Quantitative measurement of Δ9-tetrahydrocannabinol and two major metabolites in physiological specimens using capillary column gas chromatography negative ion chemical ionization mass spectrometry

Publisher Website
Google Scholar
Abstract
Δ9‐Tetrahydrocannabinol and two of its metabolites, 11‐hydroxy‐Δ9‐tetrahydrocannabinol and 11‐nor‐9‐carboxy‐Δ9‐tetrahydrocannabinol, can be measured in a single 1‐ml sample of blood, plasma, or urine by a new assay which combines a relatively rapid extraction procedure with capillary column gas chromatography and negative ion chemical ionization mass spectrometry. Deuterium‐labeled analogs of each cannabinoid are added to the physiological specimen as internal standards. Two extracts are obtained from each sample: a neutral fraction containing Δ9‐tetrahydrocannabinol and 11‐hydroxy‐Δ9‐tetrahydrocannabinol, and an acid fraction containing 11‐nor‐9‐carboxy‐Δ9‐tetrahydrocannabinol. The neutral fraction is derivatized by treatment with trifluoroacetic anhydride; the acid fraction is first treated with BF3‐methanol followed by reaction with trifluoroacetic anhydride. Under electron‐capture chemical ionization conditions the derivatized Δ9‐tetrahydrocannabinol and 11‐nor‐9‐carboxy‐Δ9‐tetrahydrocannabinol give abundant molecular anions ideally suited for selected ion monitoring. The negative ion chemical ionization spectrum of the HO‐THC‐trifluoroacetate shows no molecular anion. Consequently, quantitation of the hydroxy metabolite is achieved by monitoring a fragment ion formed by loss of CF3CO2 from its molecular anion. The limits of reliable measurement are judged to be 0.1 ng ml‐1 for 11‐nor‐9‐carboxy‐Δ9‐tetrahydrocannabinol, 0.2 ng ml−1 for Δ9‐tetrahydrocannabinol and 0.5 ng ml−1 for 11‐hydroxy‐Δ9‐tetrahydrocannabinol. Four examples are given of the application of the assay to the analysis of specimens of medico‐legal importance.