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We introduce a simple procedure allowing preparation of cation-selective electrodes with poly(n-butyl acrylate)-based membranes containing different proportions of primary and interfering ions introduced already at the membrane preparation step, by using two different liphophilic salts of the same anion. With this approach the time required to achieve saturation of polyacrylate membranes with primary ions can be significantly shortened. Moreover, depending on the ratio of the primary and interfering ions introduced to the membrane cocktail, different potentiometric responses are obtained ranging from typical (with micromolar detection limit), through lower detection limits to super-Nernstian ones.

A novel type of self-plasticizing polyacrylate-based membrane was developed for all-solid-state ion-selective potentiometric electrodes. The membrane composition contains a conducting polymer (CP): poly(3,4-ethylenedioxythiophene) end capped with methacrylate groups, chemically grafted with the membrane during the photopolymerization step. This composition results in ionselective membranes with the following advantages: lower electrical resistance compared to the CP-free membrane, facile ion-to-electron transduction between the membrane and the electrode support, controlled low activity of analyte ions, and high concentration of interferent ions (incorporated with the CP) within the membrane, potentially resulting in improved analytical parameters. [Ca.sup.2+]- and [K.sup.+]-selective membranes were chosen as model systems to study the effect of pretreatment and CP content on the potentiometric sensor's characteristics. For [Ca.sup.2+] sensors, reproducible and stable Nernstian characteristics were obtained within the range from 0.1 to [10.sup.-9] M Ca[Cl.sub.2], without a time-consuming preconditioning step. For [K.sup.+]-selective sensors, the influence on Nernstian response range was observed for varying KCl concentrations in the conditioning solution, with the lowest detection limit found close to [10.sup.-8] M KCl. Mass spectrometry coupled with laser ablation studies of the membranes revealed that in this case the detection limit is not related to primary ion content in the membrane contacting a sample solution, but is affected by interfering ion concentration close to the membrane surface.

Laser ablation inductively coupled plasma mass spectrometry was used to evaluate ion depth profiles across ion-selective membranes. Advantageously, this approach does not require incorporation of additional components (e.g., chromoionophore) in the membrane composition, as compared to that used in typical potentiometric applications. Moreover, comparison of the distribution of ions in differently pretreated membranes is possible. Concentration profiles of primary and interfering agent ([Na.sup.+]) ions were recorded, for example, of [Pb.sup.2+]-selective poly(vinyl chloride)-based membranes. It was found that the contents and the distribution of [Pb.sup.2+] and NaT ions across the membrane is strongly dependent on the composition of the solutions to which both sides of the membrane are exposed during preconditioning and on the plasticizer included in the membrane formulation. Typical plasticizers, bis(2-ethylhexyl sebacate) (DOS) and the more polar 2-nitrophenyl octyl ether (o-NPOE), were used. It was found that faster ion transport occurs for o-NPOE, and the membrane saturation with [Pb.sup.2+] ions was achieved within less than 20 h for a 400-[micro]m-thick membrane. In the case of the less polar plasticizer DOS, due to slower rate of ion transport, even after 20 h, the [Pb.sup.2+] concentration gradients were still visible within the membrane. On the basis of concentration profiles, primary ion diffusion coefficients in both membranes were calculated, and the value obtained for o-NPOE containing membrane was found to be ~2 times higher than for its DOS-plasticized counterpart.

An all-solid-state calcium-selective electrode was constructed with poly(pyrrole) solid-contact doped with calcium complexing ligand Tiron. The potentiometric response of this sensor can have a linear range down to [10.sup.-9] M with a slope close to Nernstian and detection limit equal to [10.sup.-9.6]. The effects of pH and the activity of the interfering ion in the conditioning solution on the potentiometric behavior of the constructed sensors were examined. Potential stability, reproducibility, and impedance studies were performed. The selectivity of the constructed electrode is better than that of the conventional calcium-selective electrode with internal filling solution of [10.sup.-2] M Ca[Cl.sub.2] and comparable to that of the best liquid-contact electrodes.

The goal was to identify formulations for use in valinomycin [K.sup.+] ion-selective electrodes that could routinely achieve a detection limit of

The detection limit of conducting polymer (CP) poly(pyrrole)-based potentiometric chloride-sensitive electrodes was lowered over 3 orders of magnitude, applying anodic current of density in the range microamperes per centimeter squared. This effect was attributed to compensation of doping chloride ion leakage from the membrane into adjacent solution layer, caused by self-discharge of CP. This method was successfully applied to lower the detection limit of all-solid-state chloride-selective potentiometric sensors containing plastic, poly(vinyl chloride) chloride ion-selective membrane, and conducting poly(pyrrole) film applied as ion-to-electron transducer. The control of the leakage of chloride ions from the CP transducer phase to the plastic membrane resulted in linear response of ion-selective electrode shifted down to lower activities. A 2 orders of magnitude lowered detection limit, equal to 4 x [10.sup.-7] M, was achieved for current densities corresponding to extended linear range of CP film electrode, i.e., in the range of microamperes per centimeter squared. Experiments with all-solid-state potentiometric sensors were carried out using open-sandwich arrangement (two poly(pyrrole) electrodes coated by the same ion-exchanging membrane): one part of the sensor was working under open circuit conditions, while the second electrode was polarized using anodic current. Due to arrangement used, the lowered detection limit observed for nonpolarized electrode is attributed to modification of ion fluxes in the membrane; it is interfered by neither ohmic drop nor anion depletion layer formation due to anodic current flow.

