Peak fitting was done by iteration to better adjust the peak and the
background to minimize the chi-square of the fitting on each spectra.
To obtain better peak fitting and avoid errors in peak identification by
WinQXAS, the energy calibration of the spectra was made by using
predefined regions of interest (ROIs) and the previous peak identification
obtained by the software linked to the WDXRF spectrometer. An
example of one of these ROIs is presented in Fig. 1.