Quantitative accuracy assessment of trace elements and halogens in apatite by time-of-flight secondary ion mass spectrometry (TOF-SIMS)†

Abstract

Apatite, Ca₅(PO₄)₃(F,Cl,OH), is an accessory mineral that is widely present in rocks, usually enriched in trace elements and halogens, such as REEs, S, Mn, Sr, F, Cl, etc. The concentration of the above elements in apatite relies largely on the chemical composition of the corresponding melt from which they crystallized, which can well reflect the magma–fluid evolution as well as the related metallogenic processes. Therefore, apatite research is widely used in the fields of magma genesis, isotope dating, isotope tracing, and mineral exploration. The micro-analysis of apatite mainly uses instruments such as an Electron Probe Micro-Analyzer (EPMA), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and Large Geometry-Secondary Ion Mass Spectrometry (LG-SIMS). In contrast, rapid and convenient Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) has not yet been applied to quantitative analysis of minerals. In this study, Durango apatite was at first used as the test sample to explore the analytical accuracy (precision and correctness of analysis or measurement) as well as the influencing factors for quantitative analysis of trace elements and halogens in apatite by TOF-SIMS. We further explore the feasibility of using NIST 610 glass as a standard reference material for quantitative analysis of trace elements in other matrices (e.g., apatite). The results show that TOF-SIMS quantification of apatite is feasible. When Durango apatite was used as a standard reference material for quantification, TOF-SIMS quantified trace elements (Sr, Mn, and ⁵⁴Fe) and halogens (F and Cl) in apatite with a precision of up to 4.41% (RSD) and a correctness of up to 0.07%. NIST 610 glass can be used as a standard reference material for quantitative analysis of apatite by TOF-SIMS, and the error between measured and true values is within a factor of 3.