[jwinters]

I was wondering about the expiration of a 1M ammonium acetate soln. I have seen some references ranging from 1 month to 1yr. What is ideal, and why? I ask this for guidance in setting standards for my solutions. Also, are there any sites you know of that would be able so supply expiration dates for a large variey of solutions?

[JGK]

This tends to be a very subjective issue and if you polled 100 different labs you would get about 50 different answers.

Factors would include:

storage conditions;
Is the lab performing regulatory work;
The type of analysis the lab is performing;
The grade of reagents used to prepare the solution;

to name but a few.

Generally, the more sensitive the analysis the shorter the expiry date will be set.

[Arkcon]

In the ancient days of the internet, university labs posted their findings on topics like this, and it was an easy to do a Yahoo search (Google wasn't invented yet,) for this info.  But like JGK: says, how long a solution remains usable is very subjective.  Storage conditions are a very surprising thing, you assume everyone is in a decently climate controlled lab, but local variations are common -- labs in sunny California have problems keeping weak solutions spoilage free -- and for consistency, if you're doing the same procedure elsewhere, you should adopt the same procedures.

Also, there's the issue of cross contamination.  The longer you keep a jar around, opening and sampling again and again, the sooner it'll stop being useful.  If you seal it and freeze it, it will likely last much longer.   That may be the source of quotations of longer stability.

Then there's even more personal things -- for example, the more often a bottle is handled, or even the longer it sits out -- the more it's written or printed label is going to fade, get torn, stained, whatever.  That's no good, in fact, it's even a hazard, and you look sloppy.  And people see it, and wonder, "What else do they do crappily, 'round here?"

Finally, it's very useful for you to determine it yourself.  Plan an experiment where you leave some out, and use it in a standard fashion, periodically, until it fails, documenting the procedure and results.  When you have an answer, establish it as policy, and stick your result in a file cabinet.  Then, when some hotshot shows up and goes, "Three months, aw man, I heard of a guy who kept his around for years, with no problems ...," you get your report, stick it in from of him and ask, "You heard of it, or did it yourself, like I did?"