Direct quantification of 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid and its glucuronide in urine using liquid chromatography-tandem mass spectrometry

Abstract

A liquid chromatography-electrospray ionization-tandem mass spectrometric method (LC-ESI-MS/MS) was developed and validated for the direct determination of 11-nor-Δ⁹-tetrahydrocannabinol-9-carboxylic acid (THCCOOH) and its glucuronide (THCCOOH-glu) in urine. The deuterium-labeled compounds were used as internal standards to quantify the analytes. After a simple liquid–liquid extraction with ethyl acetate at pH 4, the dried extracts were reconstituted in the mobile phase followed by injection onto the LC-ESI-MS/MS system. The mobile phase was composed of 0.2% formic acid and 2 mM ammonium formate in water and acetonitrile. A reversed phase column (C₈, 150 mm × 2.1 mm i.d., 3.5 μm) was used as the analytical column. The limit of detection and lower limit of quantification values were 0.08 and 0.3 ng mL⁻¹ for THCCOOH and 0.4 and 1.5 ng mL⁻¹ for THCCOOH-glu, respectively. The calibration curve was linear over the concentration range of 0.3–100 ng mL⁻¹ for THCCOOH and 1.5–100 ng mL⁻¹ for THCCOOH-glu with the coefficients of determination (r²) above 0.9955. The intra- and inter-day precisions (% CV) were within 16.6% and 18.3%, respectively. The intra-day accuracies (% bias) ranged from −18.4 to 1.5% while inter-day accuracies were −5.9 to 1.8%. The validated method was successfully applied for the determination of THCCOOH and THCCOOH-glu in urine samples from marijuana users.