Waters 2998, Обзор и руководство по обслуживанию

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December 5, 2017, 715004753 Rev. B
Page 88
C.7.1.1 Effects of intermolecular forces
Nonpolar gases (N
2
, O
2
, CO
2
, He) are more soluble in nonpolar solvents than in polar solvents.
Generally, a gas is most soluble in a solvent with intermolecular attractive forces similar to those in
the gas (like dissolves like).
C.7.1.2 Effects of temperature
Temperature affects the solubility of gases. If the heat of solution is exothermic, the solubility of the
gas decreases when you heat the solvent. If the heat of solution is endothermic, the solubility
increases when you heat the solvent. For example, the solubility of He in H
2
O decreases with an
increase in temperature, but the solubility of He in benzene increases with an increase in
temperature.
C.7.1.3 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.
C.8 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
C.8.1 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.
C.8.2 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.