A novel naphazoline-selective membrane sensor and its pharmaceutical applications

New naphazoline (NPZ) ion selective membrane electrodes of both conventional and coated graphite types were prepared based on the ion-pair of naphazoline tetraphenylborate (NPZ-TPB). The conventional type electrode was fully characterized in terms of membrane composition, life span, pH, ionic strength and temperature. The electrode exhibited a Nernstian response for naphazoline in the concentration range 1.0 x 10(-5) to 5.0 x 10(-2) and 5.0 x 10(-6) to 5.0 x 10(-2) M with a slope of 58.4 +/- 1.1 and 57.0 +/- 0.1 mV/concentration decade and a limit of detection of 4.0 x 10(-6) and 2.5 x 10(-6) M for conventional and coated graphite types, respectively. It could be used in the pH range 3.0-8.0. It was applied to potentiometric determination of naphazoline in pure state and pharmaceutical preparation under batch conditions. The selectivity of the electrode toward a large number of inorganic cations, sugars and amino acids was tested. The solubility product of the ion-pair and the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductometrically. (c) 2005 Elsevier B.V. All rights reserved.