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A new concept of easy to make, potentially disposable potentiometric sensors is presented. A thermoprocessable carbon black-loaded, electronically conducting, polylactide polymer composite was used to prepare substrate electrodes of user's defined shape/arrangement applying a 3D pen in a hot melt process. Covering of the carbon black-loaded polylactide 3D-drawn substrate electrode with a PVC-based ion-selective membrane cocktail results in spontaneous formation of a zip-lock structure with a large contact area. Thus, obtained ion-selective electrodes offer sensors of excellent performance, including potential stability expressed by SD of the mean value of potential recorded equal to ±1.0 mV ( n = 6) within one day and ±1.5 mV ( n = 6) between five days. The approach offers also high device-to-device potential reproducibility: SD of mean value of E 0 equal to ±1.5 mV ( n = 5).

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.

Poly(n-butyl acrylate) membranes for potentiometric ion-selective electrodes were developed and studied on example of lead-selective sensors. A novel approach resulting in Nernstian responses of tested sensor was proposed. Introduction of 5% (w/w) hydroxyethyl methacrylate into n-butyl acrylate moiety resulted in significant improvement of sensor analytical parameters. For the latter membrane material linear responses were obtained within lead activities range from 10(-2) to 10(-9) mol/dm(3), while for poly(n-butyl acrylate) based membranes pretreated in the same manner super-Nernstian behavior was obtained in a parallel experiment. Electrochemical impedance spectroscopy studies did not reveal significant differences between these two membranes, also similar lead ions diffusion coefficients were determined using inductively coupled plasma mass spectrometry with laser ablation.The difference between two kinds of membranes was found to concern higher Pb(II) ions contents in the surface part of the membrane with hydroxyethyl methacrylate, resulting in balanced Pb ions fluxes from/to the membrane.

A simple procedure of preparing low cost, planar and disposable reference electrodes for potentiometric applications is presented. This method is essentially the same as used for obtaining all-plastic ion-selective electrodes and thus promising for simple fabrication of complete cells. Commercially available aqueous dispersion of poly(3,4-ethylenedioxythiophene) doped by poly(4-styrenesulfonate) ions (PEDOT-PSS, Baytron P) is simply cast on a non-conducting plastic support (transparent foil for laser printers). This layer is covered by a non-selective poly(vinyl chloride) based membrane containing solid AgCl and KCl, added to obtain a stable potential. The conducting polymer layer plays a double role, of electrical contact and ion-to-electron transducer, enhancing the potential stability. The reference electrodes obtained exhibit independence of the kind and concentration of electrolyte applied as well as very low sensitivity to interferences: redox reactants and H+ ions; they are also characterized by both potential stability and low polarisability, sufficient for potentiometric applications. Cells of plastic electrodes (indicator and reference ones) are tested using an arrangement with Pb2+ or Ca2+ selective sensors. Potentiometric characteristic of such cells is satisfactory, well comparable with that using a classical electrode arrangement.

Potentiometric ion‐selective electrodes (ISEs) are established tools useful for the determination of activity of many ions with high selectivity. These sensors, developed originally for zero‐current conditions, are of interest for other sensing protocols, requiring tailored construction optimization with the ultimate goal to offer higher sensitivity, extended response range, offering more robust sensors, or minimizing calibration and pre‐treatment procedures. Among the different possibilities, the proposed electrochemical trigger applied for the sensing of "redox inactive ions" offers important advantages and gains significant attention. The non‐zero current applications of ISEs are typical for internal‐solution free systems; thus, the optimization of all‐solid‐state transducers receives significant research attention. The aim of this Minireview is to summarize recent research in in the field, focusing on improvements of transducers and electrochemically triggered ion‐selective sensors. [ABSTRACT FROM AUTHOR]

Amperometric responses of all‐solid‐state ion‐selective electrodes, recorded under potentiostatic conditions, were studied on example of potassium‐selective sensors with polypyrrole solid contact, at potential corresponding to reduction of the solid contact material and accompanying transfer of potassium ions across the membrane. Selective and stable in time linear dependences of current vs. logarithm of analyte concentration were recorded, resulting from high membrane resistance and changing membrane potential. The influence of experimental parameters as applied potential or thickness of the membrane was discussed. Advantages of the amperometric mode compared to potentiometric one relate to possibility of tailoring analytical parameters (sensitivity, magnitude of the signal) as well as over one order of magnitude decrease of the detection limit. The latter effect is achieved due to externally forced incorporation of potassium ions from the solution to the membrane, compensating their spontaneous release to the sample solution. A method of experimental setup simplification was proposed, with application of two‐electrode system, which can be used in the absence of external polarization source. The required driving force for the current flow was assured by spontaneous oxidation process occurring at the second electrode, coupled with reduction of the solid contact material of the ion‐selective electrode. In this case also stable in time calibration plots can be recorded. [ABSTRACT FROM AUTHOR]

