Preprocessing

This video will demonstrate some of the preprocessing operations available in GC Image.

Note

Demos 1, 2, and 3 should be completed in sequence.

The public dataset used in this demo can be downloaded here:

Supporting files to help in following along with this quick start demo can be downloaded here:

1 File Import

  1. Launch the Image software.
  2. From the menu, select File > Import Image.
  3. Browse for the CalCurve_2ppb_A.cdf data file and click Open.
  4. Enter a Modulation Period of 4.0 seconds in the Import dialog.
    • The remaining import parameters are auto-filled from the data file.
  5. Click OK to begin importing the data.

2 Phase Shift

Phase Shift can be used to synchronize the start of the sampling with the modulation cycle.

  1. From the menu, select Processing > Shift Phase.
  2. Enter a Shift Amount of 2.2 seconds.
    • The shift amount can be specified in seconds or pixels by selecting from the dropdown list.
    • The text on the top of the dialog will display the total shift applied before and after the operation.
  3. Click OK to apply the phase shift.

3 Color Map

  1. From the menu, select View > Colorize.
  2. Import the EOSB configuration.
    • At the bottom right of the Colorize dialog, select the Import/Export tab.
    • From the list, select EOSB.
    • Click Import.
  3. Set a linear value mapping with the Min and Max set to match the data.
    • Select Automatic once to set the Min and Max values based on the data
    • Change the selection back to Parametric in order to manually adjust the value mapping.
    • Click the Reset Value Mapping Scale button to set the linear value mapping.
  4. Click OK to apply the configuration.

4 Baseline Correction

  1. From the menu, select Configure > Settings.
  2. Select Baseline Correction from the list on the left.
  3. From the Data Channel dropdown list, select TIC. Click OK to save the setting.
  4. From the menu, select View > 1D View to visualize the data's baseline.
    • Select Column I from the dropdown list on the 1D View dialog to view a 1D slice of the data along the Column I dimension.
    • Click on the TIC to select a Column II location that is a good representation of the background (i.e., the horizontal red line should not cross any peaks).
  5. From the menu, select Processing > Correct Baseline to perform baseline correction.
  6. Use the 1D View after the operation to review the results.

5 MS Subtraction

Multi-Spectral Subtraction can be used to clean up column bleed or other undesired artifacts. This is especially useful if desired features are within or near the artifact.

  1. From the toolbar, select the MS cursor mode.
  2. Use the cursor to select a point within the column bleed to open the MS Viewer.
    • Select a sample point that will best represent the artifact's spectrum, such as a centrally located apex within the artifact.
  3. From the MS Viewer dialog's menu, select Arithmetic Ops > Subtract From Image.
  4. For this demo, use the default Subtract From Image settings.
    • This will perform MS subtraction from the entire image with base peak normalization.
  5. Click OK to perform the operation. The artifact should be cleaned up using the spectrum.