Determination of ultra-trace rare earth elements in olivine by laser ablation-sector field-inductively coupled plasma-mass spectrometry

Abstract

Rare earth elements (REEs) are important geochemical tracers in multiple fields of geochemistry. In this study, we develop a method for precise determination of olivine Eu/Eu* and REE concentrations (down to sub ng g⁻¹) using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Using a Thermo Element XR SF-ICP-MS, we demonstrated that the Jet + H cone combination with the guard electrode under Ar–N₂ plasma (a small amount of N₂ added into carrier gas flow) conditions provides the optimal conditions for measuring ¹⁴⁷Sm, ¹⁵³Eu, and ¹⁵⁸Gd. Although the Jet + X cone combination could achieve the highest sensitivity, the usage of the X skimmer cone led to an extremely high oxide formation (ThO⁺/Th⁺ >30%) and severe inter-element fractionation. Under optimized laser parameters (spot size: 160 μm, ablation frequency: 15 Hz, and energy density: 8 J cm⁻²) and ICP-MS conditions, detection limits of <0.03 ng g⁻¹ are obtainable for most REEs. The accuracy and precision were evaluated using GOR132-G reference glasses and three olivine reference materials (MongOL Sh11-2, 06JY31OL, and 06JY06OL). The analytical accuracy of Eu/Eu* for GOR132-G is within 5% and the precision of Eu/Eu* for olivines is better than 10% (2 RSD). Finally, we report the REE concentration data for five low-REE reference materials (olivine: MongOL Sh11-2, 06JY31OL, and 06JY06OL, orthopyroxene: 06JY34OPX, and powder pellet: DTS-2b-NP), which might be useful for further characterization of these reference materials.