Fast confirmation of 11-nor-9-carboxy-Δ 9-tetrahydrocannabinol (THCCOOH) in urine by LC/MS/MS using negative atmospheric-pressure chemical ionisation (APCI)

Abstract

A fast method using automated solid-phase extraction (SPE) and short-column liquid-chromatography coupled to tandem mass-spectrometry (LC/MS/MS) with negative atmospheric-pressure chemical ionisation (APCI) has been developed for the confirmation of 11-nor-9-carboxy-Δ 9-tetrahydrocannabinol (THCCOOH) in urine samples. This highly specific method which combines chromatographic separation and MS/MS-analysis can be used for the confirmation of positive immunoassay results with a NIDA cut-off of 15 ng/ml. The conjugates of THCCOOH were hydrolysed prior to SPE, and a standard SPE was performed using C18-SPE columns. No derivatisation of the extracts was needed as in GC/MS analysis, and the LC run-time was 6.5 min by gradient elution with a retention time of 2.4 min. Linearity of calibration was obtained in the range between 0 and 500 ng/ml (correlation coefficient R 2=0.998). Using linear regression (0–50 ng/ml) the limit of detection (LOD) was 2.0 ng/ml and the limit of quantitation (LOQ) was 5.1 ng/ml; day-to-day reproducibility and precision were tested at 15 and 250 ng/ml and were 13.4 ng/ml±3.3% and 255.8 ng/ml±4.5%, respectively.