Large organic cation-selective electrodes

Claim 1

In a cation-selective electrode for use in measuring the concentration of an organic cationic species in an aqueous test solution as a function of potentiometric response, comprising a cation-selective membrane adapted for interfacing with said test solution and either formed as a layer on a conductive substrate or in electrical contact with an internal reference electrode element, said membrane being composed of a polymeric matrix having dispersed or dissolved therein a cation-exchange material, the improvement which comprises said cation exchange material having as its counter-anion a high molecular weight alkyl or alkaryl sulfonate or sulfate of the formula R(O) n SO 3 - , wherein n is 0 or 1, R is an alkyl group having at least 13 carbon atoms or an alkaryl group of the formula R 1 --Ar--R 2 , Ar is an aryl group, R 1 is an alkyl group, and R 2 is an alkyl group or H, with the proviso that when Ar is monocyclic and R 1 has less than 12 carbon atoms, R 1 and R 2 are each the same or different alkyl groups having at least 9 carbon atoms, and when Ar is polycyclic and R 1 has less than 10 carbon atoms, R 1 and R 2 are each the same or different alkyl groups having at least 7 carbon atoms, whereby said electrode has a high degree of selectivity for large organic cationic species with respect to both smaller organic cationic species and inorganic cationic species.