Potentiometric determination of dopamine in pharmaceutical preparations by crown ether-PVC membrane sensors

Two simple, rapid and sensitive sensors for the assay of dopamine hydrochloride have been developed. The methods are based upon the formation of the membrane sensors 12-crown-4-phosphotungestic acid (crown ether-PTA)-dopamine and 12-crown-4-tetraphenylborate (crown ether-TPB)-dopamine as neutral carriers. The sensors were stable and showed fast potential responses of 10 s, and near-Nernstian cationic slopes of 53.3 - 56.2 mV/decade of activity between pH 2.2 - 6 for the monovalent dopamine cation over a wide range concentrations 1 x 10(-5) - 1 x 10(-1) M. The selectivity coefficients of the developed sensors indicated excellent selectivity for dopamine over a large number of organic and inorganic species and pharmaceutical excipients. The mediator o-nitrophenyloctyl ether significantly affected the lifetime of the fabricated sensors of dopamine. Satisfactory results were obtained for the determination of dopamine in dosage form by the proposed sensors with an average recovery of 99.85% for the nominal concentration.