Caesium-selective poly(vinyl chloride) membrane electrodes based on calix[6]arene esters

Abstract

Hexameric calix[6]arene ester compounds have shown an ability to extract large alkali metal ions such as caesium and rubidium in phase transfer studies. A potentiometric selectivity study has been made using two ester containing hexameric calix[6]arenes, p-tert-butyl hexaethyl ester (1a) and the unsubstituted hexaethyl ester (1b), as the ionophores for caesium ions. Six electrodes were prepared with 2-nitrophenyl octyl ether as the solvent mediator and various amounts of potassium tetrakis(p-chlorophenyl)borate as the ion exchanger in a poly(vinyl chloride) matrix. The ligands examined produced electrodes with near-Nernstian slopes; the selectivity coefficients for caesium with respect to rubidium, potassium, sodium, lithium, calcium, magnesium, hydrogen and ammonium were determined. Lifetimes of at least 1 month were estimated.