Reproducibility and Solvent Degassing 170
C
• Increasing the temperature of the gas/liquid solution affects the percentage of gas in
the solution.
If the heat of solution results in an exothermic reaction, the percentage of gas in solution is
reduced. If the reaction is endothermic, the percentage increases. 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 the pressure of the gas decreases,
the amount of that gas in solution also decreases.
Effects of Dissolved Oxygen
Dissolved oxygen affects detector performance in several ways. Oxygen dissolved in
solvents may form a UV-absorbing complex. The amount of complex formed varies with
the solvent. The effect is particularly evident in the solvents methanol and THF. Dissolved
O
2
has a minimal effect on the absolute responsivity of a UV detector, but can cause:
• Increased noise because less light reaches the detector
• Increased temperature response
• Baseline drift
• Reduced dynamic range (range of absorbance)
Changes in the characteristics of a solvent may adversely affect the precision and
accuracy of the solvent delivery pump. This may cause variations in retention time and
peak height or area.
C.2.2 Solvent Degassing Methods
There are four main methods used to degas solvents:
• Sparging with a less-soluble gas
• Heating
• Reducing pressure by vacuum
• Sonication
These methods may be used individually or in combinations.
Sparging
Sparging, or bubbling helium through solvent, removes the other gases from solution by
saturating the solvent with helium. Lower concentrations of unwanted gases decrease
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