A gas chromatographic procedure has been developed for the simultaneous determination of cocaine and benzoyl ecgonine in urine specimens. The two drugs are extracted by isopropanol/chloroform from urine samples saturated with a bisalt buffer. The organic extract is evaporated to dryness, and an aliquot of the residue is injected onto the gas chromatograph to determine the presence of cocaine and the location of any extraneous peaks. Benzoyl ecgonine is then analyzed as its particular alkyl ester subject to the least interference from extraneous peaks as observed in an initial underivatized injection. The reconstituted residue is co-injected with the appropriate dimethylformamide dialkyl acetal for on-column alkylation. The use of two columns or more than one benzoyl ecgonine alkyl ester gives positive identification, and the use of isopropyl benzoyl ecgonine as an internal standard allows accurate quantification.
