An analytical system for stable isotope analysis on carbon monoxide using continuous-flow isotope-ratio mass spectrometry

A fully automated system for the determination of δ¹³C and δ¹⁸O in atmospheric CO has been developed. CO is extracted from an air sample and converted into carbon dioxide (CO₂) using the Schütze reagent. The isotopic composition is determined with an isotope-ratio mass spectrometer (IRMS) technique. The entire system is continuously flushed with high-purity helium (He), the carrier gas. The blank signal of the Schütze reagent is ∼ 4 nmol mol^-1, or 1-3 % of the typical sample size. The repeatability is 0.1 ‰ for δ¹³C and 0.2 ‰ for δ¹⁸O. The peak area allows for simultaneous determination of the mole fraction with an analytical repeatability of ∼ 0.7 nmol mol^-1 for 100 mL of ambient air (185.4 nmol mol^-1 of CO). An automated single measurement is performed in only 18 min, and the achieved time efficiency (and small volume of sample air) allows for repetitive measurements practically.