A new lidocaine-selective membrane electrode based on its sulfathiazole ion-pair

A novel lidocaine ion-selective electrode is prepared, characterized and used in pharmaceutical analysis. The electrode incorporates PVC-membrane with lidocaine-sulfathiazole ion pair complex. 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 lidocaine concentration range from 1.0 ×10−5 to 1.0 × 10−1 mol L−1 with a slope of 60.1 ± 0.2 mV per decade at 25°C and was found to be very selective, precise, and usable within the pH range 5–9.5. The standard electrode potentials, E o, were determined at 10, 15, 20, 25, 30, 35 and 40°C, and used to calculate the isothermal temperature coefficient (dE o/dT=−0.0003 V °C−1) of the electrode. However, the electrode performance is significantly decreased at temperatures higher than 45°C. The electrode was successfully used for potentiometric determination of lidocaine hydrochloride in pharmaceutical products.