Abstract On separate test portions the following determinations are carried out: measurement of the apparent pH in methanolic medium; determination of the water content; determination of the distribution of primary, secondary and tertiary amines contents; determination of oxyethylene groups content; determination of sulphated ash. Furthermore an aqueous or methanolic solution of a test portion is prepared and the free polyethylene glycols are isolated. On the separated polyethylene glycols the absence of nitrogen is verified and their relative molecular mass is determined.