Indigo carmine

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Indigo carmine
Indigo carmine.svg
IUPAC name
3,3'-dioxo-2,2'-bis-indolyden-5,5'-disulfonic acid disodium salt
Other names
indigotine; 5,5'-indigodisulfonic acid sodium salt
860-22-0 YesY
ChEBI CHEBI:31695 YesY
ChemSpider 4447431 YesY
Jmol interactive 3D Image
PubChem 5284351
UNII D3741U8K7L YesY
Molar mass 466.36 g/mol
Appearance purple solid
Melting point >300 °C (572 °F)
10 g/L (25 °C (77 °F))
ATC code V04CH02
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Indigo carmine, or 5,5'-indigodisulfonic acid sodium salt, also known as indigotine or FD&C Blue #2 is a pH indicator with the chemical formula C16H8N2Na2O8S2. It is approved for use as a food colorant in the United States[1] and in Europe.[2] and has the E number E132.


Indigo Carmine (pH indicator)
below pH 11.4 above pH 13.0
11.4 13.0

Indigo carmine is commonly used as a pH indicator, often in a 0.2% aqueous solution. 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[3] through the conversion to isatin-5-sulfonic acid.[3] This reaction has been shown not to be specific to ozone, however: it also detects superoxide, an important distinction in cell physiology.[4] It is also used as a dye in the manufacturing of capsules.

In obstetric surgery, indigo carmine solutions are sometimes employed to detect amniotic fluid leaks. In urologic surgery, intravenous injection of indigo carmine is often used to highlight portions of the urinary tract. The dye is filtered rapidly by the kidneys from the blood, and colors the urine blue. This enables structures of the urinary tract to be seen in the surgical field, and demonstrate if there is a leak. However, the dye can cause a potentially dangerous increase in blood pressure in some cases.[5]

Health concerns[edit]

Indigo carmine is harmful to the respiratory tract if inhaled. It is also an irritant to the skin and eyes. Proper laboratory cautions (lab coat, gloves, goggles) are advised.

See also[edit]


  1. ^ Summary of Color Additives for Use in United States in Foods, Drugs, Cosmetics, and Medical Devices, United States Food and Drug Administration
  2. ^ Current EU approved additives and their E Numbers, Food Standards Agency, 26 November 2010
  3. ^ a b Takeuchi K, Ibusuki T (March 1989). "Quantitative determination of aqueous-phase ozone by chemiluminescence using indigo-5,5'-disulfonate". Anal. Chem. 61 (6): 619–23. doi:10.1021/ac00181a025. PMID 2729594. 
  4. ^ Kettle AJ, Clark BM, Winterbourn CC (April 2004). "Superoxide converts indigo carmine to isatin sulfonic acid: implications for the hypothesis that neutrophils produce ozone". J. Biol. Chem. 279 (18): 18521–5. doi:10.1074/jbc.M400334200. PMID 14978029. 
  5. ^ Craik, Johnathan Donaldson (January–February 2009). "The Safety of Intravenous Indigo Carmine to Assess Ureteric Patency During Transvaginal Uterosacral Suspension of the Vaginal Vault". Journal of Pelvic Medicine & Surgery 15 (1): 11–15. doi:10.1097/SPV.0b013e3181986ace. Retrieved 18 October 2012.