Waters 717plus - Solvent Degassing Considerations

Reproducibility and Solvent Degassing 171
C
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.
C.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.
• Vacuum alone is too slow to be an acceptable means of degassing solvent. However,
a 0.5-micron sintered glass vacuum filter, with 300 mm of vacuum, can filter and
degas a gallon of solvent in approximately 8 minutes. Vacuum degassing may
change the composition of mixed solvents.
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.