title: Oxygen isotope exchange with quartz during pyrolysis of silver sulfate and silver nitrate.
abstract: BACKGROUND
  Triple oxygen isotopes of sulfate and nitrate are useful metrics for the chemistry of their formation. Existing measurement methods, however, do not account for oxygen atom exchange with quartz during the thermal decomposition of sulfate. We present evidence for oxygen atom exchange, a simple modification to prevent exchange, and a correction for previous measurements.
  
  
  METHODS
  Silver sulfates and silver nitrates with excess (17)O were thermally decomposed in quartz and gold (for sulfate) and quartz and silver (for nitrate) sample containers to O(2) and byproducts in a modified Temperature Conversion/Elemental Analyzer (TC/EA). Helium carries O(2) through purification for isotope-ratio analysis of the three isotopes of oxygen in a Finnigan MAT253 isotope ratio mass spectrometer.
  
  
  RESULTS
  The Δ(17)O results show clear oxygen atom exchange from non-zero (17)O-excess reference materials to zero (17)O-excess quartz cup sample containers. Quartz sample containers lower the Δ(17)O values of designer sulfate reference materials and USGS35 nitrate by 15% relative to gold or silver sample containers for quantities of 2-10 µmol O(2).
  
  
  CONCLUSIONS
  Previous Δ(17)O measurements of sulfate that rely on pyrolysis in a quartz cup have been affected by oxygen exchange. These previous results can be corrected using a simple linear equation (Δ(17)O(gold) = Δ(17)O(quartz) * 1.14 + 0.06). Future pyrolysis of silver sulfate should be conducted in gold capsules or corrected to data obtained from gold capsules to avoid obtaining oxygen isotope exchange-affected data.
authors.affiliation: Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA. aschauer@uw.edu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Schauer
authors.forename: Shelley A
authors.initials: SA
authors.lastname: Kunasek
authors.forename: Eric D
authors.initials: ED
authors.lastname: Sofen
authors.forename: Joseph
authors.initials: J
authors.lastname: Erbland
authors.forename: Joel
authors.initials: J
authors.lastname: Savarino
authors.forename: Ben W
authors.initials: BW
authors.lastname: Johnson
authors.forename: Helen M
authors.initials: HM
authors.lastname: Amos
authors.forename: Robina
authors.initials: R
authors.lastname: Shaheen
authors.forename: Mariana
authors.initials: M
authors.lastname: Abaunza
authors.forename: Terri L
authors.initials: TL
authors.lastname: Jackson
authors.forename: Mark H
authors.initials: MH
authors.lastname: Thiemens
authors.forename: Becky
authors.initials: B
authors.lastname: Alexander