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Suppressing Nasty Signals

When the solvent is non-deuterated, you saturate it during acquisition or you use a pulse sequence that doesn't excite it. The residual signal can still be a cause of problems. Its phase may be impossible to correct; its tails can alter the baseline; peaks nearby can be difficult to recognize.

You can delete any peak, not only solvent peaks. The algorithm provided by iNMR performs a natural kind of suppression. Only the single point at the central frequency goes to zero. The surrounding region is gradually smoothed, not flattened. The result is so realistic that only close inspection can reveal the trick.

How to Suppress Peaks:

Step 1

To suppress the solvent peak at the transmitter frequency:

Start from time domain. If you have already transformed the spectrum, choose File > Reload.

Choose Process > Suppress.

iNMR automatically inserts the transmitter frequency. Just click Suppress.

Step 2

To suppress a generic peak:

Start from frequency domain. If you haven't transformed the spectrum yet, choose File > Fourier Transform, etc...

Right-click the unwanted peak and choose Suppress from the menu that pops up.

You can suppress up to 4 different peaks in the same way. If you specify a fifth frequency, the fourth peak reappears.

This simplified method deletes the frequency corresponding to the peak maximum. To delete a generic frequency, you have to type it, inside the dialog Process > Suppress, before performing the FT.

Step 3

To make the suppression milder or stronger:

Choose File > Reload and Process > Suppress.

In the first instance, you should select the highest selectivity factor. It allows an effective suppression of the unwanted peaks, while preserving the rest of the spectrum almost intact.

When the unwanted peak is broad, decrease the selectivity factor. You'll get a stronger suppression.

Step 4

To undo:

Choose File > Reload and Process > Suppress.

Empty the four cells.

Click Suppress.

The suppression is never completely selective. The signals near the suppression point can be severely attenuated and their integrals are never dependable.

In the case of a 2-D or 3-D spectrum, you can only suppress the peaks along the direct dimension.

It's also possible to substitute a piece of the spectrum, with zeroes or with a fragment taken from another spectrum, using the console commands copy() and paste() (not to be confused with the namesake menu commands).

Related Topics

Subtracting a Spectrum from Another One

Measuring the Area by Fitting to a Model


Web Tutorial

Removing Unwanted Peaks