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Question:  “What is the difference between HILIC and Normal Phase Chromatography?”

Answer:     HILIC (Hydrophilic Interaction Chromatography) is very similar to normal phase chromatography.  Both chromatographic modes make use of a very polar/hydrophilic stationary phase to retain polar compounds.  Compounds elute in the order of decreasing hydrophobicity. The major differences between HILIC and normal phase chromatography are in both the mobile phase and mechanism of separation.

Normal phase chromatography utilizes a 100% organic solvent while HILIC uses organic mobile phases that are water miscible.  When using a HILIC gradient, increasing proportions of water are used as the elution solvent.  In addition, various salt buffers may be added to the mobile phase in order to keep the analyte in a single ionic form.

HILIC’s mechanism of action is thought to be a mostly liquid to liquid partition created by the formation of a water layer on the surface of the stationary phase.  Separation also occurs by differences in hydrogen bonding and electrostatic forces.

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