Ion-selective Electrode Research Articles

Approaching to Calibration-Free Ion Detection Based on Thin Layer Coulometry with Ultrathin Ion-Selective Membranes

Approaching to Calibration-Free Ion Detection Based on Thin Layer Coulometry with Ultrathin Ion-Selective Membranes

Application of a Screen-Printed Ion-Selective Electrode Based on Hydrophobic Ti3C2/AuNPs for K+ Determination Across Variable Temperatures.

Monitoring potassium ion (K+) concentration is essential in veterinary medicine, particularly for preventing hypokalemia in dairy cows, which can severely impact their health and productivity. While traditional laboratory methods like atomic absorption spectrometry are accurate, they are also time-consuming and require complex sample preparation. Ion-selective electrodes (ISEs) provide an alternative that is faster and more suitable for field measurements, but their performance is often compromised under variable temperature conditions, leading to inaccuracies. To address this, we developed a novel screen-printed ion-selective electrode (SPE) with hydrophobic Ti3C2 Mxene and gold nanoparticles (AuNPs), integrated with a temperature sensor. This design improves stability and accuracy across fluctuating temperatures by preventing water layer formation and enhancing conductivity. The sensor was validated across temperatures from 5 °C to 45 °C, achieving a linear detection range of 10-⁵ to 10-1 M and a response time of approximately 15 s. It also demonstrated excellent repeatability, selectivity, and stability, making it a robust tool for K+ monitoring in complex environments. This advancement could lead to broader applications in other temperature-sensitive analytical fields.

Chlorophyll-Inspired Magnesium Porphyrin Array Membrane for Vis-Light-Enhanced Osmotic Energy Conversion.

Osmotic energy, a renewable clean energy, can be directly converted into electricity through ion-selective membranes. Inspired by the magnesium porphyrin (MgP) in plant chlorophyll, which absorbs vis-light and promotes photoelectric conversion, we demonstrate a MgP array membrane, realizing vis-light-enhanced ion transport regulation ability and osmotic energy conversion. The MgP arrays are self-assembled by a MgP-cored block copolymer under the coordination effect of block copolymer self-assembly and MgP π-π stacking, providing chloride-selective transport channels. Due to the unique photochemical properties of MgP, the chloride ion transport conductance and selectivity can be simultaneously increased under visible-light irradiation, benefiting the osmotic energy conversion. Specifically, the maximum power density increases from 26.7 to 34.5 W·m-2 after visible-light illumination, representing approximately a 30% increase. The construction of MgP arrays realizes photofacilitated osmotic energy conversion, providing an idea for designing an efficient photoelectric conversion system.

Anti-Swelling Polyelectrolyte Hydrogel with Submillimeter Lateral Confinement for Osmotic Energy Conversion

AbstractHarvesting the immense and renewable osmotic energy with reverse electrodialysis (RED) technology shows great promise in dealing with the ever-growing energy crisis. One key challenge is to improve the output power density with improved trade-off between membrane permeability and selectivity. Herein, polyelectrolyte hydrogels (channel width, 2.2 nm) with inherent high ion conductivity have been demonstrated to enable excellent selective ion transfer when confined in cylindrical anodized aluminum pore with lateral size even up to the submillimeter scale (radius, 0.1 mm). The membrane permeability of the anti-swelling hydrogel can also be further increased with cellulose nanofibers. With real seawater and river water, the output power density of a three-chamber cell on behalf of repeat unit of RED system can reach up to 8.99 W m−2 (per unit total membrane area), much better than state-of-the-art membranes. This work provides a new strategy for the preparation of polyelectrolyte hydrogel-based ion-selective membranes, owning broad application prospects in the fields of osmotic energy collection, electrodialysis, flow battery and so on.

Development of a hydroponic device using potassium Ion-Selective electrode and neural network technology

The rapid development of modern agricultural biotechnology and information technology has become a key driver of modern agricultural growth. The demand for ion detection is prevalent in all aspects of agriculture. This study details the research on an ion sensor agricultural system using potassium (K) ion-selective electrodes (ISEs). The main emphasis is on the application of artificial neural networks (ANNs) for driving ISE development of accuracy. ISEs based on solid contact with metal oxides, specifically manganese dioxide, are studied. Moreover, the design details of an ion signal acquisition device using the NI-9205 acquisition card and LabVIEW are presented. Finally, based on experimental results of nutrient solution samples, ANNs show better performance than the multiple linear regression method. The mean relative error of K-ISE detection was maintained within 4%. This study thoroughly discusses ISE technology to promote its adoption in agriculture.

