Cannabis consumption (and commercialisation) has been on the rise globally, with numerous countries decriminalising or legalising medical or personal consumption across the last decade. With this has come an increased interest in the various forms of the psychoactive compound tetrahydrocannabinol(THC) which are present in varying quantities within the cannabis plant. Even with decriminalisation or legalisation of cannabis, the vast majority of workplaces require staff to carry out their duties unimpaired for legal purposes, and it remains a criminal offence to perform tasks like operating heavy machinery under the influence of substances. These circumstances have combined to require more robust blood testing programmes focussed not only on the historically prevalent Δ-9-THC, but increasingly Δ-8-THC along with each of their hydroxylated and carboxylated metabolites (11-OH-Δ8/9-THC and Δ8/9-THC-COOH).
The separation of Δ-8- and Δ-9-THC along with their metabolites pose a particular chromatographic challenge, with three pairs of isomers differentiated positionally by one double bond, making quantification of these compounds particularly challenging. In this paper we explore the impact C18, Biphenyl and Fluorophenyl (PFP) HPLC column phases have upon separation of these isomers and their metabolites. With a suitable candidate phase selected, a method was then developed for optimal separation for these analytes in whole blood samples. This method demonstrated suitable response across a biologically relevant calibration range, and with suitable separation to minimise interference from other structurally similar or commonly encountered cannabinoids.
