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

A magenta subsidiary colour was isolated from commercial Food Blue No. 1 (B-1; Brilliant Blue FCF). The absorption maximum for this subsidiary colour at 580nm is outside of the range of 614-628nm found for other subsidiary colours and m,m -B-1. On the basis of MS and NMR analyses, the structure of the subsidiary colour was elucidated as the disodium salt of 2-[[4-[Nethyl-N-(3-sulphophenylmethyl)amino]phenyl][4-oxo2,5-cyclohexadienylide acid. HPL C analyses revealed that 24 batches of commercial Food Blue No. 1 (three manufacturers) contain 0.1- 0.8% (average: 0.5% ) of the magenta subsidiary colour.