D-6 Eluent Considerations
• Reproducible injection volumes for quantitation
• Stable pump operation
This section presents information on the solubility of gases, eluent degassing
methods, and eluent degassing considerations.
Gas solubility
The amount of gas that can dissolve in a given volume of liquid 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
lead to outgassing.
Effects of intermolecular forces
Nonpolar gases (N
2
, O
2
, CO
2
, He) are more soluble in nonpolar eluents than in
polar eluents. Generally, a gas is most soluble in an eluent with
intermolecular attractive forces similar to those in the gas (“like dissolves
like”).
Effects of temperature
If the heat of solution is exothermic, the solubility of the gas decreases when
you heat the eluent. If the heat of solution is endothermic, the solubility of the
gas increases when you heat the eluent. For example, the solubility of helium
in water decreases with an increase in temperature, but the solubility of
helium in benzene increases with an increase in temperature.
Effects of partial pressure
The mass of gas dissolved in a given volume of eluent is proportional to the
partial pressure of the gas in contact with the vapor phase of the eluent. If you
decrease the partial pressure of the gas, the amount of that gas in solution
also decreases.
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