Nafion-coated uranyl selective electrode based on calixarene and tri-n-octyl phosphine oxide

Uranyl ion selective electrode based on 5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexahydroxy calix[6]arene (calixarene I) and tri-n-octyl phosphine oxide (TOPO) incorporated into a poly(vinyl chloride) (PVC) membrane has been developed. The PVC membrane containing the active ingredients was casted on the surface of a graphite electrode. The electrode showed a near Nernstian response to uranyl ion in the concentration range of 10−1 to 10 M with an average slope of 27 mV per decade. The best performance of the electrode could be obtained by using a sensor mixture of calixarene and TOPO in the weight ratio of 1:100. The optimum pH range was between 3.2 and 4.6. Alkali and alkaline earth metal ions did not interfere with the determination of uranyl ion. There was nominal interference from Cu2+, Ni2+, Co2+ and Al3+, while Fe3+, Th(IV), EDTA and F− interfered seriously. The interferences from these ions could be eliminated by coating the membrane surface with Nafion. Nafion coating eliminated the anionic interference while the interference from transition metal ions and thorium, could be minimized by converting them to their anionic complexes with EDTA or F−.