Titration curves in complexometric titrations with the redox system Fe(III)/Fe(II)

Area of Science:

• Analytical Chemistry
• Electrochemistry

Background:

• Potentiometric titrations are a common method for determining metal ion concentrations.
• The Fe(III)/Fe(II) redox system offers a versatile indicator for these titrations.

Purpose of the Study:

• To investigate the applicability of potentiometric titrations with platinum or graphite electrodes for various metal ions using the Fe(III)/Fe(II) redox system.
• To analyze how complexation strength and reaction kinetics influence titration curve characteristics and analytical utility.

Main Methods:

• Potentiometric titrations of metal ions using ethylenediaminetetraacetic acid (EDTA) as the titrant.
• Employing platinum or graphite electrodes in conjunction with the Fe(III)/Fe(II) redox system.
• Conducting experiments under specific conditions, including low pH (< 2) and absence of oxygen.

Main Results:

• Titration curves for strongly complexed ions like bismuth and indium were asymmetrical and analytically useful.
• Metal ion complexation kinetics significantly affected titration curves when complexation was weaker than iron.
• Rapidly recorded curves after titrant addition showed better end-point breaks than those at thermodynamic equilibrium.
• Weakly bound and slow-reacting metals, such as nickel, exhibited minimal or no end-point break.

Conclusions:

• Potentiometric titrations with platinum/graphite electrodes and the Fe(III)/Fe(II) system are valuable for analyzing metal ions, particularly those with strong complexation.
• Titration curve analysis requires consideration of both complexation strength and reaction kinetics for accurate interpretation.
• Optimizing measurement timing (rapid recording) enhances analytical precision by improving end-point detection.