irm-EAMS (δ13C and δ15N)
CO2 in-air (δ13C and δ18O)
O2/N2 in air (+ δ18O of O2 in air or Ar/N2)
Laser Ablation
GasBench
TC/EA ('Pyrolysis', δ2H and δ18O)
Acid reaction and air mixing system (ARAMIS) (δ13C and δ18O)
CO2-in-air (δ13C and δ18O)
Isotopic analysis of CO2 in air
The high precision determination of isotope ratios for CO2-in-air has been a major activity of the IsoLab since the initial experiments during. Our extraction line ('BGC-AirTrap'), as developed in 2000 is schematically depicted in the Figure:
Home made extraction system ('BGC-AirTrap') for extracting CO2 from air samples contained in glass flasks. Using a flow rate of 60 ml/min about 600 ml of air are consumed per analysis.
From a Valco Multiport valve the air passes through a mass flow controller, over a water trap at 70°C and a trap maintained at 196°C. Here, CO2 is frozen out at a pressure of about 100 mb. The air is pumped through the pumping lines of the dual inlet system of our MAT 252 mass spectrometer. Sample CO2 is measured directly from the sampling reservoir via a crimped capillary to the Changeover valve. The system is under full computer control for reliable timing and unattended operation. The precision of the system is shown in performance chart Figures below. Since the start of the measurements in October 2000, the single-analysis precision between our working gas tank and the QA air standard on 'Matty' were 0.013‰ (δ13C) and ~0.025‰ (δ18O). In March 2002, our 2nd MAT252 ('Cora') started with routine measurements. The precision of both machines are very close. The absolute δ13C value of the QA reference gas on the VPDB scale is identical on both machines. For 18O, a small offset of +0.03‰ was found initially on a measured difference of about 15‰. This difference vanished over time. The overall agreement between the two independent machines was achieved without any machine specific scale adjustment.
Performance Chart: δ13C-values of the working reference gas Westf.10-2000 as a function of measurement time. The values are based on measurement of the CSIRO reference gas which also serves as the primary standard for establishing the δ13C scale versus VPDB. Please note that the two completely independent instruments deliver the same average for δ13C.
Performance Chart:δ18O-values of the working reference gas Westf.10-2000 as a function of measurement time. The values are based on measurement of the CSIRO reference gas which also serves as the primary standard for establishing the δ18O scale versus VPDBgas. Please note that the two completely independent instruments deliver the same average value for δ18O.
An illustration of the throughput: In 2001 and 2002, a total of 8350 isotopic analyses of CO2-in-air were made. Out of these, 54% were flask measurements, 46% were measurements from tanks including working gas, quality control and other test runs.
Storage aspects have been described in
Michael Rothe, Armin Jordan and Willi A. Brand, Trace gases, δ13C and δ18O of CO2-in-air samples: Storage in glass flasks using PCTFE seals and other effects, Proceedings of the 12th IAEA/WMO meeting of CO2 experts, Toronto, Sept. 2003, WMO-GAW Report 161, ed. D. Worthy (2005) submitted (pdf)
Full details of the experimental setup can be found in
Roland A. Werner, Michael Rothe and Willi A. Brand, Extraction of CO2 from air samples for isotopic analysis and limits to ultra high precision δ18O determination in CO2 gas, Rapid Comm. Mass Spectrom. 15 (2001) 2152-2167