Inorganic Phosphate-Mediated Efficient Fabrication of Phosphate Ester-Functionalized Stationary Phases for Full-Series Rare Earth Element Separation

Abstract

Rare earth elements (REEs) are irreplaceable in advanced new materials and high-end manufacturing industries. However, their nearly identical physicochemical properties, coupled with the associated diverse impurities, render the full separation of REEs a long-standing and formidable challenge in analytical separation science. In this work, a novel phosphate ester-functionalized cation-exchange stationary phase (Sil-PCX) was successfully developed for the first time via a simple inorganic phosphate-mediated synthesis. Benefiting from the moderate ion-exchange characteristics of phosphate ester groups, the proposed stationary phase accomplished the complete separation of the entire series of REEs within 55 min and afforded a high resolution of 2.6 for the hard-to-separate Dy/Y pair. Stability tests revealed that the relative standard deviation (RSD) of retention times for all REEs was below 0.23% following ten consecutive injections, which verified the excellent reproducibility and operational stability of the developed stationary phase. Moreover, the sub-2 μm Sil-PCX enables ultrafast separation of REEs within 10 min, providing a robust technical foundation for the precise quantitative analysis and detection of all REEs. Notably, the stationary phase demonstrated remarkable separation capability for REEs and radioactive nuclide impurities, enabling efficient removal of radioactive contaminants (U and Th) from REE matrices. Furthermore, density functional theory (DFT) calculations have elucidated the mechanism of chromatographic separation of REEs on Sil-PCX. Overall, the phosphate ester-based column exhibited superior separation performance and excellent stability, meeting the requirements of both analytical determination and large-scale preparation of high-purity REEs.