Potentiometric responses of ion-selective electrodes after galvanostatically controlled incorporation of primary ions.

A new method of quantitative incorporation of primary cations into ion-selective membrane by means of galvanostatic cathodic polarization/conditioning, before measurement step, was proposed and tested on the example of potassium-selective electrode with ionophore - valinomycin in poly(vinyl chloride) based membrane and with polypyrrole solid contact. Open circuit potential values recorded after polarization can be quantitatively explained by changes of primary cations and ionophore concentration in the surface part of the membrane. The influence of potassium ions concentration in the membrane (in relation to ion exchange sites amount) on the shape of potentiometric calibration plots was also observed. Improved characteristics, with extended linear range, can be obtained for membrane of minor loading with primary cations (around 25%), the responses are relatively stable in course of following calibrations.