Use Of Ion-selective Electrodes Research Articles

Hydrophilic redox buffers for textile-based potentiometric sensors

One of the barriers to the more widespread use of ion-selective electrodes (ISEs) in resource-limited areas is the need for frequent recalibration of such devices. The incorporation of a redox buffer to minimize the effect of redox-active impurities in the system has previously been shown to significantly improve reproducibility. To date, however, there have been no examples of redox buffers compatible with anion-sensing polymeric sensing membranes that can be incorporated into the inner filling solution of an ISE. Here, we introduce a novel hydrophilic redox buffer, cobalt(II/III) bis(terpyridine), and show the improvement of the standard deviation of E0 of chloride sensors from 2.7 to 0.3 mV upon introduction of the redox buffer into the inner filing solution of conventional, rod-shaped electrodes. The redox buffer is also compatible with a textile-based sensing platform, which was shown by incorporation into a textile-based platform with embedded ion-sensing and reference membranes. As only a surprisingly small number of hydrophilic redox buffers have been reported in the literature, the cobalt(II/III) bis(terpyridine) redox buffer may also find applications outside of the field of ISEs.

An ion-selective chemiresistive platform as demonstrated for the detection of nitrogen species in water.

The use of ion-selective electrodes (ISE) is a well-established technique for the detection of ions in aqueous solutions but requires the use of a reference electrode. Here, we introduce a platform of ion-selective chemiresistors for the detection of nitrogen species in water as an alternative method without the need for reference electrodes. Chemiresistors have a sensitive surface that is prone to damage during operation in aqueous solutions. By applying a layer of ion-selective membrane to the surface of the chemiresistive device, the surface becomes protected and highly selective. We demonstrate both anion-selective (NO3-, NO2-) and cation-selective (NH4+) membranes. The nitrate sensors are able to measure nitrate ions in a range of 2.2-220 ppm with a detection limit of 0.3 ppm. The nitrite sensors respond between 67 ppb and 67 ppm of nitrite ions (64 ppb detection limit). The ammonium sensors can measure ammonium concentrations in a wide range from 10 ppb to 100 ppm (0.5 ppb detection limit). The fast responses to nitrate and nitrite are due to a mechanism involving electrostatic gating repulsion between negative charge carriers of the film and anions while ammonium detection arises from two mechanisms based on electrostatic gating repulsion and adsorption of ammonium ions at the surface of the p-doped chemiresistive film. The adsorption phenomenon slows down the recovery time of the ammonium sensor. This sensor design is a new platform to continuously monitor ions in industrial, domestic, and environmental water resources by robust chemiresistive devices.

Identifying Hypocalcemia in Dairy Cattle By Combining 3D Printing and Paper Diagnostics

Electrochemistry is a powerful technique for advancing point-of-care (POC) diagnostics due largely to its ease of use and compatibility with electronic readers that can be controlled by ubiquitous technology such as smartphones or tablets. Specifically, potentiometry, (i.e., the use of ion-selective electrodes) is well-suited for incorporation into POC devices for the following reasons: (i) it possesses high selectivity (through the incorporation of ionophores), (ii) it is multiplexable, and (iii) provides a fast response time. This talk will focus on the development of a paper-based diagnostic device for the identification of hypocalcemia in dairy cattle at the point-of-care. Hypocalcemia is a metabolic disorder resulting from a lower-than-normal concentration of calcium in the bloodstream and can lead to deleterious outcomes such as early herd removal or death. Diagnosis and treatment of hypocalcemia lead to increased expenses on dairy operations, where low-cost and rapid testing solutions are currently not commercially available. Our approach utilizes the highly reproducible and mass-production capabilities of 3D printing to fabricate sensors that can be incorporated into paper substrates, resulting in low-cost and reliable diagnostics devices.

