Technique for analysis of air samples for ¹³C and ¹⁸O in carbon monoxide via continuous-flow isotope ratio mass spectrometry

A method has been developed to analyze both ¹³C and ¹⁸O in atmospheric CO using continuous-flow isotope ratio mass spectrometry (CF- IRMS). The CO in air is mixed with a flow of helium followed by cryogenic trapping of CO₂, H₂O, and other condensable gases. The remaining CO in the He/air mix is then oxidized to CO₂ using Schutze reagent, after which the CO-derived CO₂ is cryogenically trapped, loaded onto a GC column, eluted, and analyzed by CF-IRMS. Because Schutze reagent does not affect the ¹⁸O composition of the original CO, both ¹³C and ¹⁸O can be quantified. Analytical precision (in terms of standard deviation) of ±0.2‰ for δ¹³C and ±0.4‰ for δ¹⁸O can be realized with as little as 5 nL of CO for both elements. This is similar to the analytical precision obtained from off-line sample preparation followed by conventional dual-inlet analysis.