Non-linear least squares (NLLS) fitting involves fitting models to spectral features to quantify the spectral peak properties. Set up this fitting on the picker spectrum extracted from the spectrum image (SI) using the following workflow:

  1. Select a suitable SI and bring it to the frontmost position in the workspace. Note that if the frontmost data is not suitable, the buttons in the palette will be disabled.

  2. Use the spectrum picker tool to extract a spectrum from the SI and then select the spectrum.

  3. Follow the steps outlined in the Single Spectrum section.

  4. Optional: Move the picker marker to investigate different areas. The live-fit will automatically recompute and adjust the fit display. This can be very useful to locate sample areas that the model does not sufficiently describe the data.

  5. Fit the references to the parent SI data by pressing the Map button.

  6. Choose the fit results you want to generate. See NLLS-Fit Map Options (Output) for details.

  7. Choose how to display the fit results. See NLLS-Fit Map Options (Display) for details.

  8. Press OK to start the fitting procedure. The system will display the progress of the fitting routine. You can stop the fitting at any time using the Abort button.

Note: The map-fit is performed on single-position spectra, which may have significantly lower SNR than an integrated picker-spectrum. In particular, in low-intensity or high-noise data, it may be advisable to check fitting quality in the live-fit by shrinking the picker region of interest to a single pixel.