Direct quantification of 11-nor-Delta(9)-tetrahydrocannabinol-9-carboxylic acid in urine by liquid chromatographytandem mass spectrometry in relation to doping control analysis.
An accurate and precise method for the quantification of 11-nor-Delta(9)-tetrahydrocannabinol-9-carboxylic acid (THCA) in urine by liquid chromatographytandem mass spectrometry (LCMSMS) for doping analysis purposes has been developed. The method involves the use of only 200 microL of urine and the use of D(9)-THCA as internal standard. No extraction procedure is used. The urine samples are hydrolysed using sodium hydroxide and diluted with a mixture of methanolglacial acetic acid (11). Chromatographic separation is achieved using a C8 column with gradient elution. All MS and MSMS parameters were optimised in both positive and negative electrospray ionisation modes. For the identification and the quantification of THCA three product ions are monitored in both ionisation modes. The method is linear over the studied range (5-40 ngmL), with satisfactory intra-and inter-assay precision, and the relative standard deviations (RSDs) are lower than 15%. Good accuracy is achieved with bias less than 10% at all levels tested. No significant matrix effects are observed. The selectivity and specificity are satisfactory, and no interferences are detected. The LCMSMS method was applied for the analysis of 48 real urine samples previously analysed with a routine gas chromatographymass spectrometry (GCMS) method. A good correlation between the two methods was obtained (r(2) > 0.98) with a slope close to 1.