Analysis of exhaled breath condensate (EBC) represents a non-invasive method for detecting inhaled nanoparticles (<100nm; NP) associated with various environmental and occupational exposures. However, the few studies that have investigated inhaled NPs in EBC often assess only bulk, ionic intensities to provide information on overall elemental content, rather than on particulate content. In an attempt to assess inhaled particles in their original particulate form, we developed a methodology for the preservation and determination of inhaled welding fume NPs: a particularly relevant occupational exposure scenario due to the high concentration of metallic NPs produced in the welding process. Two EBC preservation strategies were tested: either flash freezing EBC immediately after collection, or keeping EBC at room temperature until analysis. Particle content of the differently preserved samples was assessed by Microdroplet Generation Inductively Coupled Plasma Mass Spectrometry (MDG-ICP-MS), and with Electron Microscopy. We found that welding fume NPs in EBC may quickly and uncontrollably degrade, thereby losing their original form and hampering effective characterization analysis. As such, we demonstrate the importance of flash freezing EBC samples immediately after collection and defrosting them shortly before analysis at a temperature that does not affect proteins and peptides (<38°C) in order to effectively preserve NPs in particulate form. This methodology can be applied easily, effectively, and inexpensively to preserve EBC samples for future NP content determination and characterization
