The activity coefficients at infinite dilution, gamma(infinity)(13) for 36 solutes: alkanes. cycloalkanes. alkenes, alkynes, aromatic hydrocarbons, alcohols, thiophene, tetrahydrofuran, ethers, acetone, and water in the ionic liquid 4-methyl-N-butyl-pyridinium bis(trifluoromethylsulfonyl)-imide [bmPY][NTf2] were determined by gas-liquid chromatography at temperatures from 298.15 K to 368.15 K. The partial molar excess enthalpies at infinite dilution values Delta H-1(E,infinity) were calculated from the experimental gamma(infinity)(13) values obtained over the temperature range. The selectivity for different separation problems were calculated from the gamma(infinity)(13) and compared to the literature values for other ionic liquids, N-methyl-2-pyrrolidinone (NMP) and sulfolane. (C) 2009 Published by Elsevier Ltd.