Activity coefficients at infinite dilution for 19 solutes: alkanes. cycloalkanes, alk-1-enes, alk-1-ynes, benzene and alcohols in the ionic liquid N-butyl-4-methylpyridinium tosylate ([BMPy][TOS]) were determined by gas-liquid chromatography at four temperatures T= (328.15, 333.15, 338.15, and 343.15) K. The partial molar excess enthalpy values at infinite dilution Delta H-1(E.similar to) were calculated from the experimental gamma infinity Values obtained over the temperature range. The selectivity for the hexane/benzene and cyclohexane/benzene separations was calculated from the gamma infinity values and compared to the literature values for other ionic liquids, NMP and sulfolane. (C) 2008 Elsevier B.V. All rights reserved.