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

A number of new, non-classical concepts relating to the development, princi ples, and applications of potentiometric ionophore-based polymeric membrane electrodes are reviewed. While already widely used in industry and clinica l 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 i on concentrations using sensors designed with high ion fluxes toward the in ner electrolyte solution; (c) identification of ionophore systems in which response slopes are apparently twice Nernstian due to changes in membrane i on activities as a function of sample ion concentration; (d) ion-exchanger- based membranes that respond via a non-equilibrium response mechanism to im portant polyion species (e.g. heparin); (e) the potentiometric response of membranes to neutral species, including surfactants; and (f) the EMF respon se of membranes via redox reactions between the ionophore and the target io n (e.g. sulfite/bisulfite sensors). (C) 2000 Elsevier Science B.V. All righ ts reserved.