Departamento De Química, Facultad De Ciencias, Universidad Nacional De Colombia, Cra 30 # 45-03, Edificio 451, Bogotá, Colombia.
The Bernal Institute and Department of Chemical Sciences, School of Natural Sciences, University of Limerick (UL), Limerick V94 T9PX, Ireland.
Anal Chem. 2020 Aug 4;92(15):10521-10530. doi: 10.1021/acs.analchem.0c01340. Epub 2020 Jul 23.
The interface between two immiscible electrolyte solutions (ITIES) is ideally suited to detect redox-inactive ions by their ion transfer. Such electroanalysis, based on the Nernst-Donnan equation, has been predominantly performed using amperometry, cyclic voltammetry, or differential pulse voltammetry. Here, we introduce a new electroanalytical method based on alternating-current (AC) voltammetry with inherent advantages over traditional approaches such as avoidance of positive feedback compensation, a major issue for liquid|liquid electrochemical cells containing resistive organic media and interfacial areas in the cm and mm range. A theoretical background outlining the generation of the analytical signal is provided and based on extracting the component that depends on the Warburg impedance from the total impedance. The quantitative detection of a series of model redox-inactive tetraalkylammonium cations is demonstrated, with evidence provided of the transient adsorption of these cations at the interface during the course of ion transfer. Since ion transfer is diffusion-limited, by changing the voltage excitation frequency during AC voltammetry, the intensity of the Faradaic response can be enhanced at low frequencies (1 Hz) or made to disappear completely at higher frequencies (99 Hz). The latter produces an AC voltammogram equivalent to a "blank" measurement in the absence of analyte and is ideal for background subtraction. Therefore, major opportunities exist for the sensitive detection of ionic analyte when a "blank" measurement in the absence of analyte is impossible. This approach is particularly useful to deconvolute signals related to reversible electrochemical reactions from those due to irreversible processes, which do not give AC signals.
两种不混溶电解质溶液（ITIES）之间的界面非常适合通过离子转移来检测氧化还原非活性离子。这种基于能斯特-唐南方程的电分析主要是通过电流安培法、循环伏安法或差分脉冲伏安法来进行。在这里，我们引入了一种基于交流（AC）伏安法的新电分析方法，与传统方法相比具有固有优势，例如避免正反馈补偿，这是包含电阻有机介质和厘米和毫米范围内界面面积的液|液电化学池的主要问题。提供了概述分析信号产生的理论背景，并基于从总阻抗中提取依赖于Warburg 阻抗的分量。证明了一系列模型氧化还原非活性四烷基铵阳离子的定量检测，并提供了这些阳离子在离子转移过程中在界面处瞬态吸附的证据。由于离子转移是扩散限制的，因此在 AC 伏安法中改变电压激励频率，可以在低频（1 Hz）下增强法拉第响应的强度，或者在更高频率（99 Hz）下使其完全消失。后者产生相当于在没有分析物的情况下进行“空白”测量的 AC 伏安图，非常适合背景扣除。因此，当不可能进行没有分析物的“空白”测量时，存在对离子分析物进行灵敏检测的重要机会。这种方法特别有助于从不可逆过程（不产生 AC 信号）引起的信号中解卷积与可逆电化学反应相关的信号。
