Several calibration methods and empirical formulae have been developed so far for analyzing materials quantitatively in XRF spectrometry. Many of them require reference samples to determine the relationship between the characteristic intensities of the elements and their concentrations. In order to eliminate empirical and semiempirical procedures, the fundamental parameter method (FPM) has been developed, which is one of the most helpful evaluating tools in quantitative XRF analysis. Some interpretations of this approach have the advantage that no standard samples are needed. The simultaneous application of FPM and polychromatic excitation demand an exact mathematical description of the primary spectral distribution as well as the efficiency function of the detector system.