Ammonium acetate as a buffer
You nitwit! Ammonium acetate is a salt, not a buffer!
The categories aren't exclusive. Acetic acid has a pK of 4.75; ammonia has a pK of 9.25. Ammonium acetate solutions are pH 7.
How did you discover this?
"A neutral buffered standard for hydrogen ion work and accurate titrations which can be prepared in one minute", Roger J. Williams, Carl M. Lyman, JACS 54, 1911-12 (1932) - an overlooked classic!
Why don't more people use ammonium acetate?
The following article noted the poor quality of commercial ammonium acetate. "Ammonium acetate as a neutral buffered standard", C.J. Schollenberger, JACS 54, 2568 (1932). This is no longer a problem.
Isn't it nonphysiological?
I don't recommend it for enzyme reactions, etc.
Isn't buffering capacity low?
Although the pH is 2 units from either pK, both ions buffer. Buffering capacity increases as you move away from pH 7. The buffer does an excellent job of keeping the pH between 6 and 8.
What's the buffer good for?
It's a great buffer for protein and nucleic acid purifications
It's obviously easy to prepare, but are there other advantages?
A big advantage is solubility in acetone and methanol (like LiCl). You can precipitate proteins or nucleic acids with solvents.
Won't ammonia vaporize?
Ammonia is more volatile than acetic acid. The salt is in equilibrium with free base, however ammonium acetate comes in large amounts in small bottles. As ammonia vaporizes pH drops slowing ammonia loss. Nonetheless I don't recommend storing small amounts of ammonium acetate in open containers. Ammonium acetate is hygroscopic (a negative). Even my old bottles of ammonium acetate yield neutral solutions.
Ammonium acetate is cheap, simple to prepare, soluble in organic solvents, and on the negative side, hygroscopic