High-accuracy measurement of SF signal using an ultrahigh-resolution isotope ratio mass spectrometer.

Rationale: The ΔS 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 SF 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 working gas and SF gases converted from IAEA-S1/2/3 AgS reference materials.

Results: We found that there are two resolvable peaks to the right of the SF peak when a new filament was installed, which are WF followed by CF . However, only the CF interference peak was observed after more than three days of filament use. CF is generated inside the instrument during the ionization process. Avoiding the interfering signals, we were able to achieve a ΔS standard deviation of 0.046‰ (n = 8) for SF zero-enrichment and 0.069‰ (n = 8) for overall measurement start from silver sulfide IAEA-S1.

Conclusions: Aging the filament with SF gas can avoid the interference of WF . Minimizing the presence of carbon-bearing compounds and avoiding the interfering signals of CF from SF , we can improve ΔS measurement accuracy and precision, which helps to open new territories for research using quadruple sulfur isotope composition.