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

Cerium dioxide nanoparticles (CeO NPs) are widely used in various fields, leading to concern about their effect on human health. When conducting in vivo investigations of CeO NPs, the challenge is to fractionate ionic Ce and CeO NPs and to characterize CeO 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 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 NPs. Results showed that enzymatic pretreatment was more efficient in extracting ionic Ce or CeO 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 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 NPs in mice. It was found that the thymus acts as a "holding station" in CeO NP translocation in vivo. CeO 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 NPs. This integrated ICP-MS-based analytical approach enables us to conduct in vivo biotransformation investigations of CeO NPs.