Abstract
Secondary ion mass spectrometry (SIMS) is a powerful technique for in situ triple oxygen isotope measurements that has been used for more than 30 years. Since pioneering works performed on small-radius ion microprobes in the mid-80s, tremendous progress has been made in terms of analytical precision, spatial resolution and analysis duration. In this respect, the emergence in the mid-90s of the large-radius ion microprobe equipped with a multi-collector system (MC-SIMS) was a game changer. Further developments achieved on CAMECA MC-SIMS since then (e.g., stability of the electronics, enhanced transmission of secondary ions, automatic centering of the secondary ion beam, enhanced control of the magnetic field, 1012Ω resistor for the Faraday cup amplifiers) allow nowadays to routinely measure oxygen isotopic ratios (18O/16O and 17O/16O) in various matrices with a precision (internal error and reproducibility) better than 0.5‰ (2σ), a spatial resolution smaller than 10 µm and in a few minutes per analysis. This paper focuses on the application of the MC-SIMS technique to the in situ monitoring of mass-independent triple oxygen isotope variations.
Highlights
Being third in terms of abundance in the Solar System (Lodders, 2003), oxygen is of upmost importance as it plays a critical role in most biological and geological processes
Large-radius ion microprobes are equipped with a set of electron multipliers (EMs) and Faraday cups (FCs) that cover different counting ranges
Preamplifier boards of SHRIMP instruments can be equipped with a capacitor instead of a resistor allowing FCs to work in charge mode instead of current mode (Ireland et al, 2014)
Summary
Being third in terms of abundance in the Solar System (Lodders, 2003), oxygen is of upmost importance as it plays a critical role in most biological and geological processes. Oxygen isotope measurements performed by smallradius ion microprobes were subject to several issues, for instance instabilities due to charge build-up during analyses of electrically insulating samples (e.g., silicates or oxides), low count rates, isobaric interferences (namely 16OH on 17O) or variable and unconstrained instrumental mass fractionations (IMF), leading to poor precision (at a few permil level on 18O/16O ratios) and poor accuracy.
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