If any mobile phase contains a mixture of organic solvent and buffer, then for how many days can we store it for using it again and again? Also, if the mobile phase contains only the mixture of organic solvents then for how long can we store them? Is there any guidelines for it?
There are no reliable universal guidelines as each solution is different and even mobile phases with 20% organic can still grow bugs in them over time. Only pure solvents which are kept in sealed bottles are generally safe for long term storage. The moment you add acids, bases, buffers or any additives to the solution, the stability of the solution is now a variable (e.g. pH, bacterial or alga content, particulate matter).
Some buffered or aqueous containing mobile phases will at most be good for one week at refrigerated temperatures (e.g. simple phosphate buffers), BUT some will still grow bugs in them during this time and be unsuitable for HPLC work. You really need to make up fresh solutions each day or as suggested earlier conduct a full study for each one to determine its stability over time for use in HPLC. *Please don't risk contaminating your entire instrument and column using questionable solutions.
you should have a study for "how long your mobile phase is stable"
ICH Q2 " Solution stability will be useful as a reference
For few days/ couple of weeks- no matter what solvent alone or buffer or any modifiers (Acids/ bases) etc. added. I would not trust it, as might grow contaminants from algae/ bacteria to settling of things, dust and what not! These are inexpensive and should not compromise your valuable/expensive HPLC runs. Best wishes, Biswa
There are no reliable universal guidelines as each solution is different and even mobile phases with 20% organic can still grow bugs in them over time. Only pure solvents which are kept in sealed bottles are generally safe for long term storage. The moment you add acids, bases, buffers or any additives to the solution, the stability of the solution is now a variable (e.g. pH, bacterial or alga content, particulate matter).
Some buffered or aqueous containing mobile phases will at most be good for one week at refrigerated temperatures (e.g. simple phosphate buffers), BUT some will still grow bugs in them during this time and be unsuitable for HPLC work. You really need to make up fresh solutions each day or as suggested earlier conduct a full study for each one to determine its stability over time for use in HPLC. *Please don't risk contaminating your entire instrument and column using questionable solutions.
Personally, I would change the buffered solution everyday that I am running samples but 2 days at the max! I do not want to risk microbial growth, as this may effect the chromatogram. As for the mobile phase/ organic solvent, I would try to replace every week or so as the organic solvent is much more resistant to microbial growth. However, as Bill Letter has said before that you can still accumulate microbial growth with an organic phase. Making a new buffer/mobile phase is much easier than buying a new column! (Less costly as well)
Like Bill said, there is no universal guideline on mobile phase shelf life. as an anecdote, I have used all kinds of buffer mobile phases for up to 2 weeks, and simple acidified mp for one or two months without any apparent issues. pure organic solvent should be good for at least 3 months.
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