Trace element determination by femtosecond LA-ICP-MS in 10 mg extraterrestrial geological samples prepared as lithium borate glasses†

Abstract

Bulk chemical composition analysis is a primary and pivotal analytical task for extraterrestrial geological samples (e.g., lunar soil, asteroids, or meteoroids). However, the analysis of mg-level consumption of extraterrestrial geological samples poses a significant challenge to existing analytical techniques. In this study, a new method was developed for trace element determination in bulk extraterrestrial geological samples prepared as lithium borate glasses, following customized procedures for X-ray fluorescence (XRF) analysis with a 10 mg sample by femtosecond LA-ICP-MS. All thirty-two trace elements in the borate glass samples were evenly distributed with homogeneity indices (H) < H_crit. For the borate glass samples, Si was more suitable as an internal standard for Co, Ni, Cu, and Zn, whereas Al was better for the others. The femtosecond laser greatly reduces the influence of matrix effects, making calibration with non-matrix-matched external standards (NIST 612 and 614) accurate. Although the mass ratio of the flux and sample was as high as 35 : 1, the analytical results of 32 trace elements in six silicate rock reference materials (covering mafic to felsic rock types) using the developed technique were consistent with the reference values within 10% for most elements, and analytical precision (RSD) was also within 10% for most elements. Finally, one lunar basalt (NWA14526) and one shergottite (NWA13190) were assayed using the proposed method, and a comparison with the results of solution nebulization (SN)-ICP-MS confirmed the reliability of the method. The proposed method, combined with XRF, achieved the rapid, simultaneous, and accurate determination of major and trace elements in the same small sample aliquot (10 mg), which is highly suitable for the analysis of extraterrestrial geological samples.