Ion-pair chromatography coupled to inductively coupled plasma-mass spectrometry (IPC-ICP-MS) as a method for thiomolybdate speciation in natural waters.
Ion-pair chromatography coupled to inductively coupled plasma-mass spectrometry (IPC-ICP-MS) as a method for thiomolybdate speciation in natural waters.
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DOI：
10.1021/ac5046406
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发表时间：
2015-03
影响因子：
7.4
通讯作者：
Regina Lohmayer;G. Reithmaier;E. bura-Nakić;B. Planer-Friedrich
中科院分区：
文献类型：
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作者：
Regina Lohmayer;G. Reithmaier;E. bura-Nakić;B. Planer-Friedrich
钼沉淀优先在还原条件下，因此，它在沉积物记录中的出现被用作古氧化还原条件的指标。虽然硫代钼酸盐（MoO 4-xSx（2-），x = 1-4）被认为是缺氧条件下钼沉淀过程中的必要中间体，但由于缺乏具有足够低检测限的元素特异性方法，因此没有关于其在自然环境中丰度的信息。在这里，我们优化了离子对色谱分离耦合到电感耦合等离子体质谱检测器（IPC-ICP-MS）。2-丙醇（10%-25%梯度）代替先前使用的乙腈（25%-75%）作为溶剂，以减少血浆中的碳负荷。在合成溶液中，发现硫代钼酸盐在过量硫化物存在下自发形成，并且在pH 7时硫醇化程度最高。过量的羟基导致硫代钼酸盐转化为钼酸盐。在酸性至中性条件下，观察到钼的沉淀和四硫代钼酸盐的水解。发现快速冷冻适合于稳定四硫代钼酸盐，其中2 mM）对主要在死体积中洗脱的二硫代钼酸盐的检测产生负面影响，但对较高硫醇化的二硫代钼酸盐没有负面影响。检测限为10 nM。采用新开发的IPC-ICP-MS方法，发现硫代钼酸盐在海洋富氧沃茨中加入微量添加剂后能自发生成，在硫化物地热沃茨中也能自然生成。
Molybdenum precipitates preferentially under reducing conditions; therefore, its occurrence in sediment records is used as an indicator of paleoredox conditions. Although thiomolybdates (MoO4-xSx(2-) with x = 1-4) supposedly are necessary intermediates in the process of molybdenum precipitation under anoxic conditions, there is no information about their abundance in natural environments, because of a lack of element-specific methods with sufficiently low detection limits. Here, we optimized ion-pair chromatographic separation for coupling to an inductively coupled plasma-mass spectrometry detector (IPC-ICP-MS). 2-Propanol (10%-25% gradient) replaced the previously used acetonitrile (25%-75%) as the solvent, to reduce the carbon load into the plasma. In synthetic solutions, formation of thiomolybdates was found to occur spontaneously in the presence of excess sulfide and the degree of thiolation was highest at pH 7. Excess hydroxyl led to a transformation of thiomolybdates to molybdate. Under acidic to neutral conditions, precipitation of molybdenum and hydrolysis of tetrathiomolybdate were observed. Flash-freezing was found to be suitable to stabilize tetrathiomolybdate, with 2 mM) negatively affected the detection of molybdate, which eluted mainly in the dead volume, but had no negative effect on higher thiolated molybdates. Detection limits were ∼10 nM. With the newly developed IPC-ICP-MS method, thiomolybdates were found to form spontaneously in euxinic marine waters after adding a molybdate spike and occur naturally in sulfidic geothermal waters.