Activity coefficients at infinite dilution of various solutes in the ionic liquids [MMIM]+[CH3SO4]−, [MMIM]+[CH3OC2H4SO4]−, [MMIM]+[(CH3)2PO4]−, [C5H5NC2H5]+[(CF3SO2)2N]− and [C5H5NH]+[C2H5OC2H4OSO3]−

Infinite dilution activity coefficients γ i ∞ have been measured for various solutes (alkanes, alkenes, cycloalkanes, cycloalkenes, aromatics, alcohols, ketones, esters, ethers, and water) in the five ionic liquids 1-methyl-3-methyl-imidazolium methylsulfate [MMIM]+[CH3SO4]−, 1-methyl-3-methyl-imidazolium methoxyethylsulfate [MMIM]+[CH3OC2H4SO4]−, 1-methyl-3-methyl-imidazolium dimethylphosphate [MMIM]+[(CH3)2PO4]−, N-ethylpyridinium bis(trifluoromethylsulfonyl) imide [C5H5NC2H5]+[(CF3SO2)2N]−, and pyridiniumethoxyethylsulfate [C5H5NH]+[C2H5OC2H4OSO3]− in the temperature range from 303.15 to 373.15 K. Additionally, densities of the investigated ionic liquids were measured in the temperature range from 293.15 to 353.15 K. all available γ i ∞ -data, the selectivities S i j ∞ = γ i ∞ / γ j ∞ and the capacities k i ∞ = 1 / γ i ∞ at infinite dilution were determined for different separation problems not only for ionic liquids, but also N-methyl-2-pyrrolidone (NMP) and ethylene glycol.