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Correcting the Phase

NMR signals can appear as absorption signals (symmetric, narrow) or dispersion signals (anti-symmetric, broad). There is a phase difference of 90° between the two. Most spectra need a phase correction to bring all the signals in absorption mode and iNMR contains an array of automatic algorithms that do a good job in this respect. To achieve even better results you may want to refine the phase manually.

To Correct the Phase manually:

Step 1

Choose Process > Phase Correction.

If the phase controls are disabled, it means that your spectrum is real. You can make it complex with the command Process > Make Complex.

Step 2

Choose the peak whose phase is more correct and put a mark on it with ⌘-click(on the Mac) or Alt Gr-click (on Windows); you have chosen what is improperly called the pivot point.

If you are correcting the vertical dimension, create an horizontal mark instead, with the combination alt-click.

If no peak is in absorption mode, first move slowly the big slider at the left of the panel to improve the situation, then create the mark.

Step 3

Move the big slider at the right of the panel (first-order correction) until the phase of the other peaks is also correct.

If the right slider reaches the end of the run, move the central slider to the position coarse.

If, instead, the phase changes too much, move the central slider to the position fine.

Every time you move the central slider, in either direction, the thumb of the right slider returns to the middle position.

Step 4

When there is a peak in pure absorption (perfectly symmetric), move the mark over it. Repeat from point 2.

As the correction improves, you should amplify the spectrum with the plus key. The tails of the peaks are extremely diagnostic, because they are anti-symmetric when the phase is not perfectly correct.

If there is more than a single mark, or if you enter the correction values with the keyboard, no pivot point is used.

Related Topics

Automatic Phase Correction


Web Tutorial

Phase and Baseline Correction for Absolute Beginners