Wavelength selection C-9
Solvent degassing considerations
Select the most efficient degassing operation for your application. To remove
dissolved gas quickly, consider sparging or vacuum degassing.
Sparging
In a detector, helium sparging gives stable baselines and better sensitivity
than sonication and prevents resorption of atmospheric gases. Use this
method to retard oxidation when you are using THF or other peroxide-forming
solvents.
Vacuum degassing
The longer the solvent is exposed to the vacuum, the more dissolved gases are
removed. Two factors affect the amount of time the solvent is exposed to the
vacuum:
• Flow rate – At low flow rates, most of the dissolved gas is removed as the
solvent passes through the vacuum chamber. At higher flow rates, lesser
amounts of gas per unit volume of solvent are removed.
• Surface area of the degassing membrane – The length of the degassing
membrane is fixed in each vacuum chamber. To increase the length of
membrane, you can connect two or more vacuum chambers in series.
The inline degasser is available as an option or factory-installed in the Waters
Alliance System.
Wavelength selection
In fluorescence, if the excitation monochromator is set below the UV cutoff of a
mobile phase component, the solvent will absorb some of the available
excitation light intensity. This will reduce the fluorescence emission response
for the sample.
This section includes UV cutoff ranges for:
•Common solvents
• Common mixed mobile phases
• Chromophores
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