Caesium ion-selective electrodes based on crowned benzoquinones

Abstract

Three new derivatives of benzo-15-crown-5 were examined as potential caesium ion-selective ionophores in PVC membrane electrodes. The ionophores were 2,3-benzoquino[15]crown-5,2-bromo-1,4-dihydroxybenzo[15]crown-5 and 5-bromo-2,3-benzoquino[15]crown-5. PVC membranes plasticized with 2-nitrophenyl octyl ether, and incorporating the secondary ion exchanger potassium tetrakis(4-chlorophenyl)borate were used throughout this study. Interferent studies for each electrode were carried out to assess electrode selectivity in the presence of ammonium ion, alkali and alkaline earth ions and selected transition metals. A graphical method of representing selectivity coefficients is provided together with the separate solution technique for selectivity determination. Dynamic response, precision, lifetime and temperature studies was also reported. The benzoquinone crown ethers proved to be good caesium ionophores, displaying near-Nernstian responses to this ion, in the range 10^–1–10^–4.5 mol l^–1. The electrode incorporating the 2,3-benzoquino[15]crown-5 ionophore had the highest selectivity for caesium ions over alkali and alkaline earths studied.