Using Spline for Baseline Subtraction (Pro edition only)

You can use cubic spline to subtract baseline on Fit Plot. To create spline curve click on Add button in Fit Curves tab of Fit Plot and select Spline menu item.

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. In some cases Parabola curve may be more suitable.

Editing Spline

Created spline has three anchor points by default. You can move, add and remove anchor points:

Move anchor point with mouse

Double click on spline curve to add new anchor point

Double click on anchor point to remove it

Using spline for baseline fitting

Fitting with Spline

Spline anchor point (x, y) coordinates are treated as fit parameters so you can perform fitting with spline although we don't recommend this technique. Fitting the baseline with some adequate model function is preferred.

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 Edit Interval checkbox in the bottom of the panel to edit spline interval, then click on Fit One Curve button. The anchor point coordinates will be varied but the number of points will remain. You also can lock some parameters (usually x coordinates) by setting Lock checkboxes in parameters table.

Set Baseline checkbox in spline row in curves table to subtract spline from data.

Setting Fit Interval for spline curve Spline subtraction result

See Also

Nonlinear Curve Fitting: Fit Plot

Specifying Custom Fit Equation

Guessing Peaks

Predefined Fit Curves Equations