X-ray fluorescence: chemical characterization of materials by X-ray spectrometry.

X-ray fluorescence techniques are widespread since the half of the last century for chemical investigation on rocks, minerals, industrial products, construction materials, precious materials, environmental pollutants, metals, paints, etc. Actually, they can be used to analyse almost every kind of solids and in many cases also liquid or gelatinous substances. XRF allows to obtain chemical analyses, in elements or in oxides, expressed as percent atoms or atoms in percent weight, alternatively as oxides, stoichiometrically binding the oxygen to the dosed cation. Depending on the accuracy of the desired data and on the sample characteristics, the XRF can be used as partially destructive or as absolutely non-destructive technique; consequently, the sample required for an analysis varies from few tens of milligrams up to about 12 g, depending on the selected analytical procedure and the type of instrumentation. In the last decades, the diffusion of the ED silicon drift detectors, together with the development of very accurate and high specialised software for quantitative analysis, increased the diffusion of portable spectrometers offering new possibilities for in-situ and very rapid specimen characterizations, useful during forensic investigations, particularly on samples that cannot be removed for legal reasons or difficult to transport as being too large. The theoretical physical principles and the main components of X-ray spectrometers, in energy dispersion (ED) and wavelength dispersion (WD), are described also comparing the advantages and disadvantages of each analytical technique. Some forensic case studies are also presented.