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What are the main differences between HILIC columns and a Cogent TYPE-C™ HPLC columns?

Reference Number: AA-00206 Created: 03/30/2012 04:24 PM Last Updated: 01/21/2017 01:10 PM

There are many differences between the many HILIC columns and Cogent TYPE-C™ columns but for the sake of brevity, I will only address the main differences.

The Cogent TYPE-C silica columns perform similarly to HILIC columns as far as polar compound elution order is concerned (when using higher than 70% organic composition of the mobile phase) and both columns perform separations that are based on variations of normal phase chromatography with one being called “HILIC” and the other called “Aqueous Normal Phase” (ANP). The HILIC stationary phase is typically more polar than the TYPE-C™ phases which are relatively non polar. HILIC columns will retain polar compounds that cannot be retained by reversed phase columns and so will the Cogent columns. The HILIC columns will not retain non-polar compounds while one of the biggest advantages of the Cogent columns is the ability to separate polar and many non-polar compounds in the same isocratic run.

With HILIC columns, polar compounds partition into and out of the hydration shell created by adsorbed water on the silica surface (see below). As the acetonitrile concentration increases the water layer decreases and the charged polar analytes are retained by the combination of cation exchange with the silanols under the water layer and the partitioning effect. The combination of these two mechanisms retains polar compounds in HILIC mode. For reproducibility, this water shell thickness and salt content must be managed by the chromatographer between gradient runs.

On Cogent TYPE-C™ columns, the charged polar compounds elute in a similar order as on HILIC columns as stated above; however non-polar compounds will be retained at the same time by the non polar phase of the Cogent columns which has a small hydrocarbon bonded phase on a silica hydride surface. Since there are virtually no silanols to speak of on these columns, the polar compounds are retained more by the adsorptive character of the silica-hydride and silica backbone which are now more available to the analytes due to a very shallow solvent layer which is the organic component such as acetonitrile, methanol etc. when at higher concentrations of the organic component. Because of the lack of a “hydration shell” at high organic content due the weak association with water of the Cogent columns (see below), the phase will equilibrate and change more rapidly with all silica hydride based columns than with HILIC columns. This is an advantage when rapid gradients are desired.

HILIC columns can only perform HILIC which is similar but different from ANP while Cogent TYPE-C™ columns can perform ANP, Reversed Phase and traditional Normal Phase using completely non-polar solvents such as hexane. There is no hysteresis when changing between these modes making this column extremely efficient. There are other features and benefits of the very unique column and they are addressed in other Knowledge Base articles.


       HILIC Stationary Phases have a water shell                    Cogent TYPE-C Silica has no water shell

See also: Comparison of the efficiency in ANP vs. HILIC.
See also: Wikipedia definition of ANP
See also: ANP v. HILIC Advantages

  
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