In this work, the activity coefficients at infinite dilution (gamma(infinity)(13)) for 14 solutes: alkanes, alkenes, an alkyne, cycloalkanes, benzene, and methanol in the ionic liquid 1-methyl-3-octyl-imidazolium diethyleneglycolmonomethylethersulfate were determined by gas + liquid chromatography at the temperatures (288.15, 298.15, and 313.15) K. The ionic liquid had a mass percentage packing greater than 20%. Two columns with different mass percent packing of the ionic liquid were studied at each temperature. The activity coefficient at infinite dilution (gamma(infinity)(13)) for each solute was used to calculate the excess molar enthalpies at infinite dilution (Delta H-m(E infinity)). The selectivity value for the hexane/benzene separation was calculated from the gamma(infinity)(13) and compared to the literature values for other ionic liquids and N-methyl pyrrolidone. Gas + liquid chromatography is a simple, accurate, and reliable method that requires small quantities of the liquid support and solutes. (C) 2005 Elsevier Ltd. All rights reserved.