Papaverine PVC Membrane Ion-Selective Electrodes Based on its Ion-Exchangers with Tetraphenylborate and Tetrathiocyanate Anions

The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1×10^-2 to 6×10^-5 M and 1×10^-2 to 1×10^-5 M for PA-TPB and PA-TTC respectively at 25 °C over the pH range of 3-5.0 with a cationic slope of ∼ 56.5±0.5 mV/decade for both sensors respectively. The lower detection limit is 4×10^-5 and 8×10^-6 M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0-3000.0 μg/ml of PA in aqueous solutions shows an average recovery of 99.1 % and a mean relative standard deviation of 1.4 at 100 μg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out.