Abstract: An apparatus for selecting products on the basis of their composition via X-ray fluorescence spectroscopy includes an X-ray source that emits an X-ray beam towards a product sample, and a particle detector for receiving an X-ray beam diffused by the product sample and generating a signal received that can be analysed to determine a chemical composition of the product sample and selecting a type of product corresponding to said chemical composition of the product sample. The apparatus includes a first vacuum chamber located between an output of the apparatus facing the product sample and the X-ray source, and a second vacuum chamber located between the output of the apparatus facing the product sample and the detector. The apparatus also includes an optical module with polycapillary lens located downstream of the X-ray source, which is configured for focusing the X-ray beam and is associated in a vacuum-tight way to the first vacuum chamber.