The activity coefficient at infinite dilution for 47 selected organic solutes in 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) ionic liquid (IL) was determined at 303.15 K to 343.15 K through inverse gas chromatography (IGC). The partial molar excess enthalpy, entropy, Gibbs free energy at infinite dilution, and Hildebrand solubility parameters were obtained from the values of activity coefficient at infinite dilution. The selectivity and capacity of heptane/thiophene, heptane/benzene and benzene/thiophene separation problems were also calculated based on the activity coefficient at infinite dilution values. The selectivity of three separation problems of [AMIM]Cl was 85.36, 30.65 and 2.79, which indicated that [AMIM]Cl is an ideal solvent for the separation of heptane/thiophene.