Zook Justin M, Bodor Sándor, Gyurcsányi Róbert E, Lindner Ernő
Department of Biomedical Engineering, The University of Memphis, Memphis, TN 38152, USA.
J Electroanal Chem (Lausanne). 2010 Jan 15;638(2):254-261. doi: 10.1016/j.jelechem.2009.11.007.
Passing currents through ion-selective membranes has contributed to the development of a variety of novel methods. In this work, chronopotentiometric (CP) transients with two transition times (breakpoints) are presented for the first time, with the theoretical interpretation of such voltage transients. The validity of our theory has been confirmed in experiments utilizing ETH 5294 chromoionophore-based pH sensitive membranes with and without lipophilic background electrolyte and ETH 5234 ionophore-based calcium selective membranes in which the ionophore forms 3:1 complexes with Ca(2+) ions. The conditions under which two breakpoints can be identified in the chronopotentiometric voltage transients are discussed.Spectroelectrochemical microscopy (SpECM) is used to show that the two breakpoints in the CP curves emerge approximately when the free ionophore and ion-ionophore complex concentrations approach zero at the opposite membrane-solution interfaces. The two breakpoint times can be utilized to follow simultaneously the concentration changes of the free ionophore, the ion-ionophore complex, and the mobile anionic sites in cation-selective membranes. In membranes with known composition, the time instances where breakpoints occur can be used to estimate the free ionophore and the ion-ionophore complex diffusion coefficients.
通过离子选择性膜施加电流推动了各种新方法的发展。在这项工作中，首次展示了具有两个转变时间（断点）的计时电位（CP）瞬变，并对这种电压瞬变进行了理论解释。我们的理论有效性已在实验中得到证实，这些实验使用了基于ETH 5294色离子载体的pH敏感膜，有或没有亲脂性背景电解质，以及基于ETH 5234离子载体的钙选择性膜，其中该离子载体与Ca(2+)离子形成3:1配合物。讨论了在计时电位电压瞬变中能够识别出两个断点的条件。光谱电化学显微镜（SpECM）用于表明，CP曲线中的两个断点大约在相反的膜 - 溶液界面处游离离子载体和离子 - 离子载体配合物浓度接近零时出现。这两个断点时间可用于同时跟踪阳离子选择性膜中游离离子载体、离子 - 离子载体配合物和移动阴离子位点的浓度变化。在具有已知组成的膜中，断点出现的时间实例可用于估计游离离子载体和离子 - 离子载体配合物的扩散系数。
