An integrated ICP-MS-based analytical approach to fractionate and characterize ionic and nanoparticulate Ce species.

Cerium dioxide nanoparticles (CeO 2 NPs) are widely used in various fields, leading to concern about their effect on human health. When conducting in vivo investigations of CeO 2 NPs, the challenge is to fractionate ionic Ce and CeO 2 NPs and to characterize CeO 2 NPs without changing their properties/state. To meet this challenge, we developed an integrated inductively coupled plasma-mass spectrometry (ICP-MS)-based analytical approach in which ultrafiltration is used to fractionate ionic and nanoparticulate Ce species while CeO 2 NPs are characterized by single particle-ICP-MS (sp-ICP-MS). We used this technique to compare the effects of two sample pretreatment methods, alkaline and enzymatic pretreatments, on ionic Ce and CeO 2 NPs. Results showed that enzymatic pretreatment was more efficient in extracting ionic Ce or CeO 2 NPs from animal tissues. Moreover, results further showed that the properties/states of all ionic and nanoparticulate Ce species were well preserved. The rates of recovery of both species were over 85%; the size distribution of CeO 2 NPs was comparable to that of original NPs. We then applied this analytical approach, including the enzymatic pretreatment and ICP-MS-based analytical techniques, to investigate the bioaccumulation and biotransformation of CeO 2 NPs in mice. It was found that the thymus acts as a "holding station" in CeO 2 NP translocation in vivo. CeO 2 NP biotransformation was reported to be organ-specific. This is the first study to evaluate the impact of enzymatic and alkaline pretreatment on Ce species, namely ionic Ce and CeO 2 NPs. This integrated ICP-MS-based analytical approach enables us to conduct in vivo biotransformation investigations of CeO 2 NPs.