. The limit of detection (LOD) defined as signal to noise ratio equal to 3 was 0.01ng/mL in OF for THC (0.00625pg on column) and 0.1ng/mL (0.0625pg on column) in OF for THC-COOH. Results are presented in terms of selectivity, matrix effect, linearity and reproducibility.