Abstract
WHEN an equal volume of 3 percent hydrogen peroxide is added to a slightly acidified ascorbic acid solution, no appreciable effect on the indophenol titration value is observed, unless iron or copper salts are present. The end-point is a permanent pink colour deepening very slowly on standing. With sulphited fruit and vegetable extracts the sulphur dioxide is converted into sulphuric acid, and the true ascorbic acid value is rapidly obtained on titration. When lesser quantities of peroxide are used, the titration values are slightly lower, and the pink colour deepens more rapidly. Apparently, re-oxidation of reduced indophenol takes place during the titration, along with reduction of the reformed indophenol by ascorbic acid still present. When 1.5 per cent peroxide is present in solution, this effect is negligible. The method has been used successfully for the last three years.
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LEVY, L. Determination of Ascorbic Acid in the Presence of Sulphur Dioxide. Nature 152, 599 (1943). https://doi.org/10.1038/152599c0
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DOI: https://doi.org/10.1038/152599c0
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