Threshold ionic site concentrations required for nernstian potentiometric responses of neutral ionophore-incorporated ion-selective liquid membranes

An equation that can describe the concentrations of ionic sites required fo r a Nernstian potentiometric response slope of neutral ionophore-incorporat ed ion-selective liquid membranes is presented. This equation is derived fr om a model based on electrical diffuse layers on both the membrane and the aqueous sides of the interface, in which the phase boundary potential is co rrelated to the surface charge density as well as the salt concentrations i n the bulk membrane and aqueous solution. To experimentally and accurately confirm the validity of this equation, response characteristics of field ef fect transistors covered by neutral ionophore-based liquid membranes with v arying concentrations of a derivative of tetraphenylborate as an anionic si te but free of ionic impurities were examined. The observed membrane potent ials and the response slopes for membranes with various concentrations of a nionic sites were in good agreement with the values calculated from the the ory presented in this paper with the measured complexation stability consta nts for the relevant systems. This result indicates that the theoretical pr ediction based on the proposed equation for the anionic site concentration is accessible for the preparation of neutral ionophore-incorporated ion-sel ective liquid membranes, which show Nernstian response slopes for the prima ry ions.