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 (δ ³⁴ S) analyses.
A new method to measure δ ³⁴ S 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 ₂ was used, a N ₂ purging method was employed to prolong the lifetime of the valves in the EA/IRMS interface. The 3×EA/IRMS was applied to measure δ ³⁴ S in precious samples, such as Ag ₂ S from acid-volatile and chromium-reducible sulfur extracted with a multiple-port setup.
The 3×EA/IRMS-δ ³⁴ S method was validated with replicate analyses of international reference materials and laboratory standards with a wide range of mineralogical compositions and δ ³⁴ S values. The method provided a strategic advantage for the δ ³⁴ S 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.
Compared with the conventional EA/IRMS, the proposed method provides accurate and precise δ ³⁴ S measurements of the sulfate and sulfide samples while saving approximately 50% of He, energy, SO ₂ reference gas, O ₂ , analysis time, and cost. Notably, 3×EA/IRMS can provide up to three δ ³⁴ S values unaffected by memory effects.