Isolation, Separation, and Identification of Synthetic Food Colors E. A. Dixon' and G. Renyk2 University of Calgary, Calgary, Alberta, Canada
This article describes a simple, inexpensive experiment for the extraction of synthetic dyes permitted in foodstuffs,and their separation and identification using thin-layer chromatography and ultraviolet/visible spectroscopy. In 1856, Perkin synthesized the first coal tar dye. Soon after this a host of synthetic dyes were discovered, and many of these began to be used to color food. Prior to this, only dyes from natural sources had been used for this purpose, and these included betauin (red) from beets, 0-carotene (orange) from carrots, bixin (yellow) from annato seed, carminic acid (red) from cochineal insects (Coccus cacti), chlorophyll (green), and saffron (yellow) from crocus. At the turn of the century more than 90 synthetic dyes were used in foods. In 1906 the first legislation concerning the use of dyes was passed in the U S . which left only seven dyes suitable for use in foods. One of these was the oil-soluble dye, p-dimethylaminoazohenzene, or Butter Yellow. This was removed from the list of approved dyes in 1932 after a Japanese worker showed the substance capable of producing liver tumors in rats ( I ) . By 1950 the approved list had expanded to 19, but in that same year three dyes were removed from the list when several children became seriously ill after eating popcorn colored by these substances. Food color legislation differs widely from one country to another. Table 1lists all dyes permitted in the US., Canada, and the U.K., and many of those permitted in E. E. C. (Common Market) countries. Food dyes and dyes in general are complicated by the variety of common names. However, they are described systematically by a Color Index Number (see Table 1,footnote a) and hy F. D. and C. numbers following legislation in the U S . under the Food, Drug and Cosmetics Act. I t should be noted that some dyes are restricted in their use, namely Citrus Red 2 in both Canada and the US., and Ponceau SX in Canada, and F. D. and C. Red 4 and Orange B in the U S . Isolation of the Dyes Many water-soluble materials are present in food, and various methods have been described for the separation of water-soluble food dyes. The direct identification of the colors is not generally feasible. The dyes must be extracted, purified, and concentrated prior to identification by thin-layer chromatography or U.V./visihle spectroscopy. The dyes may be extracted with quinoline (2) by mixing the aqueous solution with an equal volume of buffer at pH 3 which converts the dyes into free acids, followed by extraction with 10-20 ml of minoline. The minoline-dye extract is isolated Because the huffer solution converts
