Hi!

Apparently you SHOULD drink glutamine SOON after mixing it:

"It doesn’t really matter if you mix L-Glutamine with a shake, with juice, with water, etc. Any of those would be fine. Keep in mind, however, that L-Glutamine is not all that stable in water, so if you want the full benefits from the supplement, do not mix it until you are ready to drink it."

- From the EAS website (they manufacture a glutamine powder)

Best of luck!
Trilbe