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.