Sulfur isotope analyses using 3× elemental analysis/isotope ratio mass spectrometry: Saving helium and energy while reducing analytical time and costs.

RATIONALE

Helium (He) and energy shortages have caused price increases and reduced their availability. Using three combustion reactions per acquisition of carbon and nitrogen isotope ratios saves 50% He and energy during the elemental analysis/isotope ratio mass spectrometry (EA/IRMS). This approach needs to be tested for sulfur isotope (δS) analyses.

METHODS

A new method to measure δS in three sequential combustion reactions within one EA/IRMS acquisition was developed. The same material or blank samples could be used in the three reactions. After SO was used, a N purging method was employed to prolong the lifetime of the valves in the EA/IRMS interface. The 3×EA/IRMS was applied to measure δS in precious samples, such as AgS from acid-volatile and chromium-reducible sulfur extracted with a multiple-port setup.

RESULTS

The 3×EA/IRMS-δS method was validated with replicate analyses of international reference materials and laboratory standards with a wide range of mineralogical compositions and δS values. The method provided a strategic advantage for the δS measurements of small precious samples (measured between blanks). The accuracy and precision of the 3×EA/IRMS values effectively matched those obtained using conventional EA/IRMS, with good agreement between the mean ± SD values and the recommended values with their uncertainties.

CONCLUSIONS

Compared with the conventional EA/IRMS, the proposed method provides accurate and precise δS measurements of the sulfate and sulfide samples while saving approximately 50% of He, energy, SO reference gas, O, analysis time, and cost. Notably, 3×EA/IRMS can provide up to three δS values unaffected by memory effects.