Rapid, automated analysis of 13 C and 18 O of CO 2 in gas samples by continuous‐flow, isotope ratio mass spectrometry

A rapid, automated method for isotopic analysis of 13 C and 18 O in CO 2 has been developed. A variety of gas samples containing CO 2 can be swept from serological tubes into a helium carrier flow; impurities are separated on a GC column so that a pure pulse of CO 2 in He flows into the mass spectrometer. Isotopic ratio determinations are carried out as the pulse passes through the mass spectrometer, allowing a sample to be measured every ∼4 min. A double, concentric needle‐probe is used to flush the sample from the tube so that 100% sample recovery is achieved, maximizing sensitivity and preventing the possibility of fractionation. The precision of the technique, σ ( n –1) , is better than 0.2‰ (0.0002 atom per cent excess) for 13 C and 0.4‰ (0.83 p.p.m.) for 18 O for 10 μmol of CO 2 at natural abundance. Samples containing only atmospheric concentrations of CO 2 can also be analysed.