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Effects of nitrate and water on the oxygen isotopic analysis of barium sulfate precipitated from water samples
Author(s) -
Han Janet E.,
Böhlke John Karl,
Mroczkowski Stanley J.
Publication year - 2008
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.3832
Subject(s) - chemistry , sulfate , aqueous solution , decomposition , nitrate , stable isotope ratio , environmental chemistry , oxygen 18 , isotopes of oxygen , salt (chemistry) , ion chromatography , analytical chemistry (journal) , nuclear chemistry , chromatography , physics , organic chemistry , quantum mechanics
BaSO 4 precipitated from mixed salt solutions by common techniques for SO 4 2−isotopic analysis may contain quantities of H 2 O and NO 3 −that introduce errors in O isotope measurements. Experiments with synthetic solutions indicate that δ 18 O values of CO produced by decomposition of precipitated BaSO 4 in a carbon reactor may be either too low or too high, depending on the relative concentrations of SO 4 2−and NO 3 −and the δ 18 O values of the H 2 O, NO 3 − , and SO 4 2− . Typical δ 18 O errors are of the order of 0.5 to 1‰ in many sample types, and can be larger in samples containing atmospheric NO 3 − , which can cause similar errors in δ 17 O and Δ 17 O. These errors can be reduced by (1) ion chromatographic separation of SO 4 2−from NO 3 − , (2) increasing the salinity of the solutions before precipitating BaSO 4 to minimize incorporation of H 2 O, (3) heating BaSO 4 under vacuum to remove H 2 O, (4) preparing isotopic reference materials as aqueous samples to mimic the conditions of the samples, and (5) adjusting measured δ 18 O values based on amounts and isotopic compositions of coexisting H 2 O and NO 3 − . These procedures are demonstrated for SO 4 2−isotopic reference materials, synthetic solutions with isotopically known reagents, atmospheric deposition from Shenandoah National Park, Virginia, USA, and sulfate salt deposits from the Atacama Desert, Chile, and Mojave Desert, California, USA. These results have implications for the calibration and use of O isotope data in studies of SO 4 2−sources and reaction mechanisms. Published in 2008 by John Wiley & Sons, Ltd.