Fully resolved high-precision measurement of 36 S for sulfur reference materials

Advances in sulfur isotope measurement techniques have led to increased analytical precision. However, accurate measurement of 36 S remains a challenge, hindering research such as that focused on microbial metabolic processes. This difficulty arises partly from isobaric interferences of 36 SF 5 + at m/z = 131 amu, namely 186 WF 4 2+ and 12 C 3 F 5 + which lead to scale compression. Our study develops an interference-free four-sulfur isotope measurement method using the high-resolution mass spectrometer Panorama. Panorama’s peak scan showed that the relative intensity of 186 WF 4 2+ was initially 9.4% of 36 SF 5 + but was reduced to 1.5% through tuning, while the 12 C 3 F 5 + relative intensity dropped from 74% to 40% after flushing with air and continued to decrease over time. Theoretically, an unresolved isobaric interference with 2% relative intensity could cause a 1‰ underestimation in a sample with a real δ 36 S value of +60‰. We analyzed three IAEA sulfur isotope standards. Recommended 36 S values we obtained relative to IAEA-S-1 are Δ 36 S IAEA-S-2 = 1.238 ± 0.040‰, and Δ 36 S IAEA-S-3 = -0.882 ± 0.030‰. For cases where the interferences cannot be removed, we offer a calibration method to correct for the scale compression effect. This involves bracketing two or more IAEA standards in the sample measurement sequence and then extending the measured IAEA δ 36 S values by a calibration factor to match the values reported in this study. Applying this calibration factor to the samples effectively corrects the scale compression effect.