Waters 2489, Operator'S Manual

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D-8 Solvent Considerations
Solvent degassing methods
This section describes the solvent degassing techniques that will help you to
attain a stable baseline. Degassing your solvent also improves reproducibility
and pump performance.
You can use either of the following methods to degas solvents:
• Sparging with helium
• Vacuum degassing
Sparging
Sparging removes gases from solution by displacing dissolved gases in the
solvent with a less soluble gas, usually helium. Well-sparged solvent improves
pump performance. Helium sparging brings the solvent to a state of
equilibrium, which may be maintained by slow sparging or by keeping a
blanket of helium over the solvent. Blanketing inhibits reabsorption of
atmospheric gases.
Sparging can change the composition of mixed solvents.
Vacuum degassing
The in-line vacuum degasser operates on the principle of Henry’s Law to
remove dissolved gases from the solvent. Henry’s Law states that the mole
fraction of a gas dissolved in liquid is proportional to the partial pressure of
that gas in the vapor phase above the liquid. If the partial pressure of a gas on
the surface of the liquid is reduced, for example, by evacuation, then a
proportional amount of that gas comes out of solution.
Vacuum degassing can change the composition of mixed solvents.
Solvent degassing considerations
Select the most efficient degassing operation for your application. To remove
dissolved gas quickly, consider the following.
Sparging
Helium sparging gives stable baselines and better sensitivity than sonication
in a detector, and prevents reabsorption of atmospheric gases. Use this