Development of Novel Redox Systems in Potentiometry and Its Application to Analytical Chemistry

Abstract

The redox potential of a system involving metal ions has been modified by the complexation of metal ions with a suitable ligand. This phenomenon has a potential capacity for the development of novel redox systems which are applicable to quantitative analyses. Potentiometric titrations of vanadium(IV) with iron(III), cobalt(II) with vanadium(V) and cobalt(II) with chromium(VI) are possible in the presence of 1, 10-phenanthroline (phen) or 2, 2'bipyridine. A new spectrophotometric FIA determination of iron(II) has been presented based on the redox reaction of copper(II) with iron(II) in the presence of bathocuproinedisulfonate together with diphosphate.A new-type procedure for the spectrophotometric FIA method was developed for the simultaneous determination of redox couples of vanadium(V)/vanadium(IV) and quinone/hydroquinone based on this principle. The procedure was adapted to simultaneous determinations of iron(III) and vanadium(V) and of iron(III) and chromium(VI). It has been found that the redox reaction of cysteine with iron(III) in the presence of phen is accelerated by the addition of copper(II). A spectrophotometric FIA determination of cysteine was proposed based on the accelerating effect of copper(II) on the rate of the redox reaction. A spectrophotometric reverse FIA (rFIA) determination of complexing agents such as aminopolycarboxylic acids and polyphosphates was developed based on the redox reaction of copper(II) with iron(II) in the presence of neocuproine. By using this rFIA system, a new procedure for estimating the complexing capacity in natural water was developed.