LC–MS–MS method for simultaneous determination of THCCOOH and THCCOOH-glucuronide in urine: Application to workplace confirmation tests

Cannabis is the one of the most frequently detected drug in workplace drug testing and in cases of driving under influence of drugs, and there is a greater demand for sensitive, rapid and reliable methods for confirming the presence of this drug in biological samples. This paper describes an LC–MS–MS procedure for direct analysis of cTHC and cTHC-glucuronide in urine, without hydrolysis of the samples or derivatisation. The sample preparation is very simple and consist only in a dilution of urine with methanol 1:1 (v/v) after adding the deuterated internal standard (cTHC-d3); then 10 μl of the final solution is injected in LC–MS–MS. Chromatographic separation was performed using a reversed-phase column and gradient elution with 0.01% formic acid/acetonitrile/methanol and two MS–MS transitions for each substance were monitored. The method was fully validated and proved to be accurate (RSD <15%), precise (intra-day CV <10%) and sensitive with a limit of detection (LOD) of 5 ng/ml for both the compounds studied. Linearity was tested in the range 5–1000 ng/ml and the values of R2 resulted >0.99.The developed method was applied to several authentic samples of urine which tested positive in the immunoassay screening and 98% of them was confirmed.