Journal of Inclusion Phenomena and Molecular Recognition in Chemistry 11:303 311, 1991. 303 © 1991 Kluwer Academic Publishers. Printedin the Netherlands. The Synthesis of Bis(benzo-crown ether)s and Their Incorporation into Potassium-Selective PVC Membrane Electrodes HAOYUN AN, YANGJIE WU* and ZHIJUN ZHANG Chemistry Department, Zhengzhou University, Zhengzhou, Henan, People's Republic of China REED M. IZATT* and JERALD S. BRADSHAW Chemistry Department, Brigham Young University, Provo, Utah 84602 U.S.A. (Received: 24 August 1990; in final form: 6 August 1991) Abstract. Five bis(benzo-15-crown-5) derivatives connected with different bridge chains were synthesized as neutral carriers in K+-selective electrodes. Potassium ion-selective PVC membrane electrodes based on these bis(crown ether)s were prepared using dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as plasticizers of the PVC membrane. The selectivity coefficients (KM.+ :KK+) for various alkali and alkaline-earth metal ions were measured. The electrodes based on the bis(crown ether)s are more selective for K + than those based on monomeric crown ethers. The selectivity of one of the prepared potassium selective electrodes was higher than that of the electrode based on valinomycin and three of them were stable over a wide pH range. Key words. Bis(crown ethers), PVC membrane, potassium ion-selective electrodes, neutral carriers. 1. Introduction The discovery of the high affinity of crown ethers for alkali metal ions [ 1] provided a new approach to the choice of the neutral carrier in preparing potassium- or other metal cation-selective electrodes. Monomeric crown ethers with different ring sizes and different numbers and types of substituents have been used to prepare cation selective electrodes [2, 3, 4]. However, the selectivity coefficients of these systems were found to be much lower than that of the electrode based on the natural antibiotic valinomycin [5]. This result suggests that superior selectivity is not likely to be achieved by simply changing the molecular size and substituents of the monomeric crown ethers. High selectivity potassium-selective electrodes based on bis- and poly(crown ether)s have been prepared [6 9]. Potassium ion can form a sandwich-type complex with both of the moieties of these poly crown ethers, while Na ÷ can form a complex with only one of the moieties. Therefore, the bis(crown ether)s are more selective than the monomeric crown ethers for K ÷ over Na ÷. However, the bis(crown ether)s containing the ester or amide linkages [6] can be hydrolyzed easily. As a result, the working life of the electrodes is relatively short. The properties of these electrodes are closely related to the length, structure and flexibility of the linkage in the his(crown ether)s [6, 7]. Fung et al. [7] found that the * Authors for correspondence.