title: Generation of O2 from BaSO4 using a CO2-laser fluorination system for simultaneous analysis of delta18O and delta17O
abstract: With the observation of mass-independent isotopic anomalies in numerous atmospheric molecules, the ability to measure both delta17O and delta18O in a range of samples is needed. Sulfate oxygen isotopic studies conventionally report only delta18O values. Recent findings indicate that sulfate delta17O and delta18O values, particularly the delta17O value (= delta17O - (0.52)(delta18O)), can provide independent information on the origin, mixing, and transformation of sulfate in the atmospheric and surface environments, which is not resolvable by only delta18O measurements. Existing methods for analyzing sulfate delta17O and delta18O are extremely laborious and demand high-purity BrF5. Here we report a novel method of generating O2 directly from Barite (BaSO4) for simultaneous analysis of delta18O and delta17O by isotope ratio mass spectrometry (IRMS). The method utilizes a CO2-laser fluorination system that can also be used to quantitatively generate O2 from silicates and oxides. Partial but consistent oxygen yields from BaSO4 are obtained for samples >4 mg. Correction factors of +9.4% for delta18O and 4.89% for delta17O are obtained, and there is no deviation in the delta17O value due to the nonquantitative O2 generation. The system may process more than a dozen samples per working day, with analytical error of +/-0.05% and +/-0.8% for delta17O and delta18O, respectively. This new method is ideal for studies emphasizing an accurate sulfate delta17O value.
authors.affiliation: Department of Chemistry and Biochemistry, University of California San Diego, La Jolla 92093, USA. hbao@chem.ucsd.edu
authors.initials: H
authors.lastname: Bao
authors.initials: MH
authors.lastname: Thiemens