Qualitative and quantitative analysis of THC, 11‐hydroxy‐THC and 11‐nor‐9‐carboxy‐THC in whole blood by ultra‐performance liquid chromatography/tandem mass spectrometry

A qualitative and quantitative analytical method was developed for the simultaneous determination of Δ⁹‐tetrahydrocannabinol (THC), 11‐hydroxy‐Δ⁹‐tetrahydrocannabinol (11‐OH‐THC) and l1‐nor‐9‐carboxy‐Δ⁹‐tetrahydrocannabinol (THC‐COOH) in whole blood. The samples were prepared by solid‐phase extraction followed by ultra‐performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) analysis using positive ion electrospray ionization and multiple reaction monitoring. The chromatographic separation was performed with an Acquity UPLC® HSS T3 (50 × 2.1 mm i.d., 1.8 µm) reversed‐phase column using a methanol/2 mM ammonium formate (formic acid 0.1%) gradient in a total run time of 9.5 min. MS/MS detection was achieved with two precursor‐product ion transitions per substance. The method was fully validated, including selectivity and capacity of identification, according to the identification criteria (two transitions per substance, signal‐to‐noise ratio, relative retention time and ion ratio) without the presence of interferences, limit of detection (0.2 µg/L for THC and 0.5 µg/L for 11‐OH‐THC and THC‐COOH), limit of quantitation (0.5 µg/L for all cannabinoids), recovery (53–115%), carryover, matrix effect (34‐43%), linearity (0.5‐100 µg/L), intra‐assay precision (CV < 10% for the relative peak area ratios and <0.1% for the relative retention time), inter‐assay accuracy (mean relative error <10%) and precision (CV <11%). The method has already been successfully used in proficiency tests and subsequently applied to authentic samples in routine forensic analysis. Copyright © 2011 John Wiley & Sons, Ltd.