IONIC ADDITIVES FOR ION-SELECTIVE ELECTRODES BASED ON ELECTRICALLY CHARGED CARRIERS

The influence of ionic sites on the behavior of charged carrier-based ion-selective liquid membrane electrodes is described by theory and ex periments for cation- and for anion-selective electrodes. The cation e xchanger potassium tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate pro ved to be a beneficial additive for nitrite-selectve electrodes. On th e other hand, the anion exchanger tridodecylmethylammonium chloride im proved the potentiometric properties of cation-selective electrodes. B y the incorporation of a defined amount of these sites, the selectivit y was enhanced, the emf functions became theoretical, the electrode re sistance was lowered, and the long-term stability improved. The optima l molar ratio of additive to ionophore was in the range of 0.3-0.6 for the ionophores studied. The theory and the experiments show clearly t hat ionic sites should be used not only with neutral ionophores but al so with charged ones. ISE membranes without ionic additives should be avoided, since otherwise inherent ionic impurities could have a decisi ve influence os the response characteristics.