Evaluation of the optimum composition of neutral-carrier membrane electrodes with incorporated cation-exchanger sites

Selectivities were measured for membrane electrodes containing a given amount of a neutral carrier (ETH 1692) and varying amounts of the additive potassium tetrakis(p-chlorophenyl)borate. The pronounced selectivity changes induced by the additive agreed with a theoretical model. Both theory and experiment confirmed that an optimum composition of the membrane exists. Ideally, sensors for monovalent cations should contain only small amounts of the additive, whereas sensors for divalent cations should contain a molar ratio of additive/carrier of about 0.7 (for 1:2 cation/carrier complexes). Also described are the new desk-computer programs used for the reduction, evaluation, and graphical presentation of ion-selective electrode data.