Analysis of blood calcium levels in calcium water consumers

Introduction: Water is a primary and basic human need. One of the chemical parameters that must be met for drinking water needs is mineral content, such as calcium and magnesium. Water hardness is a condition in which there is excessive calcium and magnesium content, which is commonly known as calcareous water. If consumed long-term, high-water hardness that exceeds normal limits can interfere with body health. Specifically, excess calcium in the body can cause hypercalcemia, hyperparathyroidism, kidney stones, and muscle tissue damage (muscle weakness). Objective: This study aims to determine blood calcium levels in individuals who consume calcareous healthy water. Methods: The type of research used is descriptive-analytical, with blood calcium level analysis carried out using the Ion Selective Electrode (ISE) method through the Electrolyte Analyzer (CBS400). Result: Based on the results of the study, it was obtained that blood calcium levels in 30 community respondents in Ranomeeto District (100%) were above the reference value, indicating high blood calcium levels. Conclusion: blood calcium levels in people who consume lime juice indicate high blood calcium levels. Consuming water with a high lime content can hurt health. Therefore, people need to consider the quality of the drinking water they drink, especially those that have a high lime content, to maintain heart and kidney health in the long term.

OFF–ON stirring potentiometry with solvent polymeric membrane ion-selective electrodes: A theory-guided approach to foreign ions

The response of ion-selective electrodes (ISEs) towards a foreign ion is comprehensively investigated as a function of the nature and concentration of the ion, and of the mass transport conditions in the outer solution. Notably, a striking transient potential drift is evidenced by sheer activation of stirring in an initially quiescent solution of the foreign ion, both in the absence and presence of the primary ion. This phenomenon is rationalized in terms of the ion exchange at the outer membrane side coupled to the mass transfer of ions. This has been modelled through a novel theoretical treatment of the corresponding time-dependent mass transport problem, leading to simple closed-form expressions for the membrane potential and for the interfacial ion concentrations in the unstirring and stirring periods. The theoretical predictions are corroborated experimentally by monitoring the potential of a nitrate ISE exposed to ions of very different affinity towards the membrane (tetraphenylborate, perchlorate and chloride) before and after switching on the agitation of the solution. Such OFF-ON stirring program enables the study of foreign ions, even simultaneously with the determination of the primary species by the joint analysis of the potentials before and after the activation of the stirring.

Innovative Potentiometric Quantification of Flutamide Using Novel Ion-Selective Electrodes with Sulfonphthalein Dyes

Two potentiometric sensors, referred to as ion-selective electrodes (ISE)-A and ISE-B, were constructed and validated to quantify the flutamide (FA) in drug formulations, extended to analyse human urine samples infused with drugs. Bromocresol green and bromophenol blue were used as ion-pair complexing agents in the construction of ISE-A and ISE-B, respectively. Dibutyl phthalate served as a plasticizer within a polyvinyl chloride matrix, with tetrahydrofuran as the solvent. The methods demonstrated linearity over the ranges of 2.5 x 10-6 to 2 x 10-3 M and 5 x 10-6 to 1.8 x 10-3 M for ISE-A and ISE-B, respectively. The Nernstian slop of 58.8 ± 0.96 and 62.11 ± 0.83 were exhibited by the proposed methods employing ISE-A and ISE-B, respectively, within a response time of 25 seconds and were effective for the analysis of FA over a period of 52 days within a pH range of 1.0 to 4.2. The coefficient of determination (R2) was very close to one, indicating an excellent fit between the actual and measured data. For ISE-A, the computed limits of detection and quantification were 0.82 x 10-6 M and 2.45 x 10-6 M, respectively, and 1.64 x 10-6 M and 4.86 x 10-6 M for ISE-B. The ICH recommendations were followed during the validation process, which evaluated the methodologies' robustness, ruggedness, sensitivity, accuracy, precision, and selectivity.

