Ascorbic acid (ASC) is separated by percolating the extract solution through an anionic Sephadex column. After one or two washings with water, the vitamin is oxidized on the column by a p-benzoquinone solution to dehydroascorbic acid (DASC). This latter being actually no acid is eluted as it is formed. The DASC containing eluate is treated with a new colorimetric reagent: 4-Nitro-1,2-Phenylenediamine (NPD). After extraction of the excess reagent with ethyl acetate, the optical extinction is measured at 375 nm. DASC, if present in the extract solution, can be reduced to ASC by dimercaptopropanol prior to chromatography. The method is very specific. The rather simple chromatographic purification can be effected semi-automatically with series of 10 colums (or more).