COPPER (II) TETRASULPHO-PHTHALOCYANINE ENTRAPPED IN A PROPYLPYRIDINIUMSILSESQUIOXANE POLYMER IMMOBILIZED ON A SiO₂/Al₂O₃ SURFACE: USE FOR ELECTROCHEMICAL OXIDATION OF ASCORBIC ACID

ABSTRACT

Copper (II) tetrasulphophthalocyanine, CuPc⁴⁻, was encapsulated in a n-propylpyridinium silsesquioxane polymer, SiPy⁺Cl⁻, immobilized on the SiO₂/Al₂O₃ surface. The material obtained incorporated in a carbon paste electrode, presented the property of electrocatalysing the oxidation of ascorbic acid at 0.18 vs SCE. It was observed that the anodic peak potential at different solution pH remained practically constant between pH 5 and 8 and shifted to more positive potentials below pH 5. The electrode showed a very reproducible response and was chemically stable under various oxidation-reduction cycles. By amperometric measurements, a linear response was obtained in the range of 1 × 10⁻⁴–1.4 × 10⁻³ mol l⁻¹ of ascorbic acid. The modified electrode was used to determine ascorbic acid (vitamin C) in tablets. The results were validated by comparison with the results obtained by using the standard 2,6-dichlorophenolindophenol titration method.

Keywords:

• Copper (II) tetrasulphophthalocyanine
• Propylpyridinium silsesquioxane polymer
• SiO₂/Al₂O₃
• Oxidation of ascorbic acid

ACKNOWLEDGMENTS

YG is indebted to FAPESP for financial support; STF is indebted to FAPESP and CAP is indebted to CNPq for fellowships.