What Is the Biggest Difference Between Traditional Silica‑Based HPLC Phases and Cogent Bidentate C18™ (TYPE‑C™)?
The major difference between traditional Type A/Type B silica‑based HPLC phases and Cogent Bidentate C18™ lies in the chemistry of the silica surface—specifically, the dominance of silicon‑hydride (Si‑H) groups on TYPE‑C™ silica versus the silanol (Si‑OH) groups found on all conventional silica materials.
This fundamental structural difference drives superior performance, broader mode flexibility, and distinctive selectivity options not available with conventional bonded phases.
1. Surface Chemistry: Si‑OH vs. Si‑H
Traditional silica (Type A & B): dominated by Si‑OH
- Contains abundant silanol groups, which are polar, acidic, and highly interactive with analytes
- Can cause undesired secondary interactions
- Limits selectivity and restricts usable chromatographic modes
Cogent TYPE‑C™ silica: dominated by Si‑H
- Surface is overwhelmingly silicon‑hydride (Si‑H) rather than silanols
- Si‑H groups are non‑polar, non‑acidic, and far less interactive
- Enables unique retention mechanisms and dramatically different selectivity
This difference in surface polarity fundamentally changes how analytes interact with the stationary phase.
2. Novel Separation Mechanisms & Selectivity
Unlike traditional C18 phases, Cogent TYPE‑C™ bonded phases—including Bidentate C18™—provide enhanced selectivity flexibility due to the underlying Si‑H surface. The result is new separation mechanisms that allow users to achieve resolutions and elution patterns not possible on classical silica phases.
This expanded selectivity is especially valuable for:
- Polar analytes
- Mixed‑polarity mixtures
- Difficult or co‑eluting compounds on standard RP columns
- Orthogonal method development
3. Multi‑Mode Chromatography on a Single Column
Unlike conventional C18 columns, Cogent Bidentate C18™ can be used in three different chromatographic modes:
- ✔ Normal Phase (NP)
- ✔ Aqueous Normal Phase (ANP)
- ✔ Reversed Phase (RP)
All Cogent TYPE‑C™ phases—including Bidentate C18™—support this multi‑mode versatility because of their unique surface chemistry.
This means one column can replace three, drastically simplifying development workflows and saving time, solvent, and method‑transfer complexity.
4. Practical User Benefits
- Reduced secondary interactions (less tailing, better peak shape)
- Broader mobile‑phase compatibility
- Greater reproducibility due to lower surface polarity variability
- Access to orthogonal selectivity without changing column families
- Ability to retain polar compounds in ANP while still using a C18 ligand
In short, TYPE‑C silica provides chromatographers more capability, more flexibility, and more reliable performance across a wide range of analytes.
