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

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 screen‐printing 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 (Pb²⁺ 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.     

Solid‐contact Acetate‐selective Electrode Based on a 1,3‐bis(carbazolyl)urea‐ionophore

The construction and study of solid‐contact acetate‐selective electrodes is described using a 1,3‐bis(carbazolyl)urea derivative as a neutral hydrogen‐bonding ionophore and poly(3,4‐ethylenedioxythiophene) as the solid contact. It was shown recently that this ionophore binds acetate (logK_ass=4.98) that is used as primary ion in this study. The electrodes show linearity over the activity range of 10^?4.50–10^?1.10 with a sub‐Nernstian slope of ?51.3 mV per decade and a detection limit of 10^?5.00. The anion‐selectivity pattern of these electrodes deviates markedly from the Hofmeister pattern. When adding ionophore to the membrane the logarithm of the selectivity coefficient (logK) for SCN^? decreased from 6.5 to 1.2, logK for I^? decreased from 5.7 to 0.9, logK for NO₃^? decreased from 4.3 to 0.6 and logK for Br^? decreased from 3.3 to 0.1. The selectivity coefficients of hydrophilic anions such as Cl^?, F^?, HPO₄^2?, and SO₄^2? are significantly lower than in case of the ionophore‐free membrane. It was discovered that the constructed electrodes are also relatively selective to bicarbonate. This work is an important step towards the further development of solid‐contact anion‐selective electrodes.