Isolation, identification and determination of a magenta subsidiary colourin Food Blue No. 1 (Brilliant Blue FCF)

A magenta subsidiary colour was isolated from commercial Food Blue No, I (B -1; Brilliant Blue FCF). The absorption maximum for this subsidiary colour at 580 nm is outside of the range of 614-628 nm found for other subsidiary colours and m,m-B-l. On the basis of MS and NMR analyses, the structure of the subsidiary colour was elucidated as the disodium salt of 2-[[4-[N-ethyl -N-(3-sulphophenylmethyl)amino]phenyl][4-oxo-2,5-cyclohexadienylidene]methy l]benzenesulphonic acid. HPLC analyses revealed that 24 batches of commerci al Food Blue No. I (three manufacturers) contain 0.1-0.8% (average: 0.5%) o f the magenta subsidiary colour.