Removing Unwanted Peaks
iNMR performs selective frequency suppression in time domain. The most frequent example is water suppression in solutions of non-deuterated water. In this case it is already known that the water signal falls exactly at the center (where it is more effectively presaturated). This is by far the most usual case in which a peak is suppressed, therefore when you open the dialog for frequency-suppression, it shows by default the frequency at the center of the spectrum. In all other cases, it is necessary first to FT the spectrum, then to measure the exact frequency of the peak to suppress, then to reload the FID, before finally performing the suppression.
iNMR already knows all these things. You don't have to worry and remember them. Once you have indicated the “victim”, iNMR knows how to “kill” it with discretion. Let's suppose you want to remove the highest peak into the spectrum below. right-click the peak and the contextual menu appears:
Select the last item. iNMR will do the rest. In this case there are other peaks in close proximity and they are also affected, but not suppressed. While the example demonstrates the virtues and the limitations of the method, I can't find anything useful in what we have done. Keep the idea in store for a better opportunity.
At the time of writing, iNMR allows up to 4 frequencies to be suppressed simultaneously. You will select them in succession, however. Try multiple-peaks suppression with a spectrum of yours. Keep suppressing signal of your choice one by one. You will see that you can't suppress more than four peaks. When you select the fifth victim, the fourth one comes back in life as tall as it was before.