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Summary: Sulfur and Oxygen Isotope Analysis of Sulfate at
Micromole Levels Using a Pyrolysis Technique in a
Continuous Flow System
Joel Savarino,* Becky Alexander, Vincent Darmohusodo, and Mark H. Thiemens
Department of Chemistry and Biochemistry, 9500 Gilman Drive, University of California,
San Diego, La Jolla, California 92093-0356
The discovery of a mass-independent isotopic composition
(17O ) (17O - 0.512 * 18O) * 0) in aerosol sulfate
and the identification of its origin (aqueous-phase oxida-
tion by O3 and H2O2) have renewed interest in measuring
the oxygen isotopic content of sulfate. In this paper, we
present a new method to measure both 17O and 18O in
SO4, with the possibility of sulfur isotope analysis on the
same sample. The technique takes advantage of the easy
pyrolysis of Ag2SO4 to SO2, O2, and Ag metal in a
continuous flow system. Because the technique is not
quantitative in oxygen (yield 45% for O2), a calibration
is needed. Correction factors of +0.87 and + 0.44 were
obtained for 18O and 17O, respectively. A technique to
convert micromole levels of sulfate in any form to silver
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