Chronoamperometric Determination of Antioxidant Capacity Using an Iron Complex with 2,2'-Bipyridine

Abstract

The approach for the determination of antioxidants of various hydrophilicity using the complex of the iron(III) with bipyridine as a model oxidizing agent and chronoamperometric recording of the analytical signal is proposed. The choice of the oxidant is determined by its solubility in aqueous, organic and aqueous-organic media. The conditions for recording chronoamperograms are selected: the medium is the acetonitrile-acetate buffer solution (pH 3.6) (9 : 1), the electrolyte is the LiClO4, the potential is E = 1.25 V, the current registration time is 80 s. Antioxidants soluble in organic and aqueous-organic media are studied: α-tocopherol, quercetin, catechin, and caffeic acid. The analytical ranges are (0.5−4) × 10^–4 M. The antioxidant capacity (AOC) of ethanol extracts from medicinal plant materials is determined. A high correlation is observed between the AOC values obtained by the chronoamperometric and the spectrophotometric approaches, but only for samples whose intrinsic colors do not contribute to the absorbance of the Fe(II)-bipyridine complex. The application of the proposed approach and the potentiometric method using the K₃[Fe(CN)₆]/K₄[Fe(CN)₆] system showed that the values obtained by the potentiometric approach are significantly lower for most of the studied infusions. Thus, it is advisable to analyze multicomponent objects, containing substances of different hydrophilicity, using approaches with oxidizing agents of different solubilities, such as the Fe(III)-bipyridine complex.