A critical investigation of hydride generation-based arsenic speciation in sulfidic waters.
A critical investigation of hydride generation-based arsenic speciation in sulfidic waters.
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DOI：
10.1021/es900111z
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发表时间：
2009-05
影响因子：
11.4
通讯作者：
B. Planer-Friedrich;D. Wallschläger
中科院分区：
文献类型：
--
作者：
B. Planer-Friedrich;D. Wallschläger
在硫化物环境中，基于氢化物发生的方法不适合于砷的测定，因为在这种条件下可以构成主要砷形态(占总砷的80%)的硫代砷酸盐被完全忽略。样品酸化以保存或在氢化物发生过程中，由于砷-硫相的析出，导致总无机砷的损失。用1%的碘化钾作预还原剂可准确测定总浓度，而用L-半胱氨酸(0.16molL~(-1))时，四、三、二硫代砷酸盐向亚砷酸盐的转化仍不完全。通过降低原始样品的pH，氢化物发生破坏了硫代砷酸盐的物种分布，因为在整个pH范围内只有一硫代砷酸盐是稳定的。二硫代砷酸盐在pH 4以下转化为亚砷酸盐，四硫代砷酸盐在pH 11.9下转化为三硫代砷酸盐，三硫代砷酸盐在pH 5.6下转化为亚砷酸盐，然后在pH 5以下发生砷硫相沉淀，因此不可能用氢化物发生来测定硫代砷酸盐。“As(III)”组分含有四、三和一些二硫代砷酸盐以及亚砷酸盐，而一硫代砷酸盐用砷酸盐测定为“As(V)”。不同的分析装置对硫代砷酸氢化物生成行为有很大影响，因此提供的可比性很小，使得无法重新解释硫化物环境中现有的砷氢化物生成形态数据。在黄石国家公园天然地热水样品中，电感耦合等离子体质谱仪和氢化物发生原子荧光法测定的总砷浓度与预还原液测定结果吻合良好(相对误差<6%)。形态形成结果偏离了实验室实验对硫代砷酸盐的预测行为，可能是由于基质效应。
In sulfidic environments, hydride generation-based approaches are not suitable for arsenic determination because thioarsenates which can constitute the predominant arsenic species under these conditions (> 80% of total arsenic) are completely ignored. Sample acidification for preservation or during hydride generation leads to loss of total inorganic arsenic due to precipitation of arsenic-sulfur phases. Total concentrations can be determined correctly using 1% potassium iodide as prereducing agent while with L-cysteine (0.16 mol L(-1)), transformation of tetra-, tri-, and dithioarsenate to arsenite remains incomplete. By decreasing the original sample pH, hydride generation destroys thioarsenate species distribution because only monothioarsenate is stable over the whole pH range. Dithioarsenate transforms to arsenite below pH 4. Tetrathioarsenate transforms to trithioarsenate (pH 11.9) which subsequently transforms to arsenite (pH 5.6), followed by precipitation of arsenic-sulfur phases below pH 5. It is thus impossible to determine thioarsenates by hydride generation. The "As(III)"--fraction contains tetra-, tri-, and some dithioarsenate as well as arsenite, while monothioarsenate is determined with arsenate as "As(V)". Different analytical setups have substantial impact on thioarsenate hydride-generation behavior, thus provide little comparability and render reinterpretation of existing arsenic hydride-generation speciation data from sulfidic environments impossible. In natural geothermal water samples from Yellowstone National Park, total arsenic concentrations determined by ICP-MS and by HG-AFS with prereductant agreed well (< 6% relative difference). Speciation results deviated from the behavior predicted for thioarsenates from laboratory experiments, probably due to matrix effects.