Baseline Correction

Baseline Corrections can flatten the baseline on the Fourier Transformed data to improve integration accuracy.

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

1) Baseline Correction should be done after other FID processing including Apodization, Zero-Fill, and Phase Correction.

2) In most spectra the Full Auto (Whittaker Smoother) will work well. This is accessible below the Baseline Correction option under Baseline tab.

3) If you select Baseline Correction, there is an option for Whittaker Smoother there as well and it will show you the basline that it will use.

4) Under the Whittaker Smoother, there are options for Filter and Smooth Factor, which can be detected Auotmatically by default, but they are adjustable parameters to potentially find a better baseline. The Smooth Factor is normally correlated to the number of points acquired (or linear predicted).

5) While in most cases the Whittaker Smoother works best, Polynomial Fit or Bernstein Polynomial are sometimes better. These options are accessible under the Method drop-down menu. The Polynomial order is a settable option from 1 to 20.

6) The other option is to do a baseline correction based upon selected data points, as in the bc command in VNMR. This is accessible under the Baseline tab under Processing menu then Multipoint Baseline Correction. For this, you can select the points to be used as baseline or have the points picked automatically. If the Whittaker Smoother or Polynomial baseline corrections do not work well, selecting points as baseline would be the next option. This is most likely necessary when baseline distortions are significant.

7) After applying Baseline Correction, take careful note on the effect of it on broad resonances, to be sure they are not being treated as a baseline roll. Also, note effects from baseline correction on solvent suppressed resonances either in acquisition or processing and resonances with lineshape distortion due to shimming.