NEW AMPICILLIN SELECTIVE PLASTIC MEMBRANE AND COATED METAL-ELECTRODESBASED ON AMPICILLINIUM PHOSPHOTUNGSTATE ION-PAIR

A new ampicillin (Amp) ion-selective PVC membrane electrode based on t he ion pair complex of Amp with phosphotungstic acid is prepared and i ts performance characteristics are studied. The electrode exhibited a linear response with a good Nernstian slope over a relatively wide ran ge of concentration (1.6 x 10(-4) - 4.0 x 10(-2) M). Up to 10 h. conti nuous soaking, the calibration graph slope is constant at about 59 mV/ concentration decade, at 25 degrees C, then it decreases gradually as the time of soaking increases, reaching 42.5 mV/ concentration decade after 42 days. The changes in pH do not affect the electrode performan ce within the range 3-11. The isothermal coefficient of the electrode was 0.00184 V/degrees C. The electrode showed very good selectivity fo r Amp in presence of a large number of inorganic and organic cations. The standard addition method and potentiometric titration are used to determine Amp in pure solutions and in pharmaceutical preparations. Co ated wire electrodes are made using Cu, Cu/CuS, Pt, Ag and Ag/AgCl wir es and their performance characteristics are studied in comparison wit h those of the conventional type electrode.