Indigo carmine or 55′-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 and the EU and has the E number E132.
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IUPAC name
33'-dioxo-22'-bis-indolyden-55'-disulfonic acid disodium salt
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