Quantitation of Δ1‐tetrahydrocannabinol in plasma from cannabis smokers

A method to identify and accurately measure non-labelled Δ1-tetrahydrocannabinol (Δ1-THC) in blood of cannabis smokers has been developed. It consists of the following steps: To a 5 ml plasma sample is added deuterated Δ1-THC (Δ1-THC-d2) as internal standard. After extraction with light petroleum and evaporation, the Δ1-THC containing fraction is separated by chromatography on Sephadex LH-20 (1 times 40 cm) using light petroleum-chloroform-ethanol (10:10:1) as eluant. A fraction containing Δ1-THC is collected and subjected to mass fragmentography (LKB 9000; 3% OV-17/Gas-Chrom Q; 230°). The mass spectrometer was adjusted to record the intensities of m/e 299 and 314 of Δ1-THC and m/e 301 and 316 of Δ1-THC-d2. The standard curve was made by plotting peak height m/e 299/m/e 301. Peak levels of 19–26 ng ml−1 were reached within 10 min after smoking a cigarette containing 10 mg Δ1-THC.