Quantitative Analysis of Redox-Inactive Ions by AC Voltammetry at a Polarized Interface between Two Immiscible Electrolyte Solutions

Abstract

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 carried out by amperometry, cyclic or differential pulse voltammetry. Here, we introduce a new electroanalytical method based on AC voltammetry with inherent advantages over traditional approaches such as avoidance of positive feedback iR compensation, a major issue for liquid|liquid electrochemical cells containing resistive organic media and interfacial areas in the cm 2 and mm 2 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. As 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. Major opportunities therefore 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 2 electrochemical reactions from those due to irreversible processes, which do not give AC signals.

Ametryn detection by proton assisted transfer at a single micro-interface between two immiscible electrolyte solutions

“…We assumed that the electrochemical cell behaves as a Randles circuit. The analytical signal, Y, used to plot the AC voltammograms was determined by equation ( 1), as it was described previously [48]:…”

“…A more sensitive electrochemical method was required to overcome the mediocre limit of detection reached with cyclic voltammetry (Figure 6). Recently, AC voltammetry was described by Suárez-Herrera and Scanlon [48] as an quantitative analytical method at the ITIES. It was used here to improve the sensitivity of the ametryn detection (Figure 7).…”

Mimicking the Microbial Oxidation of Elemental Sulfur with a Biphasic Electrochemical Cell

“…Considering that TMA + transfers close to the PZC (compare Figures 2B and C), a low influence of the electrical double layer was expected as the impact of migration should be negligible. [9,34] The interfacial AuNP film was found to have no significant effect on the TMA + ion transfer kinetics as demonstrated by (i) the peak separation of the reversible TMA + ion transfer response being 58 mV ( Figure 2C), (ii) the ion transfer resistance being undetectable by EIS experiments ( Figure 2D), and (iii) the Randles circuit accurately describing the EIS spectra at the TMA + ion transfer potential of +0.311 V ( Figure 2D).…”

Plasticized PVC Membrane Modified Electrodes: Voltammetry of Highly Hydrophobic Compounds

“…ITIES was developed for the measurement of redox-inactive, generally hydrophilic anions and cations [ 22 , 23 , 24 ], but has also been utilized for the voltammetric ion transfer of biologically relevant polyions such as heparin [ 25 , 26 ] and protamine [ 27 ]. ITIES is attractive because it enables the measurements of ions without their electrolysis [ 20 , 28 ]. With the double membrane arrangement, i.e., a conductive polymer-supported thin plasticized PVC membrane, as shown in Scheme 2 b, the oxidation or reduction of the conductive polymer drives the transfer of anions or cations into the PVC membrane, respectively ( Figure 1 ).…”