Validation of the quantitative determination of tetrahydrocannabinol and its two major metabolites in plasma by ultra-high-performance liquid chromatography-tandem mass spectrometry according to the total error approach.

In Belgium, driving under the influence (DUI) of cannabis is prohibited and has severe legal consequences for the driver if the blood plasma concentration of Δ(9)-tetrahydrocannabinol (THC) exceeds 1 µg/L. A method to quantify low concentrations of THC and its hydroxylated (THC-OH) and carboxylated (THC-COOH) metabolites in plasma was developed for DUI but also for other applications. Ultra-high-performance liquid chromatography coupled to mass spectrometry seems to be a very convenient method to combine fast chromatographic separation and good sensitivity. The method was validated according to total error approach. Chromatographic separation was achieved in a 3-min total run time. The limits of quantitation were lower or equal to 1 µg/L for all compounds. The linearity of the method was acceptable in the validated range of concentrations (from 0.5 to 50 µg/L for THC, from 0.9 to 50 µg/L for THC-OH and from 1.1 to 100 µg/L for THC-COOH). The biases were lower than 13%, and the relative standard deviations for repeatability and intermediate precision did not exceed 15%. Lower and upper β-expectation tolerance limits did not exceed the acceptance limits of 20% for concentrations higher than 2 µg/L for THC and THC-OH and higher than 4 µg/L for THC-COOH. The acceptance limits were 30% for THC and THC-OH concentrations lower than 2 µg/L and for THC-COOH concentrations lower than 4 µg/L.