Any polar chromatographic surface can be used for HILIC separations. Even non-polar bonded silicas have been used with extremely high organic solvent composition, when the silica used for the chromatographic media was particularly polar. With that exception, HILIC phases can be grouped into five categories of neutral polar or ionic surfaces: * simple unbonded silica silanol or diol bonded phases * amino or anionic bonded phases * amide bonded phases * cationic bonded phases * zwitterionic bonded phases