The influence of impurities present in polymer solutions on stability of the suspension of PEO 100 000 with commercial silica was analysed. Stability was measured indirectly, with absorbance measurements of silica and polyethylene oxide suspensions. A XRF method was used to estimate the quality and quantity of impurities in polyethylene oxide solutions. Impurities left after the polymerisation process, present in polymer solutions can adsorb competitively with macromolecules of the polymer. As a result of that, they block active centres on the surface of the adsorbent thus leaving less surface available for polymer molecules. Purification process is conducted in order to improve the quality of analysed polymer material. Polyethylene oxides used in the presented research were purified by filtration process and fractionation on chromatographic column. Overall, four different samples of PEO were used: commercial of low quality, commercial of high quality, filtrated and fractionated. The stability of silica is greatly influenced by the presence of polymer of different purities. Silica without adsorbed polymer is stable in the whole period of analysis. An addition of polymer firstly stabilises the suspension but after some time the suspension is suddenly destabilised. The times of stabilisation and destabilisation of the suspensions are different for polymer samples of different purities. It is greatly dependent on the content of impurities and polydispersity index of a polymer.