Can ammonia be detected by a 1D-1H-NOESY experiment?
In the 1H,1H-NOESY experiment you are using the nuclear Overhauser effect to transfer magnetization from one proton to another proton in close proximity (&lt; 5 Å).  This only works within a single molecule, unless you have a reasonably stable complex you can't observe signals in the NOESY between protons of different molecules in your solution.

Ammonia has three protons which are at least chemically equivalent, their signals will appear at the same chemical shift. In a 1D NOESY you irradiate at the frequency of a specific proton and then observe the transferred magnetization at other frequencies. You can't observe magnetization transfer between protons at the same frequency that way, as your irradiation will destroy any signal at this specific frequency.



You can ignore the explanation above, as the NOESY experiment you are using is different. In metabolomics the NOESY 1D is used for water suppression, this is a different experiment than the 1D NOESY I explained above.

The common variant of this I found also uses presaturation to suppress water. This presaturation will also affect all signals that exchange quickly with the solvent, and the protons of ammonia are exchanging with water. So I would expect the ammonia signal to be far weaker or even not visible in such an experiment.

If you want to observe ammonia, you have to use a water suppression method that doesn't affect exchanging protons.