Effect of interferents present in the internal solution or in the conducting polymer transducer on the responses of ion-selective electrodes

Finding a perfect match of ion-exchanger and plasticizer for ion-selective sensors

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.

Bypassed ion-selective electrodes – self-powered polarization for tailoring of sensor performance

The bypass circuit with zinc wire induces spontaneous charge flow: oxidation of zinc and reduction of the solid contact of K-ISE. This effect is helpful in the improvement of analytical parameters of K-ISE.

Physically Tailoring Ion Fluxes by Introducing Foamlike Structures into Polymeric Membranes of Solid Contact Ion-Selective Electrodes

Transmembrane ion fluxes have earlier been identified as a source of potential instability in solid contact ion-selective electrodes (SC-ISEs). In this work, foamlike structures were intentionally introduced into a potassium-sensitive plasticized poly(vinyl chloride) ion-selective membrane (ISM) near the membrane|solid contact interface by controlling the temperature during membrane deposition. Foamlike structures in the ISM were shown to be effective at physically tailoring the transport of ions in the ion-selective membrane, greatly reducing the flux of interfering ions from the sample to the membrane|solid contact interface. The drifts during a conventional water layer test were hence able to be greatly mitigated, even with SC-ISEs incorporating a relatively hydrophilic poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) solid contact. In solutions with a high background concentration of interfering ions, equilibrated ion-selective electrodes with foamlike membranes were able to reproduce their initial potentials within 0.6 mV uncertainty (n = 3) from 0 to 18 h. This was achieved despite sensor exposure to solutions exceeding the selectivity limit of the ISEs in 3 h intervals, allowing improvement of the potential reproducibility of the sensors. Since the introduction of foamlike structures into ISM is linked to temperature-controlled membrane deposition, it is envisaged that the method is generally applicable to all solid contact ion-selective electrodes that are based on polymeric membranes and require membrane deposition from the cocktail solution.

Unintended Changes of Ion-Selective Membranes Composition-Origin and Effect on Analytical Performance

Ion-selective membranes, as used in potentiometric sensors, are mixtures of a few important constituents in a carefully balanced proportion. The changes of composition of the ion-selective membrane, both qualitative and quantitative, affect the analytical performance of sensors. Different constructions and materials applied to improve sensors result in specific conditions of membrane formation, in consequence, potentially can result in uncontrolled modification of the membrane composition. Clearly, these effects need to be considered, especially if preparation of miniaturized, potentially disposable internal-solution free sensors is considered. Furthermore, membrane composition changes can occur during the normal operation of sensors—accumulation of species as well as release need to be taken into account, regardless of the construction of sensors used. Issues related to spontaneous changes of membrane composition that can occur during sensor construction, pre-treatment and their operation, seem to be underestimated in the subject literature. The aim of this work is to summarize available data related to potentiometric sensors and highlight the effects that can potentially be important also for other sensors using ion-selective membranes, e.g., optodes or voltammetric sensors.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

Improved potentiometric response of all-solid-state Pb(2+)-selective electrode

Zero-current ion-flux has a great influence on the characteristics of the ion-selective electrodes. In this work the improvement of analytical performance of all-solid-state Pb(2+)-selective membrane electrodes was demonstrated by adjusting the transmembrane ion flux. The study is focused on the relationship between the conditioning solution and the linear working range of the obtained electrodes for different sample matrixes. Results show that the electrode with appropriate conditioning keeps good reproducibility within linear working range. The utility of the electrode has been tested by successfully determining Pb(2+) concentration in real water samples.