Okay, I know I asked this before (a while ago), except I lost the link to my original question and the answer to it...
What property of liquids and solids is crucial in chromatography?
1 answer
The main one is the solubility of the compounds to be separate in the mobile and stationary phases. Of course, that involves the ionic/covalent character of the solvent as well as the stationary phase and the compounds themselves.