ABSTRACT

An improved method for chlorine isotopic analysis by thermal ionization mass spectrometry of Cs₂Cl⁺ has been investigated for precise measurement of ³⁷Cl/³⁵Cl isotopic ratios for small amount of samples. Chlorine in organic and inorganic samples was recovered as AgCl and converted to CsCl with metallic Mg and Cs-form ion exchange resin. The CsCl (containing 2 μg of Cl) was loaded on a Ta filament together with graphite powder. The ³⁷Cl/³⁵Cl ratio measurement was carried out using Cs₂Cl⁺ ions with multi Faraday cup (static mode) for 80–100 min each single run. Replicate analysis of ocean water and laboratory standard (CsCl reagent) yield the in-run precision of 0.1–0.2‰ (2σ_m) for 300–400 ratios and external precision of 0.1–0.2‰ (1σ_SD). This method has been tested on a variety of chemical reagents including metal chlorides, hydrochloric acid and chlorinated organic solvents. It was found that the artificial chlorine compound show large variations of ³⁷Cl/³⁵Cl ratio (total ranges from −5 to +3‰ relative to standard mean ocean chloride) depending upon manufacturing processes. We suggest that the high sensitivity and precision technique established in this work would allow us to detect small isotopic variations of chlorine in small amounts of natural samples such as terrestrial materials (minerals/rocks, sediments, groundwater, etc, as well as environmental materials), meteorites and other planetary materials.