This product adopts methylene blue spectrophotometry. The anionic surfactant in the sample reacts with methylene blue to form blue salts. The intensity of the color is proportional to the concentration of the anionic surfactant, which can be calculated according to the color-developing photometric detection absorbance value. Concentration value of anionic surfactant. The instrument is based on the national standard or industry standard and has the characteristics of simple operation, a high degree of automation, easy maintenance, and low cost of consumables.