Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, Hermann-von-Helmholtz Platz 1, D-76344, Eggenstein Leopoldshafen, Germany.
Rapid Commun Mass Spectrom. 2012 Mar 30;26(6):583-91. doi: 10.1002/rcm.6128.
Polymerization in hexavalent uranium solutions was measured by electrospray ionization time-of-flight mass spectrometry in three different acidic media at pH values from 3 to 5.3 in order to detect all hydrolysis species present in solution. The aqueous solutions were directly measured without further dilution in organic solvents. At high uranyl concentrations ([U(VI)] = 10(- 3) M) artifacts were observed due to the presence of more than one solution species per formed microdroplet. Those artifacts were composed of ions and neutral species being present in the same droplet. However, by analyzing the detected species carefully, the origin of the artifacts could be traced back to the physically meaningful species. Still, only general trends of the hydrolysis behavior can be deduced from the measurements at [U(VI)] = 1 ⋅ 10(- 3) M. The solutions at [U(VI)] = 5 ⋅ 10(- 5) M did not show any comparable artifact formation. The detected species distributions resemble the expected trends calculated from the equilibrium constants published in the Nuclear Energy Agency Thermodynamic Database (NEA-TDB). The neutral (UO(2))(CO(3))(0) species present in solution causes, if located in the same microdroplet as a charged species, the apparent formation of dimeric and trimeric ternary hydroxo carbonate complexes at pH 5.3. As the uncharged species is not repelled from the ionic species, it might remain in the same droplet during the droplet fission process. By dividing those detected species into the uncharged (UO(2))(CO(3))(0) and a second ionic species, the relative abundances of the solution species can be corrected, leading to a good agreement with the predictions of the published equilibrium constants. In addition to the well-known trimer, we report the direct mass spectrometric detection of the dimeric (UO(2))(2)(OH)(2)(2+) species.
在三种不同的酸性介质中，通过电喷雾电离飞行时间质谱法测量了六价铀溶液的聚合反应，pH 值范围为 3 至 5.3，以检测溶液中存在的所有水解物种。水溶液未经进一步稀释直接在有机溶剂中测量。在高铀酰浓度下（[U(VI)]=10(-3)M），由于每个微滴中存在不止一种溶液物种，因此观察到了伪像。这些伪像由同一液滴中存在的离子和中性物种组成。然而，通过仔细分析检测到的物种，可以追溯到伪像的来源，回到物理上有意义的物种。尽管如此，仅能从[U(VI)]=1⋅10(-3)M 的测量中推断出水解行为的一般趋势。在[U(VI)]=5⋅10(-5)M 的溶液中没有观察到任何类似的伪像形成。检测到的物种分布与从核能源机构热力学数据库（NEA-TDB）中公布的平衡常数计算得出的预期趋势相似。溶液中存在的中性（UO(2))(CO(3))(0)物种，如果位于带电荷的物种的同一微滴中，会导致在 pH 5.3 时形成二聚体和三聚体三元羟碳酸络合物的表观形成。由于中性物种不会被排斥出离子物种，因此在液滴裂变过程中，它可能会留在同一液滴中。通过将那些检测到的物种分为不带电的（UO(2))(CO(3))(0)和第二种离子物种，可以校正溶液物种的相对丰度，从而与公布的平衡常数的预测值很好地吻合。除了众所周知的三聚体外，我们还直接通过质谱检测到二聚体（UO(2))(2)(OH)(2)(2+)物种。
