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Correcting the Baseline (1-D)

The baseline should ideally be flat and unbiased (of zero intensity everywhere), otherwise the values of the integrals are not meaningful. Even when you are not going to integrate your spectrum, you may dislike to see a rolling baseline. You can correct the spectrum by subtracting a model of its baseline.

This kind of correction is applied after the phase correction. The simplest solution is to click the icon for automatic baseline correction (a slope with a gear). If you need a little more accuracy, follow these steps:

To Correct the Baseline of a 1-D Spectrum:

Step 1

Choose View > Full.

It is important to observe the baseline, not the peaks. You'll normally move the spectrum upward with the Up-Arrow key and enhance it with the Plus key. It is not necessary, however, to perform this preparation at the beginning, you can do the same operations during the correction as well. This is always possible on the Mac. To make it possible on WIndows, click on the word “interact”, inside the baseline dialog.

Step 2

Choose Process > Baseline Correction.

A third option is: Process > Straight Baseline, which fits the beginning and the end of the spectrum with a straight line and subtracts it from the spectrum.

Step 3

If the red line coincides with your baseline, click OK and that's all. Otherwise read on.

After you click OK, the correction proposed by iNMR is subtracted from the spectrum.

Step 4

The default correction is a sequence of straight lines (where iNMR has identified a peak) and pieces of smoothed baseline.

To increase the smoothness of the latter pieces, set Degree = 0.

To prolong the straight lines, set filter = 128.

Step 5

Alternatively, you can fit the baseline with a polynomial function: check the option at the top of the dialog.

To improve the approximation of the baseline, set Degree = 5-7.

Also reduce, gradually, the filter.

Step 6

In practice, you can try changing all the values until you think that the baseline is approximated accurately enough.

To remove the polynomial correction it's enough to choose Process > Clear Correction. Removing the correction performed with the smoother is a little more complicated: choose File > Reload, then click the gears icon.

You can try different kinds of correction and repeat the process how many times you like, though this is not necessary.

Related Topics

Piecewise Baseline Correction

Baseline Correction in 2-D and 3-D

Automatic Phase Correction


Web Tutorial

Interactive Processing: Baseline Correction