Surface Resistance and Potentiometric Response of Polymeric Membranes Doped with Nonionic Surfactants

Abstract

The influence of lipophilic, electrically neutral surfactants added to the membrane on the ion transfer resistance between an aqueous sample and a polymeric ion-selective membrane has been studied by electric impedance spectroscopy and potentiometry. An increase in the surface resistance and a shift of the apparently super-Nernstian response to lower sample ion activities has been observed when using the nonpolar bis(2-ethylhexyl) sebacate as plasticizer.

Reversible electrochemical monitoring of surface confined reactions at liquid–liquid interfaces by modulation of ion transfer fluxes

“…{ The sodium-selective membrane was solvent cast as described 9 and contained 10 mmol kg 21 sodium ionophore tert-butyl calix [4]arene tetraacetic acid tetraethylester, 10 wt% inert lipophilic electrolyte tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH 500), and the plasticizer o-nitrophenyloctylether and the polymer poly(vinyl chloride) in a 2 : 1 mass ratio. An 8 mm 2 membrane disk was cut from this parent membrane, mounted in a Philips electrode body, backfilled with 0.1 M NaCl and conditioned in 0.1 M NaCl overnight before performing the electrochemical experiments in a described three electrode cell.…”

“…Very recently, Muslinkina and Pretsch explored calciumselective membranes doped with the non-ionic surfactants sorbitan monostearate and sorbitan monopalmitate with zero current potentiometry and EIS. 4 The membrane electrodes were formulated to induce a continuous inward flux of calcium ions from the sample to the membrane phase, giving a so-called super-Nernstian potential change at a critical calcium activity. Membranes doped with non-ionic surfactants showed charge transfer resistance changes as observed by EIS.…”

“…The sensor response before and after addition of surfactant may therefore be more conveniently characterized compared to doping the surfactant into the membrane during preparation. 4 The surfactant Brij35, as with most surfactants of this class, has a tendency not only to adsorb onto the membrane surface but to extract into the bulk of the *eric.bakker@auburn.edu membrane as well. Earlier work by Malinowska and Meyerhoff 7 revealed that such surfactants may, once extracted into the membrane, act as metal binding chelators for interfering ions, sometimes resulting in diminished ion selectivity of the membrane.…”

Detecting Biorecognition Events at Blocked Interface Polymeric Membrane Ion‐Selective Electrodes Using Electrochemical Impedance Spectroscopy and Atomic Force Microscopy

“…A natural extension of the work by Muslinkina and Pretsch [8,9] was to study the solution adsorption of surfactants onto the polymeric ISE membrane, and this research was undertaken by Xu et al [10]. In this paper [10], EIS showed that solution adsorption of commercially available non-ionic surfactants can be used to reproducibly produce a SAM of the surfactant at the electrode/electrolyte interface and, the electrochemically imposed ion flux at the interface of a chronopotentiometric polymer ISE, is modulated by the SAM, thereby providing a promising experimental tool for the detection of surface confined reactions (e.g.…”

“…In two papers by Muslinkina and Pretsch [8,9], these researchers showed that it is possible to dope an ISE polymer membrane cocktail with a prescribed dose of surfactant that yields a self-assembled monolayer (SAM) of surfactant at the membrane surface after casting, and EIS studies showed that the ion transfer resistance, which is a reflection of the kinetics of ion transfer at the membrane/ solution interface, was impeded when the ISE membrane had been blocked by surfactant. A significant outcome of this research was the demonstration that the natural nonionic surfactant, stearyl-b-d-glucopyranoside (S-b-d-GP), is able to form such a SAM, and the SAM of S-b-d-GP undergoes a biorecognition event when contacted with an aqueous solution containing a glucose-specific lectin bound to the protein concanavalin A [8].…”