SODIUM-ION SELECTIVE ELECTRODES BASED ON DIBENZO-16-CROWN-5 COMPOUNDS WITH PENDENT ESTER GROUPS

Selectivities of 21 dibenzo-16-crown-5 compounds with pendent ester groups for alkali metal, alkaline earth metal, and ammonium ions have been determined in solvent polymeric membrane electrodes. The ionophores include alkyl sym-R-dibenzo-16-crown-5-oxyacetates with R = hydrogen, linear alkyl, branched alkyl, fluoroalkyl, alkenyl, alkynyl, and phenyl groups. For lariat ethers with a hydrogen, linear alkyl group, or branched alkyl group attached to the ring carbon that bears the ester-containing side arm, the Na+/K+ selectivity increases as the bulkiness of the geminal substituent is enhanced; whereas the Na+/Li+ selectivity exhibits a weaker inverse relationship to the size of R. On the other hand, the Na+/K+ and Na+/Li+ selectivities are insensitive to variations in the size and shape of the ester alkyl groups. For eight of the lariat ether ester ionophores, very high Na+/Li+ selectivities of 10(3.8)-10(3.9) are observed.