A rapid and sensitive method for the identification of delta-9-tetrahydrocannabinol in oral fluid by liquid chromatography–tandem mass spectrometry

A fast and sensitive method was developed for detecting delta-9-tetrahydrocannabinol (THC) in oral fluid by liquid chromatography–tandem mass spectrometry (LC–MS/MS). The method is suitable for samples of small volume and low concentration. For method development and validation, neat oral fluid (200 μL) spiked with THC and d3-THC (internal standard) was extracted via liquid–liquid extraction (LLE). The LLE method had an extraction efficiency of 75% with no significant matrix effects observed in either diluted or neat oral fluid samples. LC was performed on a Zorbax Eclipse XDB-C18 Rapid Resolution HT column (2.1 mm × 50 mm, 1.8 μm particle size) with positive electrospray ionisation and selected reaction monitoring. The total run time was an efficient 3.5 min in isocratic elution mode. The limit of quantification was 1 ng/mL and the analysis was linear over the range of 1–500 ng/mL with a correlation coefficient of 0.9998. The imprecision (RSD) of the method was 13% and inaccuracy (MRE) was 4%. The method was subsequently applied to two neat oral fluid samples taken from a chronic cannabis smoker. It was also applied to buffer diluted residual oral fluid samples (n = 48) collected using the Cozart RapiScan® system through the Roadside Drug Testing Program (RDTP) in NSW, Australia. A stability study was performed that revealed freezing or refrigerating resulted in comparable decreases in THC recovery from neat oral fluid at the end of two weeks of storage. Storage at room temperature even for one day invoked significant losses and is not recommended.