Indigo carmine

Indigo carmine
IUPAC name

3,3'-dioxo-2,2'-bis-indolyden-5,5'-disulfonic acid disodium salt
Other names

indigotine; 5,5'-indigodisulfonic acid sodium salt
Identifiers
CAS number 860-22-0 Y
PubChem 5284351
ChemSpider 4447431 Y
UNII D3741U8K7L Y
ATC code V04CH02
Jmol-3D images Image 1
Properties
Molecular formula C16H8N2Na2O8S2
Molar mass 466.36
Appearance purple solid
Melting point

>300 °C
Solubility in water 10 g/L (25 °C)
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 USA[1] and the EU[2] and has the E number E132.

Contents

Uses

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

The primary use of Indigo carmine 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. 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, and in obstetrics, Indigo carmine-based dye is used to detect amniotic fluid leaks.

Health concerns

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

References

  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.