title: An improved CeO2 method for high-precision measurements of 17O/16O ratios for atmospheric carbon dioxide.
abstract: BACKGROUND
  The oxygen isotopic composition of carbon dioxide originating at the Earth's surface is modified in the stratosphere by interaction with ozone which has anomalous oxygen isotope ratio (Δ(17)O = 1000 * ln(1 + δ(17)O/1000) - 0.522 * 1000 * ln (1 + δ(18)O/1000) >0). The inherited anomaly provides a powerful tracer for studying biogeochemical cycles involving CO(2). However, the existing methods are either too imprecise or have difficulty in determining the small Δ(17)O variations found in the tropospheric CO(2). In this study an earlier published CeO(2) and CO(2) exchange method has been modified and improved for measuring the Δ(17)O values of atmospheric carbon dioxide with high precision.
  
  
  METHODS
  The CO(2) fraction from air samples was separated by cryogenic means and purified using gas chromatography. This CO(2) was first analyzed in an isotope ratio mass spectrometer, then artificially equilibrated with hot CeO(2) to alter its oxygen isotopes mass-dependently and re-analyzed. From these data the (17)O/(16)O and (18)O/(16)O ratios were calculated and the Δ(17)O value was determined.
  
  
  RESULTS
  The validity of the method was established in several tests by using artificially prepared CO(2) with zero and non-zero Δ(17)O values. The published value of the CO(2)-H(2) O equilibrium slope was also reproduced.
  
  
  CONCLUSIONS
  The CO(2)-CeO(2) equilibration method has been improved to measure the oxygen isotope anomaly (Δ(17)O value) of atmospheric CO(2) with an analytical precision of ±0.12‰ (2σ).
authors: Research Center for Environmental Changes, Academia Sinica, 128 Academia Road, Nangang, Taipei 11529, Taiwan.
authors: Sasadhar
authors: S
authors: Mahata
authors: Sourandra K
authors: SK
authors: Bhattacharya
authors: Chung-Ho
authors: CH
authors: Wang
authors: Mao-Chang
authors: MC
authors: Liang
mesh_terms: D001272:Atmosphere / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis / Q000737:chemistry*; D002247:Carbon Isotopes / Q000032:analysis / Q000737:chemistry; D002586:Cesium / Q000032:analysis* / Q000737:chemistry; D002587:Cesium Isotopes; D003080:Cold Temperature; D013058:Mass Spectrometry; D010087:Oxides / Q000032:analysis* / Q000737:chemistry; D010103:Oxygen Isotopes / Q000032:analysis* / Q000737:chemistry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014867:Water
chemical_list: D002247:Carbon Isotopes; D002587:Cesium Isotopes; D010087:Oxides; D010103:Oxygen Isotopes; D014867:Water; D002245:Carbon Dioxide; D002586:Cesium