A Clotrimazole-Selective Electrode and its Application to Pharmaceutical Analysis

The effect of measurement conditions and the nature of the plasticizer of an ion-selective electrode membrane (ortho-nitrophenyloctyl ether, dinonyl adipate, dibutyl phthalate) on the main performance characteristics of clotrimazole-selective electrodes with polyvinyl chloride ion-exchange membranes containing potassium tetrakis(4-chlorophenyl)borate as an ion exchanger was studied. The introduction of small (up to 20%) ethanol additives into the aqueous solution leads to a significant improvement of the potential stability and expands the working range of the electrodes. All of the studied electrodes have high selectivity to clotrimazole with respect to both inorganic and organic cations, slope of the electrode function close to the theoretical value, and low limits of detection (5.0 × 10^–8–7.5 × 10^–8 M). An electrode with a membrane plasticized with ortho-nitrophenyloctyl ether was the best for the combination of characteristics. It was demonstrated that clotrimazole can be determined in model solutions and various dosage forms (spray, cream, suppositories, tablets) using direct potentiometry and potentiometric titration with sodium tetraphenylborate. The proposed procedures are rapid (10–15 min) and characterized by excellent reproducibility (the relative standard deviation does not exceed 1.2%).