The Cogent Silica-C™ HPLC Column is a TYPE-C™ silica hydride stationary phase designed primarily for Organic Normal Phase (ONP) chromatography. Unlike conventional silica columns, Cogent Silica-C offers the advantages of silica hydride technology while maintaining the selectivity required for many normal phase applications. It is particularly useful for moderately polar compounds and separations that benefit from traditional normal phase retention mechanisms.
Although Silica-C can operate in HILIC mode and has limited use in reversed-phase chromatography, its primary strength is Organic Normal Phase (ONP) separations.
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Choosing the Appropriate Separation Mode
Organic Normal Phase (ONP) - Recommended
Organic Normal Phase is the preferred operating mode for Cogent Silica-C.
Typical Applications
- Substituted phenols
- Moderately polar compounds
- Isomer separations
- Organic synthesis products
- Specialty normal phase methods
Advantages
- Similar Traditional normal phase selectivity
- Unique silica hydride surface chemistry
- No need to completely dry mobile phases
- Simplified transitions from RP methods
Increasing Retention in ONP
To increase retention:
- Increase the percentage of weak solvent (typically hexane).
- Decrease the percentage of strong solvent.
HILIC (Limited Applications)
Cogent Silica-C can be used in HILIC mode, although more specialized TYPE-C phases are often preferred.
For dedicated HILIC applications consider:
- Cogent Diamond Hydride™
- Cogent Amide™
- Cogent Diol™
- Cogent UDC-Cholesterol™
Increasing Retention in HILIC
To increase retention:
- Increase organic solvent content.
- Reduce aqueous content.
Reversed-Phase (Limited Applications)
Because Silica-C has only slight hydrophobic character, reversed-phase applications are generally limited.
For most routine RP methods consider:
- Cogent Bidentate C18™
- Cogent Bidentate C8™
- Cogent Phenyl Hydride™
- Cogent UDC-Cholesterol™
Before Using the Column
Transitioning from RP to ONP
One advantage of Silica-C is that complete solvent drying is generally not required.
Recommended transition procedure:
- Pump 100% methanol for approximately 15 minutes at 1.0 mL/min.
- Follow with 100% methylene chloride for approximately 15 minutes.
- Equilibrate using the desired ONP mobile phase.
Unlike conventional silica columns, complete removal of residual water is typically unnecessary.
General Preparation
Before installation:
- Purge all solvent lines of previous mobile phases.
- Purge the injector system.
- Use HPLC-grade solvents only.
- Degas solvents before use.
- Prepare buffers fresh daily.
Startup Instructions
Initial Conditioning
- Install the column according to standard laboratory practices.
- Verify all fittings and tubing connections.
- Condition the column with a 50:50 organic solvent/water mixture containing any planned mobile-phase additives.
- Equilibrate for approximately 30 minutes.
- Transition to the desired operating mode and mobile-phase conditions.
Column Protection
When working with aggressive matrices:
- Use a guard column whenever possible.
- Use inline filters whenever possible.
- Replace protection devices routinely.
Related Resource
Organic - Normal Phase Method Development
Recommended Solvents
Weak Solvents
Typically:
- Hexane
Strong Solvents
Common choices include:
- Ethyl acetate
- Methylene chloride
- Chloroform
- Propanol
Simple Samples
For samples containing a limited number of analytes:
Start with:
- 50% strong solvent
- 50% weak solvent
To increase retention:
- Increase weak solvent in approximately 10% increments.
Complex Samples
Suggested scouting gradient:
- 90% hexane
- To 20% hexane
- Over approximately 10 minutes
Optimize based on retention and resolution requirements.
Important Benefit
For Silica-C ONP methods: It is typically not necessary to completely dry mobile-phase solvents before use.
HILIC Method Development
Although not the primary use of the phase, Silica-C can function in HILIC mode. For most polar compound analyses, alternative TYPE-C phases generally provide superior retention and selectivity.
Recommended alternatives:
- Cogent Diamond Hydride™
- Cogent Amide™
- Cogent Diol™
- Cogent Phenyl Hydride™
Reversed-Phase Method Development
Because Silica-C has only limited hydrophobic retention:
- RP use should generally be restricted to specialized applications.
- Dedicated RP phases usually provide better performance.
Recommended alternatives:
- Cogent Bidentate C18™
- Cogent Bidentate C8™
- Cogent Phenyl Hydride™
- Cogent UDC-Cholesterol™
Troubleshooting Common Problems
Most chromatographic issues are caused by:
- Inadequate equilibration
- Incorrect solvent selection
- Contaminated mobile phases
- Improper solvent transitions
- Dirty sample matrices
- Sample overload
- Failing fittings or tubing
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Storage Instructions
When analysis is complete:
- Flush the column with approximately 90:10 weak solvent/strong solvent mixture.
- Allow all system pressure to return to zero.
- Disconnect and cap the column for storage.
Important
Never disconnect a column while pressure remains in the system. Pressure shock can damage both hardware and stationary phase performance.
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Best Practices Summary
- Use Silica-C primarily for Organic Normal Phase chromatography.
- Use HPLC-grade solvents only.
- Degas all solvents.
- Prepare buffers fresh daily.
- Allow adequate equilibration.
- Use hexane-based mobile phases for ONP methods.
- Increase weak solvent to increase retention in ONP.
- Use filters and guard columns when appropriate.
- Store in approximately 90:10 weak solvent/strong solvent mixture.
- Remove all pressure before disconnecting the column.