Waters 2998, Обзор и руководство по обслуживанию

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December 5, 2017, 715004753 Rev. B
Page 89
C.8.3 Solvent degassing considerations
Select the most efficient degassing operation for your application. To remove dissolved gas
quickly, consider the following.
C.8.3.1 Sparging
Helium sparging gives stable baselines and better sensitivity than sonication in a detector, and
prevents reabsorption of atmospheric gases. Use this method to retard oxidation when you are
using tetrahydrofuran or other peroxide-forming solvents.
C.8.3.2 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.
C.9 Wavelength selection
This section addresses UV cutoff ranges for
• common solvents;
• common mixed mobile phases;
• chromophores.
C.9.1 UV cutoffs for common solvents
The table below shows the UV cutoff (the wavelength at which the absorbance of the solvent is
equal to 1 AU) for some common chromatographic solvents. Operating at a wavelength near or
below the cutoff increases baseline noise because of the absorbance of the solvent.
Table C–2: UV cutoff wavelengths for common chromatographic solvents
Solvent UV Cutoff (nm) Solvent UV Cutoff (nm)
1-Nitropropane 380 Ethylene glycol 210
2-Butoxyethanol 220 Iso-octane 215
Acetone 330 Isopropanol 205
Acetonitrile 190 Isopropyl chloride 225
Amyl alcohol 210 Isopropyl ether 220
Amyl chloride 225 Methanol 205
Benzene 280 Methyl acetate 260