Ionophore-based membrane electrodes: new analytical concepts and non-classical response mechanisms Original Research Article

A number of new, non-classical concepts relating to the development, principles, and applications of potentiometric ionophore-based polymeric membrane electrodes are reviewed. While already widely used in industry and clinical laboratory instrumentation for measurement of simple cations and anions, recent research efforts have suggested exciting new advances in this field. These advances include: (a) a dramatic lowering of the detection limits by controlling the magnitude and direction of flux of the analyte ion through the polymeric membrane; (b) direct potentiometric determination of total ion concentrations using sensors designed with high ion fluxes toward the inner electrolyte solution; (c) identification of ionophore systems in which response slopes are apparently twice Nernstian due to changes in membrane ion activities as a function of sample ion concentration; (d) ion-exchanger-based membranes that respond via a non-equilibrium response mechanism to important polyion species (e.g. heparin); (e) the potentiometric response of membranes to neutral species, including surfactants; and (f) the EMF response of membranes via redox reactions between the ionophore and the target ion (e.g. sulfite/bisulfite sensors).