Indigo carmine is a reduction indicator, and methylene blue is a chemical indicator.
Indigo carmine is mainly used as oxidant reduction indicator and biological dye. Soluble in water, insoluble in ethanol. Methylene blue is also called methylene blue and methylene blue. Methylene blue is used as a chemical indicator, dye, biological stain, and pharmaceutical use.
In the presence of concentrated sulfuric acid, indigo carmine loses one molecule of water and condenses into a colorless matrix. It is oxidized into triarylmethane pigment with manganese dioxide in a weak acid solution. The aqueous solution of methylene blue is blue in an oxidizing environment, but will be reduced to a colorless state when exposed to reducing agents such as zinc and ammonia. At high concentrations, methylene blue directly oxidizes hemoglobin to methemoglobin.