ELECTROCHEMICAL CHARACTERIZATION OF AMINATED PVC-BASED ION-SELECTIVE MEMBRANES

The potentiometric and impedance characteristics of a large number of pH sensitive, piperazine-based aminated PVC membranes are summarized. The main goal of the work was to predict the differences between ''good'' and ''bad'' responsive potentiometric pH membranes with very similar overall nitrogen contents. The only conclusion gained previously from other methods was that the N content should be between 0.5 and 0.8% for Nernstian response. The detailed analysis of the data show that a given N content of the basic material is a necessary but not a sufficient requirement with respect of the quality of potentiometric response. Conditions for appropriate pH response of the membrane are formulated in terms of surface and bulk impedance characteristics. The ideal pH response of an optimized aminated PVC membrane, which corresponds to a minimum surface impedance, is presented. The primary importance of surface amines relative to bulk amines (the conformation and distribution of active sites) is proven in a simple experiment.