Oxygen isotope analyses of biogenic opal and quartz using a novel microfluorination technique

Authors


Correspondence to: A. J. Menicucci, Department of Geology and Stable Isotope Laboratory, University of California, Davis, Davis, CA 95616, USA.

E-mail: ajmenicucci@gmail.com

Abstract

RATIONALE

Measuring δ18O values in silicates is difficult and hazardous in comparison with measurements of carbonate minerals due to the difficulty in breaking Si–O–Si bonds. A novel method for measurement of δ18O values from quartz and biogenic silica utilizing high-temperature pyrolysis with continuous-flow isotope ratio mass spectrometry (CF-IRMS) is presented.

METHODS

Samples were prepared by offline dehydroxylation/dehydration under vacuum at 1060°C. The dehydroxylated samples are mixed with polytetrafluoroethylene (PTFE) powder (2.3:1 PTFE/Si) and graphite in silver foil capsules and reacted in a vario PYRO cube TC/EA system in a glassy carbon reaction tube. Quartz and biogenic opal samples react with available carbon in a microfluorination environment upon decomposition of the PTFE, producing CO for analysis via CF-IRMS.

RESULTS

Silicate samples reacted quantitatively, producing data with yields ≥88% from ~400 µg samples. Multiple analyses with international standards demonstrated accuracy for replicate measurements (1σ range ±0.3–0.6‰), comparing favorably with previously published techniques.

CONCLUSIONS

New data produced with the microfluorination technique are comparable with data from studies using existing methodologies. The microfluorination technique has the potential to greatly increase the number of laboratories producing silicate oxygen isotope data for mineralogic, paleoclimatic and biogeochemical applications. Copyright © 2013 John Wiley & Sons, Ltd.

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