Molecular Design of Calix[4]arene-Based Sodium-Selective Electrodes Which Show Remarkably High 105.0–105.3 Sodium/Potassium Selectivity

Abstract Several ionophores for the Na+-selective electrode were developed from calix[4]arene crown ethers with a short –(CH2CH2O)2CH2CH2– crown loop on the lower rim. The ionophoric cavities generated in these ionophores are much smaller and more rigid than those derived from calix[4]arene crown ethers with a long –(CH2CH2O)3CH2CH2– crown loop. It was shown that two electrodes possess Na+ selectivity (with respect to K+) exceeding a factor of 105 which is higher by more than two orders of magnitude than that of the former calix[4]arene-based Na+-selective electrodes!