Structural analysis of subsidiary tar dyes contained in Food red No. 102

: Three unknown colors (A1, A2 and A3) in Food red No. 102 (R102) were identified by LC-MS and NMR analysis. Red dye A1 was azo rubine (AZO), which is not designated as a coloring agent in Japan. Red dye A2 was a structural isomer of Fast Red E (FRE), which is also not designated as a coloring agent in Japan. Red dye A3 was predicted to be an overreaction product of R102, possessing the R102 structural framework. Furthermore, AZO, which was assumed to have been produced by dimerization of a diazonium salt used as a synthetic intermediate of R102, was also identified in Food red No. 2 (R2).