Tailoring the surface of a polymeric membrane with a thin-layer Nafion membrane: Construction of an anti-surfactant solid-contact ion-selective electrode

Surfactants are a type of amphiphilic chemicals that comprise both hydrophilic and hydrophobic regions, and the presence of surfactants would bring a detrimental effect on the potential responses of the solid-contact ion-selective electrodes induced by their extraction from the aqueous solution into the polymeric membrane phase. Herein, an anti-surfactant solid-contact Ca2+-selective electrode is proposed based on tailoring the surface of the polymeric membrane with the thin-layer Nafion membrane. The extraction of surfactants into the polymeric membrane can be eliminated through using the hydrophobic group of Nafion acting as “a polymer brush”, while the Ca2+ diffusion from the aqueous solution to the membrane phase is promoted by the hydrophilic group of Nafion based on the electrostatic interaction. The Nafion-functionalized solid-contact Ca2+-ISE shows an improved potential stability and an excellent potentiometric performance for detection of Ca2+ in the presence of cationic and anionic surfactants as compared to the traditional solid-contact Ca2+-ISE. Moreover, the anti-surfactant solid-contact ion-selective electrode is feasible for in situ measurement of Ca2+ at the interface between the seawater and the sediment. This work provides a general and facile strategy to eliminate the interferences of surfactants during the potentiometric measurements, and is favorable for in situ, on-site measurement with high accuracy and precision in the aquatic environment.

Evaluation of Fluoride and Silver Ion Concentrations in e-Silver Diamine Fluoride and Advantage Arrest: An Ion Chromatography and Atomic Absorption Spectrometer Study.

Dentin hypersensitivity (DH) is characterized by sharp shooting pain due to exposed dentin, and the most common method for treating this pain is the occlusion of the dentinal tubules with the help of desensitizing agents. E-silver diamine fluoride (e-SDF) (Kids-e-Dental, Mumbai, India) is a commercially available 38% SDF solution in the Indian market. Despite the fact that its application for caries prevention has been proven, the fluoride (Fl) and silver (Ag) ion concentrations of e-SDF for use in treating DH have yet to be standardized. The aim of this study is to determine and compare the Fl and Ag ion concentrations released from two commercially available 38% silver diamine fluoride (SDF) solutions. The two most common commercially available 38% SDF solution brands, namely Advantage Arrest and e-SDF were used. Two drops of each of these solutions were taken in three beakers and diluted with distilled water. The Fl ion concentration was evaluated using a calibrated ion-specific electrode. The free Ag ion concentration was assessed using an atomic absorption spectrometry (AAS). Release of Ag ions shows that on days 1, 2, 5, 6, and 7, concentration (mg/L) was higher in the Advantage Arrest group but is statistically nonsignificant. On days 3 and 4, it is higher in an e-SDF group with a t-value of 1.085 and 0.243 and is statistically nonsignificant. Release of Fl ion showed that in comparison to the baseline, it was more with Advantage Arrest on days 2, 4, and 7 with a t-value of -3.766, -0.999, and 0.347 and on day 2 was statistically significant. On days 3, 5, and 6 Fl ion release from baseline was more with e-SDF in comparison with Advantage Arrest but statistically insignificant. The AAS analysis as well as the ion chromatography showed that the Ag and Fl ion release respectively on days 1-7 from e-SDF was similar to the one seen in the case of Advantage Arrest. This helps dentists choose among different brands of the same commercially available 38% SDF solutions depending on the cost and availability of the product. Kamath P, Kamath P, P AN, et al. Evaluation of Fluoride and Silver Ion Concentrations in e-Silver Diamine Fluoride and Advantage Arrest: An Ion Chromatography and Atomic Absorption Spectrometer Study. Int J Clin Pediatr Dent 2024;17(10):1141-1145.

