Waters 1500-Series, Operator'S Manual

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Head height C-9
Head height
Position the solvent reservoirs in the bottle holder supplied with the
1500-series HPLC pump (with adequate spill protection).
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 affect the analysis is not known,
monitor the pressure during the run.
Mobile phase solvent degassing
Mobile phase difficulties account for the majority 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
This section presents information on the solubility of gases, solvent degassing
methods, and solvent degassing considerations.
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