Evaluation of Ionic Liquids Based on Amino Acid Anions for Use in Liquid‐junction Free Reference Electrodes

Abstract

In this paper we report on the novel polymeric membranes for the liquid junction‐free reference electrodes. The membranes contain the ionic liquids (ILs) based on the amino acid anions, namely valine‐, leucine‐, lysine‐ and histidine‐anions, and 1‐butyl‐3‐methylimidazolium cation. Addition of the ILs, and especially of the valine‐based one, to the polymeric plasticized membranes allows significant stabilization of the electrode potential and makes it insensitive to the solution composition. A simple criterion based on the calculated lipophilicities of the cation and anion of the IL is proposed for a priori estimation of its applicability for potential stabilization. The addition of the IL as a microcomponent is found to be advantageous over plasticizing the membrane with the IL due to better potential stability, higher dissociation degree and mobility of the species. The resistance of the novel reference membranes can be tuned by addition of the lipophilic membrane electrolytes, e. g. ETH500. The applicability of the developed reference electrodes is verified in the potentiometric calibration of the indicator K+‐ and Ca2+‐selective electrodes. Implementation of the amino acid‐based ionic liquids with low environmental toxicity can make a significant contribution to the development of nature‐friendly potentiometry.

Chronopotentiometric Evaluation of Ionization Degree and Dissociation Constant of Imidazolium-Based Ionic Liquid [C6Meim][NTf2] in Polymeric Plasticized Membranes

“…Electrodes with 11 types of membranes were prepared, with three replicate electrodes of each membrane type. Before measurements, the electrodes were filled with 10 −3 M KCl and conditioned in the same solution for 2 h (as in [7,14]). The internal reference electrode was electrochemically chlorinated silver wire.…”

“…The use of ILs in the polymeric membranes of both potentiometric [7,8] and optical [9][10][11] sensors has been the focus of the chemical sensor community over the past decade, mainly due to their multifunctional performance. ILs can serve as active sensor components (ionophores and/or ionic additives) [8,12,13], at the same time plasticizing the polymeric sensing phase [7,14,15].…”

“…The use of ILs in the polymeric membranes of both potentiometric [7,8] and optical [9][10][11] sensors has been the focus of the chemical sensor community over the past decade, mainly due to their multifunctional performance. ILs can serve as active sensor components (ionophores and/or ionic additives) [8,12,13], at the same time plasticizing the polymeric sensing phase [7,14,15]. High stability and reproducibility of electrochemical sensor characteristics was achieved in [15] by using asymmetric imidazolium-based ILs in a double-functional mode: as a plasticizer and as an active component simultaneously.…”

“…The principles of developing IL-based liquid-junction free reference electrodes were formulated in one of the pioneering works [14]. The theoretical background to the stabilization of the interfacial potential when a lipophilic electrolyte is introduced into the sensing phase is given in [7,20]. Critical revision on the use of ILs for developing liquid-junction free REs and non-aqueous electrolyte bridges is comprehensively performed in [21].…”

Potentiometric Sensing

“…The reference electrode based on poly­(3,3,3-trifluoropropylmethylsiloxane) and 1-methyl-3-alkylimidazolium bis­(trifluoromethylsulfonyl)­imide was shown to possess the best performance characteristics when tested in solutions containing electrolytes in concentrations representative for blood samples, but unfortunately, no undiluted blood was evaluated. Galiullin et al studied a number of ILs based on amino acid anions for use in liquid junction free reference electrodes . The studied ILs were composed of 1-butyl-3-methylimidazolium cation and valine, leucine, lysine, or histidine anions.…”