Determination of metal oxide and metallic nanoparticles in indoor air samples using mixed cellulose esters filters and spICP-MS: dissolve and shoot

In recent years, there has been increasing concern about the adverse health effects of the metallic and metal-containing nanoparticles (NPs) present in indoor environments. Unfortunately, there is no well-stablish method to simultaneously characterize their number and composition. Recently, our research group proposed a strategy for the determination of metallic nanoparticles in air by means spICP-MS based on the aerosol collection on micro-quartz filters and the subsequent extraction using microwave heating in basic media. Although the proposed method allows accurate and precise characterization of NPs, it suffers from practical drawbacks: (i) micro-quartz filter fibers are released into the sample and must be removed prior to analysis to avoid clogging the nebulizer and (ii) the particle distribution detection limits (LOD_size) achieved are not low enough (28 nm). In this work, we evaluate the NPs trapping capabilities and possible fiber release of filters of different nature commonly used for indoor air quality control (polytetrafluoroethylene (PTFE), nylon, polycarbonate, and mixed cellulose ester (MCE) filters) and NPs of different chemical composition (ZrO₂-, TiO₂-, Pt-, AuNPs), size (20-150 nm), and capping agent (citrate, polyethylene glycol, branched polyethyleneimine, and lipoic acid). The results show that MCE is an optimal solution because it is completely dissolved during the microwave heating step and NPs are recovered quantitatively irrespective of their composition and size. The LODs are also improved down to 15 nm and 120 particles per liter of air, low enough to be used for indoor air pollution control. Finally, the proposed method was successfully tested in a simulated (NPs enriched) indoor environment.