Verapamil-Sensitive Electrodes: Main Factors Responsible for Analytical Performance and Use in Drug Analysis

It has been established that the correct choice of the plasticizer and the measurement conditions makes it possible to achieve better analytical characteristics of verapamil-sensitive electrodes based on commercially available components in comparison with the best described in the literature. Particularly, the effect of pH on the verapamil-sensitive electrodes response was found to manifest itself in much more acidic media than might be expected from protolytic equilibrium and is due to the non-exchangeable extraction of verapamil into the membrane phase. The best parameters of selectivity, lower detection limit (4 × 10 −8 M), and potential reproducibility (0.15–0.22 mV) are achieved when using ortho-nitrophenyloctyl ether as a plasticizer and creating conditions that exclude non-exchangeable extraction of verapamil into the membrane. The proposed methods for the determination of verapamil in dosage forms are characterized by simplicity, rapidity, and high metrological characteristics.