D.2.3 Solvent Degassing Considerations - Waters 717plus Operator's Manual

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
background absorbance of UV detectors. Well-sparged solvent also improves pump
performance. Gas sparging brings the solvent to a state of equilibrium, which may be
maintained by keeping a blanket of helium over the solvent.
Heat
Heat raises the vapor pressure of the solvent at its surface. As the partial pressure of the
solvent is raised, the partial pressure of the gas decreases proportionally. This prevents
any further absorption of the gas into solution. This is true for most gases in water, but not
necessarily true with organic solvents.
Vacuum
A vacuum reduces the pressure on the surface of the solvent. Since the mass of gas in
solution is proportional to the partial pressure of the gas at the surface of the solvent, the
mass of gas in solution decreases as the pressure decreases.
Sonication
Sonication with high energy sound waves drives energy into the solvent and causes the
submicron size "bubbles" of gas to aggregate. As the gas aggregates, the bubbles
become large enough to float out of the solvent and dissipate. Sonication alone degases
a gallon of solvent in approximately 20 minutes. However, sonication does not remove as
much oxygen as the helium sparge method.

D.2.3 Solvent Degassing Considerations

Select the most efficient degassing operation for your application. To remove the gas in as
short a time as possible, consider the following:
• Helium sparging gives stable baselines and better sensitivity in a detector, and
prevents reabsorption of atmospheric gases.
• To degas a solvent by heat, you must boil the solvent. This is not practical for mixed
solvents. However, low levels of heat reduce the rate of reabsorption of the gas.
Caution: Do not apply vacuum to the brown gallon bottles in which solvent is
shipped. There is a high risk of implosion under these conditions.
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Reproducibility and Solvent Degassing
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