C-8 Solvent Considerations
temperature, but the solubility of He in benzene increases with an increase in
temperature.
Effects of partial pressure
The mass of gas dissolved in a given volume of solvent is proportional to the
partial pressure of the gas in the vapor phase of the solvent. If you decrease
the partial pressure of the gas, the amount of that gas in solution also
decreases.
Solvent degassing methods
This section describes the solvent degassing techniques that will help you
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 can be maintained by slow sparging or by keeping a
blanket of helium over the solvent. Blanketing inhibits resorption 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.
To Next Page
Loading...
