Waters 1500-Series, Руководство оператора

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C-10 Solvent Considerations
Changes in the composition, temperature, or pressure of the mobile phase can
lead to outgassing.
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 whose
intermolecular attractive forces are similar to those in the gas (“like dissolves
like”).
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.
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.
Eluent degassing methods
You can degas eluents using any of the following methods:
• In-line vacuum degassing
• Heating
• Vacuum sonication
Vacuum degassing
An in-line vacuum degasser operates on the principle of Henry’s Law to
remove dissolved gases from the solvent. According to Henry’s Law, the mole
fraction of a gas dissolved in a 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.