Qualitative XRF analysis identifies the elements present in a sample exposed to X-ray photons of suitable energies based on their characteristic X-ray fluorescence emitted from the sample .Fig. shows a portion of the XRF spectrum acquired from a certified reference material (NIST SRM 2783 -Air particulate on filter media) prepared using the SMART STORE® and measured by a TXRF instrument equipped with Mo-Ka target X-ray tube. Elements with characteristic X-ray fluorescence emission below the excitation energy (about 17.485 KeV) can be identified comparing the peak energy with that of the characteristic X-ray emission lines tabulated or stored in the software database. Fig. shows the unambiguous presence of some elements identified by their Kα lines: K, Ca Cr, Mn, Fe, Cu, Zn, Br, Rb, and Sr. The main challenge in qualitative XRF analysis is to establish the presence of elements with overlapping XRF emissions. Generally, this is observed with the K lines of lighter elements and the L lines of heavier elements. In the spectrum of Fig. one can observe the overlap of Ti with Ba, and As with Pb, all present in NIST SRM 2783. In this case, the fitting of the spectrum using software based on fundamental parameters, such as PyMCA or reference spectra (such as the Bruker Spectra 5.1 evaluation software) can be useful to distinguish the presence of one or the other element or both. To address these challenges, advanced techniques such as high-resolution XRF or different excitation energies to resolve overlapping peaks can be also used. Quantitative XRF analysis converts the characteristic X-ray emission signal from the elements present in the sample, measured as peak height or area, into mass or concentration amounts. The determination of relative concentration, usually in %, of the elements identified in the sample is often called semi-quantitative analysis.