title: Precision trace gas analysis by FT-IR spectroscopy. 2. The 13C/12C isotope ratio of CO2.
abstract: We report the development of a method of carbon stable isotope ratio analysis based on 1-cm-1 resolution Fourier transform infrared (FT-IR) spectroscopy, deployable in both laboratory and field applications. We demonstrate the determination of the 13C/12C ratio of CO2 (i.e., delta 13CO2) in air with an analytical precision of the order of +/- 0.1/1000 (i.e., +/- 0.01%). The FT-IR method relies on calibration using synthetically calculated absorbance spectra and a multivariate calibration algorithm. The method requires no sample preparation other than optional drying of the sample and may be applied directly to ambient air samples containing approximately 350 mumol mol-1 CO2 (molar mixing ratio). It may also be applied to samples more concentrated in CO2, such as human breath, approximately 5% CO2. We demonstrate the utility of the technique to the analysis of delta 13CO2 in air during an experimental field campaign and to the laboratory-based analysis of human breath. A similar method could also be used to determine the H/D ratio in atmospheric water vapor.
authors.affiliation: Department of Chemistry, University of Wollongong, Australia. mesler@uow.edu.au
authors.forename: M B
authors.initials: MB
authors.lastname: Esler
authors.forename: D W
authors.initials: DW
authors.lastname: Griffith
authors.forename: S R
authors.initials: SR
authors.lastname: Wilson
authors.forename: L P
authors.initials: LP
authors.lastname: Steele
mesh_terms: D000388:Air / Q000032:analysis; D002244:Carbon / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D002247:Carbon Isotopes; D016481:Helicobacter Infections / Q000175:diagnosis; D006801:Humans; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D002244:Carbon