The challenge lies in establishing the reliability and accuracy of the XRF technique through calibration procedures that utilize fit-for-purpose RM. The accuracy of determination heavily relies on the selection of appropriate calibration samples, RM, or certified RM. Unfortunately, there is a lack of CRM specifically tailored for PM analysis. Presently, only one certified RM, NIST SRM 2783, provided by the US National Institute of Standards and Technology, is available in the market, but it is not suitable for all types of PM as it is specific to PM2.5. While some RM are fabricated by depositing thin films of various compounds in a vacuum, only a few handmade secondary reference materials are mentioned in the literature and EPA methods . These limited options suffer from low representativeness due to differences in matrix composition between thin films and actual particles, as well as the method of preparation. There are some important features to meet in order to obtain the ideal filter-based reference material such as: i) the material to be deposited should be a contemporary material, containing an elemental pattern representative of the real samples of interest; ii) the standard solutions should consider the whole range of size-fractionated, focusing more on the "inhalable fraction"; iii) a sufficiently large batches of uniform filters should be tested before distributing them as reference materials . Recently, several attempts have been made to produce reference materials and calibration samples on various substrates. Aerosol generation systems are used to produce RM of analytes of interest on filter membranes with assigned mass loadings , or calibration samples by using nanoparticles suspension or salt based water solutions trying to mimick ambient or workplace aerosol composition .