hydrophillic - "water-loving"; refers both to stationary phases that are compatible with water and to water-soluble molecules in general. Most columns used to separate proteins are hydrophilic in nature and should not sorb or denature protein in the aqueous environment.

hydrophobic - "water-hating"; refers both to stationary phases that are not compatible with water and to molecules in general that have little affinity for water. Hydrophobic molecules have few polar functional groups; most are hydrocarbons or have high hydrocarbon content.

hydrophobic interaction - more rigorously called dispersive interaction. Intermolecular interaction based on the Van-der-Waals forces, very weak.

See also surface interactions.

hydrophobic interaction chromatography - a technique in which reversed-phase packings are used to separate molecules by virtue of the interactions between their hydrophobic moieties and the hydrophobic sites on the surface. High salt concentrations are used in the mobile phase; separations are effected by changing the salt concentration. The technique is analogous to "salting out" molecules from solution. Gradients are run by decreasing the salt concentration over time.