Simultaneous Quantitation of Minoxidil and Tretinoin in Magistral and Pharmaceutical Preparations by First Derivative Spectrophotometry

A first derivative spectrophotometry method has been developed for the simultaneous quantitation of minoxidil and tretinoin. The method is based on measuring the first derivative signals (D 1 ) of minoxidil and tretinoin at 290 and 351 nm, respectively, without any interference from each other, or any other coexisting materials. Beer's law was valid over the concentration range 2-10 μg/ml of minoxidil and 0.25-1.25 μg/ml of tretinoin. The proposed method has been applied successfully to the determination of some magistral and pharmaceutical preparations. Relative standard deviations for the assay of both drugs were less than 0.95%.