The molecule is an organic sodium salt resulting from the formal condensation of indigo carmine (acid form) with two equivalents of sodium hydroxide. It is an indicator at pH 11.5-14, changing from blue to yellow. It has a role as a food colouring, a histological dye and a two-colour indicator. It contains an indigo carmine(2-).
disodium;2-(3-hydroxy-5-sulfonato-1H-indol-2-yl)-3-oxoindole-5-sulfonate