Indigo carmine, or 5,5′-indigodisulfonic acid sodium salt, is an organic salt derived from

indigo Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', ...

aromatic sulfonation Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution. Aryl sulfonic acids are used as detergents, dye, and drugs. Stoichiometr ...

, which renders the compound soluble in water. It is approved for use as a food colorant in the U.S and E.U. to produce a

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when ...

color.Summary of Color Additives for Use in United States in Foods, Drugs, Cosmetics, and Medical Devices

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

Current EU approved additives and their E Numbers

Food Standards Agency The Food Standards Agency is a non-ministerial government department of the Government of the United Kingdom. It is responsible for protecting public health in relation to food in England, Wales and Northern Ireland. It is led by a board ap ...

, 26 November 2010 It has the

E number E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

E132. It is also a

pH indicator A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, ...

Uses

Indigo carmine in a 0.2%

aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be r ...

is blue at pH 11.4 and yellow at 13.0. Indigo carmine is also a

redox indicator A redox indicator (also called an oxidation-reduction indicator) is an indicator which undergoes a definite color change at a specific electrode potential. The requirement for fast and reversible color change means that the oxidation-reduction e ...

, turning yellow upon reduction. Another use is as a dissolved

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the l ...

indicator through the conversion to isatin-5-sulfonic acid. This reaction has been shown not to be specific to ozone, however: it also detects

superoxide In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of t ...

, an important distinction in cell physiology. It is also used as a dye in the manufacturing of capsules.

Medical uses

Indigotindisulfonate sodium, sold under the brand name Bludigo, is used as a diagnostic dye during surgical procedures. It is

indicated In medicine, an indication is a valid reason to use a certain test, medication, procedure, or surgery. There can be multiple indications to use a procedure or medication. An indication can commonly be confused with the term diagnosis. A diagnosi ...

for use as a visualization aid in the cystoscopic assessment of the integrity of the

ureter The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...

s in adults following urological and gynecological open, robotic, or endoscopic surgical procedures. It was approved for medical use in the United States in July 2022. In obstetric surgery, indigo carmine solutions are sometimes employed to detect

amniotic fluid The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products between ...

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. Although not absorbed by the cells, indigo carmine stain, sprayed onto regions of interest, highlights the topography of the mucosal surface with its blue coloring. Generally used at a concentration around 0.2%, indigo carmine stain is useful as a screening method for diagnosing minute lesions, to differentiate between benign and malignant lesions, as well as to facilitate application of magnifying endoscopes to observe and analyze the surface structure of a lesion, delineate boundaries of early stage malignant lesions and estimate the invasion depth of cancer. It has been used to diagnose Barrett’s esophagus, evaluate villous atrophy, diagnose and discriminate polypoid and non-polypoid lesions in the colon, and diagnose gastric adenoma and cancer.

References

External links

* {{DEFAULTSORT:Indigo Carmine PH indicators Sulfonates Organic sodium salts Indoles Enones Food colorings Redox indicators E-number additives Acid dyes