GB/T 31414-2015 "Waterborne coatings—Determination of surfactants—Alkylphenol ethoxylates" specifies a method for determining the content of alkylphenol ethoxylates (APEO) and alkylphenol (AP) in waterborne coatings and raw materials using high-performance liquid chromatography (HPLC). The sample is extracted with a methanol-water solution, subjected to centrifugal separation and Soxhlet extraction, and then analyzed by normal-phase and reversed-phase HPLC to determine the average ethoxylation number and content, with quantification performed using the external standard method. The detection process requires instruments such as an HPLC system equipped with an ultraviolet detector, a centrifuge with a rotation speed of ≥20,000 rpm, a Soxhlet extraction apparatus, a rotary evaporator, and a solid-phase extraction device. This method is applicable for quality control and testing of related products.