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

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.