Abstract
ON adding hydrochloric acid to a solution of ascorbic acid, reversible oxidation with 2: 6-dichloro-phenolindophenol and iodine becomes progressively slower as the mineral acid content increases. When the hydrochloric acid concentration reaches 20 percent in the case of indophenol and 29 per cent in the case of iodine, reduction of the reagent is completely inhibited. On diluting the acid mixture with water, the total reducing capacity of the ascorbic acid is restored, and can be titrated with both reagents. This property is exhibited only by ascorbic acid, and, consequently, substances which interfere in the titration under the usual conditions can be differentiated from the vitamin. With certain other reducing substances the rate of reduction of the reagents is somewhat retarded, but redaction proceeds to completion. With orange juice a small titration is observed in the presence of the mineral acid, and the true ascorbic acid content is obtained either by subtracting this figure from the original titration value or by determining the renewed titration value obtained on diluting with water. With fruits and vegetables of high vitamin content (guava, lucerne and parsley) no interfering substance is found to be present.
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LEVY, L. A Specific Reaction for Ascorbic Acid. Nature 152, 693 (1943). https://doi.org/10.1038/152693a0
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DOI: https://doi.org/10.1038/152693a0
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