Storage of HILIC columns with buffer is recommended to decrease equilibration time.
Storing a column with buffer in the mobile phase is typically not recommended for a number of reasons, most have little to do with sorbent stability. Buffers can precipitate if the organic concentration is too high but water will evaporate first. So unless the column completely dries or the buffer is very close to its solubility limit, precipitation should not be a problem.
If the buffer pH is <2.5, for long term storage (>1week) you should flush it out to reduce ligand hydrolysis. If the buffer pH is >7 (non amine buffer, >1 week) you should flush it out to reduce silica dissolution.
If the buffer pH is 6-7 (non amine buffer, >1 week) and you have >50 v/v% ACN you might want to flush it out to reduce silica dissolution but the ACN reduces the solubility of silica, so no major problem. If the buffer pH is 6-7 (non amine buffer, >1 week) and you have >50 v/v% MeOH you might want to flush it out to reduce silica dissolution since the solubility of silica higher in MeOH than ACN.
The generic recommendation of storing without buffer eliminates all of the above disclaimers/conditions.
The mobile phase (including buffer) we leave in the HILIC columns when they leave Phenomenex is suitable (preferred actually) for long term storage. This does not mean that any buffered mobile phase can be used for long term storage, only the one we use. Otherwise the standby mixture of organic and water only applies. (sk)
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