Plastic membrane electrode for selective determination of diclofenac (voltaren) in pharmaceutical preparations

A novel plastic membrane ion-selective electrode for determining the diclofenac anion is described. The sensing membrane of the electrode consists of diclofenac-nickel(II) bathophenanthroline as an ion-exchanger site in a poly(vinyl chloride) matrix plasticized with o–nitrophenyl phenyl ether. In borate buffer solutions of pH 8–12, the electrode exhibits a fast, stable and linear response for 1 × 10–2–5 × 10–5 mol dm–3 diclofenac with an anionic slope of 55.1 ± 0.2 mV decade–1 at 25 °C. Potentiometric selectivity measurements revealed negligible interferences from 14 different anions including aromatic and aliphatic carboxylic acid salts. The electrode displays useful analytical characteristics for the direct determination of diclofenac in various pharmaceutical preparations. Results with an average recovery of 98 ± 0.6% of the nominal value were obtained.