Create tangential baseline for DSC data.

PURPOSE
This app can be used to create a tangential baseline for DSC data according to start and end positions for linear segments around each peak.

INSTALLATION
Download the file Tangential_Baseline.opx, and then drag-and-drop onto the Origin workspace. An icon will appear in the Apps Gallery window.
NOTE: This tool requires OriginPro.

OPERATION

1. Make a graph with DSC curve active. Click on the Tangential Baseline icon in the Apps Gallery window. A dialog with five buttons will appear.
2. Click the first Add Markers button. Double click on a peak. Two cursors will appear around the peak. Drag two cursors to the start and end locations for linear segments around the peak. If the curve includes multiple peaks, click Add Markers button several times to add a pair of cursors for each peak.
3. Click the second Create/Update Baseline button. A tangential baseline will be shown in the graph.
4. To adjust the baseline, besides moving cursors of linear segments for each peak, click the third Settings button. In the opened dialog, Number of Points to Fit Linear Segment can determine to use how many points to fit each linear segment around each peak. Maximum Number of Iterations and Tolerance are used to specify when to terminate the iteration of tangential baseline.
5. Click the fourth OK button. The tangential baseline will be created in the graph. In the Project Explorer window, double click on the hidden workbook for the created baseline, column C includes the data for baseline subtracted curve.

SAMPLE OPJU FILE
This app provides a sample OPJU file. Right click on the Tangential Baseline icon in the Apps Gallery window, and choose Show Samples Folder from the short-cut menu. A folder will open. Drag-and-drop the project file TBaselineEx.opju from the folder onto Origin. The Notes window in the project shows detailed steps.
Note: If you wish to save the OPJU after changing, it is recommended that you save to a different folder location (e.g. User Files Folder).

ALGORITHM

\(B_k(t)=(1-\gamma(t))(a_0+a_1t) + \gamma(t)( b_0 + b_1( t_f-t ))\)
where \(\gamma(t) = \frac{ \int \limits _{t_s}^t ( D(t) -B_{k-1}(t) ) dt}{ \int \limits _{t_s}^{t_f} ( D(t) -B_{k-1}(t) ) dt}\),
\(B_k(t)\): baseline in the kth iteration.
\(B_{k-1}(t)\): baseline in the last iteration.
\( D(t) \): the input spectrum.
\( t_s \) and \( t_f \): start and end time of linear segments.
\( a_0,\ a_1,\ b_0,\ b_1 \): linear coefficients for two linear segments.

NOTES

• If the graph layer includes more than one curve, it will create the baseline for the selected curve or the active plot in the layer if no plot is selected. You can create baselines to other plots in turn by clicking on the plot in the graph window or by selecting it in Object Manager, then relaunching the app.