Acid Orange 7-13C6 (Orange II-13C6) is the 13C-labeled Acid orange 7 (HY-N1442). Acid Orange 7 (Orange II, D&C Orange NO. 4) is an azo dye widely used in the textile, food and cosmetic industries. Acid Orange 7 is mainly used as a colorant by combining with fibers and other substances through azo bonds. Acid Orange 7 has a maximum absorption wavelength at 484-485 nm, and the concentration is measured using a UV-visible spectrophotometer. Acid Orange 7 is difficult to degrade and has a certain degree of toxicity. It is often used to study various sewage treatment technologies and photocatalytic degradation reactions, and to evaluate the removal effects of different treatment methods on organic pollutants[1][2][3].