Potentiometric layered membranes

Abstract

In this work a new concept of potentiometric layered membranes is introduced. In most cases described so far a potentiometric membrane is made of one polymer (or one copolymer) used with ion-exchanger and ionophore, for some polymers/copolymers optionally used with a plasticizer of choice. Application of just one polymer (or copolymer) with additives as membrane material is the classical concept of potentiometry. On the other hand, in potentiometry often different materials are applied as ion-selective membranes, resulting in receptor layers characterized with different parameters including ion-transport, although they contain the same ionophore and ion-exchanger.From the point of view of optimization of the sensor performance, especially for practical applications, it would be beneficial to control the ion diffusion rate in the membrane, for example to prevent the unwanted (as leading to impaired performance) accumulation of the analyte ions close to the outer membrane surface, but on the other hand, to prevent or to slow down the full saturation of the membrane phase with primary ions. Achieving this goal with single membrane composition (based on one polymer/copolymer) is, however, difficult. This can be done, for example, by using a membrane being an ordered composition of different thin layers, arranged in such a way that diffusion coefficients gradually change through the membrane thickness. This novel approach is presented here by introducing the layered membranes concept.The novel structurized potentiometric membranes are composed of a sequence of layers of tailored polymers containing the same contents of ionophore and ion-exchanger. Thus, due to consecutive changes in properties of polymers applied, the primary ion diffusion rate can be controlled through the membrane allowing improvement of the sensor performance.