Mobile Phase Stability

[gbalock]

All,
A recent question from our Quality Group prompts me to ask the question, How long do you keep MP? Do you have a standard maximum time? How did you arrive at that time?
Thanks in advance.

[PJ8]

We give >95% aqueous mobile phases 2 weeks and <95 organic one month.

The exception to this rule is MeOH with TFA which gets 2 weeks because there have been stability issues associated with it.

Neat organic gets 3 months.

I'll have a look into how these figures were arrived at, I expect they will be explained in the SOP.

Cheers, Pat.

[PJ8]

No explanation in the SOP other than "scientific judgement" The number of times that buzzword got me out of a tight corner

The aqueous shortened expiry is due to the potential for microbial growth because you see their metabolites and it makes the blank look horrible. The MeOH TFA is because we've seen some changes in chromtography using older MeOH TFA suggesting mobile phase instability.

[Bruce Hamilton]

Depends.

For regulatory purposes.

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 reanalyse 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 nutrient has 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, are probably going togenerate serious questions from auditors.

Good auditors will want to see the experimental rationale for stated shelf lives that are longer than typical, and will want to know the basis for any generic policy for the whole laboratory that is longer than typical.

For research use.

Whatever works. I frequently use some solvents past the manufacturer's expiry date, including TFA ( different manufacturers I've used have expiry dates from " 2 years after manufacture or 3 months after opening - whichever is first ", to no expiry date ).

Some manuafacturers requalify older batches of chemicals, and so the expiry date on the CoA can change. It's worth downloading a new CoA to check before dumping expensive chemicals. Finally, manufacturers are realising that blanket values ( eg 2 years for all of their catalog ), doesn't encourage further sales, people will move to suppliers with rational chemical shelf lives.

Bruce Hamilton

[ntruong]

Some regulators define the maximum shelf life of mobile phases, so you just follow their guidelines

Where can I find this information, by any chance?
Thanks,

[Bruce Hamilton]

Some regulators define the maximum shelf life of mobile phases, so you just follow their guidelines

Where can I find this information, by any chance?
Thanks,

Usually in the mongraph method. From memory, the Bristih Pharmacopoeia used "freshly prepared" for 1 day, and "recently prepared" for 1 month. The USP used "prepare fresh" for 1 day, and specified 3 months for standard buffer solutions if they were stored in sealed containers.

Bruce Hamilton