The determination of ultra-trace rare-earth elements in iron minerals via HR-ICP-MS following chemical purification by polyurethane foam

Abstract

This study describes a simple and low-cost method that requires small samples (<20 mg) for the determination of rare-earth elements (REEs) in iron minerals using high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) following chemical purification by polyurethane foam (PUF). Powdered samples were digested via a conventional dissolution protocol with a HF, HCl, and HNO₃ acid mixture. The elimination of matrix iron was performed using 0.14 g of PUF under the static sorption mode with 8 M HCl. To obtain a high iron removal rate, we investigated the separation conditions (e.g., HCl concentration and initial iron concentration). Under the optimized extraction conditions, the iron removal rate reached 98.8% ± 0.1% (n = 6, SD) and the REE recoveries were between 98% and 104%. Three reference materials, FER-1, FER-2 (from iron formations) and pyrite GBW07267, were used to validate and evaluate the feasibility and robustness of our protocol. Our results agreed well with previously reported values within error, and the precision relative standard deviation (RSD) values for most of the REEs were <5%. Our results showed that this simple method provides an efficient way to precisely determine ultra-low REEs in iron-rich monominerals. Compared with previous approaches, the current protocol can be applied to the analysis of limited or precious terrestrial and extraterrestrial iron-rich samples (e.g., Fe-olivine and meteorites).