Kinetically labile equilibrium shifts induced by the electrospray process.
Kinetically labile equilibrium shifts induced by the electrospray process.
复制标题
电喷雾过程引起动力学不稳定的平衡位移。
DOI：
10.1021/ac981375u
复制
发表时间：
1999
影响因子：
7.4
通讯作者：
George R. Agnes
中科院分区：
文献类型：
--
作者：
Hongjun Wang† and;George R. Agnes
通过电喷雾质谱法研究碱土金属离子与EDTA之间的络合反应，以测量气相中金属离子-EDTA络合物（MY（2）（-））的浓度相对于溶液相平衡浓度的变化。这项工作集中在溶液的pH值范围从4到7，其中存在的自由金属离子在溶液中处于平衡。通过对气相中MY（2）（-）物种丰度增加的定量测定，钡的平衡位移最大，镁的平衡位移最小。MY（2）（-）物质的净平衡移动的原因是毛细管内pH值的电解增加加上蒸发液滴内的额外移动的综合效应。在ES毛细管尖端，电解产物与本体溶液混合产生的薄扩散限制层中，不稳定物质在新的更高pH下重新平衡。在蒸发液滴中，由于溶质浓度增加而形成的新不稳定物质受到动力学控制，因为解吸前液滴中的离子停留时间仅为0.55 μs。这些结果进行了简要讨论，相对于利用电喷雾质谱动力学不稳定平衡研究的潜力。
The complexation reactions between the alkaline earth metal ions and EDTA were studied by electrospray mass spectrometry to measure the change in concentration of the metal ion-EDTA complex (MY(2)(-)) in the gas phase relative to the solution-phase equilibrium concentration. This work focused on the solution pH range from 4 to 7 where there exists free metal ions in solution at equilibrium. The equilibrium shift, measured through quantitation of the increased abundance of the MY(2)(-) species in the gas phase, was largest for barium and smallest for magnesium. The cause of the net equilibrium shift of the MY(2)(-) species is the combined effect of an electrolytic increase in pH within the capillary plus an additional shift within the evaporating droplets. In a thin diffusion-limited layer created by the products of electrolysis mixing with the bulk solution at the ES capillary tip, the labile species reequilibrate at a new, higher pH. In the evaporating droplets, the formation of new labile species due to increased solute concentrations is kinetically controlled because the ion residence time in the droplet prior to desorption is only ∼5 μs. These results are briefly discussed with respect to the potential for utilizing electrospray mass spectrometry for kinetically labile equilibrium studies.