Ion-selective Electrode Research Articles

Improved performance of Prussian blue solid contact allowing flow injection amperometric detection of potassium ions in the excess of sodium

Catalytically synthesized Prussian blue nanoparticles are a versatile solid contact for potassium and sodium ion-selective screen-printed electrodes. The cathodic peak current proportional to cation concentration was registered in flow injection amperometry regime. The ability of K+ to penetrate Prussian blue lattice resulted in 2–4-fold higher response to potassium ions relatively to sodium ions. Such intrinsic selectivity of Prussian blue to potassium provided an order of magnitude higher sensitivity of K+-selective electrodes in comparison to Na+-sensors, based on nanoparticles covered with the corresponding ion-selective membranes. In contrast to other known solid contacts, Prussian blue provides the highest sensitivity of potassium-selective electrodes in an amperometric regime (20–50 mA·cm−2·M−1). Moreover, 1 × 10-6 M is the lowest limit of detection ever achieved for Prussian blue-based ion-selective electrodes. The improved sensitivity and selectivity allowed flow injection amperometric detection of potassium ions in the presence of interfering ions. Despite K+ concentration is approximately 40-fold lower than Na+, sensors are applicable for detection of pathological and normal potassium and sodium ions in blood serum. The sensors designed in this work have opened a new opportunity for analyzing biological fluids with ion-selective electrodes in an amperometric regime.

Pinecone derived hierarchical carbon nanostructure as a transducer in a solid-state ion-selective electrode for in vivo analysis of calcium ion

Monitoring extracellular calcium ion (Ca2+) chemical signals in neurons is crucial for tracking physiological and pathological changes associated with brain diseases in live animals. Potentiometry based solid-state ion-selective electrodes (ISEs) with the assist of functional carbon nanomaterials as ideal solid-contact layer could realize the potential response for in vitro and in vivo analysis. Herein, we employ a kind of biomass derived porous carbon as a transducing layer to prompt efficient ion to electron transduction while stabilizes the potential drift. The eco-friendly porous carbon after activation (APB) displays a high specific area with inherit macropores, micropores, and large specific capacitance. When employed as transducer in ISEs, a stable potential response, minimized potential drift can be obtained. Benefiting from these excellent properties, a solid-state Ca2+ selective carbon fiber electrodes (CFEs) with a sandwich structure is constructed and employed for real time sensing of Ca2+ under electrical stimulation. This study presents a new approach to develop sustainable and versatile transducers in solid-state ISEs, a crucial way for in vivo sensing.

Increasing the Sensitivity of pH Glass Electrodes with Constant Potential Coulometry at Zero Current.

It has recently become possible to increase the sensitivity of ion-selective electrodes (ISEs) by imposing a constant cell potential, allowing one to record current spikes with a capacitor placed in series in the circuit. The approach requires a transient current to pass through the measurement cell, which unfortunately may introduce measurement errors and additionally excludes the use of high-impedance indicator electrodes, such as pH glass electrodes. We present here an electronic circuit that overcomes these limitations, where the cell is measured at zero current in combination with a voltage follower, and the current spike and capacitor charging occur entirely within the instrument. The approach avoids the need for a counter electrode, and one may use any electrode useful in potentiometry regardless of its impedance. The characteristics of the circuit were found to approach ideality when evaluated with either an external potential source or an Ag/AgCl electrode. The current may be linearized and extrapolated to further reduce the measurement time. The circuit is further tested with the most common yet very challenging electrode, the pH glass electrode. A precision of 64 μpH was obtained for 0.01 pH change up to 0.05 from a reference solution. Similar pH changes were also measured reliably further away from the reference solution (0.5-0.55) and resulted in a precision of 377 μpH. The limitations of this experimental setup were explored by performing pH calibrations within the measuring range of the probe.

