Background: The retention mechanisms of hydrophilic interaction liquid chromatography
(HILIC) have been reported as inconclusive and of mixed mode, and have not been explained
quantitatively. Packing materials used in HILIC are bare silica gel, polar bonded-silica gels, and
ion-exchangers. The chromatography is performed in aqueous solution. Under such condition, the
stability of these packing materials is not guaranteed by manufacturers. The fundamental problem
associated with such discussions is the lack of definition of experimental conditions, which led to
Objective: To define the experimental conditions, to clarify the differences of HILIC from other
liquid chromatography techniques, and to quantitatively explain HILIC retention mechanisms.
Method: Molecular interaction (MI) between an analyte and a simple model phase was quantitatively
analyzed in silico in terms of MI energy value difference. MI between an analyte and a solvent
molecule was also studied. An analyte was inserted between the model phase and the solvent
molecule, and the movement of the analyte was analyzed in terms of the strength of MI energy values.
Results: The analyte moved toward the favorite site based on van der Waals force in reversedphase
liquid chromatography, hydrogen bonding in HILIC, and electrostatic interaction in ionexchange
Conclusion: For explaining the retention mechanism in HILIC, the experimental condition should
be defined, and not be mixed with other liquid chromatographic conditions based on the properties
of analytes and packing materials. The HILIC technique described herein is aqueous HILIC, while
normal-phase liquid chromatography should be non-aqueous HILIC. Ion-exchange should be
clearly classified as an independent liquid chromatographic method.