Sodium Ion-Selective Electrodes Based on Dibenzo-16-crown-5 Compounds with Pendent Ester Groups

Abstract

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{sup +}/K{sup -} selectivity increases as the bulkiness of the geminal substituent is enhanced; whereas the Na{sup +}/Li{sup +} selectivity exhibits a weaker inverse relationship to the size of R. On the other hand, the Na{sup +}/K{sup +} and Na{sup +}/Li{sup +} 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{sup +}/Li{sup +} selectivities of 10{sup 3.8}-10{sup 3.9} are observed. 22 refs., 3 figs., 2 tabs.