This paper reports activity coefficients at infinite dilution for a series of organic solutes in the ionic liquid 1-hexyl-3-methylirnidazolium nitrate by gas-liquid chromatography at different temperatures between 313.15 and 363.15 K. The contribution of gas-liquid partitioning and interfacial adsorption to the retention mechanism was estimated by changing the loading of ionic liquid in stationary phase, and the influence of different loading of ionic liquid on the experimental values of activity coefficients at infinite dilution was discussed. The partial molar excess enthalpies at infinite dilution and the solubility parameters of ionic liquid were also calculated from the experimental values of activity coefficients at infinite dilution.