Indigo carmine is an organic salt derived from indigo by sulfonation, which renders the compound soluble in water. It is approved for use as a food colorant. It is also a pH indicator.
Indigo Carmine (IC), commonly known as acid blue 74 or food blue 1 or FD and C blue 2 is a blue synthetic dye. It is used as a redox indicator in analytical chemistry and as a microscopic stain in biology. IC is also employed as a photometric detector. IC is a highly toxic.