A NEW METFORMIN SELECTIVE PLASTIC MEMBRANE-ELECTRODE BASED ON METFORMIN TETRAPHENYLBORATE

A new metformin (Mf) ion selective PVC membrane electrode based on the ion-pair complex of Mf with sodium tetraphenylborate was prepared and its performance characteristics were studied. The electrode exhibited a linear response with a good Nemstian slope over a relatively wide r ange of concentration. The calibration graph slope was constant for up to 14 days with continuous soaking at 54 mv/ concentration decade at 30-degrees-C. Then the slope decreased as the time of soaking increase d, reaching 42 mv/decade after 21 days. The changes in pH did not affe ct the electrode performance within the range 4.0 - 11.0. The standard electrode potentials were determined at different temperatures and we re used to calculate the isothermal coefficient of the electrode (0.00 04 V/degrees-C). The electrode showed a very good selectivity for Mf w ith respect to a large number of inorganic and organic cations. The st andard addition method and potentiometric titration were used to deter mine Mf in pure solutions and in pharmaceutical preparations.