SELECTIVITY-MODIFYING INFLUENCE OF ANIONIC SITES IN NEUTRAL-CARRIER-BASED MEMBRANE ELECTRODES

The potentiometric ion selectivity of liquid membrane electrodes is largely dependent on the amount of anionic sites incorporated into the membrane phase. Selectivities were measured for membrane electrodes containing a given amount of neutral carrier and varying amounts of the additive potassium tetrakis(p-chlorophenyl)borate. The measured data are compared to an earlier published model for which the basic assumptions, a general solution, as well as a table with the optimum anionic site:neutral carrier ratios for some cases of practical relevance are given. The pronounced selectivity changes and the selectivity maxima agreed with the theoretical model. Both theory and experiment confirmed that a well-defined optimum ratio exists if the primary ion either has a higher charge or/and if it is complexed by fewer ligand molecules as compared to the interfering ions.