Presentation Information
[PPS12-P15]Ruthenium isotope analysis of carbonaceous chondrites
*Akio Nomura1, Nao Nakanishi1, Tetsuya Yokoyama1 (1.Department of Earth and Planetary Sciences, School of Science, Institute of Science Tokyo)
Keywords:
Ruthenium isotope,Carbonaceous chondrite,N-TIMS,Nucleosynthetic isotope anomaly
In recent years, nucleosynthetic isotope anomalies have been reported for ruthenium (Ru) in a variety of meteorites and terrestrial samples. High-precision measurements of Ru isotopic ratios in meteorites provide insights into the origin and mixing processes of Solar System materials. Furthermore, when Ru and molybdenum (Mo) isotopic ratios in meteorites are plotted in two-dimensional isotope space, the isotopic anomalies are clearly divided into carbonaceous (CC) and non-carbonaceous (NC) groups. This dichotomy suggests that the parent bodies of CC and NC meteorites formed in distinct regions and under different conditions within the protoplanetary disk [1]. In addition, because Ru is classified as HSEs, the isotopic composition of Ru in impact melts accreted onto planetary bodies or in the silicate part of the Earth can be used to constrain the nature of impactor materials and the sources of late accretional components [2, 3].
Ruthenium isotope measurements of meteorites and terrestrial samples are commonly performed using MC-ICP-MS or N-TIMS [2, 4]. For Ru isotope analysis by N-TIMS, samples are digested using acids, followed by one- or two-stage column chromatography and micro-distillation to separate and purify Ru [4]. The objective of this study is to optimize the chemical separation and TIMS analytical procedures for Ru isotopes in carbonaceous chondrites and to apply the optimized method to actual isotope analyses. Previous studies on Ru isotope analysis of carbonaceous chondrites are limited, and most existing measurements have been conducted using MC-ICP-MS [2].
In this study, three carbonaceous chondrites Murchison (CM2), Allende (CV3), and Tagish Lake (C2-ung), as well as two iron meteorites Chinga (ungrouped) and Canyon Diablo (IAB), were investigated. To optimize the analytical procedure, experiments were first conducted on the two iron meteorite samples. Thoroughly cleaned fragments of the iron meteorites were digested in HCl at a high temperature, followed by two-stage ion-exchange chromatography and micro-distillation. In the first column, using the cation-exchange resin AG50W-X8, Ru and Mo were collected in the same fraction. Complete separation of Ru and Mo was then achieved in the second column using the anion-exchange resin 1-X8. The Ru fraction recovered from the second column was further purified from remaining matrix elements by micro-distillation. The purified Ru was loaded onto metal filaments, introduced into the TIMS, and analyzed for isotopic composition. The overall Ru recovery yields during chemical processing of the two iron meteorite samples were approximately 40% for Chinga and 60% for Canyon Diablo, which provided sufficient Ru for measurements. In contrast, the recovery yield of Mo up to the second column was approximately 100%. The Ru isotopic ratios obtained for both iron meteorites are consistent, within analytical uncertainties, with previously reported values for all isotope ratios [5]. These results demonstrate that the Ru isotope analytical method using TIMS developed in this study is both accurate and reliable.
In future work, the optimized procedure established for the iron meteorites will be applied to the three carbonaceous chondrite samples. Powdered samples will be digested at high temperature using HCl, HNO3, and HF, followed by two-stage column chromatography to purify Ru while simultaneously recovering Mo, and Ru isotope ratios will then be measured by TIMS. Ru recovery yields will be evaluated, and the isotopic ratios and their analytical reproducibility will be compared with previous studies to assess the performance of the method. In addition, isotopic analyses of Mo separated from the same solutions will be conducted by increasing the number of samples analyzed. Using the combined Ru and Mo isotopic data, nucleosynthetic isotope anomalies in carbonaceous chondrites will be examined, and implications for the formation processes of their parent bodies will be discussed.
Ruthenium isotope measurements of meteorites and terrestrial samples are commonly performed using MC-ICP-MS or N-TIMS [2, 4]. For Ru isotope analysis by N-TIMS, samples are digested using acids, followed by one- or two-stage column chromatography and micro-distillation to separate and purify Ru [4]. The objective of this study is to optimize the chemical separation and TIMS analytical procedures for Ru isotopes in carbonaceous chondrites and to apply the optimized method to actual isotope analyses. Previous studies on Ru isotope analysis of carbonaceous chondrites are limited, and most existing measurements have been conducted using MC-ICP-MS [2].
In this study, three carbonaceous chondrites Murchison (CM2), Allende (CV3), and Tagish Lake (C2-ung), as well as two iron meteorites Chinga (ungrouped) and Canyon Diablo (IAB), were investigated. To optimize the analytical procedure, experiments were first conducted on the two iron meteorite samples. Thoroughly cleaned fragments of the iron meteorites were digested in HCl at a high temperature, followed by two-stage ion-exchange chromatography and micro-distillation. In the first column, using the cation-exchange resin AG50W-X8, Ru and Mo were collected in the same fraction. Complete separation of Ru and Mo was then achieved in the second column using the anion-exchange resin 1-X8. The Ru fraction recovered from the second column was further purified from remaining matrix elements by micro-distillation. The purified Ru was loaded onto metal filaments, introduced into the TIMS, and analyzed for isotopic composition. The overall Ru recovery yields during chemical processing of the two iron meteorite samples were approximately 40% for Chinga and 60% for Canyon Diablo, which provided sufficient Ru for measurements. In contrast, the recovery yield of Mo up to the second column was approximately 100%. The Ru isotopic ratios obtained for both iron meteorites are consistent, within analytical uncertainties, with previously reported values for all isotope ratios [5]. These results demonstrate that the Ru isotope analytical method using TIMS developed in this study is both accurate and reliable.
In future work, the optimized procedure established for the iron meteorites will be applied to the three carbonaceous chondrite samples. Powdered samples will be digested at high temperature using HCl, HNO3, and HF, followed by two-stage column chromatography to purify Ru while simultaneously recovering Mo, and Ru isotope ratios will then be measured by TIMS. Ru recovery yields will be evaluated, and the isotopic ratios and their analytical reproducibility will be compared with previous studies to assess the performance of the method. In addition, isotopic analyses of Mo separated from the same solutions will be conducted by increasing the number of samples analyzed. Using the combined Ru and Mo isotopic data, nucleosynthetic isotope anomalies in carbonaceous chondrites will be examined, and implications for the formation processes of their parent bodies will be discussed.