| Popis: |
A considerable interest has been focused recently on analytical methods for evaluation of antioxidant activity of food and biological samples. One of the most widely used method for antioxidant activity evaluation is the DPPH decolourisation assay based on the scavenging of stable 2, 2-diphenyl-1-picrylhydrazyl (DPPH· ; ) free radical by the antioxidant present in the sample. DPPH free radical reacts with antioxidant (AH) according to the equation: DPPH· ; + AH ® ; DPPH· ; H + A. Two methods were used to evaluate antioxidant activity and were compared with classic spectrophotometric measurements. Nonreacted DPPH· ; absorbs in the visible range and spectrophotometric method is based on colour intensity measured at 518 nm. Electrochemical measurements of antioxidant activity are based on the same equation but detection of residual concentration of nonreacted free radical is determined amperometrically i.e. biamperometrically. Current response, for amperometric method, obtained by glassy carbon electrode polarized at fixed potential is proportional to the concentration of nonreacted DPPH· ; . In biamperometric determination of antioxidant activity two identical glassy carbon disc electrodes were mounted in a classic electrochemical cell containing DPPH· ; │ DPPH redox couple and tested in a range of working potential difference. Antioxidant activity of some water-soluble antioxidants present in the blood, as well as ethanol-soluble antioxidants typically present in certain foods and drinks were determined. Proposed electrochemical methods, based on glassy carbon electrode, show good chemical stability and allow analysis of nontransparent and turbid samples since the response of detector is not affected as in spectrophotometric measurements. |
