GB/T 743-2003 "Pulp—Determination of ether soluble substances" specifies the method for determining ether soluble substances in pulp, applicable to all types of pulp. The method employs the Soxhlet extraction technique, where a pulp sample is continuously extracted with ether. After evaporating the ether, the residue is dried and weighed, and the content of soluble substances is calculated as the mass ratio of the residue to the oven-dry pulp sample. The standard defines extraction time, temperature, and operational procedures to evaluate the content of ether-extractable, fat-soluble substances in pulp.