GC/MS and EMIT Analyses for / 9-Tetrahydrocannabinol Metabolites in Plasma and Urine of Human Subjects*

Ten male subjects smoked placebo marijuana cigarettes spiked with,W.tetrahydrocannabinol (THC) at 150/~g/kg body weight. Plasma and urine samples were collected for 22 hr after smoking. Total cross-reacting cannabinoids were measured by immunoassay (EMIT) and THC and major metabolites were identified and quantitated by gas chromatographic/mass spectrometric (GC/MS) procedures. In plasma, THC concentration provided the best indication of recent (<6 hr) smoking. In enzyme-hydrolyzed urine, 8/3, 11-dihydroxy-THC at high concentration was identified in the earliest voidings, falling rapidly to the limit of detection before 22 hr in most subjects. Levels above 15 to 20 ng/mL were indicative of use within the previous 4 to 6 hr. Introduct ion The detection of marijuana use by immunoassay drug screen-ing procedures for cannabinoids in human body fluids is now widely used (1-5). Because of the potential for false positive results and for cross-reactivity of antibody with a broad spec-trum of cannabinoids in biological samples, such methods may not be considered specific for A%tetrahydrocannabinol (THC) or its metabolites. For forensic purposes, positive results must be validated by other more specific methods. Gas chromato-graphy/mass pectrometry (GC/MS) is frequently recommended and used for confirmation of the results obtained by im-munoassay techniques, and to generate quantitative data for metabolite profiling in clinical studies on marijuana use (5,6). For medicolegal purposes, the demonstration f recent mari-juana usage through analysis of THC and its metabolites in human biological specimens i receiving increasing attention (7-9). It has been shown frequently that ll-nor-9-carboxy-A%tetrahydrocannabinol (THC-COOH) is the major metabolite in both blood and urine (10-13). However, as indicated by the persistence of measurable cannabinoid levels using immune