High-precision measurement of Eu isotopes enabled by Nd internal normalization†

Abstract

Eu isotopes are recognized as potential indicators for understanding continental crust evolution, ocean circulation, and rare earth element mineralization. However, methods for achieving high-precision Eu isotopic analysis remain underdeveloped. This study pioneers a comprehensive application of the Nd internal normalization technique in Eu isotope analysis, facilitating high-precision measurements of Eu isotope compositions in geological reference materials. It assesses the correction effectiveness of various Nd isotopic ratios (¹⁴⁶Nd/¹⁴⁴Nd, ¹⁴⁶Nd/¹⁴⁵Nd, and ¹⁵⁰Nd/¹⁴⁸Nd) on Eu isotopic measurements and investigates the fractionation behavior of Eu–Nd in mass spectrometers. These findings demonstrate that the ¹⁴⁶Nd/¹⁴⁵Nd ratio significantly enhances the stability and reproducibility of Eu isotope measurements, achieving a long-term external precision of δ^153/151Eu at 0.04‰ (2SD). Additionally, the study reveals that the fractionation behavior of Eu–Nd in mass spectrometry theoretically aligns more closely with the power law rather than the traditionally assumed exponential law. However, in practical tests, no significant difference in results is observed whether employing the power law or the exponential law. These insights advance Eu isotope geochemistry and provide a valuable reference for the high-precision analysis of other rare earth elements.