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 δC and δO 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, or 1– 3 % of the typical sample size. The repeatability is 0.1 ‰ for δC and 0.2 ‰ for δO. The peak area allows for simultaneous determination of the mole fraction with an analytical repeatability of ∼ 0.7 nmol mol for 100 mL of ambient air (185.4 nmol mol 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.