An Efficient, Robust Method for the Determination of Cannabinoids in Whole Blood by LC–MS-MS

Due to the high prevalence of cannabinoids in forensic toxicology casework, it is desirable to have an efficient method that uses a small volume of blood and requires a minimal sample preparation. Although many methods have been reported, they are often labor intensive, require special sample preparation materials, use 1 mL or more of specimen or are difficult to replicate. The liquid chromatography with tandem mass spectrometry (LC–MS-MS) method presented herein employs a rapid and simple liquid–liquid extraction, has been successfully applied in two different laboratories, uses 0.5 mL of specimen and was extensively validated. The validated limit of detection and limit of quantitation were 1 ng/mL for delta-9-tetrahydrocannabinol (THC) and 11-hydroxy-delta-9-tetrahydrocannabinol (OH-THC) and 5 ng/mL for 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THCA). Each analyte demonstrated a zero-order linear range (r2 > 0.990) with 1/x weighting of 1–40 ng/mL for THC and OH-THC and 5–200 ng/mL for THCA. The coefficient of variation of replicate analyses was within 14%. Bias was within ±13% of the prepared concentration. The validated method provides a sensitive, efficient and robust procedure for the quantitation of cannabinoids in blood using LC–MS-MS and a sample volume of 0.5 mL.