Purification of BaSO4precipitate contaminated with organic matter for oxygen isotope measurements (δ18O and Δ17O).
Sulfate precipitates are often contaminated with nitrates and organic materials (OM), which reduce the precision and accuracy of measurements of δ18O and Δ17O values in the sulfate. Although nitrates can be effectively removed using diethylenetriaminepentaacetic acid solution, removing OM from the precipitates is often difficult. One effective approach is to heat powdered precipitates to high temperatures. In this study, the effect of this procedure on the δ18O and Δ17O values of BaSO4precipitate was fully examined.



OM-contaminated BaSO4precipitates and18O- and17O-labeled purified BaSO4precipitates were loaded into alumina and gold crucibles and heated at 450 °C, 600 °C and 800 °C for 2 h. The nitrogen and carbon contents in the initial and the final BaSO4were measured using an elemental analyzer. The values of δ18O and Δ17O were measured using a temperature conversion/elemental analyzer coupled with an isotope ratio mass spectrometer, and a CO2laser system coupled with an isotopic ratio mass spectrometer.



OM was effectively (88 ± 17%) removed from the BaSO4precipitates by this treatment, and heating at 800 °C had the highest removal efficiency (98%). The differences in δ18O and Δ17O values between the final and initial BaSO4precipitates was -0.6‰ to 0.3‰ (average of -0.1‰) and -0.24‰ to 0.10‰ (average of -0.02‰), respectively. Significant positive relationships between the δ18O and Δ17O values of the initial BaSO4precipitate and those of the high-T-treated aliquots were found, with slopes having mean values of 0.96 ± 0.06 and 1.04 ± 0.01, respectively.



The result demonstrates high removal efficiency for OM in BaSO4precipitates and no significant differences in the oxygen isotopic compositions between high-T treated BaSO4and initial BaSO4. This study indicates that the modified high-T treatment (800 °C, 2 h) is an effective method for purifying BaSO4precipitated from geological and environmental samples with a high OM content for δ18O and Δ17O measurements. Copyright © 2016 John Wiley & Sons, Ltd.
State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, P.R. China.|Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, P.R. China.
Luhua
L
Xie
Department of Mineralogy, Natural Science Museum, London, SW7 5BD, UK.
Baruch
B
Spiro
State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, P.R. China.|Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, P.R. China.
Gangjian
G
Wei