Optimization of SIMS analytical parameters for water content measurement of olivine

Abstract

Secondary ion mass spectrometry (SIMS) has a wide range of applications in Earth Science research, thanks to its high precision and sensitivity, and its capacity in direct insitu micromeasurement. The technique is operated in ultra‐high vacuum (UHV) conditions, especially for the measurement of volatiles such as hydrogen, or the water content in nominally anhydrous minerals (NAMs). To minimize the water background and obtain accurate and precise water contents in NAMs (eg, olivine) critical parameters such as presputtering time, field aperture (FA), dynamic transfer on/off, and primary beam current intensity were investigated for a CAMECA IMS 1280‐HR system. When the chamber vacuum reaches approximately 2 × 10−9 mbar, we set the DTOS OFF, raster size to 50 μm and primary beam current to 5 nA, and used 2000 μm FA and 170‐second presputtering time. Consequently, an approximately 1.2 ppmw water background and 3.6 ppmw limit of detection (LOD) were yielded, from analyzing the San Carlos olivine. Meanwhile, the water content and homogeneity of a range of olivine minerals were characterized for potential use as reference materials for SIMS water content measurement. Olivine water content calibration curve was also established by comparing the Fourier transform infrared (FTIR) results with the SIMS‐measured 16O1H−/16O− ratios. Accuracy and precision of water content measurement were estimated to be better than approximately 10% in this study.

A dry lunar mantle reservoir for young mare basalts of Chang’e-5

“…A chip of the anhydrous San Carlos olivine reference with a reported water content of 1.4 μg g −1 (ref. 55 ) was used for H background (bg) corrections, following the relationship: H/O bg = (H counts − H bg )/O counts and D/H measured = (1 − f ) × D/H true + f × D/H bg , where O is oxygen and f is the proportion of H emitted from the instrumental background 56 . Here D/H bg was 3.36 (±0.55) × 10 −4 and H bg = 689 ± 139 counts per second (2 s.d., N = 11, corresponding to a water background abundance of 25 ± 8 μg g −1 (2 s.d.)).…”

“…San Carlos olivine (H 2 O = 1.4 g.g -1 , ref. 55 ) was used for determining instrumental background of H. The analytical results are listed in Extended Data Table 4.…”

The Origin of Late Cenozoic Magmatism in the South China Sea and Southeast Asia

“…Xia et al., 2019; W.‐F. Zhang et al., 2020). To monitor accuracy and repeatability of H 2 O content analysis, BCR‐2G and MORB glass were repeatedly analyzed during the analytical session (Table ).…”

“…Samples were mounted on tin‐based alloy mount and stored under vacuum for at least 6 h prior to analysis (W.‐F. Zhang et al., 2020). A normal‐incidence electron gun was used for sample charge compensation during the course of analysis and the nuclear magnetic resonance controller was used to stabilize the magnetic field.…”

“…The relative signal intensity of 16 O 1 H to 16 O with a calibration curve of three well-characterized hydrous glass standards was used to yield estimates of water content for each spot analysis. The hydrogen background during the analyses was on the order of 10 ppm (X.-P. Xia et al, 2019;W.-F. Zhang et al, 2020). To monitor accuracy and repeatability of H 2 O content analysis, BCR-2G and MORB glass were repeatedly analyzed during the analytical session (Table S7).…”