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.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.