Successive Potentiometric Titration of Iron(II) and Iron(III) with Cobalt(II) in the Presence of 1,10-Phenanthroline

Abstract

The chemical speciation 1,2 and simultaneous determination 3 of metal ions have been increasingly needed in areas such as clinical chemistry, environmental pollution and industrial control. Iron is present as bivalent and trivalent states in the natural environment. The changes between these two forms of iron are important in various biological 4 and geochemical 5 processes. Thus, the development of a simultaneous method for iron(II), iron(III) and thus the total iron is still desired. The redox potential of a system involving metal ions is modified by complexation of metal ions with a suitable ligand.6 Vydra and Pribil 7,8 reported on the effect of 1,10-phenanthroline (phen) on the redox reaction of cobalt(II) with iron(III) and developed a method for the potentiometric titration of cobalt(II) with iron(III) in the presence of this ligand. By using this phenomenon, we have recently proposed novel redox systems, which are applicable to potentiometric titrimetry for the determination of metal ions. [9][10][11][12][13] In the presence of phen or 2,2′-bipyridine (bpy), a remarkable potential break is observed in the titration of vanadium(IV) with iron(III), cobalt(II) with vanadium(V) and cobalt(II) with chromium(VI). 11 Furthermore, we have reported on the successive potentiometric titration of chromium(VI) and iron(III) with cobalt(II) in the presence of phen. 12We also developed a new flow-injection spectrophtometric method for the simultaneous determination of vanadium(IV) and vanadium(V), based on the effect of phen and diphosphate on the redox potential of the Fe(III)/Fe(II) system. 14 In this paper, the successive potentiometric titration of chromium(VI) and iron(III) 12 is further developed, that is, successive potentiometric titration of iron(II) and iron(III) with cobalt(II) is presented. The redox potential of the Cr(VI)/Cr(III) system is higher than that of the Fe(III)/Fe(II) system at low pH. Thus, iron(II) was oxidized to iron(III) by adding excess chromium(VI) as an oxidizing agent before the titration. Then, non-reacted chromium(VI) and total iron were titrated with cobalt(II) in the presence of phen. The present method can determine iron(II) and iron(III) in the range 3×10 -4 -1×10 -3 mol dm -3 ; the relative standard deviations of this method were 0.66 and 0.81% for four determinations of 5×10 -4 mol dm -3 iron(II) and 1×10 -3 mol dm -3 iron(III), respectively. The method was successfully applied to the determination of total iron in standard iron-ore samples and to the successive determination of iron(II) and iron(III) in a Mosan iron-ore sample issued by The Japan Iron and Steel Federation. Experimental ReagentsAn iron(II) standard solution (0.01 mol dm -3 ) was prepared daily by dissolving 0.098 g of iron (II) A novel potentiometric titration of iron(II) and iron(III) is proposed. The method is based on the effect of 1,10-phenanthroline (phen) on the redox reactions of chromium(VI) and iron(III) with cobalt(II). In the presence of phen the conditional redox potential of the Co(III)/Co(II) syst...

Voltammetric Method for Determining Ferric Ions with Quercetin

“…Many analytical methods for determining ferric ions have been reported including high‐performance liquid chromatography [10], chemiluminescence [11], potentiometric titration [12], UV‐visible spectrophotometry [2, 13–15], spectrofluorimetry [3, 16–18], atomic absorption spectrometry [19], inductively coupled plasma mass spectrometry [20, 21] and voltammetry [22–31]. Whereas some of those methods pose certain disadvantages – time‐intensive analysis and matrix interference – that require sophisticated, expensive equipment as well as time‐consuming extraction and pre‐concentration, voltammetric ones are relatively inexpensive, fast, selective and sensitive.…”

Development of Novel Redox Systems by Use of Ligand Effect and Its Application to Potentiometry

“…3·5·2 Successive titration of iron(II) and iron(III) in the presence of phen A novel successive potentiometric titration of iron(II) and iron(III) was also developed by using reactions (4), (12), and (14) in the presence of phen. 24 Firstly, in the absence of phen, a known amount of chromium(VI) is added in excess to a sample solution containing iron(II) and iron(III) at pH around 1 so that iron(II) can be oxidized to iron(III). After the pretreatment, the sample solution containing excess of chromium(VI) and iron(III) (total iron) is titrated with a standard cobalt(II) solution in the presence of phen.…”

Flow Injection Analysis for Oxidation State Speciation of Vanadium(IV) and Vanadium(V) in Natural Water

“…23 This phenomenon has been applied to potentiometric titrations of some metal ions. [24][25][26][27][28][29] For example, potentials of iron(III)/iron(II) and cobalt(III)/cobalt(II) systems were affected by 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen), and the redox systems were applied to the potentiometric titrations of vanadium(IV) and cobalt(II). 26 Flow injection analysis (FIA) has been widely used because of its simplicity, rapidity, great convenience, high accuracy and less consumption of reagents.…”