Size determination and quantification of engineered cerium oxide nanoparticles by flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry

Abstract Facing the lack of studies on characterization and quantification of cerium oxide nanoparticles (CeO 2 NPs), whose consumption and release is greatly increasing, this work proposes a method for their sizing and quantification by Flow Field-flow Fractionation (FFFF) coupled to Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Two modalities of FFFF (Asymmetric Flow- and Hollow Fiber-Flow Field Flow Fractionation, AF4 and HF5, respectively) are compared, and their advantages and limitations discussed. Experimental conditions (carrier composition, pH, ionic strength, crossflow and carrier flow rates) are studied in detail in terms of NP separation, recovery, and repeatability. Size characterization of CeO 2 NPs was addressed by different approaches. In the absence of feasible size standards of CeO 2 NPs, suspensions of Ag, Au, and SiO 2 NPs of known size were investigated. Ag and Au NPs failed to show a comparable behavior to that of the CeO 2 NPs, whereas the use of SiO 2 NPs provided size estimations in agreement to those predicted by the theory. The latter approach was thus used for characterizing the size of CeO 2 NPs in a commercial suspension. Results were in adequate concordance with those achieved by transmission electron microscopy, X-ray diffraction and dynamic light scattering. The quantification of CeO 2 NPs in the commercial suspension by AF4-ICP-MS required the use of a CeO 2 NPs standards, since the use of ionic cerium resulted in low recoveries (99 ± 9% vs. 73 ± 7%, respectively). A limit of detection of 0.9 μg L −1 CeO 2 corresponding to a number concentration of 1.8 × 1012 L −1 for NPs of 5 nm was achieved for an injection volume of 100 μL.