Ionic Liquid‐Based, Liquid‐Junction‐Free Reference Electrode

Abstract

In this paper, we describe a new type of polymer membrane-based reference electrode (RE) based on ionic liquids (ILs), in both liquid-contact (LCRE) and solid-contact reference electrode (SCRE) forms. The ILs used were bis(-trifluoromethane sulfonyl)amid with 1-alkyl-3-methyl-imidazolium as well as phosphonium and ammonium cations. In addition to their charge stabilisation role, it was found that the ILs also functioned as effective plasticizers in the PVC matrix. The LCREs and SCREs were prepared using the same design as their corresponding indicator electrodes. LCREs were prepared by casting in glass rings while SCREs were prepared on platforms made using screenprinting technology, with poly(3-octylthiophene-2,5 diyl) (POT) as the intermediate polymer. After potentiometric characterization of the response mechanism, the practical performance of the REs was studied using potentiometric titrations (Pb 2 + and pH), and characterised using cyclic voltammetry and impedance spectroscopy. All results were compared via parallel experiments in which the novel RE was substituted by a conventional double junction Ag/ AgCl reference electrode. The mechanism of response is most likely based on a limited degree of partitioning of IL ions into the sample thereby defining aquo-membrane interfacial potential. Despite their simple nature and construction, the REs showed excellent signal stability, and performed well in the analytical experiments. The identical mode of fabrication to that of the equivalent indicator (or Ion-Selective Electrode, ISE) will facilitate mass-production of both indicator and reference electrode using the same fabrication line, the only difference being the final capping membrane composition.

Analysis of water in room temperature ionic liquids by linear sweep, differential pulse and square wave cathodic stripping voltammetries

“…Each reference electrode was filled with an internal solution of [C 2 mim][Cl] in the corresponding RTIL and all of them were stored five days before use [28]. The stability of their electrode potential values through time was determined by cyclic voltammetry (CV) of the cobaltocenium ion, [Co(Cp) 2 ] + , at gold electrodes, since the cobaltocenium/cobaltocene redox couple, [Co(Cp) 2 ] +/0 , is a reliable internal standard for calibration of the RE potential in different nonaqueous media, as well as in RTILs [15,29] 2 ] +/0 couple.…”

All-Solid-State Reference Electrodes Based on Colloid-Imprinted Mesoporous Carbon and Their Application in Disposable Paper-based Potentiometric Sensing Devices

“…The reference membranes are usually doped with ions that can leach into the samples on a slow but continuous basis so that the phase boundary potentials at the reference membrane/sample interfaces are sample-independent and defined by the interfacial distribution of the doping ions. Several ions have been doped into reference membranes, including polyions, 18 ionic liquids, [19][20][21] lipophilic and hydrophilic salts. [22][23][24] At the reference membrane/solid contact interface, the interfacial potential can be stabilized by employing various solid contacts that are also used in all-solid-state ISEs.…”

Properties and Customization of Sensor Materials for Biomedical Applications

“…As novel designs for reference electrodes that, for example, do not rely on an inner-filling solution, are much needed, IL related developments emerging from materials science research may offer advantages. For instance, Cicmil et al (115,116) reported on the use of ILs in polyvinyl chloride (PVC) matrices for the preparation of disposable reference electrodes in which the partitioning of the ions into the liquid phase defines the interfacial potential. After comparing several ILs, the authors found that reference electrodes prepared with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide [C 2 mim][NTf 2 ] were least sensitive to changes in the concentration of common alkali metal chlorides.…”