Fabrication of Ion selective PVC Membrane Sensor for Potentiometric Determination of Escitalopram Oxalate in its Pure Form and Pharmaceutical Tablet

Fabrication of Ion selective PVC Membrane Sensor for Potentiometric Determination of Escitalopram Oxalate in its Pure Form and Pharmaceutical Tablet

A highly sensitive, long-time stable Ag/AgCl ultra-micro sensor for in situ monitoring chloride ions inside the crevice using SECM

Tracking the variation of Cl− timely within the crevice is of great significance for comprehending the dynamic mechanism of crevice corrosion. The reported chloride ion selective electrodes are difficult to realize the long-time Cl− detection inside the confined crevice, due to their millimeter size or a relative limited lifespan. For this purpose, an Ag/AgCl ultra-micro sensor (UMS) with a radius of 12.5 μm was fabricated and optimized using laser drawing and electrodeposition techniques. Results show the AgCl film's structure is significantly impacted by the deposited current density, and further affects the linear response, life span and stability of Ag/AgCl UMS. The UMS prepared at current density of 0.1 mA/cm2 for 2 h shows a rapid response (several seconds), excellent stability and reproducibility, strong acid/alkali tolerance, sufficient linearity (R2 > 0.99), and long lifespan (86 days). Moreover, combined with the potentiometric mode of scanning electrochemical microscope (SECM), the Ag/AgCl UMS was successfully applied to monitor the in-situ radial Cl− concentration in micro-regions inside a 100 μm gap of stainless steel. The findings demonstrated that there was obvious radial difference in Cl− concentration inside the crevice, where the fastest rise in Cl− concentration was at the opening. The proposed method which combines the UMS with SECM has attractive practical applications for microzone Cl− monitoring in real time inside crevice. It may further promote the study of other localized corrosion mechanism and the development of microzone ions detection method.

Potentiometric determination of terbinafine hydrochloride antifungal drug in pharmaceutical and biological fluids using ion selective electrodes

Potentiometric determination of terbinafine hydrochloride antifungal drug in pharmaceutical and biological fluids using ion selective electrodes

Lithium management around delivery: a retrospective observational cohort study

IntroductionDuring the perinatal period lithium is proven effective as maintenance therapy and to prevent postpartum psychosis. Pregnancy affects all aspects of kidney physiology altering the pharmacokinetics of lithium. To minimize the risk of both maternal and neonatal complications around delivery, several authors have provided clinical advice on lithium dosing around delivery: decreasing dose by 30-50%, suspend lithium therapy 24-48 hours before scheduled cesarean section or induced delivery or even discontinuing lithium after first signs of labour.ObjectivesTo evaluate the validity of these recommendations by investigating 1) maternal lithium serum concentrations changes around delivery, 2) the lithium trasplacental passage at delivery and 3) the association between neonatal lithium serum concentration at delivery and neonatal outcomes.MethodsPsychopathologically stable women with a singleton pregnancy (n=66) who used lithium around delivery, were included in this retrospective observational cohort study (HCB/2020/1305). All women were advised to suspend lithium administration at the onset of labour in the event spontaneous deliveries. Study date: demographic, psychiatric, obstetric and neonatal outcomes for each mother-infant pair obtained from the hospital medical records.Lithium serum concentrations were determined by means of an AVL 9180 electrolyte analyzer based on the ion- selective electrode (ISE) measurement principle. Limit of quantification (LoQ) was 0.20 mEq/L.ResultsThe most common psychiatric diagnosis was a bipolar disorder type I (n=54, 90%). Forty mothers (61%) were on lithium monotherapy. Mean (SD) umbilical cord and intrapartum maternal lithium serum concentration was 0.59 (0.13) mEq/L and 0.55 (0.13) mEq/L respectively. There was a strong positive correlation between umbilical cord and maternal lithium serum concentrations (Pearson correlation coefficient 0.95 (95%IC: 0.91,0.97). In a subsample (N=22) a paired t test indicates that the maternal serum lithium concentrations at delivery were significantly lower (mean difference=0.19 mEq/L, 95%CI=0.13-0.25) than those during obtained the day before delivery hospitalization, after a mean (SD) of 31.29 (±11.92) hours (SD=11.92) have elapsed since the taking the last dose of lithium prior to delivery. Four women (6%) relapsed early postpartum.There were no significant differences between lithium monotherapy (N=18/40) and polytherapy (N=11/26) groups with regard to acute neonatal complications (p>0.05). The only acute neonatal complication associated to umbilical cord lithium serum concentration was hypotonia [0.712 (0.298) vs. 0.534 (0.214) (F=5.065; df=1,60; p=0.028)].ConclusionsWhen lithium is used around delivery, maternal and neonatal well-being can be maximized by maintaining maternal serum lithium concentrations at the minimal effective level and discontinuing briefly when presenting to hospital for delivery.Disclosure of InterestNone Declared

