GB/T 6365-2006 stipulates that the Titrimetric method is used to determine the free alkalinity or free acidity of surfactants, which is suitable for all kinds of surfactant products. When measuring free alkalinity, choose the appropriate acid standard solution for titration; when measuring free acidity, use the alkali standard solution for titration. The standard specifies the required instruments, such as Burette, etc., and specifies the preparation and calibration method of the standard solution. Detailed description of sample preparation and titration operation process, including Mixing method in the titration process, titration speed control and endpoint judgment basis. According to this standard, the free acid alkalinity of surfactants can be accurately determined, providing key data support for product quality control and formulation optimization.