Determination of the antioxidant activity of phenolic compounds by coulometric detection.

The combination of reversed-phase high-performance liquid chromatography with coulometric detection allows the detection of phenolic antioxidants in complex matrices like plant extracts with a high degree of sensitivity and selectivity. According to their voltammetric behaviour, phenolic acids and tocopherols show maximal detector response at low potentials (100-450 mV) while flavonoids show optimal response at two different potential values (one at 0-300 mV and one at 600-900 mV). The potential corresponding to maximal detector response (MDRP) of phenolic acids was shown to be inversely proportional to their antioxidant efficiency as determined in a lipidic model system under strong oxidizing conditions (110 degrees C, intensive oxygenation) or by the DPPH() test. However, such a relationship was not observed for flavonoids.