An improved narrower-diameter EA/IRMS method with a built-in desulfurization reactor: optimization for nitrogen and carbon measurement without sulfur matrix interference

Abstract Elemental analysis with isotope ratio mass spectrometry (EA/IRMS) is a widely used technique for stable isotope ratio analysis of nitrogen and carbon. Although the narrower-diameter EA/IRMS method developed to date has effectively enhanced sensitivity and addressed issues associated with low organic content, it may result in the drawback of reduced analytical precision when analyzing samples with high sulfur matrix levels due to interference from sulfur oxides. To address the sulfur breakthrough issue, this study incorporated an additional desulfurization reactor into an existing EA system. The improved method achieved high sensitivity (approximately a fivefold increase over conventional methods) and high sulfur resistance (sulfur tolerance exceeding that of conventional methods by up to 580 mg S). In addition, we applied this method to the analysis of environmental samples with low organic and high sulfur (S/C ratio: 0.7–343.1) contents, including native sulfur-rich seafloor sediments, sulfide chimneys of submarine hydrothermal deposits, and subseafloor sediments from hydrothermal regions. Moreover, in this study, we investigated the types of interference that occurred during sulfur breakthrough in EA/IRMS analysis. Consequently, broad non-integer peaks (hypothesized to result from metastable ions and charge exchanges generated within the flight tube of the mass spectrometer) originating from SO 2 molecular and fragment ions were observed, and the background levels of N 2 and CO 2 were affected. Here, we recommend applying this improvement to the NC analysis of samples with low organic and high S contents.