Indigo carmine
（重定向自Indigotine）
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 and in Europe. and has the E number E132.