Graphene oxide-based nanofluidic system for power generation from salinity difference

In converting a salinity difference to the electrical power by using an ion-selective membrane, achieving a high-power density necessitates both a high ion permeability and ion selectivity of the membrane. However, meeting these two requirements often leads to the conflicting tradeoff in the membrane properties. In this study, we introduce a new mechanistic approach to meeting both requirements by combining an ultra-thin (<100 nm thickness) graphene oxide-based membrane for a high permeability with an asymmetric access area for a high ion selectivity, forming a new type of ionic-diode nanofluidic system. With a graphene oxide/silk fibroin composite membrane, a large power density of 2kW/m2 is achieved with 32% conversion efficiency under a 1000-fold salt concentration ratio. This approach can be utilized to overcome the low power density limitation with any ultra-thin membranes, and thereby it will provide a new route to utilize blue energy in a reliable and efficient way.

Research on self-made zinc ion microfluidic chip detection system based on all solid state ion selective electrodetrode

This paper first prepared and characterized an all solid zinc ion selective electrode using electrode deposition, and further established a microfluidic chip system integrating zinc ion ASS-ISE and a self-made potential detection device. The stability of the self-made potential detection device was verified by comparing it with traditional electrochemical workstations. The accuracy of the microfluidic chip detection system was verified through comparative testing with traditional atomic absorption spectrophotometry (AAS). The experimental results show that the accuracy and stability of the microfluidic chip system integrated with ASS-ISE and self-made potential detection device meet the requirements of on-site rapid detection.

Nonequilibrium Anion Detection in Solid-Contact Ion-Selective Electrodes.

Low-cost and portable nitrate and phosphate sensors are needed to improve farming efficiency and reduce environmental and economic impact arising from the release of these nutrients into waterways. Ion selective electrodes (ISEs) could provide a convenient platform for detecting nitrate and phosphate, but existing ionophore-based nitrate and phosphate selective membrane layers used in ISEs are high cost, and ISEs using these membrane layers suffer from long equilibration time, reference potential drift, and poor selectivity. In this work, we demonstrate that constant current operation overcomes these shortcomings for ionophore-based anion-selective ISEs through a qualitatively different response mechanism arising from differences in ion mobility rather than differences in ion binding thermodynamics. We develop a theoretical treatment of phase boundary potential and ion diffusion that allows for quantitative prediction of electrode response under applied current. We also demonstrate that under pulsed current operation, we can create functional solid-contact ISEs using lower-cost molecularly imprinted polymers (MIPs). MIP-based nitrate sensors provide comparable selectivity against chloride to costlier ionophore-based sensors and exhibit >100,000 times higher selectivity against perchlorate. Likewise, MIP-based solid contact ion-selective electrode phosphate sensors operated under pulsed current provide competitive selectivity against chloride, nitrate, perchlorate, and carbonate anions. The theoretical treatment and conceptual demonstration of pulsed-current ISE operation we report will inform the development of new materials for membrane layers in ISEs based on differences in ion mobility and will allow for improved ISE sensor designs.

Transfer of Sodium Ion across Interface between Na+-Selective Electrode Membrane and Aqueous Electrolyte Solution: Can We Use Nernst Equation If Current Flows through Electrode?

