Why are reversed-phase separations done with only three organic solvents?
The short answer is that these are the three solvents that are the most different from one another and still miscible with water in all proportions. If we need selectivity which is “less different”, we can always obtain it by blending two (or all three) of the “most different” solvents. Need discussion here of strength, selectivity, and solvent characterization.
