Abstract:

An on-line HPLC method was developed to analyze natural antioxidants in a mixed juice by testing ABTS
radical scavenging activity. Rutin was used as a model antioxidant. Optimized system settings for improved RSN (signal/
noise) were obtained when 0.32 mmol/L ABTS radical solution was flowed through a 10.0 m reaction coil at a flow rate
0.5 mL/min. The limits of detection of the method for rutin, ascorbic acid, quercetin and α-tocopherol were in the range of
0.12－0.37 μmol/L. About 20 antioixdants were detected in the tert-butyl methyl ether of a commercial mixed juice by this
method. The most dominant antioxidants in the extract were chlorogenic acid and a compound similar structure. This method
is simple, convinent, fast and suitable for online assay of soluble antioxidants.

Key words: antioxidant, free radical, on-line detection