Electrochemical impedance and chronopotentiometric measurements with Na+-selective solvent polymeric (PVC) membranes containing a neutral ionophore and a cation exchanger revealed low-frequency resistance, which is ascribed to Na+ ion transfer across the interface between the membrane and aqueous solution. The attribution is based on the observed regular dependence of this resistance on the concentration of Na+ in solutions. The respective values of the exchange current densities were found to be significantly larger than the currents flowing through ion-selective electrodes (ISEs) during an analysis in non-zero-current mode. This fact suggests that the interfacial electrochemical equilibrium is not violated by the current flow and implies that the Nernst equation can be applied to interpret the data obtained in non-zero-current mode, e.g., constant potential coulometry.

Estimation of Soil Nutrients and Fertilizer Dosage Using Ion-Selective Electrodes for Efficient Soil Management

ABSTRACT The recent advancements in precision agriculture have led to a high demand for a portable and intelligent device capable of accurately measuring soil nutrients with reduced use of chemicals. Instead of relying on chemical-based laboratory tests, a smart portable device has been developed. The device measures soil nutrients, such as ammonium, calcium, potassium, nitrate, and chloride, and provides fertilizer dose recommendations. The device uses ion-selective electrodes, a microcontroller, multiplexer, operational amplifier, data logger, and input/output units. It reports soil health status to farmers or users via WhatsApp and e-mail. The measured soil nutrient values are uploaded to a database, which generates soil health cards and fertilizer dose recommendations. The device’s performance was compared to standard methods, with a correlation coefficient of 0.9906 for ammonium, 0.9949 for calcium, 0.9852 for potassium, 0.9716 for nitrate, and 0.9716 for calcium. The sensor-based soil nutrient analyzer demonstrated similar performance to other established standard methods when tested on 250 soil samples of agricultural fields. Consequently, this device holds great potential for utilization in soil testing laboratories as well as for on-site soil monitoring in agricultural fields, specifically for the purpose of precision farming.

Fluoride and Chloride Ions Concentration and their Health Implications in Groundwater within Bwari Area Council, Abuja, Nigeria

According to the World Health Organization, fluoride in drinking water, either below or above the established permissible range, can adversely affect oral health, including tooth decay and dental fluorosis. The objective of this study was to evaluate fluoride and chloride ion concentration and their health implications in groundwater within Bwari Area Council, Abuja, Nigeria using ion-selective electrode potentiometric titration for fluoride ion and Argentometric titration for chloride ion determinations. The results showed a high fluoride concentration in well water samples ranging from 0.126 mg/L to 0.216 mg/L, compared to borehole water samples ranging from 0.013 mg/mL to 0.052 mg/L. Among the chloride concentrations, the highest levels were observed in the well water sample A (96.09 mg/L), followed by borehole samples, A (63.08 mg/L) and B (49.35 mg/L). The lowest chloride concentration was recorded in the borehole sample H (11.82 mg/L). Notably, both well and borehole water sources in the studied communities had fluoride concentrations below the established minimum WHO standard (0.5 mg/L). The chloride concentrations in the groundwater samples from the study area fell within WHO standards (&lt; 250 mg/L). The results from this study suggest that the continuous consumption of water from these community sources, without additional sources of fluoride, may increase the risk of tooth decay. Therefore, addressing this issue and ensuring appropriate water treatment measures is vital for maintaining optimal oral health in the region.

Analysis of an underlimiting and overlimiting current regime in a single electrodialysis channel

Overlimiting ionic transfer is considered a mechanism to intensify transport processes in electrodialysis, potentially providing a smaller required footprint of electromembrane units. However, its applicability in desalination is still questionable. To address this aspect of electrodialysis, we characterized desalination in a single-channel electrodialysis unit operated under various current densities, yielding various diluate desalination degrees. Our analysis revealed that the conditions providing <100 % desalination were pertinent to an underlimiting regime with no indication of overlimiting processes. Specifically, no (electro-) convective structures intensifying ionic transfer occurred in the channel under these conditions. Applying electric current densities yielding theoretical desalination larger than 100 % significantly increased the necessary voltage, driving electroconvective vortices. The observation suggested that overlimiting phenomena occur upon setting conditions corresponding to complete desalination and, thus, do not positively contribute to desalination. Notably, the partial loss of membrane ion selectivity was associated with an operation in the overlimiting regime, worsening desalination efficiency. Our results imply that the overlimiting regime is, at least with the tested membranes, unsuitable for enhancing ionic transfer. Conversely, the small voltage required to remove ions in the underlimiting regime was attributed to the effect of natural convection, which readily occurs in the model system.

