Indigo carmine, is a water soluble organic dye derived from indigo by aromatic sulfonation. It is approved for use as a food colorant in the United States and European Union to produce a blue color. It has the E number E132.
A 0.2% aqueous solution of Indigo carmine in used as a pH indicator. It is blue at pH 11.4 and yellow at 13.0. Indigo carmine is also a redox indicator, turning yellow upon reduction. Another use is as a dissolved ozone indicator.
Some applications include food colorant, surgical stain, biological stain,

EC Number:212-728-8
CAS Number: 860-22-0
Molecular Weight: 466.35
Color Index Number:73015