Triple Oxygen Isotope Measurements by Multi-Collector Secondary Ion Mass Spectrometry

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.

Labeling and Probing the Silica Surface Using Mechanochemistry and 17O NMR Spectroscopy**

“…A 133 Cs + primary ion beam was used, and secondary ions were extracted, allowing 16 O, 17 O, and 18 O to be monitored at a mass resolution of > 2000. The instrument has been recently upgraded with high sensitivity faraday cups (FC 10 12 Ω amplifiers, as described by Bouden et al) 36 This new type of collector offers optimal performances for secondary ion intensities varying from 1 to 2 x 10 6 count per second, which correspond to the typical range of 17 O measured in the present study. These conditions significantly improve the statistical errors (within spot uncertainties <0.2 ‰ 2, as shown in Fig 3 . of the recent study by Bouden et al) 36 associated with the collection of minor masses while working at high resolution.…”

“…Large-geometry secondary-ion mass spectrometry (LG-SIMS) was used to determine the absolute 17 O enrichment of milled silica, this technique allowing the composition of the first few atomic layers to be analyzed. 36 S1), leading to an estimated absolute enrichment of ~5.3 % for BM15min-SiO2. It is worth noting here that this overall increase in 17 O content was also observed in 17 O NMR, when recording the 17 O MAS NMR spectra of BM5min-SiO2 and BM15min-SiO2 samples using "quantitative" acquisition conditions (see supporting information, Figure S2).…”

“…This technique allows the composition of the first few atomic layers to be analyzed. [35] For the synthetic conditions used in our LAG protocol (one equivalent H 2 17 O (90 % 17 O) reacting with one equivalent SiO 2 ), the maximum absolute enrichment was expected to be � 30 % when considering a full isotopic scrambling between 17 O and 16 O sites upon milling. Here, the absolute 17 O enrichment was found to be � 2.2 (� 0.2) % after 5 minutes of milling.…”

“…These conditions significantly improve the statistical errors (within spot uncertainties < 0.2 % 2σ, as shown in Figure 3. of the recent study by Bouden et al) [35] associated with the collection of minor masses while working at high resolution. Data were acquired in both mono-collection (i. e. peak jumping) and multicollection (i. e. simultaneously) modes, in order to identify the best analytical protocol.…”

“…Both settings return comparable analytical precision and provide identical results. [35] For each sample, average 17 O/ 16 O ratios were determined by analyzing a minimum of three different zones of the surface and recording 30 cycles for each zone. The isotopic ratios reported herein (together with the corresponding standard deviations) correspond to an average over the different points of the surface which were analyzed, as shown in Table S1 (Supporting Information).…”