Development of Machine Learning Models for Ion-Selective Electrode Cation Sensor Design.

Polyvinyl chloride (PVC) membrane-based ion-selective electrode (ISE) sensors are common tools for water assessments, but their development relies on time-consuming and costly experimental investigations. To address this challenge, this study combines machine learning (ML), Morgan fingerprint, and Bayesian optimization technologies with experimental results to develop high-performance PVC-based ISE cation sensors. By using 1745 data sets collected from 20 years of literature, appropriate ML models are trained to enable accurate prediction and a deep understanding of the relationship between ISE components and sensor performance (R 2 = 0.75). Rapid ionophore screening is achieved using the Morgan fingerprint based on atomic groups derived from ML model interpretation. Bayesian optimization is then applied to identify optimal combinations of ISE materials with the potential to deliver desirable ISE sensor performance. Na+, Mg2+, and Al3+ sensors fabricated from Bayesian optimization results exhibit excellent Nernst slopes with less than 8.2% deviation from the ideal value and superb detection limits at 10-7 M level based on experimental validation results. This approach can potentially transform sensor development into a more time-efficient, cost-effective, and rational design process, guided by ML-based techniques.

Cu1.4Mn1.6O4 as a bifunctional transducer for potentiometric Cu2+ solid-contact ion-selective electrode

Current potentiometric Cu2+ sensors mostly rely on polymer-membrane-based solid-contact ion-selective electrodes (SC-ISEs) that constitute ion-selective membranes (ISM) and solid contact (SC) for respective ion recognition and ion-to-electron transduction. Herein, we report an ISM-free Cu2+-SC-ISE based on Cu–Mn oxide (Cu1.4Mn1.6O4) as a bifunctional SC layer. The starting point is simplifying complex multi-interfaces for Cu2+-SC-ISEs. Specifically, ion recognition and signal transduction have been achieved synchronously by an ion-coupled-electron transfer of crystal ion transport and electron transfer of Mn4+/3+ in Cu1.4Mn1.6O4. The proposed Cu1.4Mn1.6O4 electrode discloses comparable sensitivity, response time, high selectivity and stability compared with present ISM-based potentiometric Cu2+ sensors. In addition, the Cu1.4Mn1.6O4 electrode also exhibits near Nernstian responses toward Cu2+ in natural water background. This work emphasizes an ISM-free concept and presents a scheme for the development of potentiometric Cu2+ sensors.

Perspective on the coulometric transduction principle for ion-selective electrodes

A new type of coulometric transduction method for solid-contact ion-selective electrodes was introduced in 2015. The coulometric method utilized the capacitance of the solid contact to convert a potential change into a current transient that was integrated to obtain the corresponding charge. For a given potential change, the charge was increased by increasing the capacitance of the solid contact, which improved the sensitivity of solid-contact ion-selective electrodes. By introducing an electronic capacitor in series with the ion-selective electrode (ISE), the coulometric method became faster and feasible also for conventional ISEs with an internal filling solution. Alternative electrode configurations, where the ISE was connected as the reference electrode in the electrochemical cell, was used to avoid polarization of the ISE during the coulometric readout. Results published so far indicate that the coulometric readout method can significantly improve the analytical performance of ISEs, especially for detection of very small changes in ion activity. In this perspective article, the coulometric transduction method is revisited and critically evaluated.

