Dyeing with natural colorants, procedure

From ancient times, mankind was enchanted by the marvelous colors arising from the treatment of cloth with the natural dyes extracted from various animals or plants. As early as the 13th century B.C., Phoenicians knew how to manufacture indigoid dyes (Tyrian purple) from the secretions of certain Mediterranean Sea mollusks. To produce 1 gram of the dye, 10000 animals were required for a lengthy and laborious procedure. Its price was up to 10-20 times its weight in gold. 

There are two standard procedures for vitamin C determination in vegetables and legumes. The sample preparation is common to both and involves macer-ation/dilution of the sample in a stabilizing solution, such as 5% metaphosphoric acid or trichloroacetic acid, followed by filtration. The ascorbic acid can then be determined by titration with 2,6-dichloroin-dophenol, where the ascorbic acid reduces the oxidation/reduction indicator dye to a colorless solution or by fluorimetric detection, in which the ascorbic acid is oxidized to dehydroascorbic acid, which then reacts with o-phenylenediamine (1,2-diamino benzene) to produce a fluorophore. The latter method has the advantages that it is suitable for colored solutions and can be used to measure levels of naturally occurring dehydroascorbic acid as well as ascorbic acid. Many other methods are available for determination of vitamin C with the use of LC techniques, currently the subject of much interest. Reversed-phase LC techniques can be used to determine dehydroascorbic acid, ascorbic acid, and their isomers. 

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