Tandem Elemental Analysis of Chang’e-6 Lunar Soil Samples Using X-ray Fluorescence and Femtosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Abstract

The Chang’e-6 (CE6) lunar mission returned the first lunar soil samples from the far side of the Moon in June 2024. We analyzed 10 major elements, one minor element, and 31 trace elements in two CE6 lunar soil samples using a tandem X-ray fluorescence (XRF) and femtosecond laser ablation inductively coupled plasma mass spectrometry (ICP-MS) technique. To reduce sample consumption, a procedure combining the automatic and manual preparation of lithium borate glass discs was implemented. In total, 30 mg of samples was prepared in a highly diluted form as glass discs (with a flux-to-sample ratio of 100:1) by fusing the CE6 soil with a lithium borate flux. For major element analysis using XRF, the lithium borate glass discs were prepared by using an improved method that eliminates the need for a releasing agent to effectively avoid the interference of Br on Mn. Furthermore, a femtosecond laser was used for large-area line scanning to increase the sampling volume to address the challenges associated with trace element analysis via ICP-MS in high-dilution-ratio fused glass discs. This tandem elemental analysis technique allows for the measurement of major and trace element mass fractions from a single sample, using a rapid and straightforward preparation method that effectively addresses resistant phases (e.g., zircon) while significantly reducing sample usage for these precious samples and enhancing the sample preparation efficiency.