Fabricating Potentiometric Biosensors Using 3D Printing

Potentiometry, the use of ion-selective electrodes (ISEs), has been incorporated in many point-of-care (POC) applications due to its selectivity and sensitivity. Importantly, ISEs can be translated to low-cost POC devices (e.g., paper-based, thread-based, etc.), making them ideal candidates for commercial applications as they cover many of the guidelines established by the World Health Organization for successful diagnostics in low to middle income countries. Biosensors are an important class of diagnostic tools used to increase specificity and sensitivity for a particular analyte through the incorporation of molecular recognition elements, aptamers, enzymes, etc. Potentiometric enzymatic biosensors have previously been fabricated where an enzyme is immobilized into an ion-selective membrane (ISM) and used to convert important biomarkers into detectable ions for potentiometric sensing. Although this approach has been previously demonstrated using conventional PVC-based ISMs, the lack of mass production capabilities and the routinely high cost of individual membranes has hindered the advancement of deliverable POC devices for potentiometric biosensing. We recently reported a 3D printing protocol for the fabrication of ISMs, which was shown to reduce both the cost associated with sensor fabrication as well as the time. Herein we report on the advancement of 3D printing techniques to fabricate biosensing membranes for their use in POC applications.

Ion-selective potentiometric sensors with silicone sensing membranes: A review

Ion-selective electrodes (ISEs) are used widely in mainframe analyzers for clinical chemistry, but there is also an increasing interest in the development of paper-based devices, wearable and implantable sensors, and other miniaturized ISEs. This trend is spurring much research in developing solid contact materials that enable miniaturization. The development of suitable polymeric matrixes for such sensors has only received less attention. In particular, in spite of lifetime limitations and toxicity concerns, polymeric matrixes comprising plasticizers are still commonly used. To that end, we note the benefits of silicone materials as alternative polymeric matrixes and, in particular, their promise for enhanced biocompatibility. While there has been steady progress in the development of ISEs with silicone membranes, this topic has not been reviewed for many years. This review critically discusses key fundamental characteristics of ISEs with silicone sensing and reference membranes, including their biocompatibility, adhesion to device substrates, water uptake, polarity, common impurities, and commercial availabilities. This is followed by a discussion of specific types of silicones and their use in ISEs, with the goal to inform and stimulate future research efforts into such devices.

PH-metric method determining the solubility and solubility products of slightly soluble salts of arbitrary composition

The developed method of determining KS from pH metric data has a number of advantages compared to those used traditionally. First, in place of the residual concentrations of the salt components, only the pH value of the saturated solution is used in the derived expressions. Thus, the number of independent variables, which need to be measured experimentally, is reduced. Furthermore, the potentiometric method, used to determine the pH, is sufficiently accurate, simple and universal and does not necessitate the use of ion-selective electrodes. At the same time, the residual concentrations are usually measured by chemical methods, which are inferior in most cases, for several reasons, compared to the potentiometric method. Second, the KS value calculated by the developed method has a thermodynamic character. The organization of the experiment must be appropriate to the applied equations. Therefore, it is necessary to draw attention to the need for high accuracy in the process of preparing the initial solutions, because the initial concentrations of the precipitate components are included in the calculation formulas. The developed method for determining Ks can be applied for systems of any degree of complexity, which contain additional complexing agents.

Applications of 3D Printing Technology Towards Potentiometric Sensing and Point-of-Care Diagnostics

The development of robust, low-cost and reproducible sensors for point-of-care (POC) applications is of the utmost importance and electrochemical techniques have been thoroughly implemented into POC devices. Electrochemistry is a powerful candidate for advancements in POC diagnostics due largely to its ease of use and its compatibility with electronic readers that can be controlled by smartphones. Of the various electrochemical techniques used in fabricating POC devices, potentiometry (i.e., the use of ion-selective electrodes (ISEs)) is extremely useful for the following reasons: (i) it is highly selective (through the incorporation of molecular recognition elements), (ii) requires simple equipment for the signal readout, (iii) it is multiplexable, and (iv) provides a fast response time. This talk will focus on the development of a new approach, utilizing 3-D printing, to fabricate the sensing element of ISEs, the ion-selective membrane (ISM). 3-D printing has already made a significant impact on the field of chemistry and is rapidly being utilized in various electrochemical endeavors, ranging from printing HPLC columns to conductive electrodes. Here, we highlight the advantages of utilizing 3-D printing for ion-selective membrane (ISM) fabrication and discuss examples of using 3-D printed ISMs towards the detection of various analytes related to human health (i.e., electrolytes and biomarkers). The precise control over the dimensions and shapes of ISMs, afforded by the precision of modern 3-D printers, allows for the fabrication of ISMs of various sizes and topographies for seamless integration into POC diagnostics. Beyond the ISE, 3D-printing is also a convenient tool for developing stable and reliable reference electrodes. These advancements, coupled with new 3-D printing capabilities will lead to unique opportunities in the fabrication of complete, low-cost diagnostic “packages” with extreme utility for broad applications at the POC.

