This International Standard specifies a method for the determination of the polyethylene glycol (PEG) content in aromatic and aliphatic non-ionic surface active agents of the type R-(O-C2H4) n OH; where n is the mean ethylene oxide (EO) value. It is applicable to all ethoxylated products soluble in methanol or methanol/water mixture. This method applies to PEG concentrations as mass fraction greater than or equal to 0,1 %. This International Standard is not applicable to PEG whose molar mass is lower than 400 g/mol. Monomeric ethylene glycol, diethylene glycol, triethylene glycol, and glycerol are not detected.