Cecylia Wardak

Potentiometric sensors constitute one of the most important groups of electrochemical sensors. Among them, ion-selective electrodes hold a prominent place. Potentiometry with fluoride ion-selective electrodes remains among the most common analytical methods for fluoride determination due to its high selectivity, cost-effectiveness, capability for in situ analysis, and wide-ranging environmental and biomedical applications. This paper provides a critical review of the development of fluoride ion-selective electrodes over the past decade, with particular emphasis on their design and analytical properties. It discusses the most important design approaches, highlighting their advantages, limitations, and challenges associated with miniaturisation or even leaching of the membrane. The properties of active membrane components responsible for fluoride-ion detection are discussed, along with the key analytical performance parameters that determine the selectivity, sensitivity, and reliability of fluoride determination. In the final section, the main areas of application for fluoride electrodes are characterised, with particular emphasis on their role in the analysis of environmental samples and biological materials.

A new method is described for the determination of vanadium using adsorptive stripping voltammetry of V(V) complexed with cupferron at a CNTs/SGC electrode modified with a lead film. The CNTs/SGC electrode is based on carbon nanomaterials such as carbon nanotubes and spherical glassy carbon, which form the foundation of modern sensor technology. Optimal conditions of adsorptive voltammetric measurement were found to be modification/accumulation potential and time of −1.6 V and 60 s, respectively, and supporting electrolyte of 0.2 mol/L NaAc–HAc buffer (pH 5.3) containing 0.3 mmol/L cupferron and 0.15 mmol/L Pb(II). The response of the system was found to be linear in a range of V(V) concentrations from 0.25 nmol/L to 10 nmol/L. The detection limit was found to be 0.08 nmol/L. The selectivity of the procedure was determined by analysing the effect of other interfering ions on the vanadium analytical signal. The method was successfully validated by analysing natural environmental waters.

Rare earth metals play a critical role in advanced industrial technologies such as their increased use in batteries, but their accelerating processing of these metals raises concerns about environmental pollution and public health. Therefore, accurate and precise determination of rare earth elements in complex matrices has become a significant analytical priority. The determination of these metal ions in potential sources and their isolation for further use are also of high industrial importance. Potentiometric ion-selective electrodes offer a promising alternative to conventional analytical methods due to their certain advantages such as their low cost, rapid response, and suitability for in situ analysis. This article provides an overview of recent advances and applications in potentiometric approaches for rare earth element determination, including novel electrode materials, selective membrane designs, and ion-selective electrode configurations. Moreover, here we covered important analytical parameters, and sensor materials and types, all of which need to be taken into account in potentiometric sensor design, to be able to develop optimized analytical devices based on potentiometry.

In response to increasing environmental protection requirements and the rapid advancement of analytical technologies, particular attention is being paid to the development of environmentally friendly, cost-effective, and sensitive measurement tools. One of the key challenges in modern analytics is the effective monitoring of inorganic nitrogen in the natural environment. In this review, we present a variety of ammonium and nitrate ion-selective electrodes. The review includes the years 2020–2026. It was divided into sections based on sensitivity to a given ion, as well as into subsections based on application: monitoring of soil and aquatic environments, the use of sensors for the determination of specific ions in a wide range of samples, and electrode designs that were used only in laboratory studies. A total of 64 nitrate electrodes and 22 ammonium electrodes were analyzed. Comparisons were made based on electrode type, type of internal contact, materials used to enhance ion-to-electron conductivity, and type of ionophore. Additionally, analytical parameters were compiled, including sensitivity, detection limit, linearity range, potential stability, operating pH range, and actual application scenarios. This review allows for an assessment of current trends and may serve as a basis for the design of new potentiometric sensors.

A new universal construction of intermediate-layer-free solid-contact ion-selective electrodes using a novel inner electrode, namely microelectrodes array composed of a large number of individual microelectrodes, was developed. This approach eliminates the need for a conventional solid-contact intermediate layer while maintaining excellent electrochemical performance. The studies were performed on two membrane model systems: potassium-ion-sensitive membranes based on valinomycin and nitrate-ion-sensitive membranes based on tridodecyldimethylammonium nitrate. In both cases, the membrane was applied directly onto the surface of the electrode substrate. The obtained results with such an ion-selective electrode based on a gold microelectrode array (GMA), a glassy carbon electrode (GCE), and a gold electrode (GE) were compared. It has been proven that, despite the lack of solid contact, whether in the form of an intermediate layer or as an addition directly to the membrane, ion-selective electrodes based on gold microelectrode arrays were characterized by very good analytical parameters. For those electrodes, a notable improvement in stability, reversibility, and repeatability of the electrode potential was observed and compared with electrodes using a glassy carbon disc electrode or a gold disc electrode as the electrode substrate. Thanks to the use of such an innovative electrode substrate, the final sensor preparation is shortened and simplified while maintaining good performance and stable readings.

