Accurate identification and quantification of 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid in urine drug testing: Evaluation of a direct high efficiency liquid chromatographic–mass spectrometric method

A direct liquid chromatographic–tandem mass spectrometric (LC–MS/MS) method for measurement of urinary Δ9-tetrahydrocannabinol carboxylic acid (THCA) was developed. The method involved dilution of the urine sample with water containing 2H9-deuterated analogue as internal standard, hydrolysis with ammonia, reversed phase chromatography using a Waters ultra-performance liquid chromatography (UPLC™) equipment with gradient elution, negative electrospray ionization, and monitoring of two product ions in selected reaction monitoring mode. The measuring range was 2–1000 ng/mL for THCA, and the intra- and inter-assay imprecision, expressed as the coefficient of variation, was below 5%. Influence from urine matrix on ionization efficiency was noted in infusion experiments, but was compensated for by the internal standard. Comparison with established gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry methods in authentic patient samples demonstrated accuracy in both qualitative and quantitative results. A small difference in mean ratios (∼15%) may be explained by the use of different hydrolysis procedures between methods. In conclusion, the high efficiency LC–MS/MS method was capable of accurately identify and quantify THCA in urine with a capacity of 14 samples per hour.