Introduction
Simple sugars are among the most challenging compounds to separate by HPLC because they are highly polar, structurally similar, and often exhibit limited UV absorption. Achieving adequate retention and selectivity frequently requires optimization of both the stationary phase and mobile phase chemistry.
One additive that has been used successfully in some HILIC methods for carbohydrate analysis is triethylamine (TEA). When used appropriately with Cogent™ TYPE-C™ columns, TEA may improve chromatographic performance for certain sugar separations by influencing analyte-stationary phase interactions and peak shape.
However, TEA is not a universally preferred additive and should be selected with an understanding of both its benefits and limitations.
Why TEA Is Used in Sugar Separations
Triethylamine is an organic base commonly employed in chromatography to:
- Modify mobile phase pH
- Improve peak symmetry
- Alter selectivity
- Reduce unwanted secondary interactions
For simple sugars and other highly polar compounds, TEA may help produce:
- Sharper peaks
- Improved resolution
- Better chromatographic efficiency
- More reproducible integration
The resulting changes in selectivity can sometimes provide separations that are difficult to achieve using standard acidic mobile phases alone.
Recommended TEA Concentrations
When evaluating TEA during method development, relatively low concentrations are generally recommended.
Typical starting levels are:
- 0.01%
- 0.05%
- Up to approximately 0.1%
Higher concentrations are generally unnecessary and may complicate both chromatography and system maintenance.
For most applications, TEA concentration should remain at or below 0.1%.
How TEA Influences Chromatography
Although the exact chromatographic behavior depends on the analytes and method conditions, TEA is believed to influence retention through modification of interactions occurring at the stationary phase surface.
Potential effects include:
- Improved peak symmetry
- Reduced tailing
- Altered selectivity
- Enhanced resolution of structurally similar compounds
For carbohydrate analyses, even small selectivity changes can significantly improve separation quality.
Alternative Additives for HILIC Methods
While TEA may be effective for some sugar separations, many routine HILIC methods utilize more conventional additives.
A common alternative is:
Ammonium Acetate
Benefits include:
- Near-neutral mobile phase conditions
- Good retention of many polar compounds
- Compatibility with LC-MS detection
- Simple mobile phase preparation
Ammonium acetate is often preferred when ionizable compounds need to remain in their charged state during analysis.
LC-MS Considerations
TEA is generally less attractive for LC-MS applications than volatile additives such as:
- Formic acid
- Acetic acid
- Ammonium acetate
- Ammonium formate
When LC-MS compatibility is required, method developers should carefully evaluate the impact of TEA on:
- Sensitivity
- Signal stability
- Source cleanliness
- Long-term instrument maintenance
In many LC-MS workflows, volatile ammonium-based additives remain the preferred choice.
Important Column Usage Considerations
A significant consideration when using TEA is its persistence within the chromatographic system and column. Internal studies have suggested that TEA can be difficult to remove completely once introduced into a column. Because of this, laboratories often dedicate a column specifically to TEA-containing methods.
This approach may help:
- Preserve method reproducibility
- Prevent unexpected retention shifts
- Reduce variability when switching between applications
Method developers should take this into account before introducing TEA into a routinely used column.
Recommended Method Development Approach
When developing sugar separations:
Start with Conventional Additives
Evaluate:
- Formic acid
- Acetic acid
- Ammonium acetate
- Ammonium formate
Evaluate TEA if Needed
When resolution or peak shape remains unsatisfactory, test low levels of TEA.
Compare Critical Performance Parameters
Monitor:
- Resolution
- Selectivity
- Peak shape
- Reproducibility
- Detector response
Consider Column Dedication
If TEA provides substantial benefits, consider reserving the column for TEA-based methods.
Key Takeaways
- TEA can improve peak shape and selectivity for certain simple sugar separations on Cogent™ TYPE-C™ columns.
- Concentrations should generally remain at or below 0.1%.
- TEA may alter stationary phase interactions in ways that improve chromatographic performance.
- Ammonium acetate remains a popular alternative because of its LC-MS compatibility and near-neutral pH behavior.
- TEA may be difficult to remove completely once introduced into a column.
- Dedicated columns are often recommended for methods that routinely use TEA.
- TEA should be evaluated as a method-development tool when conventional additives do not provide adequate separation.
