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°C, intensive oxygenation) or by the DPPH test. However, such a relationship was not observed for flavonoids.