Kind of ion-selective membranes used in an ISE which is a support matrix, containing an ion exchanger (either cationic or anionic), a plasticizer solvent, and possibly an uncharged, selectivity-enhancing species, form the ion-selective membrane which is usually interposed between two aqueous solutions. The matrix can be either macroporous (e.g., poly(propylene carbonate) filter, glass frit, etc.) or microporous (e.g., “thirsty” glass or polymeric material such as \(\ce{PVC}\)) yielding with the ion-exchanger and the solvent a “solidified” homogeneous mixture.