Chemical analysis of Chang'e-5 lunar soil using LA-ICP-MS in highly diluted fused glass discs

Abstract

The bulk chemical compositions of extraterrestrial materials can provide critical information on the evolution and magmatism of planetary bodies. However, accurate measurements are challenging because these samples, particularly returned samples, are extremely limited and valuable. We demonstrate the practicality of chemical analysis using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on highly diluted fused glass discs (lithium borate flux : sample = 100 : 1). Only 30 mg of sample is required to produce a lithium borate disc, which is one magnitude lower than previously used (>300 mg). We proposed a modified Jet sample cone (the orifice diameter enlarging from 1.1 mm to 1.2 mm) to improve the sensitivity by a factor of ∼4.5 compared to that of standard sample cone. The interferences from the lithium borate discs were evaluated systemically, and corrections are necessary for some elements (e.g., Si, Ca, Pb). The limits of detection for most elements are in the range of 0.1–1.0 μg g⁻¹. The analytical precision is better than 30% (relative standard deviation) for elements with concentrations of >0.5 μg g⁻¹. The accuracy is better than 15% (relative deviation), as demonstrated by analyses of BCR-2 and BHVO-1 rock powder reference materials. This innovative technique was applied to lunar samples collected by Chang'e-5 (CE-5) mission, and an independent dataset of 38 major and trace elements was obtained. We report the average chemical composition of the CE-5 lunar soil samples, which will be an important reference for future study. This method will be useful for other precious extraterrestrial samples (e.g., CE-6 lunar samples).