It is reported data concerning the thermodynamic properties of organic mixtures in pyrrolidinium based DES with ethylene glycol at different temperatures ranging from T = 313.15 to 343.15 K. The infinite dilution activity coefficients (IDACs) for 32 various organic solutes (e.g., alkanes, alkenes, alkynes, aromatics, cycloalkanes, cycloalkenes, alcohols, and ketones) as part of the limiting thermodynamic properties were studied using Gas Liquid Chromatography (GLC). The excess thermodynamic properties (enthalpies, entropies, and Gibbs free energies) were subsequently calculated from the experimental infinite dilution activity coefficients. Moreover, the values of the selectivities and capacities at infinite dilution were determined from the experimental infinite dilution activity coefficients achieved at the fixed experimental temperature, T = 313.15 K. The obtained selectivity and capacity values were compared to those found in the literature. Lastly, the results of the investigated [[EMPYR]Br + EG] DES in a molar ratio of 1:4 proved that this investigated system could be utilized for all the selected separation problems: benzene/toluene, cyclohexane/benzene, acetone/ethanol, and n-butanol/MEK.