Isotopic analysis of atmospheric CO2 (δ13C and δ18O)
High precision analysis of oxygen and carbon isotopic ratios of CO2 in air
High precision analysis of oxygen and carbon isotopic ratios of CO2 in air continues to be a major activity of the BGC-IsoLab since the initial experiments at the turn of the century.
From a Valco Multiport valve the air passes through a mass flow controller over an ethanol/dry ice (-70 °C) water trap into a LN2 (-196 °C) trap that removes CO2 and N2O at a pressure of about 100 mbar. Upon thawing the trapped CO2 is analysed on one of two MAT252 isotope ratio mass spectrometers (Matty and Cora) equipped with dual inlet systems.
Performance charts of our quality control measurements illustrate the measurement precision of Cora. The single-analysis precision of “Cora” is better than 0.02 and 0.03 ‰ for δ13C and δ18O measurements, respectively, since 2002. The single-analysis precision of „Matty“ is slightly worse, with 0.05 ‰ and 0.08 ‰ for for δ13C and δ18O measurements, respectively. This is due to the fact that “Matty” analyses all kinds of air samples (e.g. air from soils) that may be contaminated with VOCs, while “Cora” is dedicated to clean atmospheric air samples, only.
Storage aspects have been described in:
Rothe, M.; Jordan, A.; Brand, W. A.: Trace gases, δ13C and δ18O of CO2-in-air samples: Storage in glass flasks using PCTFE seals and other effects. In: Proceedings of the 12th IAEA/WMO meeting of CO2 experts, Toronto, Sept. 2003, pp. 64 - 70 (Eds. Worthy, D.; Huang, L.) (2005)
See also "Central Flask Facility" under "Activities"
Werner, R. A.; Rothe, M.; Brand, W. A.: Extraction of CO2 from air samples for isotopic analysis and limits to ultra high precision δ18O determination in CO2 gas. Rapid Communications in Mass Spectrometry 15, pp. 2152 - 2167 (2001)
Ghosh, P.; Patecki, M.; Rothe, M.; Brand, W. A.: Calcite-CO2 mixed into CO2-free air: a new CO2-in-air stable isotope reference material for the VPDB scale. Rapid Communications in Mass Spectrometry 19 (8), pp. 1097 - 1119 (2005)