Optimization of selectivity in micellar chromatographic procedures for the determination of drugs in urine by direct injection.

Selectivity was optimized for the determination of drugs in urine by direct injection micellar chromatography through changes in specific mobile phase parameters. The rôle of mobile phase pH and the type of surfactant used for mobile phase preparation was investigated. The retention of the urine matrix was found to be minimal between pH 5.5 and 7.5. The non-ionic surfactant, polyoxyethylene 23 lauryl ether (Brij 35), was found to be the surfactant of choice for the separation of drugs from urine. Favourable retention of both the urine background and the analyte was achieved with this surfactant. Micellar mobile phases of optimal composition were used to develop chromatographic procedures for the determination of furosemide, hydrochlorothiazide and propranolol in urine. Good accuracy (98-102% of drug recovered), precision (1-4% RSD) and linearity were obtained for all methods. Limits of detection for all drugs were adequate.