The hydroxyethyl starch purification was performed by means of supercritical and near-critical fluid extraction within single-phase conditions using CO2 and a mixture of CO2-ethanol. Hydroxyethyl starch with concentrations of ethylene glycol in the range of 28,000 to 3000 ppm was successfully purified in a single stage. The intraparticle mass transfer was determined through a hot sphere diffusion model. The values of the effective diffusion coefficients, obtained from the model fitted to experimental data, indicate that the hindrance for ethylene glycol extraction is due to mass transfer limitations attributed to the closed pore structure generated during the crystallization of the solid. In the same sense, the strong interaction between the contaminant and the hydroxyethyl starch at specific points of the surface could also be a detrimental factor. We show that, under these working conditions, most of the contamination can be removed, providing a simple process which saves the high consumptions of deionized water employed in the traditional ultrafiltration. (C) 2014 Elsevier B.V. All rights reserved.