Ligand-Functionalized Membranes for Lithium-Selective Electrodialysis Separations

Selective electrodialysis requires further development of ion-selective membranes to enable the selective recovery of target ions from aqueous streams. In this work, we evaluated a library of commercial membranes to assess their potential for ion-ion separations and to elucidate the fundamental mechanisms of ion permselectivity in these materials. This screening of commercial membranes confirmed the limitations of size and electrostatic selectivity mechanisms in the separation of ions of similar size and/or charge. We then synthesized a library of novel ligand-functionalized membranes to study the impact of additional ion-specific coordinative interactions on lithium permselectivity under diffusive transport and selective electrodialysis. The complete characterization of the library of novel, ligand-functionalized membranes provides additional experimental data on the effect of not only ligand-cation interaction free energies, but also the effect of ligand grafting densities on ion permeabilities and permselectivities. For example, variation of membrane pyridine content from 0-50 mol% in a subset of the membrane library was found to have substantial impact on lithium/nickel permselectivities, including 3-4 times higher than the permselectivities measured with the commercial membranes. In the future, these experimental results could support further development of ion transport theory in ligand-functionalized membranes with ligand grafting densities included as model parameters. This work could also lead to future grafting density optimization studies with the goal of maximizing ion permeability and/or permselectivity. Membranes were also tested in four-chamber electrodialysis reactors to characterize performance during electrolysis; selectivity was still observed during operation. Note: This presentation reflects research funded by an ECS/Toyota Young Investigator Fellowship.

Controlling Electronic and Ionic Conductivity in oMLD Polymer Coatings

Thin film polymer coatings formed by oxidative molecular layer deposition (oMLD) are of interest as ion-selective membranes for electrochemical sensors, and as protective coatings for lithium ion batteries. In both of these applications, it is critical to control the electronic conductivity, the ionic conductivity, and the ion selectivity of the MLD coatings. Recent understanding of the oMLD mechanism reveals this synthesis method as a path to control the molecular sequence of conjugated heteroatom-containing copolymers. We employ oMLD to reveal fundamental insights into how the molecular sequence of these copolymers influences conductivity, shifting the electronic conductivity by more than three orders of magnitude by altering the molecular sequence. We also summarize the development of new oMLD chemistries including polythiourea (PTU), polyhydroquinone (PHQ), and poly(2,5‐Dimercapto‐1,3,4‐Thiadiazole) (PDMCT). We employ in-situ quartz crystal microbalance (QCM) studies during oMLD growth to understand the chemical growth mechanisms, as well as ex-situ spectroscopic ellipsometry (SE), electrical impedance spectroscopy (EIS), and electrical Van der Pauw measurements, and electrochemical characterization to identify material properties. We examine PTU as an anion-selective membrane for ion sensor applications, and PHQ and PDMCT as protective coatings for lithium-ion battery applications that provide enhanced Li+-ion conductivity with control over electronic conductivity.

To Evaluate Efficacy of Bajra husk and Moringa leaf Powder on Water Defluoridation – A Comparative Study

Introduction: AIM: To evaluate and compare efficacy of naturally available adsorbents Moringa oleifera and Bajra husk in reducing the fluoride content in the high fluoridated drinking water.Methodology: A community with high fluoride content in its water was selected and a sample was taken. The baseline fluoride level was determined using an ion selective electrode. Two naturally occurring adsorbents, powdered moringa leaf and bajra husk, were used. The husk and dried leaves were processed, sieved, and heated to 400 degrees Celsius for 30 minutes in a muffle furnace. The water sample was mixed with biochar and agitated for an hour at 500 rpm. Filter paper was used to filter the water sample and added TISAB. The fluoride content of the water sample was estimated using an ion selective electrode approach.Results: The highest removal of fluoride is significantly done by Moringa leaf biochar (23%) as compared to bajra husk (15%). when 2 grams of this biochar were added in 200ml of water sample separately.Conclusion: Drinking water defluoridation can be effectively achieved by using moringa leaves and bajra husk as adsorbents. On the other hand, Moring leaf powder proved to be more successful.

Printed Potentiometric Ammonium Sensors for Agriculture Applications.

