The red dye consisting mainly of the disodium salt of 3-hydroxy-4-[(4-methyl-2-sulfophenyl)azo]-2-naphthalenecarboxylic acid (Colour Index No. 15850) and a related pigment consisting mainly of the calcium salt of that compound (Colour Index No. 15850:1) are known by many common names, including Pigment Red 57. If they are certified by the U.S. Food and Drug Administration (FDA) as complying with limiting specifications for certain impurities and good manufacturing practices as set forth in the Code of Federal Regulations (CFR), they are called D&C Red No. 6 and D&C Red No. 7, respectively, and may be used in drugs and cosmetics. In the European Union, the calcium salt form, under the name E180, is permitted for use as a food additive for coloring edible cheese rinds. The compounds are manufactured as follows: diazotized 2-amino-5-methylbenzenesulfonic acid is coupled with 3-hydroxy-2-naphthalenecarboxylic acid; and the resulting product is precipitated as the disodium salt, which may then be converted to the calcium salt by adding calcium chloride. During manufacture, various side-reaction impurities may be produced and carried over into the final product. The presence of such impurities, whether specified or not in the CFR, can cause a batch to be denied certification by FDA. The present work reports (i) the identification and characterization of a non-CFR-specified impurity, 3-hydroxy-4-[(4-methyl-2-sulfophenyl)azo]-naphthalene (the decarboxylated form of Pigment Red 57), in the color additives D&C Red No. 6 and D&C Red No. 7, and (ii) the UHPLC determination of this impurity in batches of these color additives.

Identification of the decarboxylated analog of Pigment Red 57 and its quantification in the color additives D&C Red Nos. 6 and 7 using UHPLC

256th National Meeting (2018)

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