Sensitive determination of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol and complementary cannabinoids in hair using alkaline digestion and mixed-mode solid phase extraction followed by liquid-chromatography-tandem mass spectrometry.

Hair drug testing can be used for the evaluation of cannabis use with a large detection window, and is required for professional driving license granting in Brazil. A positive hair result for cannabis use requires quantification of the metabolite THC-COOH above the cutoff value of 0.2 ng/g. The achievement of such lower limit of quantification is challenging, particularly with the use of liquid chromatography coupled to triple quadrupole mass spectrometers (LC-MS/MS). In this study, a very sensitive LCMS/ MS assay for the simultaneous quantification of THC-COOH along with THC, CBD, and CBN was developed and validated. Sample preparation was based on hair hydrolysis, followed by selective ion-exchange solid-phase extraction. The extraction yield was 101.5-101.6% for THC-COOH, 92.3-97.4% for THC, 89.7-95.2% for CBN, and 104.9-121.1% for CBD. Internal standard corrected matrix effects were - 2.7 to - 1,1 for THCCOOH and - 11.5 to - 0.1% for the other analytes. The lower limit of quantification was 01 ng/g for THC-COOH and 25 ng/g for THC, CBD, and CBN. The assay fulfilled validation guidelines acceptance criteria. The measurement uncertainties were determined and the assay was ISO17025 accredited, being currently used in routine testing.