Experimental observations of marine iodide oxidation using a novel sparge-interface MC-ICP-MS technique
Experimental observations of marine iodide oxidation using a novel sparge-interface MC-ICP-MS technique
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DOI：
10.1016/j.chemgeo.2019.119360
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发表时间：
2020-01-20
期刊：
影响因子：
3.9
通讯作者：
Nielsen, S. G.
中科院分区：
文献类型：
--
作者：
Hardisty, D. S.;Horner, T. J.;Nielsen, S. G.
碘形态被用作氧化还原指示剂和水团示踪剂。然而，还原的碘物种碘(I-)在海水中的氧化动力学和机理在很大程度上仍未得到解决。在这里，我们使用高精度质谱学的灵敏放射性示踪剂孵化方法，对海水孵化实验中的I-氧化速率进行了限制。用碘-129作为I-接种样品，在控制的条件下孵育，然后用液相色谱分离氧化和还原的碘物种。随后使用新的喷雾界面吸入样品，并通过多收集器电感耦合等离子体质谱测定两种碘的I-129/I-127比率。这种高度灵敏的分析方法被优化，用于估计与海洋相关的总碘浓度下小体积海水样品中碘氧化还原转化的预测缓慢速率。将该方法应用于美国玛莎葡萄园湾的海岸样品，证明了在海洋模拟条件下迄今难以捉摸的I-的氧化。我们的结果表明，在未经修饰的海水中，水中氧化碘物种的I-129/I-127增加，很可能是由于形成次碘酸，然后是溶解的有机碘，速度为118-189 NM/年。这些速率与以前的公海物质平衡方法推算的速率相当，但具有直接将碘的形态变化与原位I-氧化联系起来的好处。尽管我们的治疗实验没有明确地分离氧化机制，但它们为非生物和生物因素以及溶解形式、颗粒形式和气体形式之间的碘转化的重要作用提供了初步的见解。最终，得出的速率和新的实验技术有可能改进海洋碘循环模型，并限制原位过程在确定碘形态形成模式方面的重要性。
Iodine speciation is used as a redox indicator and water mass tracer. However, the kinetics and mechanisms of oxidation of the reduced iodine species, iodide (I-), in seawater remain largely unresolved. Here, we provide constraints on I- oxidation rates from seawater incubation experiments using a sensitive radiotracer-incubation approach with high-precision mass spectrometry. Samples are inoculated with iodine-129 as I-, incubated under controlled conditions, then oxidized and reduced iodine species are isolated using liquid chromatographic separation. Samples are subsequently aspirated using a novel sparging interface, and the I-129/I-127 ratio of both iodine species is determined via multi-collector inductively-coupled plasma mass spectrometry. This highly-sensitive analytical approach is optimized for estimating the predicted slow rates of iodine redox transformations in small volume seawater samples at marine-relevant total iodine concentrations. Application of this method to coastal samples from Martha's Vineyard Sound, USA, evidences the heretofore-elusive oxidation of I- under marine-analogue conditions. Our results demonstrate an increase in the I-129/I-127 of aqueous oxidized iodine species in unamended seawater, most likely due to formation of hypoiodous acid and then dissolved organic iodine, at rates of 118-189 nM/yr. These rates are comparable to those inferred from previous open ocean mass balance approaches but have the benefit of directly linking iodine speciation changes to in situ I- oxidation. Though our treatment experiments do not definitively isolate the oxidation mechanism, they provide preliminary insight into important roles for both abiotic and biotic factors as well as iodine transformations between dissolved, particulate, and gaseous forms. Ultimately, the derived rates and novel experimental technique have potential to improve marine iodine cycling models and provide constraints on the importance of in situ processes in setting patterns of iodine speciation.