In this study, for the first time, ZnO nanoparticles doped with noble metals (Pt, Ag, Au) were employed as a solid contact in nitrate ion-selective electrodes based on a glassy carbon internal electrode, and their performance was described and studied. Nanoparticles were synthesized by pulsed laser ablation in liquid. They were placed as an intermediate layer between the inner electrode and the ion-selective membrane. The impact of nanoparticle type on electrode performance was assessed by analyzing their analytical and electrical parameters using both potentiometry and electrochemical impedance spectroscopy. It was found that the determined properties of hybrid nanoparticles, as well as their effectiveness as a solid contact, depend significantly on the type of metal doping. Doping ZnO nanoparticles with metals increases their electrical capacity and reduces contact angles. The best results were obtained for the electrode modified with platinum-doped zinc oxide nanoparticles, characterized by the largest electric capacitance and the most hydrophobic properties among the hybrid nanoparticles. This electrode has been successfully used for the potentiometric determination of nitrate content in soil.

This paper presents a new type of ammonium electrode that shows a significant improvement in analytical performance compared to unmodified electrodes. The aim of the study was to develop electrodes with better electrochemical parameters, achieved by applying a modification in the form of a solid contact layer based on a carbon nanocomposite consisting of carbon nanofibers and multi-walled carbon nanotubes. Measurements were made to evaluate the basic analytical parameters of both unmodified electrodes and those enriched with an intermediate layer in the form of a carbon nanocomposite. The composite-modified electrodes showed an almost ideal theoretical slope value (58.4 mV·dec⁻¹), a lower detection limit, and linearity that remained constant over time. Stability tests showed that electrodes with nanocomposites achieved a potential drift that was almost 50 times lower. An improvement in potential reversibility was also achieved. Another important advantage of the modified electrodes is their resistance to external conditions such as light and the presence of O₂ and CO₂. In addition, they exhibit selectivity typical for ammonium electrodes. Based on the results obtained, it was found that the multiwalled carbon nanotubes and carbon nanofibers nanocomposite effectively acts as a solid contact layer, which may form the basis for the development of modern, durable, and precise sensors for the determination of ammonium ions in various environments. The determination of NH₄⁺ ions in soil was conducted with success.

In this study, the use of terpene‐based hydrophobic deep eutectic solvents (HDESs) in the preparation of polymeric membrane ion‐selective electrodes is presented. HDES obtained from terpenes (menthol and thymol) and octanoic acid are used as a new component of polymeric membrane of potentiometric sensors sensitive to lead ions. Electrodes containing different amounts of HDES in the membrane (from 1 to 12 % wt./wt.) are prepared, and potentiometric measurements are carried out for these electrodes to determine the detection limit, the slope of the characteristic, and the response linear range. Based on the analysis of electrode performance, it is found that the optimum concentration of HDES in the membrane is 5 wt%. For such membranes, a more detailed study is carried out using a solid contact sensor. Selectivity toward interfering species as well as potential stability and reversibility, optimum pH range, effect of light, and presence of gases in the sample solution are investigated for such sensors. The obtained measurement results indicate that the tested sensor containing HDES in the membrane has good analytical parameters, and excellent selectivity (log K ≤ −4.4). It has been successfully used to determine lead in real environmental water samples after a brief pretreatment with XAD‐7 resin.

Estradiol is a natural estrogen belonging to the group of natural steroid hormones. This paper presents new electrochemical biosensors—simple and low-cost tools for the determination of β-estradiol. The receptor layer of the sensor is the enzyme laccase, which was immobilized on the substrate surface using the soft plasma polymerization technique. This technique is innovative and environmentally friendly as it allows for the effective deposition of the enzyme onto unmodified and modified electrode substrates. Three types of substrates were used: an unmodified glassy carbon electrode and two electrodes modified with composite layers—multi-walled carbon nanotubes combined with CuO nanoparticles and multi-walled carbon nanotubes combined with carbon nanofibers, respectively. Biosensors modified with such materials have not been described previously. In the course of the study, electrochemical measurement conditions (composition, concentration and pH of the base electrolyte, sensor response time, and interference effects) were optimized, and sensor parameters were determined. It was found that the modification of the substrate electrode increased the sensitivity of the sensor by more than 25 times in both cases and led to a lower detection limit for the sensor modified with the carbon nanotubes/carbon nanofiber composite. The best performance was achieved with the sensor containing the carbon nanotube/carbon nanofiber composite layer, which showed a linearity range of 0.1–5 µM, a sensitivity of 7.32 ± 0.22 µA/µM, and a limit of quantification of 0.078 µM. The analytical utility of this biosensor was confirmed by its successful application in the determination of estradiol in pharmaceutical preparations and river water samples.

Perinone polymer is the latest type of conductive polymer used in solid contact ion-selective electrodes. This paper presents the application of the above-mentioned perinone polymer in two different potential ranges (-1.3-1.45 V and 0-1.45V) in potassium-selective electrodes, and the effect of the polymerization range on the basic analytical parameters was determined. The use of the conductive medium applied in both polymerization ranges significantly improved the characteristics of the electrode (higher slope), stability, and reversibility of the electrode.