An all-solid-state calcium-selective electrode with a plastic membrane phase containing a calcium ionophore ETH-1001 placed on poly(3-methylthiophene) ion-to-electron transducting layer functionalized to bind calcium cations has been constructed. The obtained potentiometric sensors were characterized with a calibration line of slope close to Nernstian within the activity from [10.sup.-5] to 0.1 M. For [Ca.sup.2+] activity lower than [10.sup.-5] M, super-Nernstian behavior was observed. The super-Nernstian response that is observed for electrodes with an internal solution strongly binding primary ions was in this case attributed to incorporation of calcium ions in the modified solid-contact phase. With this arrangement, the evaluation of selectivity coefficients much closer to those that depend on the properties of the ion-selective membrane itself was possible.

The influence of different polymerization conditions and electrochemical processes provoked by soaking on the potentiometric sensitivity of conducting polymer films is discussed. Poly(pyrrole) doped with hexacyanoferrate-(II) is selected as a model polymer. It is shown that, depending on the conditions applied during film deposition and soaking, either anionic or cationic potentiometric responses can be observed and related to the composition of the film. The potentiometric sensitivity of the conducting polymer films is analyzed and interpreted by means of generalized theoretical schema.

Carrier-based ion-selective electrodes have long been in routine analytical use, yet they still attract an important focus for further research, for example trying to push their capabilities into new dimensions. In the normal construction, the polymeric/ionophore membrane interfaces with the sample and, on the backside, with an aqueous electrolyte in which an internal reference electrode is placed. At low sample activities, zero current ion fluxes across the membrane due to extraction processes at the membrane interfaces can cause analyte ion activity in the phase boundary to be significantly higher than in the sample bulk. This influences the measured potential, so that consideration of these processes and their management has become a prime objective to attain lower detection limits and optimum selectivity.

Electrospun nanofibers were used to support palladium nanocubes, resulting in a highly active, stable, and reusable catalyst. The system proposed herein offers significant advantages compared to catalysts in the form of nanoparticles suspension. The porous, solvent permeable structure of the nanofiber mat ensures uniform and stable time distribution of palladium nanoparticles; preventing coalescence and allowing multiple use of the catalyst. The proposed cross-linked poly(vinyl alcohol) nanofiber mat loaded with Pd nanocubes during the nanofiber preparation step is a macroscopic structure of intrinsically nanostructural character of the catalyst that can be easily transferred between different solutions without compromising its effectiveness in consecutive cycles. Thus, obtained system was characterized with high catalytic activity as tested on a model example of 4-nitrophenol (4-NP) reduction by NaBH 4 to 4-aminophenol (4-AP). It is shown that loading nanofibers with Pd nanocubes during electrospinning resulted in a significantly more stable system compared to surface modification of obtained nanofibers with nanocube suspension., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Classical application of ion-selective membranes is limited to either electrochemical or optical experiments. Herein, the proposed ion-selective membrane system can be used in both modes; each of them offering competitive analytical parameters: high selectivity and linear dependence of the signal on logarithm of analyte concentration, high potential stability in potentiometric mode, or applicability for alkaline solutions in optical mode. Incorporation of analyte ions into the membrane results in potentiometric signals, as in a classical system. However, due to the presence of lipophilic positively charged ions, polymer backbones, full saturation of the membrane is prevented even for long contact time with solution. The presence of both positively charged and neutral forms of conducting polymers in the membrane results in high stability of potential readings in time. Optical signal generation is based on polythiophene particulates dispersed within the ion-selective membrane as the optical transducer. An increase of emission is observed with an increase of analyte contents in the sample.

We report for the first time on in situ transduction of electrochemical responses of ion-selective electrodes, operating under non-zero-current conditions, to emission change signals. The proposed novel-type PVC-based membrane comprises a dispersed redox and emission active ion-to-electron transducer. The electrochemical trigger applied induces a redox process of the transducer, inducing ion exchange between the membrane and the solution, resulting also in change of its emission spectrum. It is shown that electrochemical signals recorded for ion-selective electrodes operating under voltammetric/coulometric conditions correlate with emission intensity changes recorded in the same experiments. Moreover, the proposed optical readout offers extended linear response range compared to electrical signals recorded in voltammetric or coulometric mode.