High‐accuracy measurement of 36SF5+ signal using an ultrahigh‐resolution isotope ratio mass spectrometer

Rationale The Δ 36 S standard deviation measured in a conventional isotope ratio mass spectrometer such as MAT 253 is ca 0.1‰ to 0.3‰. At this precision, it is difficult to resolve the origin of non‐mass‐dependent sulfur isotope fractionation in tropospheric sulfate aerosol and in Martian meteorites or small deviations from the canonical mass‐dependent fractionation laws. Interfering ions with m / z at 131 of 36 SF 5 + are suggested by the community as the cause of the poor precision, but the exact ion species has not been identified or confirmed. Methods Here we examined the potential interfering ions by using a Thermo Scientific ultrahigh‐resolution isotope ratio mass spectrometer to measure SF 6 working gas and SF 6 gases converted from IAEA‐S1/2/3 Ag 2 S reference materials. Results We found that there are two resolvable peaks to the right of the 36 SF 5 + peak when a new filament was installed, which are 186 WF 4 2+ followed by 12 C 3 F 5 + . However, only the 12 C 3 F 5 + interference peak was observed after more than three days of filament use. 12 C 3 F 5 + is generated inside the instrument during the ionization process. Avoiding the interfering signals, we were able to achieve a Δ 36 S standard deviation of 0.046‰ ( n = 8) for SF 6 zero‐enrichment and 0.069‰ ( n = 8) for overall measurement start from silver sulfide IAEA‐S1. Conclusions Aging the filament with SF 6 gas can avoid the interference of 186 WF 4 2+ . Minimizing the presence of carbon‐bearing compounds and avoiding the interfering signals of 12 C 3 F 5 + from 36 SF 5 + , we can improve Δ 36 S measurement accuracy and precision, which helps to open new territories for research using quadruple sulfur isotope composition.