title: Measurement of oxygen isotope ratios ((18)O/(16)O) of aqueous O2 in small samples by gas chromatography/isotope ratio mass spectrometry.
abstract: BACKGROUND
  Oxygen isotope fractionation of molecular O2 is an important process for the study of aerobic metabolism, photosynthesis, and formation of reactive oxygen species. The latter is of particular interest for investigating the mechanism of enzyme-catalyzed reactions, such as the oxygenation of organic pollutants, which is an important detoxification mechanism.
  
  
  METHODS
  We developed a simple method to measure the δ(18) O values of dissolved O2 in small samples using automated split injection for gas chromatography coupled to isotope ratio mass spectrometry (GC/IRMS). After creating a N2 headspace, the dissolved O2 partitions from aqueous solution to the headspace, from which it can be injected into the gas chromatograph.
  
  
  RESULTS
  In aqueous samples of 10 mL and in diluted air samples, we quantified the δ(18) O values at O2 concentrations of 16 μM and 86 μM, respectively. The chromatographic separation of O2 and N2 with a molecular sieve column made it possible to use N2 as the headspace gas for the extraction of dissolved O2 from water. We were therefore able to apply a rigorous δ(18) O blank correction for the quantification of (18) O/(16) O ratios in 20 nmol of injected O2 .
  
  
  CONCLUSIONS
  The successful quantification of (18) O-kinetic isotope effects associated with enzymatic and chemical reduction of dissolved O2 illustrates how the proposed method can be applied for studying enzymatic O2 activation mechanisms in a variety of (bio)chemical processes.
authors: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092, Zürich, Switzerland.
authors: Sarah G
authors: SG
authors: Pati
authors: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland.
authors: Jakov
authors: J
authors: Bolotin
authors: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland.
authors: Matthias S
authors: MS
authors: Brennwald
authors: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092, Zürich, Switzerland.
authors: Hans-Peter E
authors: HP
authors: Kohler
authors: Institute of Agricultural Sciences, ETH Zürich, CH-8092, Zürich, Switzerland.
authors: Roland A
authors: RA
authors: Werner
authors: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092, Zürich, Switzerland.
authors: Thomas B
authors: TB
authors: Hofstetter
mesh_terms: D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D005949:Glucose Oxidase / Q000378:metabolism; D007501:Iron; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010103:Oxygen Isotopes / Q000032:analysis*; D015203:Reproducibility of Results
chemical_list: D010103:Oxygen Isotopes; D007501:Iron; D005949:Glucose Oxidase