Dear Nitzan,

By L-glutamate i take it that you mean L-Glutamic acid in its dissasociated anionin form, correct?

The Sigma Aldrich Product Information Sheet mentions that "Aqueous glutamic acid solutions will form pyrrolidonecarboxylic acid slowly at room temperature

and more rapidly at 100 C" (see link 1) and this degradation is known to be hastened in acidic conditions (see link 2).

Given the many factors involved ("several years", if it is already prepared how many times have they been thawed, what other agents are in the solution) and the relative inexpensive nature of L-glutamic acid (or monosodium glutamate used by some labs) i would rather prepare fresh solutions each time or freeze it in aliquotes for mid-term storage. In our lab we have used solutions of monodosium glutamate frozen for 2-3 years with no apparent issues, but better be safe than sorry. Do you use it for excitotoxicity studies? Maybe a quick test would be to expose a cell line known to respond to glutamate to the old aliquotes and note if it is capable of eliciting the response although it may be more time-consuming and expensive than simply preparing a fresh solution.

https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma/Product_Information_Sheet/g1251pis.pdf

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1985.tb13399.x/pdf

Dear Nitzan,

I had some stock aliquots dissolved in milliq water in the feezer for -20 degrees for many ~5 years and when used them recently there was no problem producing excitotoxicity. I agree with points that Theofanis mentioned.

Best wishes,

Refik