Reactions of superoxide anion radical with antioxidants and their use in voltammetry

Kinetic parameters were calculated for the electrochemical reduction of oxygen at a glassy-carbon electrode with the generation of superoxide radical anions in a 0.05 M solution of (C2H5)(4)NI in dimethylformamide in the presence of fat-soluble antioxidants, retinol and alpha-tocopherol. A procedure based on the protonation of the radical anion with antioxidant molecules is proposed for the voltammetric determination of antioxidants to determine milligram amounts of retinol and alpha-tocopherol in model solutions (RSD = 1-2%). The calibration graphs for retinol and alpha-tocopherol are linear in the concentration ranges 9.7 x 10(-5)-2.3 x 10(-3) and 6.2 x 10(-4)-3.1 x 10(-4) M, respectively. The detection limits for retinol and alpha-tocopherol are 4.8 x 10(-5) and 4.1 x 10(-4) M, respectively. The procedure was applied to the determination of the active component (retinol and alpha-tocopherol) in pharmaceuticals.