Working with Plasma Samples on Cogent TYPE‑C™ Columns – Best Practices for Cleaning and Mobile Phase Selection
Plasma and other biological matrices present unique challenges in HPLC and LC‑MS due to their high protein, lipid, and phospholipid content. These materials can accumulate on the column surface, causing retention shifts, peak distortion, rising backpressure, and shortened column lifetime. When using Cogent TYPE‑C™ silica columns, proper washing and solvent selection are essential to maintain performance and reproducibility.
This guide outlines practical recommendations for column care and mobile phase selection when analyzing plasma extracts.
Why Plasma Samples Require Special Care
Plasma contains:
- Proteins
- Lipids
- Fatty acids
- Phospholipids
- Endogenous metabolites
These components can adsorb to the stationary phase, causing:
- Reduced retention over time
- Peak tailing or splitting
- Elevated baseline noise
- Clogging and pressure increase
Appropriate solvent strategies help mitigate these issues.
Recommended Column‑Cleaning Solvent Between Injections
To keep TYPE‑C™ columns clean during plasma analysis:
Use a 50:50 methanol / DI water mixture
- Apply at 0.5 mL/min
- Flush for 20–30 minutes on a 4.6 mm × 250 mm column
This solvent composition effectively removes proteins and hydrophobic residues without damaging the TYPE‑C™ silica surface.
Recommended A Solvent for LC‑MS with Biological Samples
When running LC‑MS methods involving plasma extract samples:
Use 50:50 methanol / DI water as Solvent A
- Helps continuously clean the column between injections
- Maintains strong ANP compatibility with TYPE‑C™ phases
This is especially important because biological matrices introduce contaminants that accumulate gradually with each injection.
Special Case: Lipid‑Rich Plasma Samples
Some plasma samples—particularly those with high phospholipid or triglyceride levels—require more aggressive cleaning.
Use 50:50 DI water / IPA (isopropanol) as Solvent A
- IPA is more effective than methanol at solubilizing lipophilic residues
- Prevents long‑term buildup of lipid contaminants
This modification keeps the column running clean and reduces the chance of unexpected retention shifts caused by lipid fouling.
Conclusion
Plasma extracts demand stricter column maintenance due to their complex and contamination‑prone nature. Using 50:50 methanol / DI water for routine column washing and as an A solvent provides consistent performance for most plasma samples. For more lipid‑rich matrices, switching to 50:50 DI water / IPA gives superior cleanup and extends column life.
These strategies help ensure robust, reproducible chromatography on Cogent TYPE‑C™ columns in demanding LC‑MS workflows.
