Adsorptive Cathodic Stripping Determination of Minoxidil in Pharmaceutical, Cream, and Shampoo Products

The study investigated the electrochemical behavior of minoxidil, finding that it exhibits a single 2-electron irreversible reduction wave at pH 3, which is contrary to previous findings. This reduction wave diminishes with increasing pH and disappears at pH 7.2. Researchers developed a sensitive method using adsorptive cathodic stripping voltammetry at a hanging mercury drop electrode for quantifying minoxidil. The optimal conditions for minoxidil accumulation were determined to be in 0.1 M Britton–Robinson buffer at pH 2.0, with specific parameters for accumulation potential, time, scan rate, and pulse height. This method was successfully applied to measure minoxidil in pharmaceutical topical solutions, as well as in illegal shampoo and cream products, with mean recoveries of 99.8%, 97.8%, and 96.7%, and relative standard deviations (RSD) of 0.86%, 1.24%, and 1.89%, respectively.