Method Optimization for the Determination of Cannabinoids in Blood by Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

Delta-9-tetrahydrocannabinol (THC) continues to be one of the most popular drugs in the USA. Along with THC, other cannabinoids such as cannabidiol (CBD), are on the rise due to an increase in medicinal usage as well as the passage of different legislations removing these products from their current schedule I status. Thus, an urgency exists to develop robust and sensitive analytical methods to determine cannabinoids, especially THC, CBD and metabolites, in biological samples. The purpose of this study was to investigate different analytical procedures to determine the best method to identify and quantify CBD, THC and their metabolites in whole blood by liquid chromatography tandem mass spectrometry (LC-MS/MS). In LC-MS/MS, we found that most cannabinoids worked better in electrospray (ESI) under negative mode except THC, which showed higher intensity under positive mode. Regarding extraction procedures, we optimized four different methods including liquid-liquid extraction (LLE), supported-liquid extraction (SLE), solid phase extraction (SPE) and QuEChERS. The optimal LLE employed hexane:ethyl acetate (70:30) as extraction solvent; the optimal SLE eluted the samples with dichloromethane and hexane; and the optimal SPE procedure employed mixed mode cation exchange cartridges. The procedure that yielded the best process efficiency was LLE (28.5-121.2%), and the poorest was QuEChERS (7.3-27.5%). Although the evaluated methods showed different matrix effect, extraction efficiency and process efficiency, all of them were able to achieve low limits of quantification (LOQs) between 0.5 and 5 ng/mL. Compared to currently published literature, the present methods were more sensitive in identifying THC-COOH and CBD metabolites in blood with LOQs of 0.5 ng/mL