Application of Tri-n-octylphosphine Oxide as an Ionophorefor a Vanadyl Ion-Selective Membrane Electrode

Abstract

We found that tri-n-octylphosphine oxide (TOPO) acts as an excellent ionophore for vanadyl ion (VO2+). An electrode constructed using this ionophore and 2-fluoro-2′-nitrodiphenyl ether as a solvent mediator in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to VO2+ in the concentration range of 1×10−5–1×10−2 M with a slope of 29.5 mV per concentration decade in a solution containing 0.1 M Na2SO4. The limit of detection was 1×10−6 M. The electrode showed high selectivity for VO2+ over other cations including uranyl ion (UO22+). Other phosphine oxides such as triphenylphosphine oxide and tribenzylphosphine oxide, as well as phosphonate and phosphate analogs responded weakly to VO2+, indicating that the TOPO with the strong basicity of the P=O group was especially useful for constructing a VO2+-selective electrode.