Analytical Sciences

Abstract − Analytical Sciences, 14(1), 169 (1998).

Synthesis and Evaluation of a Bis(crown ether)Ionophore with aConformationally Constrained Bridge in Ion-Selective Electrodes
Zhiren XIA, Ibrahim H. A.BADR, Shawn L. PLUMMER, Lawrence CULLEN, and Leonidas G. BACHAS *
Department of Chemistry,University of Kentucky, Lexington, Kentucky 40506-0055, USA
A new bis(crown ether) ionophore containing two benzo-15-crown-5 moietiesconnected with each other via aconformationally constrained bridge attached to a C18-lipophilic side chain was designed andsynthesized. The bridgeconsisted of an isophthalic acid derivative, which was selected in order toenhance potassium over sodium binding.Liquid-polymeric membrane ion-selective electrodes (ISEs) based on thisionophore were prepared using differentplasticizers and mole ratios of lipophilic ionic additives. Membraneelectrodes with optimum composition (using o-nitrophenyloctylether or bis(1-butylpentyl)adipate as plasticizer and 60 mol% lipophilic borate additive) show Nernstianresponses toward potassium (57 and 58 mV/decade, respectively) over a wideconcentration range with a micromolardetection limit. These ISEs exhibit enhanced potassium over sodiumselectivity (KpotK + ,Na +=6¥10 -4 ).In addition, theelectrodes show selectivities for potassium over Cs +and NH4 + thatare better than those of valinomycin-based ISEs. (Keywords: Ion-selective electrode, cation sensor, bis(crown ether),neutral carrier, liquid-polymeric membrane,lipophilic salt)