Waters 2489, Operator'S Manual

Page: 213 / 234

Mobile phase solvent degassing D-7
• stable pump operation.
Gas solubility
Only a finite amount of gas can be dissolved in a given volume of liquid. This
amount depends on
• the chemical affinity of the gas for the liquid.
• the temperature of the liquid.
• the pressure applied to the liquid.
Changes in the composition, temperature, or pressure of the mobile phase can
all 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 with
intermolecular attractive forces 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.