All-Solid-State Potentiometric Ion-Sensors Based on Tailored Imprinted Polymers for Pholcodine Determination.

In recent times, the application of the use of ion-selective electrodes has expanded in the field of pharmaceutical analyses due to their distinction from other sensors in their high selectivity and low cost of measurement, in addition to their high measurement sensitivity. Cost-effective, reliable, and robust all-solid-state potentiometric selective electrodes were designed, characterized, and successfully used for pholcodine determination. The design of the sensor device was based on the use of a screen-printed electrode modified with multiwalled carbon nanotubes (MWCNTs) as a solid-contact transducer. Tailored pholcodine (PHO) molecularly imprinted polymers (MIPs) were prepared, characterized, and used as sensory receptors in the presented potentiometric sensing devices. The sensors exhibited a sensitivity of 31.6 ± 0.5 mV/decade (n = 5, R2 = 0.9980) over the linear range of 5.5 × 10−6 M with a detection limit of 2.5 × 10−7 M. Real serum samples in addition to pharmaceutical formulations containing PHO were analyzed, and the results were compared with those obtained by the conventional standard liquid chromatographic approach. The presented analytical device showed an outstanding efficiency for fast, direct, and low-cost assessment of pholcodine levels in different matrices.

Potentiometric Study of Carbon Nanotube/Surfactant Interactions by Ion-Selective Electrodes. Driving Forces in the Adsorption and Dispersion Processes.

The interaction (adsorption process) of commercial ionic surfactants with non-functionalized and functionalized carbon nanotubes (CNTs) has been studied by potentiometric measurements based on the use of ion-selective electrodes. The goal of this work was to investigate the role of the CNTs’ charge and structure in the CNT/surfactant interactions. Non-functionalized single- (SWCNT) and multi-walled carbon nanotubes (MWCNT), and amine functionalized SWCNT were used. The influence of the surfactant architecture on the CNT/surfactant interactions was also studied. Surfactants with different charge and hydrophobic tail length (sodium dodecyl sulfate (SDS), octyltrimethyl ammonium bromide (OTAB), dodecyltrimethyl ammonium bromide (DoTAB) and hexadecyltrimethyl ammonium bromide (CTAB)) were studied. According to the results, the adsorption process shows a cooperative character, with the hydrophobic interaction contribution playing a key role. This is made evident by the correlation between the free surfactant concentration (at a fixed [CNT]) and the critical micellar concentration, cmc, found for all the CNTs and surfactants investigated. The electrostatic interactions mainly determine the CNT dispersion, although hydrophobic interactions also contribute to this process.

Novel Potentiometric 2,6-Dichlorophenolindo-phenolate (DCPIP) Membrane-Based Sensors: Assessment of Their Input in the Determination of Total Phenolics and Ascorbic Acid in Beverages

In this work, we demonstrated proof-of-concept for the use of ion-selective electrodes (ISEs) as a promising tool for the assessment of total antioxidant capacity (TAC). Novel membrane sensors for 2,6-dichlorophenolindophenolate (DCPIP) ions were prepared and characterized. The sensors membranes were based on the use of either CuII-neocuproin/2,6-dichlorophenolindo-phenolate ([Cu(Neocup)2][DCPIP]2) (sensor I), or methylene blue/2,6-dichlorophenolindophenolate (MB/DCPIP) (sensor II) ion association complexes in a plasticized PVC matrix. The sensors revealed significantly enhanced response towards DCPIP ions over the concentration range 5.13 × 10−5–1.0 × 10−2 and 5.15 × 10−5–1.0 × 10−2 M at pH 7 with detection limits of 6.3 and 9.2 µg/mL with near-Nernstian slope of −56.2 ± 1.7 and −51.6 ± 2 mV/decade for sensors I and II, respectively. The effects of plasticizers and various foreign common ions were also tested. The sensors showed enhanced selectivity towards DCPIP over many other phenolic and inorganic ions. Long life span, high potential stability, high reproducibility, and fast response were also observed. Method validation was also verified by measuring the detection limit, linearity range, accuracy, precision, repeatability and between-day-variability. The sensors were introduced for direct determination of TAC in fresh and canned juice samples collected from local markets. The obtained results agreed fairly well with the data obtained by the standard method.

