Potentiometric liquid membrane pH sensors based on calix[4]-aza-crowns

The calix[4]-aza-crown derivatives have been used in polymeric ion selective electrodes (ISEs) for pH sensing. The membranes containing ionophores and cation exchangers showed near Nernstian response to hydrogen ions and wide dynamic range. New carrier based electrodes exhibited high selectivity over alkali metal ions. The binding properties of ionophores with hydrogen ions (acidity constants pKa) in solvent polymeric membranes were characterized in situ by the so-called sandwich membrane method. The influence of membrane solvents (plasticizers) and the types of the ion exchangers were studied.