Waters ACQUITY UPLC Operator's, Overview And Maintenance Manual page 111

Water
Use water only from a high-quality water purification system. If the water
system does not deliver filtered water, filter it through a 0.45-µm membrane
filter before use.
Using 100% water can cause microbial growth. Waters
Caution:
recommends changing 100% water solutions daily. Adding a small
amount of an organic solvent (~10%) prevents microbial growth.
Using buffers
Adjust the pH of aqueous buffers. Filter them to remove insoluble material,
and then blend them with appropriate organic modifiers. After you use a
buffer, flush it from the pump by running a wet-prime with at least five
system volumes of HPLC-grade distilled or deionized water.
For shutdowns of more than a day, flush the pump with a 20%
methanol/water solution to prevent microbial growth.
Some buffers can be incompatible with mass spectrometers.
Caution:
Consult the documentation that accompanies your instrument for
compatible buffers.
To avoid salt precipitation, nonvolatile buffer concentrations must not
Tip:
exceed 100 mM.
Buffered solvents
When using a buffer, choose good quality reagents, filtering them through a
0.2-µm membrane filter.
Recommendation:
aqueous phase daily.
Controlling Contamination in Ultra Performance LC/MS and
See also:
HPLC/MS Systems (part number 715001307).
To discourage microbial growth, replace 100% mobile
Solvent considerations 99