A μ-SPE procedure for the determination of cannabinoids and their metabolites in urine by LC–MS/MS

Abstract In this paper the development and validation of a method for the analysis of THC-COOH, THC, THC-OH, CBD and CBN in their total form in urine by LC–MS/MS is presented. Tandem hydrolysis, i.e. enzymatic and basic, has been found optimal for the simultaneous analysis of the selected analytes in urine: basic hydrolysis is more effective for the cleavage of THC-COOH glucuronide while enzymatic hydrolysis allows the cleavage of the conjugated cannabinoids possessing ether bonds (THC, THC-OH, CBD). The whole procedure requires a 2 h enzymatic hydrolysis using only 90 μL of urine by μ-SPE extraction technique with C 18 tips. Clear advantages in terms of time and of enzyme reduction are obtained and the cost of the analysis can be dramatically reduced. Satisfactory recovery values and matrix effect are obtained, and the chromatographic run, performed with a fused-core column, allowed the complete analyte separation in only 3 min (total run 5.8 min) with a common HPLC system. Furthermore the whole procedure has been validated according to SWGTOX guidelines: LOQs are between 6 and 10 ppb, quite lower than the requested cut-off for urine testing; intermediate reproducibility of the selected analytes is below 10% and accuracy is between 85% and 113%, except for CBD, included only for semi-quantitative determination.