Nanofiltration (NF) can be used to isolate nonvolatile compounds from solutions containing ionic liquids (IL). This was shown for the mixtures bromophenol blue/IL and lactose/IL. In both cases the product was rejected while the ionic liquid permeated. Alternatively, the rejection of the ionic liquid is possible as well. Such separations are possible because nanofiltration membranes are selective towards size and charge of the components.