Automatic Phase-Correction Algorithms
iNMR provides several algorithms for automatic phase correction. Some are general-purpose, while
others are designed for specific situations. Separate methods are available for 1-D and 2-D spectra.
In each category, the recommended method is presented first.
Sometimes running the same algorithm a second time improves the result,
because the optimum solution is not always reached on the first pass.
That's why it is a good idea to use a shortcut
instead of the menu command.
To obtain accurate results it is normally necessary to refine the correction manually.
In 3-D spectroscopy, only the manual correction is possible.
1-D methods
1-D Advanced Method
Use it when:
- The baseline is flat or V-shaped.
- The edges of the spectrum do not contain peaks.
- Most of the peaks are positive.
How to apply it:
- If you have created marks in the window, delete them (for example, with command-alt-double-click on the Mac; Alt-Alt Gr-double-click on Windows); then:
- Either Choose Process > Automatic Phase.
- Or Click the corresponding palette icon (blue dispersion signal with a gear).
- Or Press command-alt-K (on the Mac) or ctrl-alt-K (on Windows).
1-D Simple Method
Use it when:
- All the peaks are positive.
How to apply it:
- Either Do nothing, because iNMR automatically applies this method to new 1-D documents.
- Or create a horizontal mark (Alt-click), then choose Process > Automatic Phase or use any equivalent shortcut.
1-D Selective Method
Use it when:
- You have both positive and negative peaks.
- There are two or more sharp singlets.
How to apply it:
- Create marks on two or, preferably, more singlets with command-click (on the Mac) or alt gr-click (on Windows).
- Choose Process > Automatic Phase or any of the equivalent shortcuts.
2-D methods
2-D Global Method
Use it
- ...As the first method to try.
How to apply it:
- Verify that no region is selected.
- Choose Process > Automatic Phase or any of the equivalent shortcuts.
2-D Selective Method
Use it when...
- The global method does not work.
How to apply it:
- The spectrum must be hyper-complex.
- Select a region (the algorithm will try to make the peaks inside it positive).
- Optionally create a horizontal and/or a vertical mark. The algorithm will leave the phase unchanged at the frequencies indicated by the marks, unless they intersect the selected region.
- Choose Process > Automatic Phase or any of the equivalent shortcuts.
Algorithms that can handle both positive and negative peaks may occasionally return a spectrum rotated by 180°. To reverse the rotation, use Command-Control-K (Mac) or Ctrl-Shift-K (Windows).