Ultra-Sensitive Potentiometric Measurements of Dilute Redox Molecule Solutions and Determination of Sensitivity Factors at Platinum Ultramicroelectrodes
Ultra-Sensitive Potentiometric Measurements of Dilute Redox Molecule Solutions and Determination of Sensitivity Factors at Platinum Ultramicroelectrodes
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DOI：
10.1021/acs.analchem.7b01856
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发表时间：
2017-09-19
影响因子：
7.4
通讯作者：
Bard, Allen J.
中科院分区：
文献类型：
--
作者：
Percival, Stephen J.;Bard, Allen J.
开路电位（OCP）测量可以对电极环境中的小变化非常敏感，并且可以允许检测涉及很少的电子并且可能是单个电子的电子转移事件。影响OCP测量的整体灵敏度的因素进行了研究，以达到最高的灵敏度。铂超微电极（UME）的OCP测定在最初只包含支持电解质的溶液中，其中OCP是由背景法拉第过程控制的混合电位。然后，以等摩尔量的氧化形式和还原形式添加增加量的氧化还原对。在氧化还原对的稀溶液中，由于在电极处发生的额外背景半反应，OCP偏离氧化还原电位。这些通过其部分电流贡献主导OCP，将OCP转移到混合电位区域。铂UME下的OCP与电解质水溶液混合电位相比保持不变，直到达到类似于10（-6）至10（-7）M浓度的氧化还原分子。在更高的浓度下，OCP向氧化还原对的形式电位移动，并最终保持在该值。通过使用简单的表面改性，对浓度变化的灵敏度可以提高近2个数量级。用Butler Volmer形式的数值计算可以估计来自背景半反应电流的对OCP混合电势的贡献，所述背景半反应电流用于从电势相对于电流的变化中提取灵敏度因子。随着电极尺寸的减小，对浓度变化的相对灵敏度增加。
Open circuit potential (OCP) measurements can be very sensitive to small changes in the electrode environment and may allow detection of electron transfer events involving few, and maybe single, electrons. Factors affecting the overall sensitivity of OCP measurements were investigated to achieve the highest sensitivity. The OCP of platinum ultramicroelectrodes (UMEs) was determined in solutions that initially contained only supporting electrolyte where the OCP is a mixed potential governed by background faradaic processes. Then, increasing amounts of a redox couple at equimolar amounts of oxidized and reduced forms were added. In dilute solutions of the redox couple, the OCP deviates from the redox potential because of additional background half reactions occurring at the electrode. These dominate the OCP through their partial current contributions, shifting the OCP to a mixed potential region. The OCP at a platinum UME remains unchanged from the aqueous electrolyte solution mixed potential until similar to 10(-6) to 10(-7) M concentrations of redox molecules are reached. At higher concentrations, the OCP moves toward the formal potential of the redox couple and eventually becomes poised at this value. By using a simple surface modification, the sensitivity to changing concentrations can be increased by almost 2 orders of magnitude. Numerical calculations with a Butler Volmer formalism can estimate the contribution to the OCP mixed potential from background half reaction currents which are used to extract sensitivity factors from the change in potential with respect to current. The relative sensitivity to changing concentrations is shown to increase as the electrode size decreases.