Department of Chemistry and ‡Department of Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States.
Anal Chem. 2016 Sep 6;88(17):8706-13. doi: 10.1021/acs.analchem.6b02025. Epub 2016 Aug 10.
In many commercially available and in-house-prepared reference electrodes, nanoporous glass frits (often of the brand named Vycor) contain the electrolyte solution that forms a salt bridge between the sample and the reference solution. Recently, we showed that in samples with low ionic strength, the half-cell potentials of reference electrodes comprising nanoporous Vycor frits are affected by the sample and can shift in response to the sample composition by more than 50 mV (which can cause up to 900% error in potentiometric measurements). It was confirmed that the large potential variations result from electrostatic screening of ion transfer through the frit due to the negatively charged surfaces of the glass nanopores. Since the commercial production of porous Vycor glass was recently discontinued, new materials have been used lately as porous frits in commercially available reference electrodes, namely frits made of Teflon, polyethylene, or one of two porous glasses sold under the brand names CoralPor and Electro-porous KT. In this work, we studied the effect of the frit characteristics on the performance of reference electrodes, and show that the unwanted changes in the reference potential are not unique to electrodes with Vycor frits. Increasing the pore size in the glass frits from the <10 nm into the 1 μm range or switching to polymeric frits with pores in the 1 to 10 μm range nearly eliminates the potential variations caused by electrostatic screening of ion transport through the frit pores. Unfortunately, bigger frit pores result in larger flow rates of the reference solution through the pores, which can result in the contamination of test solutions.
在许多市售和内部制备的参比电极中，纳米多孔玻璃滤器（通常是 Vycor 品牌）包含电解质溶液，该溶液在样品和参比溶液之间形成盐桥。最近，我们表明，在离子强度低的样品中，包含纳米多孔 Vycor 滤器的参比电极的半电池电势受样品影响，并可因样品组成而发生超过 50 mV 的变化（这可能导致电位测量的误差高达 900%）。证实了大的电位变化是由于玻璃纳米孔的带负电荷表面对离子通过滤器的转移产生静电屏蔽所致。由于多孔 Vycor 玻璃的商业生产最近已停产，最近在市售参比电极中使用了新材料作为多孔滤器，即由 Teflon、聚乙烯或两种多孔玻璃制成的滤器，这两种玻璃分别以 CoralPor 和 Electro-porous KT 的品牌出售。在这项工作中，我们研究了滤器特性对参比电极性能的影响，并表明参比电位的不期望变化并非仅存在于具有 Vycor 滤器的电极中。将玻璃滤器中的孔径从<10nm 增大到 1μm 范围，或切换到具有 1 至 10μm 范围的孔的聚合物滤器，几乎消除了由离子通过滤器孔的静电屏蔽引起的电位变化。不幸的是，更大的滤器孔会导致参比溶液通过孔的流速更大，这可能会导致测试溶液受到污染。
