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

Rationale: Advances in sulfur isotope measurement techniques have led to increased analytical precision. However, accurate measurement of S remains a challenge. This difficulty arises primarily from unresolved isobaric interferences of SF at m/z = 131 u, WF and CF , which lead to scale compression. Theoretically, unresolved interference with 2% relative intensity could cause 1‰ underestimation in a sample with real δS = +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 WF and CF from SF .

Results: The WF relative intensity was initially 9.4% that of SF but reduced to 1.5% through tuning, while CF relative intensity dropped from 74% to 40% after flushing with air. Three IAEA standards were analyzed with both Panorama and MAT 253. We obtained ΔS = 1.238 ± 0.040‰ and ΔS = -0.882 ± 0.030‰, relative to IAEA-S-1, from Panorama, and ΔS = 0.18 ± 0.02‰ and ΔS = 0.11 ± 0.14‰ from MAT 253, while δS values from the two instruments are consistent.

Conclusion: The measurement discrepancies on S between Panorama and MAT 253 highlight the impact of scale compression due to unresolved isobaric interferences. Resolving this problem is crucial for accurate 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 δS, δS, and δS 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.