Ion-selective electrode for the determination of prenalterol.

A new prenalterol (Pr) ion-selective PVC membrane electrode based on the ion-pair complex of Pr with sodium tetraphenylborate was prepared and its performance characteristics were studied. The electrode exhibited a linear response with a good Nernstian slope over a relatively wide range of concentration. The electrode whose membrane was made of 8.0% (w/w) of ion pair, 49.5% (w/w) of dioctyl phthalate (DOP) and 43.5% (w/w) of PVC showed characteristics higher than those obtained with the other ones, namely, slope of 56.3 mV per concentration decade, at 25 degrees C; usable concentration range 1.2x10(-5)-3.2x10(-2) M prenalterol; response time </=20 s. Up to 24 h continuous soaking, the calibration graph slope was constant at 56.0 mV per concentration decade, at 25 degrees C, then it decreased gradually as the time of soaking increases reaching 41 mV per decade after 11 days. The changes in pH did not affect the electrode performance within the range 2.2-7.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The electrode showed very good selectivity for Pr with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were used to determine Pr in pure solutions and in pharmaceutical formulations. The relative standard deviations (R.S.D.) of the three methods used for the determination of prenalterol in pharmaceutical formulations were 0.8, 2.1 and 1.9% of the extrapolation, standard addition and potentiometric methods, respectively.