Reduction of Hg2+ by Individual Phenolics and Complex Samples and Its Application in Polarographic Antioxidant Assay

Abstract

Direct current (DC) polarographic antioxidant (AO) HPMC assay based on the decrease of anodic limiting current of [Hg(O2H)(OH)] (HydroxoPerhydroxoMercury(II) Complex-HPMC), formed in alkaline solution of H2O2, at potential of mercury oxidation, occurring upon AO addition, was validated and widely used recently. Here, a novel DC polarographic assay, MRAP (Mercury Reduction Antioxidant Power), based on the decrease of Hg2+ cathodic current with addition of AOs was applied. Percentage of this decrease was plotted versus the amount of various individual phenolics or the volume of medicinal plant extracts, and the slope obtained was used to express AO activity. A high correlation between MRAP and HPMC assays was found for individual compounds (r = 0.974) and real samples (r = 0.968). MRAP was shown to be effective in the determination of AO activity of both synthetic mixtures of individual AOs and real samples containing various AOs. Agreement between the decrease of Hg2+ cathodic current and HPMC anodic current lead to the assumption that Hg2+ reduction causes a decrease in concentration of Hg2+ available for HMPC complex formation, i.e. its anodic current decrease. The validity Of MRAP assay was also confirmed through good correlation with FRAP assay.