Buffered Solvents; Head Height; Solvent Viscosity; Mobile Phase Solvent Degassing - Waters 1525M Installation And Maintenance Manual

A liquid is classified in the M-number system by testing for miscibility with a sequence of
standard solvents. A correction term of 15 units is then either added or subtracted from the
cutoff point for miscibility.
C.4 Buffered Solvents
When using a buffer, use a good quality reagent and filter it through a 0.45-µm filter.
Do not leave the buffer stored in the system after use. Flush all fluidic pathways with
HPLC-quality water before shutting down the system and leave water in the system (flush
with 90% HPLC-quality water:10% methanol for shutdowns scheduled to be more than
one day). Flush using a minimum of 15 mL.
C.5 Head Height
Position the solvent reservoirs in the bottle holder supplied with the 1525 HPLC Pump
(with adequate spill protection).
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 affect the analysis is not known, monitor the
pressure during the run.
C.7 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
Solvent Considerations 102
C