Vacuum Degassing; Wavelength Selection; Uv Cutoffs For Common Solvents; Mixed Mobile Phases - Waters 2489 Operator's Manual

method to retard oxidation when you are using tetrahydrofuran 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 in-line degasser is available as an option or factory-installed in the

Waters 2695 Separations Module, XE model.

Wavelength selection

This section includes UV cutoff ranges for
• common solvents.
• common mixed mobile phases.
• chromophores.

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.
UV cutoff wavelengths for common chromatographic solvents
Solvent
1-Nitropropane
2-Butoxyethanol
UV Cutoff
Solvent
(nm)
380 Ethylene glycol
220 Iso-octane
UV Cutoff
(nm)
210
215
Wavelength selection D-9