Construction of a naproxen ion-selective electrode and its application to pharmaceutical analysis

A naproxenate-selective electrode with a liquid membrane consisting of a tetraheptylammonium-naproxenate ion pair dissolved in p-nitrocumene is described. The electrode exhibits a rapid and near-Nernstian response to naproxenate activity from 10(-1) to 10(-4) M at pH 9.0 (borate buffer). No serious interference from common ions and tablet excipients was found and the electrode was used for the direct assay of naproxen tablets by means of the calibration graph technique and of suppositories using the standard additions technique. A dissolution study of naproxen tablets was also carried out and the results compared favourably with those given by the USP XXI methods.