DETERMINATION OF ASCORBIC-ACID AND DEHYDROASCORBIC ACID IN JUICES BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION USING L-CYSTEINE AS PRECOLUMN REDUCTANT

Determination of ascorbic acid (AA) and dehydroascorbic acid (DHAA) in juices was performed by high-performance liquid chromatography with e lectrochemical detection using L-cysteine as precolumn reductant. This method was suitable for the determination of AA and total AA (AA + DH AA) in juices. The mild reduction of DHAA to AA with L-cysteine took c a. 15 min, and the retention time of AA was ca. 15 min. The detection limit (signal-to-noise ratio = 2) was ca. 0.15 ng. The method was sele ctive and reproducible (relative standard deviation 2.6-3.2% for AA an d 2.1-3.2% for total AA). The calibration graph for AA was linear in t he range 0.1-10 ng. The recovery of AA was over 90% by the standard ad dition method.