SYNTHESIS AND EVALUATION OF A BIS(CROWN ETHER) IONOPHORE WITH A CONFORMATIONALLY CONSTRAINED BRIDGE IN ION-SELECTIVE ELECTRODES

A new bis(crown ether) ionophore containing two benzo-15-crown-5 moiet ies connected with each other via a conformationally constrained bridg e attached to a C-18-lipophilic side chain was designed and synthesize d. The bridge consisted of an isophthalic acid derivative, which was s elected in order to enhance potassium over sodium binding. Liquid-poly meric membrane ion-selective electrodes (ISEs) based on this ionophore were prepared using different plasticizers and mole ratios of lipophi lic ionic additives. Membrane electrodes with optimum composition (usi ng o-nitrophenyloctyl ether or bis(1-butylpentyl)adipate as plasticize r and 60 mol% lipophilic berate additive) show Nernstian responses tow ard potassium (57 and 58 mV/decade, respectively) over a wide concentr ation range with a micromolar detection limit. These ISEs exhibit enha nced potassium over sodium selectivity (K-K+,Na+(pot)=6x10(-4)). In ad dition, the electrodes show selectivities for potassium over Cs+ and N H4+ that are better than those of valinomycin-based ISEs.