Date: 26-AUGUST-2020 Last Updated: 14-AUGUST-2026
Overview
A common belief in chromatography is that there are few effective alternatives when conventional reversed-phase methods cannot provide sufficient retention for highly polar compounds.
The reality is that HILIC (Hydrophilic Interaction Liquid Chromatography) is one of the most effective approaches for retaining and separating polar analytes. However, not all HILIC columns operate through the same retention mechanisms.
Cogent™ TYPE-C™ Silica columns are HILIC columns designed for the analysis of polar compounds. Unlike traditional HILIC columns based on ordinary silica, TYPE-C™ columns utilize a silica-hydride surface and operate through the Aqueous Normal Phase (ANP) retention mechanism.
As a result, ANP should not be viewed as an alternative to HILIC. Rather, ANP is the mechanism by which Cogent™ TYPE-C™ HILIC columns achieve retention and separation of polar compounds.
HILIC and ANP
HILIC is generally defined as a chromatographic mode used to retain and separate hydrophilic compounds under highly organic mobile phase conditions.
Traditional HILIC columns rely heavily on a water-rich layer that forms on the surface of conventional silica.
TYPE-C™ columns function differently.
The silica-hydride surface used in TYPE-C™ technology produces HILIC retention through the ANP mechanism, allowing polar compounds to be retained without dependence on the extensive hydration layer associated with conventional silica-based HILIC phases.
This distinction contributes to several practical advantages for method development and routine analysis.
Retention of Polar and Ionic Compounds
Many traditional silica-based HILIC columns can exhibit complex ionic interactions due to surface silanol groups.
For certain analytes, these interactions can affect retention, peak shape, reproducibility, and selectivity.
Examples include:
- Strong organic acids
- Sulfonic acids
- Highly polar metabolites
- Charged pharmaceutical compounds
Because TYPE-C™ silica-hydride surfaces do not contain exposed silanol groups, undesired ionic interactions may be reduced for many applications.
This can often result in:
- Improved peak shapes
- Better reproducibility
- More predictable retention behavior
- Reduced dependence on high buffer concentrations
Reduced Buffer Requirements
Many conventional HILIC methods utilize elevated salt concentrations to manage analyte retention and interactions with the water layer present on silica surfaces.
TYPE-C™ columns often require only modest concentrations of volatile additives for successful separations.
Benefits can include:
- Improved LC-MS compatibility
- Reduced source contamination
- Simpler mobile phase preparation
- Easier method transfer
For many methods, low concentrations of volatile additives such as formic acid, acetic acid, or ammonium salts provide effective performance.
Faster Equilibration
One challenge frequently encountered with conventional HILIC methods is equilibration time.
Because retention on traditional silica-based HILIC columns depends heavily on the formation and maintenance of a variable surface water layer, longer equilibration times are often required between runs and gradients.
TYPE-C™ columns operating through the ANP mechanism generally equilibrate much more rapidly.
Advantages include:
- Shorter method cycle times
- Improved retention-time reproducibility
- Faster gradient recovery
- Increased laboratory productivity
For many applications, full equilibration can be achieved significantly faster than with conventional silica-based HILIC columns.
Flexible Selectivity and Method Development
Changing selectivity on conventional HILIC columns often requires testing multiple stationary phases.
TYPE-C™ columns offer considerable flexibility through adjustment of:
- Mobile phase composition
- Buffer concentration
- Organic solvent content
- pH conditions
The Cogent™ Diamond Hydride column is particularly versatile and has demonstrated retention of a broad range of hydrophilic compounds while also providing useful retention for certain hydrophobic analytes.
Dual Retention Capability
A unique characteristic of TYPE-C™ phases is their ability to operate in both:
- HILIC (ANP) mode
- Reversed-phase mode
This dual-retention behavior can be valuable when analyzing samples containing both polar and non-polar compounds.
In some cases, chromatographers can develop multiple successful approaches using the same stationary phase, simply by adjusting mobile phase conditions.
Benefits of TYPE-C™ HILIC Columns
Compared to many traditional silica-based HILIC columns, TYPE-C™ columns may provide:
- Excellent retention of polar compounds
- Rapid equilibration
- Improved reproducibility
- Reduced dependence on high salt concentrations
- Enhanced LC-MS compatibility
- Flexible selectivity options
- HILIC and reversed-phase operating capability
These advantages make TYPE-C™ columns valuable tools for the analysis of challenging polar compounds.
Key Takeaways
- HILIC remains one of the most effective approaches for retaining highly polar compounds.
- Cogent™ TYPE-C™ columns are HILIC columns designed for polar analyte separations.
- TYPE-C™ columns use the Aqueous Normal Phase (ANP) retention mechanism to perform HILIC separations.
- ANP is not an alternative to HILIC but rather the mechanism used by TYPE-C™ HILIC columns.
- TYPE-C™ columns often provide faster equilibration and excellent reproducibility.
- Lower buffer concentrations are frequently sufficient compared to traditional silica-based HILIC methods.
- The dual-retention capabilities of TYPE-C™ phases support both HILIC and reversed-phase method development.
