Effect of Ligands on the Iron(III)/Iron(II) System and Its Novel Application to the Simultaneous Flow Injection Determination of Vanadium(IV) and Vanadium(V)

Abstract

A new simultaneous flow injection determination of vanadium(IV) and vanadium(V) has been proposed with photometric detection. The method is based on the effect of ligands on the formal redox potential of the iron(III)/iron(II) system. The potential of the redox system increases due to the presence of 1, 10-phenanthroline (phen); vanadium(IV) is thus easily oxidized by iron(III) to vanadium(V), producing an Iron(II)-phen complex (λ_max=510nm). On the other hand, the presence of diphosphate causes an increase in the reducing power of iron(II) because of a decrease in the potential of the system. Thus, the reduction of vanadium(V) by iron(II) takes place easily. By using an FIA system and measuring the absorbance of the complex at 510nm, the simultaneous determination of vanadium(IV) and vanadium(V) is possible based on both reactions. The proposed method makes it possible to obtain both positive and negative FIA peaks corresponding to the concentrations of vanadium(IV) and vanadium(V) alternatively by a single injection of the sample solution. Vanadium(IV) and vanadium(V) at the 10^-6mol dm^-3 level can be determined at a rate of 30 samples h^-1(60 peaks h^-1).