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Optimizing sulfate pyrolysis triple oxygen isotope analysis for samples from desert environments.
Swea Klipsch1, Daniel Herwartz1, Michael Staubwasser1
1Institute of Geology and Mineralogy, University of Cologne, Cologne, Germany.
Rapid Communications in Mass Spectrometry : RCM
|April 17, 2021
Summary
This study presents a fast, accurate, and cost-efficient method for analyzing sulfate oxygen isotopes using pyrolysis mass spectrometry. This technique enables reliable environmental profiling and comparison with traditional methods.
Area of Science:
- Geochemistry
- Environmental Science
- Analytical Chemistry
Background:
- Triple oxygen isotope composition of sulfate (Δ17OSO4) can reveal sulfate formation pathways, depositional sources, and biological cycling.
- Pyrolysis mass spectrometry (PMS) is suitable for high-throughput environmental analysis, but requires high precision and accuracy for comparison with laser fluorination data.
Purpose of the Study:
- To develop and validate a modified pyrolysis mass spectrometry method for high-throughput analysis of sulfate oxygen isotopes.
- To ensure the accuracy and precision of the PMS method for environmental sulfate analysis.
Main Methods:
- Quantitative sulfate extraction from soil at neutral pH, followed by purification and conversion to silver sulfate (Ag-SO4).
- Analysis of Ag-SO4 using pyrolysis mass spectrometry in a modified elemental analyzer (EuroVector model 3000).
- Oxygen isotope analysis (O2) using a Thermo Finnigan MAT253 isotope ratio mass spectrometer with cryo-trapping and chromatography.
Main Results:
- Achieved 1σ external reproducibility of 0.12‰ for Δ17OSO4 values on 30 μmol samples.
- Demonstrated comparable precision and accuracy using quartz cups versus gold capsules.
- Identical results between PMS and laser fluorination methods for in-house standards and an Atacama Desert soil profile confirm method accuracy.
Conclusions:
- Modified PMS in quartz cups offers an accurate, precise, fast, cost-efficient, and non-hazardous method for sulfate oxygen isotope analysis.
- Demonstrated data exchangeability between PMS and laser fluorination methods, even with interfering salts like nitrates and chlorides.
- The validated PMS method facilitates reliable environmental profiling and source apportionment of sulfate.
