More than a Liquid Junction: Effect of Stirring, Flow Rate, and Inward and Outward Electrolyte Diffusion on Reference Electrodes with Salt Bridges Contained in Nanoporous Glass
More than a Liquid Junction: Effect of Stirring, Flow Rate, and Inward and Outward Electrolyte Diffusion on Reference Electrodes with Salt Bridges Contained in Nanoporous Glass
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不仅仅是液体接界：搅拌、流速和电解质向内和向外扩散对纳米多孔玻璃中含有盐桥的参比电极的影响
DOI：
10.1021/acs.analchem.9b00876
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发表时间：
2019
影响因子：
7.4
通讯作者：
Bühlmann, Philippe
中科院分区：
文献类型：
--
作者：
Anderson, Evan L.;Lodge, Timothy P.;Gopinath, Tata;Veglia, Gianluigi;Bühlmann, Philippe
亨德森方程通常用于计算可混溶电解质溶液之间的液结电势。然而，包括电解质填充的纳米多孔玻璃熔块的参比电极的电位也可能受到电荷筛选的影响。如前所述，当德拜长度接近或超过玻璃孔径时，参考电位取决于桥式电解液的组成、熔块的孔径和样品中电解液的浓度。我们在这里报道，样品的搅拌可能会改变参考电势，因为它会影响面向样品溶液的纳米多孔玻璃熔块部分的电解液浓度。当桥接电解液进入样品的流量较小时，样品进入纳米多孔熔体的对流传质发生。熔块的渗透深度只有几个纳米，但尽管使用了浓缩盐桥，这足以影响在测量低离子强度的样品时静电屏蔽的程度。通过观察深色的Fe[(SCN)(H2O)5]2+络合物，对样品和盐桥溶液的混合--特别是样品组分对熔块的渗透--进行光学监测，该络合物仅在样品和盐桥混合的区域形成。重要的是，由于流经纳米孔熔块的流动非常缓慢，通过这些熔块的质量传输以扩散为主。因此，在短短1小时内，低流速的参比电极熔块就会被样品组分污染，熔块中的电解质会耗尽到几毫米的深度，这可能会对后续的实验产生负面影响。
The Henderson equation is usually used to calculate liquid-junction potentials between miscible electrolyte solutions. However, the potentials of reference electrodes that comprise an electrolyte-filled nanoporous glass frit may also be affected by charge screening. As reported previously, when the Debye length approaches or surpasses the glass pore diameter, reference potentials depend on the composition of the bridge electrolyte, the pore size of the frit, and the concentration of electrolyte in the sample. We report here that stirring of samples may alter the reference potential as it affects the electrolyte concentration in the section of the nanoporous glass frit that is facing the sample solution. When the flow rate of bridge electrolyte into the sample is small, convective mass transport of sample into the nanoporous frit occurs. The depth of penetration into the frit is only a few nanometers but, despite the use of concentrated salt bridges, this is enough to affect the extent of electrostatic screening when samples of low ionic strength are measured. Mixing of sample and salt bridge solutions—and in particular penetration of sample components into the frit—was optically monitored by observation of a deeply colored Fe[(SCN)(H2O)5]2+complex that formed in situ exclusively in the region where the sample and salt bridge mixed. Importantly, because flow through nanoporous frits is very slow, mass transport through these frits is dominated by diffusion. Consequently, over as little as 1 h, reference electrode frits with low flow rates become contaminated with sample components and undergo depletion of electrolyte within the frit to a depth of several millimeters, which can negatively affect subsequent experiments.