High-Precision Erbium Isotopes Analysis by MC-ICP-MS Using a Two-Column Chromatographic Protocol with Dysprosium Internal Normalization

Abstract

Erbium (Er) isotopes are promising analytes of significant interest to the original building blocks of the Solar System, the evolution of the Earth, and modern marine geochemical cycles. However, high-precision Er isotope analysis is hindered by the difficulty of separating Er from neighboring rare earth elements, as well as the absence of a robust, internationally standardized protocol. This study presents an optimized purification procedure using AG50W-X12 and LN resins, which achieves quantitative Er recovery (99.5 ± 0.4%), low procedural blanks (< 25 pg), and complete removal of all interfering matrix elements (e.g., Ba, La−Dy, Ho, and Tm). For Er isotope measurement, a combined standard-sample bracketing with Dy internal normalization (C-SSBIN) was conducted to normalize instrumental mass bias on a Nu Plasma 1700 multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). This yields long-term external reproducibility of ±0.04‰ (2SD) for δ168Er values. The robustness and accuracy of the method are validated by replicate analyses of seven geological reference materials (GRMs), providing the first δ168Er values for rhyolite (JR-2), granites (JG-2 and GSR-1), and Mn nodules (Nod-P-1 and Nod-A-1). The distinct isotopic signatures observed between igneous rocks and Mn nodules highlight the potential of Er isotopes as tracers for high- and low-temperature geochemical processes. This study provides practical, highly efficient, and high-precise analytical techniques that address a critical gap in REEs stable isotope geochemistry, opening up new possibilities for the broader application of Er isotopes in cosmochemistry, geochemistry, and marine geology.