An automated system for stable isotope and concentration analyses of CO 2 from small atmospheric samples

We have developed an automated, continuous‐flow isotope ratio mass spectrometry (CF‐IRMS) system for the analysis of δ 13 C, δ 18 O, and CO 2 concentration (μmol mol −1 ) ([CO 2 ]) from 2 mL of atmospheric air. Two replicate 1 mL aliquots of atmospheric air are sequentially sampled from fifteen 100 mL flasks. The atmospheric sample is inserted into a helium stream and sent through a gas chromatograph for separation of the gases and subsequent IRMS analysis. Two δ 13 C and δ 18 O standards and five [CO 2 ] standards are run with each set of fifteen samples. We obtained a precision of 0.06‰, 0.11‰, and 0.48 μmol mol −1 for δ 13 C, δ 18 O, and [CO 2 ], respectively, by analyzing fifty 100 mL samples filled from five cylinders with a [CO 2 ] range of 275 μmol mol −1 . Accuracy was determined by comparison with established methods (dual‐inlet IRMS, and nondispersive infrared gas analysis) and found to have a mean offset of 0.00‰, −0.09‰, and −0.26 μmol mol −1 for δ 13 C and δ 18 O, and [CO 2 ], respectively. Copyright © 2005 John Wiley & Sons, Ltd.