Sulfur isotope analysis by IC-MC-ICP-MS provides insight into fractionation of thioarsenates during abiotic oxidation
Sulfur isotope analysis by IC-MC-ICP-MS provides insight into fractionation of thioarsenates during abiotic oxidation
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DOI：
10.1016/j.chemgeo.2017.12.008
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发表时间：
2018-01
期刊：
影响因子：
3.9
通讯作者：
M. Ullrich;F. Gelman;Y. Zakon;L. Halicz;K. Knöller;B. Planer-Friedrich
中科院分区：
文献类型：
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作者：
M. Ullrich;F. Gelman;Y. Zakon;L. Halicz;K. Knöller;B. Planer-Friedrich
含水样品的标准硫同位素分析主要针对硫化物和硫酸盐，而往往忽略中间物质，主要是由于分析的局限性。然而，硫可以在环境中形成许多中间物质，包括硫金属（类），如硫代砷酸盐（[HAsVS−IInO4−n]2−,n = 1-4），它们在同位素分选中起关键作用。硫化物和硫酸盐分离的标准沉淀程序应用于硫代砷酸盐溶液。发现单硫代砷酸盐与硫化物共沉淀，从而可能阻碍正确的硫化物同位素分析。为了克服该标准沉淀程序的局限性，开发了一种基于离子色谱分离硫种，然后在多收集器ICP-MS （IC-MC-ICP-MS）上进行在线同位素检测的新方法。应用该方法，发现硫代砷酸盐氧化过程中，硫代砷酸盐与硫酸盐的分馏率高达- 6.1‰。相反，四硫代砷酸盐通过三硫代和二硫代砷酸盐氧化为一硫代砷酸盐不会导致分馏。然而，释放出的硫化物由于氧化成硫酸盐，在34s中越来越富集。该过程通过溶液中砷结合硫和硫化物的分子间同位素交换，为单硫胂酸盐引入了高达9.1‰的额外富集。这些结果有助于阐明硫砷酸盐转化的途径，从而为硫化物环境中同位素分馏模式的解释提供有价值的信息。
Standard sulfur isotope analysis of aqueous samples is aimed at sulfide and sulfate, while often disregarding intermediate species, mainly due to analytical limitations. However, sulfur can form numerous intermediate species in the environment, including thiometal(loid)s such as thioarsenates ([HAsVS− IInO4 − n]2 −, n = 1–4), which can play a key role in isotope fractionation. The standard precipitation procedure for separation of sulfide and sulfate was applied to monothioarsenate solutions. Monothioarsenate was found to co-precipitate together with sulfide, thus potentially impeding correct sulfide isotope analysis. To overcome the limitations associated with this standard precipitation procedure, a new method was developed based on separating sulfur species by ion chromatography followed by online isotope detection on multi-collector ICP-MS (IC-MC-ICP-MS). Applying this new method, fractionation between monothioarsenate and sulfate of up to − 6.1‰ was found during monothioarsenate oxidation. In contrast, oxidation of tetrathioarsenate via tri- and di- to monothioarsenate did not result in fractionation. However, the released sulfide became increasingly enriched in34S due to oxidation to sulfate. This process was found to introduce additional enrichment of up to 9.1‰ to monothioarsenate through intermolecular isotope exchange between arsenic-bound sulfur and sulfide in solution. These results help elucidate pathways of thioarsenate transformation, and thus provide valuable information for the interpretation of isotope fractionation patterns in sulfidic environments.