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Uncertainties in the oxygen isotopic composition of barium sulfate induced by coprecipitation of nitrate
Author(s) -
Michalski Greg,
Kasem Michelle,
Rech Jason A.,
Adieu Sabine,
Showers William S.,
Genna Bernie,
Thiemens Mark
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.3687
Subject(s) - chemistry , coprecipitation , barium , nitrate , oxygen , sulfate , environmental chemistry , composition (language) , inorganic chemistry , radiochemistry , organic chemistry , linguistics , philosophy
Coprecipitation of nitrate and sulfate by barium has probably resulted in significant error in numerous studies dealing with the oxygen isotopic composition of natural sulfates using chemical/thermal conversion of BaSO 4 and analysis by isotope ratio mass spectrometry. In solutions where NO 3 − /SO 4 2−molar ratios are above 2 the amount of nitrate coprecipitated with BaSO 4 reaches a maximum of approximately 7% and decreases roughly linearly as the molar ratio decreases. The fraction of coprecipitated nitrate appears to increase with decreasing pH and is also affected by the nature of the cations in the precipitating solution. The size of the oxygen isotope artifact in sulfate depends both on the amount of coprecipitated nitrate and the δ 18 O and Δ 17 O values of the nitrate, both of which can be highly variable. The oxygen isotopic composition of sulfate extracted from atmospheric aerosols or rain waters are probably severely biased because photochemical nitrate is usually also present and it is highly enriched in 18 O ( δ 18 O ∼50–90‰) and has a large mass‐independent isotopic composition (Δ 17 O ∼20–32‰). The sulfate δ 18 O error can be 2–5‰ with Δ 17 O artifacts reaching as high as 4.0‰. Copyright © 2008 John Wiley & Sons, Ltd.