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

Rationale Advances in sulfur isotope measurement techniques have led to increased analytical precision. However, accurate measurement of 36 S remains a challenge. This difficulty arises primarily from unresolved isobaric interferences of 36 SF 5 + at m / z = 131 u, 186 WF 4 2+ and 12 C 3 F 5 + , which lead to scale compression. Theoretically, unresolved interference with 2% relative intensity could cause 1‰ underestimation in a sample with real δ 36 S = +60‰. Methods Our study develops an interference‐free four‐sulfur isotope measurement method by using the high‐resolution mass spectrometer Panorama. The mass resolving power of Panorama allows the distinction of 186 WF 4 2+ and 12 C 3 F 5 + from 36 SF 5 + . Results The 186 WF 4 2+ relative intensity was initially 9.4% that of 36 SF 5 + but reduced to 1.5% through tuning, while 12 C 3 F 5 + relative intensity dropped from 74% to 40% after flushing with air. Three IAEA standards were analyzed with both Panorama and MAT 253. We obtained Δ 36 S IAEA‐S‐2 = 1.238 ± 0.040‰ and Δ 36 S IAEA‐S‐3 = −0.882 ± 0.030‰, relative to IAEA‐S‐1, from Panorama, and Δ 36 S IAEA‐S‐2 = 0.18 ± 0.02‰ and Δ 36 S IAEA‐S‐3 = 0.11 ± 0.14‰ from MAT 253, while δ 34 S values from the two instruments are consistent. Conclusion The measurement discrepancies on 36 S between Panorama and MAT 253 highlight the impact of scale compression due to unresolved isobaric interferences. Resolving this problem is crucial for accurate 36 S analysis. We recommend replacing the filament material with rhenium, tuning the filament voltage, and avoiding carbon in instruments to eliminate or mitigate interferences. We propose future systematic efforts to calibrate the δ 33 S, δ 34 S, and δ 36 S of IAEA‐S‐1, IAEA‐S‐2, and IAEA‐S‐3 and advise bracketing all three reference materials in the measurement sequences, to enable calibration.