Development of a dual sensitive N,N,N’,N’,N”,N”-hexa-n-octylnitrilotriacetamide (HONTA) based potentiometric sensor for direct thorium(IV) estimation

A dual sensitive, simple, and rapid membrane-based potentiometric sensor was developed to determine thorium (Th) ion in nuclear fuel samples which does not require any prior chemical separation of other matrix elements. Sensor was prepared by incorporating N,N,N’,N’,N”,N”-hexa-n-octylnitrilotriacetamide (HONTA) in a polyvinyl chloride (PVC) matrix in presence of 2-nitrophenyl octyl ether (NPOE) and sodium tetraphenyl borate (NaTPB). The optimum membrane composition was found to be 14.1% HONTA, 3.2% NaTPB, 54.9% NPOE, 27.8% PVC, which showed a dual sensitive linear region in the calibration plot with sub-Nernstian and super-Nernstian slopes of 12.1 ± 0.4 mV/decade and 71.7 ± 3.5 mV/decade, respectively, with the corresponding linear dynamic ranges of 2.0 × 10−5 to 5.3 × 10−4 M and 3.8 ×10−3 to 1.4 × 10−2 M, respectively. The super-Nernstian sensitivity exhibited by the sensor increases with Th(IV) as well as HONTA concentrations in the membrane and can be thought to be due to micelle-mediated selective adsorption (MMSA) sensing of the metal ion. Solution speciation of Th(IV) in acetate buffer was determined by laser desorption/ionization mass spectrometry (LDI-MS) and Medusa software. Pristine and used membranes were characterized by Fourier transform infrared (FTIR), scanning electron microscopy–energy dispersive x–rays (SEM-EDS) and small angle neutron scattering (SAXS). Thorium was measured in an actual (Th–U) mixed solution and in a synthetic advance heavy water reactor (AHWR) fuel sample. The present study describes a new approach for the detection of Th(IV) ion through MMSA in an ion selective electrode (ISE).

Highly ion-selective graphene-oxide-based membranes for nanofluidic osmotic energy conversion

Graphene oxide (GO) membranes have shown great potential for water treatment and osmotic energy conversion. However, the inherent challenge with GO membranes lies in their instability in water. While reduction techniques can improve stability, they simultaneously compromise selective ion transport properties due to the loss of functional groups. Here, we report preassembly modified GO (GOTA) membranes by using tannic acid (TA) as modification reagent. It is found that the TA molecules not only act as reducing agent, enhancing the aqueous stability of the membrane by generating stacked graphitic sp2 domains but also serve as intercalating agent, improving the selective ion transport properties by creating localized areas with high charge density and enlarged interlayer spacing. The cation selective number of GOTA membranes is ∼0.94–0.89 for different salinity gradients, much better than the thermally reduced GO membranes. In energy conversion system, the output power density approaches ∼0.32 W m−2 for the artificial seawater and river water with energy conversion efficiency of 41.7%. Meanwhile, the GOTA membranes exhibit excellent structural stability in various solution environments. This work demonstrates the importance of nanofluidic structure in improving the performance of ion-selective membranes and provides insights into the construction of advanced osmotic energy conversion system.

Large-Scale, Vertically Aligned 2D Subnanochannel Arrays by a Smectic Liquid Crystal Network for High-Performance Osmotic Energy Conversion.

The osmotic energy, an abundant renewable energy source, can be directly converted to electricity by nanofluidic devices with ion-selective membranes. 2D nanochannels constructed by nanosheets possess abundant lateral interfacial ion-exchange sites and exhibit great superiority in nanofluidic devices. However, the most accessible orientation of the 2D nanochannels is parallel to the membrane surface, undoubtedly resulting in the conductivity loss. Herein, first vertically aligned 2D subnanochannel arrays self-assembled by a smectic liquid crystal (LC) network that exhibit high-performance osmotic energy conversion are demonstrated. The 2D subnanochannel arrays are fabricated by in situ photopolymerization of monomers in the LC phase. The as-prepared membrane exhibits excellent water-resistance and mechanical strength. The 2D subnanochannels with excellent cation selectivity and conductivity show high-performance osmotic energy conversion. The power density reaches up to about 22.5W m-2 with NaCl solution under a 50-fold concentration gradient, which is among with ultrahigh power density. This membrane design concept provides promising applications in osmotic energy conversion.