Ammonium (NH4 +) concentration is critical to both nutrient availability and nitrogen (N) loss in soil ecosystems but can be highly variable across spatial and temporal scales. For this reason, effectively informing agricultural practices such as fertilizer management and understanding of mechanisms of soil N loss require sensor technologies to monitor ammonium concentrations in real time. Our work investigates the performance of fully printed ammonium ion-selective sensors used in diverse soil environments. Ammonium sensors consisting of a printed ammonium ion-selective electrode and a printed Ag/AgCl reference were fabricated and characterized in aqueous solutions and three different soil types (sand, peat, and clay) under the range of ion concentrations likely to be present in soil (0.01-100 mM). The response of ammonium sensors was further evaluated under variable gravimetric moisture content in the soil to reflect their reliability under field conditions. Ammonium sensors demonstrated a sensitivity of 53.6 ± 5.1 mV/decade when tested in aqueous solution, and a sensitivity of 55.7 ± 11 mV/dec, 57.5 ± 4.1 mV/dec, and 43.7 ± 4 mV/dec was measured in sand, clay, and peat soils, respectively.

Poly(3,4-ethylenedioxythiophene) and Poly(3-octylthiophene-2,5-diyl) Molecules as Composite Transducers in Potentiometric Sensors-Synthesis and Application.

The aim of this paper is to investigate the influence of the molecules of conducting polymers on the properties of potentiometric sensors. Two conducting polymers, poly(3-octylthiophene-2,5-diyl) and poly(3,4-ethylene-1,4-dioxythiophene), were compared in the context of the design of ion-selective electrodes. This study offers a comparison of the most popular conducting polymers in the context of the design of potentiometric sensors. Firstly, the properties of both materials, such as their microstructure, electrical performance, wettability, and thermic properties, were examined. Subsequently, conducting polymers were applied as transducer layers in potassium-selective sensors. The properties of both groups of sensors were evaluated using the potentiometry method. Research has shown that the presence of poly(3-octylthiophene-2,5-diyl) (POT) in the transducer layer makes it superhydrophobic, leading to a long lifetime of sensors. On the other hand, the addition of poly(3,4-ethylene-1,4-dioxythiophene) polystyrene sulfonate (PEDOT:PSS) allows for the enhancement of electrical capacitance parameter values, which beneficially influence the stability of the potentiometric response of sensors. Both examined conducting polymers turned out to be perfect materials for transducer layers in potentiometric sensors, each being responsible for enhancing different properties of electrodes.

A Simple Preparation of Crosslinked, Highly Alkaline Diallyldimethylammonium Hydroxide Hydrogel Particles via Inverse Static Anion Exchange.

Highly alkaline hydrogels are gaining increasing attention in building materials research. Specifically, cationic alkaline hydrogels based on diallyldimethylammonium hydroxide (DADMAOH) as the monomer have been effectively used to seal water-bearing cracks or serve as coupling media for electrochemical chloride extraction. However, the residual halogen content and challenges in scaling up monomer production have hindered broader application. Attempts to use a commercially available cation-selective membrane for ion exchange achieved up to 90% chloride-to-hydroxide switch, but the approach proved ineffective due to significant monomer decomposition during the process. By contrast, neutral gels and gel particles can be readily prepared from diallyldimethylammonium chloride (DADMAC) in large quantities and with a wide range of compositions. It is demonstrated here that these neutral gel particles undergo inverse static anion exchange when suspended in NaOH solution, generating DADMAOH particles with residual halide contents of <0.3%, without the need for ion-selective or dialysis membranes. This corresponds to an up to 100-fold reduction in residual chloride content compared to particles produced directly from alkaline monomer solutions, thereby significantly enhancing the efficiency of hydroxide ion release. The swelling behaviour of the particles is primarily influenced by the initial monomer concentration, while conductivity remains largely unaffected, indicating that charge transport occurs mainly along the particle surface. Despite the pronounced increase in swelling with decreasing particle radii, the specific conductivity of 2.8 Ω-1 m-1 is still sufficient for their use as coupling media in concrete applications. In summary, the alkaline particles prepared via inverse static anion exchange meet all necessary requirements for building materials applications, offering a broader range of tuneable properties and greater ease of production compared to gels or particles derived from DADMAOH.

Design of Miniaturized Ion-Selective Electrodes and Practical Applications

Design of Miniaturized Ion-Selective Electrodes and Practical Applications

In Situ Potentiometric Monitoring of Nitrate Removal from Aqueous Solution by Activated Carbon and Ion Exchange Resin.

