This standard specifies a method for the analysis of two quaternary ammonium salts, didecyldimethylammonium chloride (DDAC) and dodecylbenzyldimethylammonium chloride (BAC), in ammonia (amine) soluble quaternary ammonium copper (ACQ) preservative wood. It is suitable for the detection of these two quaternary ammonium salts in ACQ preservative wood. The standard uses the two-phase Titrimetric method, which is analyzed by using micro-Burette, Glass measuringflask, ultrasonic water bath and other instruments, combined with acid blue-1 and Miscellaneous reagent. The method provides specific reagent preparation and analysis steps to ensure the accurate determination of quaternary ammonium salt content in preservative wood.