Accurate and Efficient SIMS Oxygen Isotope Analysis of Composition-Variable Minerals: Online Matrix Effect Calibration for Dolomite

Abstract

High-quality oxygen isotope analysis of composition-variable minerals (e.g., ubiquitous carbonates) using secondary ion mass spectrometry (SIMS) is extremely challenging. The classical off-line procedure, which requires additional electron probe microanalyzer (EPMA) chemical compositions for calibrating instrumental mass fractionation (IMF), is inherently inaccurate and analytically inefficient. In this study, the first accurate and paired SIMS analysis of δ18O and Fe# [molar Fe/(Mg + Fe)] in dolomite is reported. Based on five newly developed dolomite O-isotopic standards with an Fe# range of 0.01–0.35 obtained by SIMS, a novel accurate and rapid online matrix effect calibration method for dolomite O-isotope analysis was developed using concurrent SIMS 18O–16O–56Fe16O–24Mg16O measurements without additional chemical electron probe microanalysis. A logistic equation was proposed as the best-fit curve to represent the δ18O matrix effect based on the 56Fe16O/24Mg16O ratios. For CTD-4 carbonatitic dolomite with variable Fe# but homogeneous oxygen isotopes, the off-line method exhibited highly variable apparent δ18O values in the range of 5.74–10.11‰. The online method yielded a homogeneous δ18O value of 7.94 ± 0.34‰ (2SD, n = 40), which is comparable with that of bulk analysis (7.94 ± 0.20‰; 2SD). Comprehensive analyses validated the online method as the best strategy for performing accurate δ18O analysis of samples with highly heterogeneous compositions. Based on its accuracy, simplicity, and economic feasibility, this method has potential applications in the analysis of composition-complex dolomites, detrital dolomites, and other precious terrestrial and extraterrestrial materials.

In situ Ti isotopic analysis by femtosecond laser ablation MC-ICP-MS

“…One of the important issues that affect the accuracy of microbeam analysis is the matrix effect. [66][67][68][69][70] In this case systematical assessment of the matrix effect was conducted by using PZH12-15 ilmenite, the most homogeneous natural mineral assessed on a 35 mm-scale and precision of the measurement in this study, as the bracketing reference material to analyze the other ilmenites, rutiles and Alfa-Ti metal. The results are summarized in Table 3 and illustrated in Fig.…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Certied U particles were used 26 in a comparison of AMS, SIMS and TIMS for the determination of isotope ratios in individual U particles, an application important for nuclear provenance and safeguarding purposes. The relative errors in the determination of 234 U/ 235 U and 234 U/ 236 U in NBL CRM U200 (uranium isotopic standard) by AMS were <10 and <20%, respectively, whereas the results obtained by ssion track-TIMS and SIMS were within ±5% and ±10% of the certied values, respectively, for both techniques. The relative error and external precision of 234 U/ 238 U and 235 U/ 238 U in the analysis of NBL CRM U850 (uranium (U 3 O 8 ) isotopic standard, 85% U-235) by AMS, SEM-TIMS or SIMS were <10% and <5%, respectively.…”

“…The relative errors in the determination of 234 U/ 235 U and 234 U/ 236 U in NBL CRM U200 (uranium isotopic standard) by AMS were <10 and <20%, respectively, whereas the results obtained by ssion track-TIMS and SIMS were within ±5% and ±10% of the certied values, respectively, for both techniques. The relative error and external precision of 234 U/ 238 U and 235 U/ 238 U in the analysis of NBL CRM U850 (uranium (U 3 O 8 ) isotopic standard, 85% U-235) by AMS, SEM-TIMS or SIMS were <10% and <5%, respectively. The average values of the relative error and external precision for 236 U/ 238 U were both <5% for AMS analysis but <10% for SEM-TIMS or SIMS analyses.…”

“…A new suite of olivine and pyroxene RMs with an expanded range of compositions was developed to provide better analytical precision and instrumental bias correction in the analysis of olivine and low-Ca pyroxene in primitive chondrule minerals. A novel method for the determination of d 18 O and molar ratio Fe/(Mg + Fe) (known as Fe#) in dolomite by SIMS involved 235 the concurrent measurement of 18 O 16 O, 56 Fe 16 O and 24 Mg 16 O, thereby avoiding the need for additional EPMA compositional information. Five newly developed dolomite RMs with an Fe# range of 0.01 to 0.35 were employed for calibration.…”

A silica-related matrix effect on NanoSIMS Li isotopic analysis of glasses and its online calibration

“…"Offline" methods to calibrate the matrix effect are commonly used, by which the quantitative determination of SiO 2 contents using EMPA in unknown samples is required to estimate IMF subsequently based on empirical correction curves. 24,25,29,33,34,76,77 Here, we compare the IMF-correction efficacy of the up-to-date "online" method with that of the conventional "offline" method.…”