Membranes for chemical sensors selective to doubly charged anions

The main results concerning selective properties fur carbonate sulfate and phosphate polyvinyl chloride (PVC) membranes based on neutral carriers and anion-exchangers are discussed. It is shown that for the investigated systems selectivity depends on the concentration ratio between anion-exchanger and neutral carrier. The shape of the curves (selectivity.vs. neutral carrier concentration) corresponds to a mathematical model described earlier and determines the stoichiometry of the complexes of the anions with neutral carrier. The incorporation of anionic sites inside the anion-selective membrane, e.g., carbonate-selective. leads to an increase of carbonate selectivity in presence of lipophilic anions of the internal solution.