Synergistic Effect of Some Transition Metal Ions on the Sulfite Induced Autoxidation of Cu(II)/Tetraglycine Complex. Analytical Applications

Abstract

The present work describes an alternative spectrophotometric method for sulfite determination based on its effect of accelerating the oxidation of Cu(II)/tetraglycine complex by oxygen. The analytical range was (0.5–10)× 10⁻⁵ mol L⁻¹ sulfite and the detection limit 6.15 × 10⁻⁷ mol L⁻¹; the relative standard deviation for a 5 × 10⁻⁵ mol L⁻¹ sulfite solution (n = 6) was 0.11%. The potentiality of this method was employed for the determination of S(IV) in wine. The synergistic effects of Ni(II), Co(II), Mn(II), Cr(III), Fe(II), and Fe(III) ions (at low concentration, 10⁻⁶–10⁻⁴ mol L⁻¹) on this reaction were investigated. The metal ions in the trivalent oxidation state react with to initiate a radical chain reaction in which sulfite is oxidized to sulfate and the metal ion is reduced to the divalent state. The influence of some stabilizing agents of sulfite solutions, such as aldehydes and amines, is also discussed based on its effect on the reaction rate.

Keywords:

• Cu(III)
• Tetraglycine complexes
• Transition metal ions
• Synergistic effect
• Sulfite
• Wine

Acknowledgments

We gratefully acknowledge the financial support from Fundação de Amparo á Pesquisa do Estado de São Paulo (FAPESP), Conselho Nacional de Pesquisa e Desenvolvimento Tecnológico (CNPq) (Brazilian Agencies) and to Prof. Elisabeth de Oliveira (IQ-USP) for the ICP analyses.