DETERMINATION OF ION-SELECTIVE ELECTRODE CHARACTERISTICS BY NONLINEARCURVE-FITTING

A simple practical method of determining potentiometric selectivity co efficients of ion-selective electrodes (ISEs) is described in which el ectrode characteristics (slope, potentiometric selectivity coefficient s and cell constant) can be determined by fitting the experimental dat a obtained using the fixed interference (FI) method to an appropriate model by non-linear least-squares regression. The proposed method is s imple to implement practically, and data processing can be easily achi eved through use of the optimisation add-on, Solver, bundled with Micr osoft Excel. The flexibility of the method is demonstrated by modellin g the response of a valinomycin potassium-selective electrode with the Nikolskii-Eisenman equation and a recently proposed alternative to th e Nikolskii-Eisenman equation for cases where the ionic charges on the primary and interfering ions are unequal. (C) 1997 Elsevier Science B .V.