Cosmo and Geochemical studies of chlorine isotopes

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Stable isotopes such as hydrogen and oxygen have been used as an important tool in Cosmic and geochemistry and have significantly contributed to the solution of a wide variety of geochemical problems. Chlorine isotopes, however, have rarely been used for these purposes due to difficulties in precise isotopic analyses. Particularly, almost no isotopic data have been reported for meteorites. The purpose of this project is to establish high precision analytical technique of chlorine isotopes for planetary materials (including meteorites) by a thermal ionization mass spectrometry.In the first year, the mass spectrometric technique using molecular species of C_<s2>Cl^+ ions have been developed successfully and the precision of 0.1 permil (‰) for ^<37>Cl/^<35>Cl ratio was established using reagent standard (CsCl). We have carried out analyses of chlorine in many organic and inorganic chloride compounds and found large variations of δ^<37>Cl_<SMOC> from -5 to +3 ‰ for commercial chloride comp … More ounds. In the second year, mass discrimination processes during reductive dechlorination of chlorinated ethenes by anaerobic bacteria have been investigated and found ssite-dependent isotopic discrimination. Chlorine concentrations were determined using an ion chromatography. Replicate analyses have been carried for standard mean ocean chloride (SMOC) and reagent standard (CsCl) and then established ^<37>Cl/^<35>Cl ratio ; 0.319790±60, which was defined as reference (δ^<37>Cl_<SMOC> = 0.00 ‰) and one of reagents (CsCl) was employed as laboratory standard with the ratio of δ^<37>Cl_<SMOC> = -2.56±0.21 ‰. The HF-leaching method has been successfully developed for efficient extraction of chlorine from rock samples (recovery : 85-90%).In the 3^<rd> year, we have carried out analyses of meteorites and terrestrial standards. The results are ; δ^<37>Cl_<SMOC> = -0.74±0.24 (‰) for JR-1 ; δ^<37>Cl_<SMOC> = -2.87±0.32 (‰) for Allende chondrite ; ^<37>Cl_<SMOC> = +0.47±0.52 (‰) for Allegan ordinary chondrites. It is remarkable that isotopic compositions area clearly resolvable among these planetary materials including two chondrites, although the isotopic data area still preliminary. We, therefore, suggest that the high precision technique established in this project is now applicable to analyses for a wide variety of planetary materials including meteorites. Less