Quantitation of cocaine and its principal metabolite, benzoylecgonine, by GLC-mass spectrometry using stable isotope labeled analogs as internal standards.

A quantitative GLC-mass spectrometric assay was developed for the determination of cocaine and its principal metabolite, benzoylecgonine, in human urine. The assay utilizes selective ion focusing to monitor in a GLC effluent the molecular ions of cocaine and benzoylecgonine generated by electron-impact ionization. Cocaine-d(3) and benzoylecgonine-d(3) were the internal standards. The assay can measure 2 ng of cocaine/ml and 5 ng of benzoylecgonine/ml with about 5% precision. The curves relating the amounts of cocaine and benzoylecgonine added versus the amounts found over a large range of cocaine and benzoylecgonine concentrations were straight lines with nearly zero intercepts and slopes of 0.98 +/- 0.01 and 0.97 +/- 0.01, respectively. The method was used for the analysis of urinary cocaine and benzoylecgonine in cocaine addicts. Assay specificity was confirmed by complete identity of the mass spectra of cocaine and benzoylecgonine with those of authentic materials.