The influence of dispersing agent used to prepare carbon nanotubes solid-contact on the performance of all-solid state ion-selective electrodes has been evaluated. It is shown that excess of surfactant dispersing agent is leading to deterioration of sensor performance, however, removal of dispersing agent - a typically applied approach - is resulting in substantial change of transducer layer physical properties, which can influence sensor performance. As remedy we propose application of a polymeric dispersing agent - carboxymethylcellulose. Thus obtained ion-selective electrodes are characterized by high potential readings stability both within day and between days. [ABSTRACT FROM AUTHOR]

In most cases described so far a potentiometric ion-selective membrane is made of one polymer (or one copolymer) used with ion-exchanger, ionophore and with a plasticizer of choice. In this work a concept of potentiometric bilayer membranes is introduced and their benefits from both theoretical and practical point of view are presented. They are related to response mechanism interpretation and to detection limit lowering of ion-selective electrodes. The novel structurized bilayer potentiometric membranes represent a sequence of polyacrylate polymers with ion-exchangers (the same or different), the polymers applied were either poly(hexyl acrylate) or poly(lauryl acrylate) characterized by different ionic mobilities. It was shown that tailoring of the polymer material for the component layers, kind of ion-exchanger and the layer thickness can result in significantly improved analytical performance represented by wide linear response range and low detection limit, as shown in example of potassium-selective electrode. This effect was achieved due to controlled compensation of spontaneous ion fluxes in bilayer system. The experimental data were supplemented by digital simulation results explaining the role of the thickness of the internal layer on the ion fluxes and thus on the detection limit. [ABSTRACT FROM AUTHOR]

All-solid-state ion-selective electrodes with conducting polymer solid contact represent good analytical parameters, comparable with those of classical sensors with internal filling solution. One of parameters characterizing quality of the solid contact, related to ion-to-electron transduction, is the electrical capacitance. However, in many cases this capacitance is lower than for the solid contact only, in the absence of ion-selective membrane. This effect can be disadvantageous, particularly for sensors working under polarization conditions, in galvanostatic mode. The capacitance reduction effect was studied on example of model systems of anion- and cation-selective electrodes with poly(3,4-ethylenedioxythiophene) solid contact with anion- or cation-exchange properties. Basing on results obtained for these membranes and contacts as well as some model calculations, the reasons of reduced capacitance were ascribed to low amount of ions transferrable across the solid contact/membrane interface. This effect can result from low concentration of mobile ions in the conducting polymer contact or concentration polarization effects. Procedures or pretreatment methods were proposed to minimize the effect of capacitance decrease. [ABSTRACT FROM AUTHOR]

In this work the problem of upper detection limit of potentiometric sensors is addressed. Due to deviation of potentiometric plots from cationic Nernstian responses determination of analytes like silver cations in concentrations above 10−2 M is hardly possible, especially in the presence of background electrolyte containing lipophilic anions. Herein proposed approach applied classical complexing ligand, dithizone, attached to gold nanoparticles as ionophore. Immobilization on gold nanoparticles surface effectively anchores ligand molecules within the membrane phase. Thus obtained sensors are characterized with stable, Nernstian, potentiometric responses and selectivity comparable with classical membrane compositions. Moreover, due to lower formation constant of Ag+ with dithizone based ligand, herein reported sensors offer linear, Nernstian responses also in the range of high activity of AgNO3 solutions. [ABSTRACT FROM AUTHOR]

This paper is aiming to give a brief overview of recent research in the field of all-solid-state, internal solution free, ion-selective electrodes and reference electrodes, employing conducting polymers or nano-/microstructures as solid contacts beneath the polymeric, ion-selective or reference membranes. The emphasis is on papers published in the last five years (after 2006). According to the papers published, poly(3-octylthiophene) conducting polymer transducers offer highly reliable sensors for various applications, involving demanding analytical approaches and miniature sensors. On the other hand, the search for alternative materials continues: the sensors obtained by placing nano-/microstructures (conducting polymers but also other materials, like, e.g., carbon nanotubes) underneath the receptor membrane are intensively tested. The recent years have also shown how useful the application of advanced instrumental methods is for the investigation of processes occurring within all-solid-state ion-selective electrodes. [ABSTRACT FROM AUTHOR]

