format or acetate

[che313]

newly installed qtrap 3200 with method for forensic toxicolgy.
they recommend a mobile phase with ammonium formate as a buffer.
we don't have this but we have ammonium acetate. can I use the acetate or not using any buffer? can i prepare ammonium formate by reaction ammonia with formic acid?

[Uwe Neue]

You can use ammonium acetate buffers with equal ease as ammonium formate buffers. A buffer is a mix of the buffer salt (ammonium acetate) and the acid (acetic acid here) best in a 1:1 molar mixture. The advantage of a formic acid buffer is its lower pH (3.75) compared to ammonium acetate (4.75).

You can prepare the buffers from mixtures of ammonia with formic acid.

In general, you will be better off in MS applications to just use formic acid, instead of ammonium formate buffer, but this may create tailing peaks under many circumstances. So the use of formic acid versus ammonium formate buffer is a trade-off of MS response versus good chromatography.