The method relies on the facts that both non-ionic adducts and polyethylene glycols are soluble in sodium chloride solution, but one is soluble in ethyl acetate whereas the other is not. Separation of the polyethylene glycols and the adducts is, therefore, possible by the following methods: Dissolution of the sample in ethyl acetate and extraction of polyethylene glycols by sodium chloride solution. Extraction of the polyethylene glycols isolated in the sodium chloride solution with chloroform, removal of the solvent and weighing of the residue. Evaporation of the ethyl acetate solution which contains the adducts and weighing of the residue.