Abstract: A new method of quantitative incorporation of primary cations into ion-selective membrane by means of galvanostatic cathodic polarization/conditioning, before measurement step, was proposed and tested on the example of potassium-selective electrode with ionophore – valinomycin in poly(vinyl chloride) based membrane and with polypyrrole solid contact. Open circuit potential values recorded after polarization can be quantitatively explained by changes of primary cations and ionophore concentration in the surface part of the membrane. The influence of potassium ions concentration in the membrane (in relation to ion exchange sites amount) on the shape of potentiometric calibration plots was also observed. Improved characteristics, with extended linear range, can be obtained for membrane of minor loading with primary cations (around 25%), the responses are relatively stable in course of following calibrations. [Copyright &y& Elsevier]

Application of neutral ionophore based ion-selective sensors requires presence of ion-exchanger in the receptor phase, silently assuming that it is not only soluble but also dissociates to ions in the applied plasticizer. Although for typically applied ion-selective membrane constituents (plasticizers - ion-exchanger pairs) dissociation of ion-exchangers to ions is proven by theoretical (or close to) performance of resulting sensors, search for alternative plasticizers or ion-exchangers requires a method allowing estimation of the match of properties of involved compounds. In this work we propose a simple optical approach allowing estimation of ion-exchanger interactions with plasticizer. The results were confirmed by conductivity studies of model plasticizers solutions. The estimated dissociation constants of model ion-exchangers in plasticizers used are in excellent agreement with the results of optical studies. It was shown that solubility coupled with poor dissociation to ions of ion-exchanger affects performance of the resulting ion-selective membrane. Rational choice of properties of ion-exchanger and plasticizer allows finding a perfect match of the two, that results in improvements in performance of sensors (e.g. detection limits). As model sensors potassium and sodium ion-selective electrodes with poly(vinyl chloride) (PVC) based membranes, plasticized with classical plasticizer bis(2-ethylhexyl sebacate) or biodegradable alternative acetyl tributyl citrate, were prepared and studied using selected ion-exchangers. [Display omitted] • The effect of ion pair formation with the ion-selective receptor is studied with emphasis on sensor performance. • An optical approach allowing easy visualization of the dissociation of ion-exchanger in the plasticizer is proposed. • Ion pair formation between cation-exchanger and analyte cations affects performance of sensor. • The proposed optical approach can be helpful to predict suitability of ion-exchanger for the plasticizer. [ABSTRACT FROM AUTHOR]

Abstract: Carboxy-functionalized graphene was used as a solid contact for potassium ion-selective electrodes with poly(vinyl chloride) based membrane. Transducer layers were obtained simply by application of a dispersion of graphene derivative in water. Analytical performance of thus obtained sensors was compared with that of all-solid-state sensors with typical transducer materials: poly(octylthiophene) applied as chloroform solution, conducting polymers available as aqueous dispersions of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) ions or polyaniline. It was found that all sensors tested were characterized with similar analytical parameters. Carboxy-functionalized graphene contact layer was in some respect similar to polyaniline one, what most probably results from the presence of pH sensitive groups in both materials. [Copyright &y& Elsevier]

Abstract: In this work a novel method for introduction of ionophore and ion-exchanger to the ion-selective polyacrylate based membrane is proposed. These compounds (and optionally primary ions) are introduced to polyacrylate microspheres, used to prepare ion-selective membrane. The approach proposed here can be used to prepare membranes containing primary ions equally distributed through the receptor phase, i.e. membranes that do not require conditioning in primary ions solution and are free from problems related to slow diffusion of primary ions. Thus obtained sensors were characterized with linear responses (also at relatively high activities) and high selectivities, despite considerable reduction of ionophore and ion-exchanger amount introduced to the membrane. To be able to prepare ion-selective membranes using this approach, a method for quantification of ionophore and ion-exchanger introduced into microspheres is required. In this work a novel method utilizing high performance liquid chromatography (HPLC) with DAD or FLD detection is proposed. Incorporation of ionophore and ion-exchanger into the microspheres was achieved either by absorption into ready spheres or in course of photopolymerization of polymeric beads. The obtained results have proven that both procedures led to incorporation of ionophore/ion-exchanger into polymeric spheres, however, the content of the compounds in the spheres post process is different from their ratio in solution from which they had been introduced. These effects need to be considered/compensated while preparing microspheres containing ion-selective membranes. As a model system poly(n-butyl acrylate) spheres, silver selective ionophore and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate were chosen, resulting ultimately in silver-selective electrodes. [Copyright &y& Elsevier]