Response Behavior of Poly(vinyl chloride)‐ and Polyurethane‐Based Ca²⁺‐Selective Membrane Electrodes with Polypyrrole‐ and Poly(3‐octylthiophene)‐Mediated Internal Solid Contact

Abstract

The potentiometric response behavior of Ca 2þ -selective poly(vinyl chloride) (PVC) and polyurethane (PU) membranes with different inner contacts has been compared. Evidence for the formation of a water film between membrane and internal contact and, hence, a less than optimal lower detection limit have been found for membranes directly in contact with bare Au or with polypyrrole generated by electropolymerization in the presence of KCl. A significantly better behavior is shown by membranes with polypyrrole prepared in the presence of potassium hexacyanoferrate. Best performances have been obtained with solvent-cast poly(3-octylthiophene) as the internal contacting layer. As compared with the PVC membranes, those with PU had a significantly worse performance throughout.

Development of miniature all-solid-state potentiometric sensing system

“…at the inner membrane phase boundary (membrane/water layer), as reported previously by Sutter et al [11,32]. This confirms the benefit of using PEDOT as an intermediate layer and its effectiveness as a water layer suppressant.…”

“…a mediating layer between the electronically conducting substrate and ionically conducting ISE membrane, which was possible due to the mixed conductivity of CPs [21]. Various conductive polymers have been examined as possible internal contact materials that could simultaneously stabilize the overall electrode potential and remove the need for an inner filling solution [9][10][11]. This application of CPs was supported by fundamental theoretical interpretation of signal formation by Lewenstam at al [28] and, in particular, a deeper understanding of the instabilities of solid-contact sensors as provided by Fibbioli and co-authors [29].…”

An all-solid-state polymeric membrane Pb2+-selective electrode with bimodal pore C60 as solid contact

“…Unfortunately, coated wire electrodes show long-term potential instability, which is attributed to the lack of a well-defined interface between the ionically conductive sensing membrane and the electronically conductive conductor and the formation of a thin water layer between them [2,3]. By incorporation of appropriate redox-active compounds to the ISE membranes [4,5] or using conducting polymers (CPs) such as polypyrrole, poly(3-octylthiophene), polyaniline and poly (3,4-ethlyenedioxythiophene) as solid contacts [6], the potential stabilities of all-solid-state ISEs can be largely improved.…”

All-Solid-State Polymeric Membrane Ion-Selective Miniaturized Electrodes Based on a Nanoporous Gold Film as Solid Contact

“…3 Such sensor configuration shows potential instability and ill-reproducibility for long-term use, due to the lack of a thermodynamically well-defined interface between the electronic conductor and the ion-selective membrane. 4 Additionally, an undesired water layer with about 100 Å thickness under the ion-selective membrane is another resource of potential drift, 5 which unintentionally acts as an inner filling solution with extremely small volume that reequilibrates on each and every change in sample composition and subsequently influences the boundary potential. 6 Both sources of potential instability can be eliminated by applying a variety of materials as solid contacts, such as lipophilic redox-active self-assembled monolayers, 7 conducting polymers, 8 fullerene, 9 three-dimensionally ordered macroporous (3DOM) carbon, 10 carbon nanotubes, 11 graphene, 12,13 gold nanoparticles, 14 and nanoclusters.…”