Chemistry and analysis of the permitted coal-tar food dyes /

Abstract

The present procedure for certification is outlined in United States Department of Agriculture Miscellaneous Circular 52; the chemistry of the permitted coal-tar food colors and the revised methods of their analysis are fully described in the following pages. CHEMISTRY OF THE PERMITTED COAL-TAR FOOD DYES In the preparation and purification of dyes to be certified care must be taken not only in the final steps of their manufacture, but also in the synthesis or purification of their intermediates. Many intermediates are commercial products containing relatively large proportions of isomeric and subsidiary compounds, which will produce isomeric and subsidiary colors during the preparation of the dye. Some of these impurities are harmful, and all are undesirable adulterants. Purification of adulterated intermediates is not worth trying. The only safe method is to use intermediates of the best possible quality. The Bureau of Chemistry has refused to approve for certification several batches of dyes because they contained foreign coloring matter.

Chemistry and analysis of the permitted coal-tar food dyes ponceau SX, sunset yellow FCF, and brilliant blue FCF /

“…The analytical data given here should be incorporated in the foundation and supplemental affidavits (12). (2), as for light green SF yellowish.…”

“…(*). 2 Although no limit is defined here, a statement of the percentage found by analysis should be incorporated in the foundation and supplemental affidavits. 3 Theoretical.…”

“…For amaranth and ponceau 3R substitute the following method for that given in Department Bulletin 1390 (revised) (2 To determine the acid extractives, proceed as directed in Bulletin 1390 (2, p. 29, last paragraph), except that for "wash once with 25 c. c. of benzene," in line 5, substitute "wash with 25 c. c. portions of benzene until the benzene is practically colorless." ANALYTICAL CONSTANTS 8 In case very small quantities of lead are present, it will be necessary to use the 15 gm.…”

“…Since the revision, in December, 1927, of Department Bulletin 1390 (2) 1 three new colorsponceau SX, sunset yellow FCF, and brilliant blue FCF-have been approved and added to the list of permitted coal-tar food colors. The chemistry and special analytical methods for these three new dyes, as well as a revised method for lead, follow.…”