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Oxygen isotope exchange with quartz during pyrolysis of silver sulfate and silver nitrate
Author(s) -
Schauer Andrew J.,
Kunasek Shelley A.,
Sofen Eric D.,
Erbland Joseph,
Savarino Joel,
Johnson Ben W.,
Amos Helen M.,
Shaheen Robina,
Abaunza Mariana,
Jackson Terri L.,
Thiemens Mark H.,
Alexander Becky
Publication year - 2012
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6332
Subject(s) - chemistry , sulfate , quartz , oxygen , isotopes of oxygen , analytical chemistry (journal) , inorganic chemistry , silver nitrate , pyrolysis , nuclear chemistry , environmental chemistry , metallurgy , organic chemistry , materials science
RATIONALE 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. Copyright © 2012 John Wiley & Sons, Ltd.