Modified CUPRAC method with electrochemical detection for the determination of antioxidant capacity of gallic acid

A modified cupric reducing antioxidant capacity (CUPRAC) method based on electrochemical monitoring of the Cu(II) ion reduction signal has been developed for the determination of the antioxidant capacity (AOC) of gallic acid. Different electrochemical techniques have been used, namely cyclic voltammetry, differential pulse voltammetry, and square-wave voltammetry (SWV). The SWV method is used in direct scanning and reverse scanning modes. The technique used is SWV in the reverse scanning mode due to the reproducibility of the signal, the sensibility of the technique, and the absence of interferences. The AOC of a given molecule can be measured from the decrease in the reduction signal after the addition of an antioxidant. The relative AOC of gallic versus ascorbic acid obtained by these measurements is 1.9. This value agrees with those obtained from the spectrophotometric methods CUPRAC (1.9) and activity versus 2,2-diphenyl-1-picrylhydrazyl radical (1.8), thus indicating that themethod proposed here is valid. Moreover, the electrochemical measurements are not affected by excess or defect due to the turbidity or the colour of samples or the product of the reaction (or both) and are carried out under near-physiological conditions (medium-high ionic strength and absence of non-aqueous solvent).