Polyethylene oxide (PEO) was purified by a filtration process and fractionation on a chromatographic column. The influence of impurities present in the polymer solutions on the adsorption of PEO 100,000 and PEO 300,000 onto synthesised hematite at pH 3, 6 and 9 was analysed. Both electrokinetical properties (surface charge density and zeta potential) and thickness of the adsorption layer (calculated from viscosity and zeta potential measurements) were also analysed. X-ray fluorescence spectroscopy was used to estimate the quality and quantity of the impurities in the polyethylene oxide solutions. The adsorption amount as well as the shape of the adsorption isotherms of PEO is significantly influenced by impurities. PEO as a non-ionic polymer does not change the surface charge density. Nevertheless, commercial PEO (non-purified) does change the surface charge density as well as shift the point of zero charge because of the presence of various impurities. Those impurities also affect the zeta potential and isoelectric point of the analysed system. The adsorption layer thickness decreases with improvement of the quality of the used polymer solution. © 2005 Elsevier B.V. All rights reserved.