CONSTRUCTION AND PERFORMANCE-CHARACTERISTICS OF A METFORMIN ELECTRODEBASED ON THE METFORMIN PHOSPHOTUNGSTATE ION-ASSOCIATE

A new metformin (Mf) ion selective PVC membrane electrode based on the ion-associate of Mf with phosphotungstic acid was prepared. The elect rode exhibited a mean calibration graph slope of 58 mV Mf concentratio n decade-1, at 25-degrees-C, within the concentration range 2.0 x 10(- 5)-1.0 x 10(-2) M MfCl. The change of pH within the range 4.0-11.0 did not affect the electrode performance. The standard electrode potentia ls were determined at different temperatures and used to calculate the isothermal coefficient of the electrode (0.000352 V-degrees-C-1). The electrode showed a very good selectivity for Mf with respect to a lar ge number of inorganic and organic cations. The standard addition meth od and potentiometric titration were applied to determine Mf in pure s olutions and in metformin-containing tablets.