Potentiometric and thermal studies of a coated-wire benazepril-selective electrode

A coated-wire benazepril-selective electrode based on incorporation of the benazepril-tetraphenylborate ion pair in a poly(vinylchloride) coating membrane was constructed. The influences of membrane composition, temperature, pH of the test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a benazepril concentration range of 1.26x10(-5) to 0.58x10(-2) M, at 25 degrees C, and was found to be very selective, precise, and usable within the pH range 2.5-9.2. The standard electrode potentials, E degrees, were determined at 20, 25, 30, 35, 40 and 45 degrees C, and used to calculate the isothermal temperature coefficient (dE degrees /dT) of the electrode. Temperatures higher than 45 degrees C seriously affect the electrode performance. The electrode was successfully used for potentiometric determination of benazepril hydrochloride both in pure solutions and in pharmaceutical preparations.