Voltammetric interpretation of the potential at an ion-selective electrode, based on current-scan polarograms...

The potential-generating process at ion-selective electrodes (ISE) of liquid-membrane types has been interpreted by comparing the ISE potential with the current-scan polarogram which indicates the transfer of a particular ion i(z+) at the aqueous/organic solution (w/o) interface. The potential at zero current, DeltaV(l = 0), in the composite polarogram observed with i(z+) in both w and o, corresponds to the ISE potential. A stable potential giving Nernstian response to the concentration of i(z+) in w is obtained at the ISE only when the w/o interface is depolarized byi(z+). The detection limits are controlled by the final rise and final descent of the residual current in the polarogram. The interference of a second ion,j(z+), in the ISE measurement of i(z+), and the role of an ionophore in the membrane of the ISE can be explained by considering the shift of DeltaV(l = 0) in the composite polarogram ofi(z+) in the presence of j(z+) in w or the ionophore in o. Equations which express the ISE potential, the interference at the ISE, and the effect of an ionophore on the ISE potential have been derived, connected with the polarographic equations for ion-transfer at the w/o interface.