Antioxidant assays by reducing potential and 2,2-diphenyl-1-picrylhydrazyl radical scavenging techniques as affected by pH and ion concentrations

The aim of the study is to investigate the effect of varying pH and different metal ion concentrations on the analyses of antioxidants by reducing potential (RP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging techniques. The investigation was conducted by examining the effects of various pH values (4, 5, 6, 7, 8 and 9) and potassium chloride concentrations (50, 100, 150, 200, 250 and 300 ug/mL) on the optical densities of reducing potential and DPPH radical scavenging potential of aqueous infusions of Cassia alata (L.) Roxb. The determinations were also conducted on the extraction media with the intention of identifying the probable source of variation in the investigation. The antioxidant potentials for both the aqueous infusion and media were most efficient at the least pH 4.0. Moreover, the antioxidant potentials decrease as the ion concentrations increase. The study revealed that the colorimetric methods for the determinations of DPPH radical scavenging and RP could be liable to errors arising from slight changes in acidity and concentrations of the metal ions thus affecting the performance characteristics in terms of repeatability and reproducibility of reports and meaningful comparisons of antioxidant capacity of dietary products among different authors.