An analytical system for studying the stable isotopes of carbon monoxide using continuous flow-isotope ratio mass spectrometry (CF-IRMS)

Abstract

Abstract. In the atmosphere, carbon monoxide (CO) is the major sink for the hydroxyl radical (OH •), has multiple anthropogenic and natural sources and considerable spatial and seasonal variability. Measurements of CO isotopic composition are useful in constraining the strengths of its individual source and sink processes and thus its global cycle. A fully automated system for δ13C and δ18O analysis has been developed to extract CO from an air sample, convert CO into carbon dioxide (CO2) using the Schütze reagent, and then determine the isotopic composition in an isotope ratio mass spectrometer (IRMS). The entire system is continuously flushed with high-purity helium (He), the carrier gas. The blank signal of the Schütze reagent is only 1–3% of the typical sample size. The repeatability is 0.1‰ for δ13C and 0.2‰ for δ18O. The peak area allows simultaneous determination of the mole fraction with an analytical repeatability of ~0.7 nmol mol−1 for 100 mL of typical ambient air (185.4 nmol mol−1 of CO). A single, automated, measurement is performed in 18 min, so multiple measurements can be combined conveniently to improve precision.