Waters 2998, Обзор и руководство по обслуживанию

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December 5, 2017, 715004753 Rev. B
Page 87
C.6 Solvent viscosity
Generally, viscosity is not important when you are operating with a single solvent or under low
pressure. However, when you are running a gradient, the viscosity changes that occur as the
solvents are mixed in different proportions can result in pressure changes during the run. For
example, a 1:1 mixture of water and methanol produces twice the pressure of either water or
methanol alone.
If the extent to which the pressure changes will affect the analysis is not known, monitor the
pressure during the run using the Chart Out terminal.
C.7 Mobile phase solvent degassing
Mobile phase difficulties account for 70% or more of all liquid chromatographic problems. Using
degassed solvents is important, especially at wavelengths below 220 nm.
Degassing provides
• stable baselines and enhanced sensitivity;
• reproducible retention times for eluting peaks;
• reproducible injection volumes for quantitation;
• stable pump operation.
C.7.1 Gas solubility
Only a finite amount of gas can be dissolved in a given volume of liquid. This amount depends on
• the chemical affinity of the gas for the liquid;
• the temperature of the liquid;
• the pressure applied to the liquid.
Changes in the composition, temperature, or pressure of the mobile phase can lead to outgassing.
1/8-inch tubing 1/2-inch
Figure C–1: Minimum bend radius for stainless steel tubing (continued)
Tubing size (OD) Minimum bend radius
R