Determination of betamethasone sodium phosphate in pharmaceuticals by potentiometric membrane sensor based on its lidocaine ion pair

Betamethasone sodium phosphate (BMNaP) has been employed as an electroactive material in the design of an ion-selective electrode (ISE). The electrode incorporates PVC membrane with betamethasone sodium phosphate-lidocaine ion pair complex. The influences of membrane composition, temperature, pH of the test solution, and the interfering ions on the electrode performance were investigated. The sensor exhibits a Nernstian response for betamethasone sodium phosphate ions over a relatively wide concentration range (1.0 × 10−1 to 1.0 × 10−5 M) with a slope of 28.4 ± 0.9 mV per decade at 25°C. It can be used in the pH range 4.0–10.0. The isothermal temperature coefficient of this electrode amounted to −0.0008 V/°C. The membrane sensor was successfully applied to the determination of betamethasone sodium phosphate in pharmaceutical products.