Quantitative gas chromatographic analysis of 3-cyano-3,3-diphenylpropionic acid, the acidic metabolite of bezitramide (Burgodin((R))), in urine

A sensitive gas chromatographic procedure with nitrogen-phosphorus detection was developed for the quantitative determination of 3-cyano-3,3-diphenylpropionic acid, the acidic metabolite of the narcotic analgesic bezitramide (Burgodin®). Gas chromatography with mass spectrometric detection was used for confirmation. An internal standard, 5-cyano-5,5-diphenylvaleric acid, was synthesized and purified in our laboratory. The compound was extracted from 5 mL of hydrolyzed urine with n-hexane-ethyl acetate (85:15, v/v). Derivatization of the extract with an ethereal diazomethane solution was performed immediately before chromatographic analysis. Under the described conditions, the quantitation limit for 3-cyano-3,3-diphenylpropionic acid in urine was 10 ng/mL. The extraction recovery was 82%. The calibration graph was linear over the concentration range from 10 to 500 ng/mL; at a 100-ng/mL concentration, within-day and day-to-day percent coefficients of variation of 1.9 and 3.7%, respectively, were obtained. Urine samples from 16 persons suspected of using bezitramide were analyzed, and they revealed metabolite concentrations that ranged from 10.5 to 88 ng/mL.