GB/T 21883-2008 "Determination of Fluorescence intensity of fluorescent whitening agents", specifies the determination method of fluorescence intensity of fluorescent whitening agents. The standard clarifies the test principle, standardizes the requirements of equipment and reagent materials, details the sample preparation, measurement steps and result calculation process, and clarifies the key details and influencing factors in the measurement process. It provides a unified technical specification for the accurate determination of fluorescence intensity of fluorescent whitening agents, and helps the quality control and performance evaluation of fluorescent whitening agent products.