How long can I keep or leave idle in mobile phase reservoir organic solvents like methanol and acetonitrile in HPLC for analysis and column wash purposes?
Generally, for >95% aqueous mobile phases 2 weeks and <95 organic phases one month validity is assigned.
The exception to this rule is MeOH with TFA which gets 2 weeks because there have been stability issues associated with it. Pure organic phases get 3 months.
The aqueous phase shortened expiry is due to the potential for microbial growth because you see their metabolites and it makes the blank runs look abnormal.
If it’s an in-house method, you have to demonstrate the assigned shelf life will not affect the analysis. If it’s a routine QC analysis, make up some extra mobile phase and reanalyze fresh standards and samples in the next few batches if you want to extend the life.
Water is cheap, and wildlife likes it, so it’s unlikely you will want to keep it more than a few days ( max 1 week ), especially if nutrients have been added ( eg phosphate buffers ).
If you have made the water slightly less amenable, by pH adjustment ( eg TFA ) or organic solvents, you could go out to months or so ( after all, some manufacturers sell water preblended with TFA or Formic Acid ). Always assuming that the manufacturer’s shelf like of components is not exceeded.
For all other solvents and chemicals, then shelf life should be close to that of the manufacturer, but you still have to demonstrate that older solvent doesn’t affect the analysis. Buy smaller quantities regularly for short shelf-life products.
Some regulators define the maximum shelf life of mobile phases, so you just follow their guidelines. Any blended solvent mobile phase over a month or two, or aqueous buffer over a week or two, is probably going to generate serious questions from auditors.
Good auditors want to see the experimental rationale for stated shelf lives that are longer than typical and want to know the basis for any generic policy/SOP for the whole laboratory that is longer than typical.
Thank you for your explanation.
You are always welcome…!!
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