Phase Correction

Phase Correction is used to make the resonances in the Fourier Transformed data all in-phase (positive) in most experiments or sometimes positive for some resonances, negative for others (such as 1D NOE).

The Phase Correction menu is located under the Processing tab then Phase Correction.

There are 4 options under the Phase Correction menu- Automatic (with Options below it), Manual Correction, Magnitude and Power. In most cases, Automatic Phase Correction will work well, but if it does not then you will need to use the Manual Phase Correction. The Magnitude and Power options are used to make all parts of the spectrum positive and lead to long tails on resonances.

1) In most 1D spectra, the Automatic Phase Correction will work well. To confirm, increase the vertical scale to see the base of the resonances. The resonance should be flat into the baseline, essentially symmetric on either side of the resonance. The symmetry may not be perfect due to shimming, but the base of the peak should not dip below the baseline on one side and above the baseline on the other. If the baseline is curved, that can be fixed with baseline correction:
Baseline Correction

2) If Automatic Phase Correction is not optimal, then choose Manual Phase Correction. The most likely reasons for imperfect phasing are low signal-to-noise, poor shimming, very broad resonances, or spectra with resonances that are not all in-phase (such as NOE or solvent suppression).

3) The 2 phase parameters are PH0 and PH1, the zero-order and first-order phase corrects, so frequency independent and frequency dependent (rp and lp in VNMR). The PH0 should change the phase equivalently across the spectrum, the PH1 will change the phase differently across the spectrum as it has a frequency component.

4) Set the pivot parameter to the biggest peak in the spectrum (you can click on Biggest to do this). The pivot point will not change when adjusting the PH1 parameter. Next adjust the PH0 parameter with the left mouse button until the biggest peak is phased well. Finally, adjust the PH1 with the right mouse button until the rest of the spectrum is phased.