A nitrate selective electrode was used for real-time in situ potentiometric monitoring of a batch nitrate removal process using activated carbon and ion exchange resin. A plasticized polymeric membrane consisting of polyvinyl chloride, 2-nitrophenyl octyl ether and tridodecyl methyl ammonium chloride was incorporated into an ion-selective electrode body. First, the dynamic potential response of the electrode to nitrate was investigated. Two commercial activated carbons with different physical properties were then tested. Nitrate removal with these carbons was monitored potentiometrically using several nitrate concentrations. The extreme turbidity of the solutions was not a drawback during potentiometric monitoring of the process, which is a clear advantage over other methods such as optical monitoring. The potential versus time recordings were converted into nitrate concentration versus time plots, which were evaluated with different adsorption kinetic models. A pseudo-second order kinetic model for nitrate adsorption on both activated carbons was found to fit the experimental data very well. The values of the kinetic parameters were very different between the two activated carbons. The proposed methodology was also satisfactorily applied to the study of nitrate removal by an ion exchange resin. In this case, the experimental results clearly follow a pseudo-first order kinetic model. Potential applications of the proposed methodology for monitoring nitrate removal in real water samples are discussed.

Real-Time Wireless Detection of Heavy Metal Ions Using a Self-Powered Triboelectric Nanosensor Integrated with an Autonomous Thermoelectric Generator-Powered Robotic System.

The integration of the Internet of Things (IoT) with advanced sensing technologies is transforming environmental monitoring and public health protection. In this study, a fully self-powered and automated chemical sensing system is developed and integrated with a robotic hand for "touch and sense" detection of toxic heavy metal ions (Pb2⁺, Cr⁶⁺, As3⁺) in aquatic environments. The system combines a self-powered solid-liquid triboelectric nanosensor (SL-TENS) with a thermoelectric generator (TEG), which harnesses ambient heat to power the robotic hand, eliminating the need for external power sources. The robotic hand is controlled wirelessly via an exo-hand, minimizing the risk of exposure during remote monitoring. The sensing component uses copper oxide nanowires (CuO NWs) coated with ion-selective membranes (ISMs) to enhance triboelectric output and enable highly selective ion detection. The system demonstrates effective real-time, on-site detection in lake water and data transmitted wirelessly to the user. This innovative approach provides a highly safe and efficient method for detecting hazardous pollutants in difficult-to-access areas, offering significant potential for wireless and real-time environmental monitoring and hazard prevention, thus contributing to the safeguarding of human health. This study presents a novel advancement in the field of IoT-enabled environmental monitoring systems.

The effect of water filter pitchers on the mineral concentration of tap water.

To investigate the effect of water filter pitchers on the concentration of different minerals in tap water. Nine water filter pitchers (A-I) were chosen based on consumer preferences and Amazon reviews. Each filter was tested for its ability to modify the concentrations of fluoride, calcium, magnesium, potassium, and sodium in tap water. Tap water samples were collected before and after filtration, at various intervals (1, 5, 10, 30, 50, 75, and 100 L) during filtration, and analyzed using an ion-specific electrode (fluoride) and atomic absorption spectrometry (other minerals). Statistical analyses were conducted to compare filtered and unfiltered water mineral concentrations. Water filter pitcher effect: Filters F (p < 0.001) and G (p = 0.030) decreased fluoride concentrations. All filters except I (p = 0.235) and H (p = 0.717) decreased calcium concentrations (p < 0.01). Filters E (p = 0.018), D (p = 0.014), and G (p = 0.010) decreased magnesium concentrations. Filters I (p = 0.028) and D (p = 0.009) increased potassium concentrations. Filter A (p = 0.002) increased sodium concentrations, while C (p = 0.034) decreased sodium concentrations. Effect of filter aging: All filters affected mineral concentrations over time but to varying extents. Filter G had the most pronounced effect on reducing mineral concentrations compared to all others. No filter was able to completely remove fluoride from tap water, contrary to the claims made by three manufacturers. The present study highlighted that water filter pitchers vary greatly in their ability to affect mineral concentrations in tap water during their use. Further research is needed to develop more effective water treatment solutions.