Testing human blood for cannabis by GC-MS

A method for cannabis testing in human whole blood is presented. The procedure involves extraction of a 2 mL specimen acidified with 0.2 mL of 10% acetic acid in a silanized vial in presence of deuterated internal standards into hexane:ethyl acetate. After evaporation to dryness the drug and its metabolite were derivatized by methylation with iodomethane in tetrabutylammonium hydroxide-dimethyl sulphoxide (DMSO). The derivatives were extracted into isoocatane for analysis by gas chromatography-mass spectrometry (GC-MS). The limit of quantification was 1.0 and 0.5 ng/mL for delta 9-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-delta 9-tetrahydrocannabinol (THC-COOH), respectively.