Indigo Carmine is a dark blue to purple powder. The primary use is 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.

Biological Dye

C.I.73015
Minimum Assay: >80%
Molecular Formula C16H8N2Na2O8S2
Molecular Weight 466.36 g/mol
Loss on drying: 5.0% maximum
Visual Transition Interval: From pH 11.5 (Blue) To pH 14.0 (yellow)
Aqueous solubility: 1 g in 100 ml at 25°C
Subsidiary dyes, excluding disodium
3,3-dioxo 2,2’-bi-indolylidine-5,7’-disulfonate: 1.00% maximum
Dye intermediates: < 0.50%
Lead: <0.001%
Sulfur: 13.0 – 14.0%


Hazard Phrases: Harmful if swallowed.



Cas No: 860-22-0
Einecs No: 212-728-8