An automated system for stable isotope and concentration analyses of CO2 from small atmospheric samples

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Abstract
We have developed an automated, continuous-flow isotope ratio mass spectrometry (CF-IRMS) system for the analysis of δ13C, δ18O, and CO2 concentration (μmol mol−1) ([CO2]) 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 δ13C and δ18O standards and five [CO2] 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 δ13C, δ18O, and [CO2], respectively, by analyzing fifty 100 mL samples filled from five cylinders with a [CO2] 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 δ13C and δ18O, and [CO2], respectively. Copyright © 2005 John Wiley & Sons, Ltd.

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