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You can use cubic spline to fit and subtract baseline on Fit Plot. To create spline curve click on Add
button in Fit Curves
tab of Fit Plot.
Do not use splines to subtract baselines which can be fit well enough with line curve (line or constant baseline). You may mistakenly subtract wide peaks using spline.
Created spline has three anchor points by default. You can move, add and remove anchor points:
Spline anchor point (x, y) coordinates are treated as fit parameters so you can perform fitting with spline. Note that the anchor point coordinates will be varied but the number of point will remain. You also can lock some parameters (usually x coordinates) by setting Lock
check boxes in parameters table.
It is recommended to set appropriate fit intervals which contain only baseline without peaks. In such case Fit One Curve
button is more acceptable than Fit by Sum
button, because the individual interval for current curve will be used and the interval from Fit Interval
tab (which is used to fit by sum of curves) is ignored. Select spline curve and set Set Interval
checkbox in the bottom of the panel to edit spline interval, then click on Fit One Curve
button.
Set Baseline
checkbox in spline row in curves table to subtract spline from data.