X-Ray fluorescence (XRF) spectrometry has been a powerful technique for elemental analysis for almost 100 years based on Moseley’s well known law which relates “characteristic” fluorescence radiation to the atomic number of the emitting atom. Today composition analysis by measuring fluorescence spectra has become a routine technique utilized in a vast number of research areas ranging from material science to biomedical science. X-Ray fluorescence analysis is nondestructive, high precise and multi-elemental method to analyze most elements of the periodic table (Z>5 (B), most effective for Z>11 (Na)) with simple or even no sample preparation. Moreover, as the fluorescence intensity is proportional to the concentration of an element present in the sample, not only qualitative but also quantitative analysis is possible. As wavelength and energy are equivalent the fluorescence radiation can be evaluated in wavelength or energy dispersive mode. However, classical XRF analysis is not applicable for ultra-trace elemental analysis and susceptible to systematic errors due to sample matrix effects.