Transmembrane ion fluxes for lowering detection limit of ion-selective electrodes

This chapter is devoted to the description of the detection limit (DL) of ion-selective electrodes (ISEs) with special attention to the role of transmembrane fluxes. The DL of ISEs has been radically improved, that is, lowered. This has led to the prospect of significantly expanding the use of ISEs in such important fields as clinical or environmental analysis. The lower DL of ion-selective polymeric membrane electrodes are in the micromolar range, except when ion buffers are used to keep the activities of the ions in the sample at low and constant levels through complexation or solubility equilibria. The Nernst–Planck–Poisson (NPP) model is an attempt at creating a general model. It considers both diffusion and migration; an unlimited number of ions, each with its own specific charge and its own specific diffusion coefficients in different phases; as well as the different dielectric permittivities of the different phases.