Physical data concerning the absorption kinetics like the diffusion coefficients are important values for designing an economically working gas separation processes. Considering ionic liquids, which emerged in recent years as interesting alternative solvent media for versatile industrial purposes, usually only solubility data for gases are available if at all. Therefore in order to gain additional information such as diffusion coefficients of gases in ionic liquids, we established an efficient and easily assembled set-up based on time-resolved FTIR measurements. Applying this methodology, the diffusion coefficient of carbon dioxide in 1-ethyl-3-methyl-imidizolium bis[(trifluoromethyl) sulfonyl]amide (EMIM NTf2) was determined at a temperature of 303 K. (C) 2011 Elsevier Ltd. All rights reserved.