Development of Potentiometric Method for In Situ Testing of Terbinafine HCl Dissolution Behavior Using Liquid Inner Contact Ion-Selective Electrode Membrane

A novel potentiometric method for in-situ testing of terbinafine HCl dissolution behavior using novel liquid inner contact ion-selective electrode membrane was developed. Terbinafine HCl is slightly soluble in water so, the use of ion-selective electrode for its determination is challenge. The sensor was polyvinyl chloride matrix membrane electrode in which sodium tetraphenylborate was used as cation exchanger and bis (2-ethyl hexyl) sebacate as plasticizer. The ion pair was formed by soaking membrane in drug solution. Linear response of terbinafine HCl was found in the dynamic range of 10−6 to 10−2 mol L−1. Dissolution test was performed according to FDA regulations using paddle- (USP type 2). So, the proposed ion selective electrode membrane was successfully used as a benchtop in-situ monitor to study the dissolution behavior of terbinafine HCl tablets without need of sample pretreatment or complicated withdrawal steps. Also, the proposed sensor was successfully used for terbinafine HCl determination in dosage forms including spray formulation which contains alcohol percentage as solvent and urine with good recovery.

Comparative enzymatic studies using ion-selective electrodes. The case of cholinesterases

The application of traditional ion-selective electrodes for comparative enzymatic analysis was demonstrated for the first time in this study. A kinetic-potentiometric method based on the monitoring of the concentration of the ionic substrate involved in the enzymatic reaction catalyzed by different cholinesterases is used for this purpose. A comparative study was performed comprising both enzymatic assays using different ionic substrates and the corresponding inhibited reactions in presence of neostigmine (a synthetic anticholinesterase). The developed approach is used to obtain valuable comparative results through calculation of kinetic parameters, such as Michaelis and inhibition constants. Interesting results were obtained for acetylcholinesterase and butyrylcholinesterase enzymes, which were selected as proof-of-concept: (i) the binding affinity that these enzymes have for their natural substrates showed to be higher (acetylcholine and butyrylcholine respectively) than for their corresponding thiol derivatives (acetylthiocholine and butyrylthiocholine), which are traditionally used in spectrophotometric enzymatic assays; (ii) as expected, the maximum hydrolysis rate found in the assays of each enzyme was independent of the substrate used; (iii) acetylcholinesterase enzyme inhibition due to neostigmine was found to be higher (higher inhibition constant). Advantageously, the use of ion-selective electrodes permits to perform cholinesterases’ enzymatic assays using their natural substrates and under physiological conditions, unlike the traditional spectrophotometric methods used in routine enzymatic assays. Importantly, while well-known enzymes are use throughout this work, this approach can be extended to other types of enzymatic assays as a tangible alternative to traditional spectrophotometric methods.

Integrated multi-ISE arrays with improved sensitivity, accuracy and precision

Increasing use of ion-selective electrodes (ISEs) in the biological and environmental fields has generated demand for high-sensitivity ISEs. However, improving the sensitivities of ISEs remains a challenge because of the limit of the Nernstian slope (59.2/n mV). Here, we present a universal ion detection method using an electronic integrated multi-electrode system (EIMES) that bypasses the Nernstian slope limit of 59.2/n mV, thereby enabling substantial enhancement of the sensitivity of ISEs. The results reveal that the response slope is greatly increased from 57.2 to 1711.3 mV, 57.3 to 564.7 mV and 57.7 to 576.2 mV by electronic integrated 30 Cl− electrodes, 10 F− electrodes and 10 glass pH electrodes, respectively. Thus, a tiny change in the ion concentration can be monitored, and correspondingly, the accuracy and precision are substantially improved. The EIMES is suited for all types of potentiometric sensors and may pave the way for monitoring of various ions with high accuracy and precision because of its high sensitivity.

Study of ionic surfactants interactions with carboxylated single-walled carbon nanotubes by using ion-selective electrodes

Potentiometric measurements based on the use of ion-selective electrodes have been used to study the interaction (adsorption) of anionic and cationic surfactants with functionalized single-walled carbon nanotubes (SWCNT–COOH). According to results, the interaction is driven by hydrophobic forces between the hydrocarbon tails of the surfactants and the nanotube walls. Electrostatic interactions practically exert no influence on the interaction. Driving forces in the dispersion processes are different.

Methods of quantitative determination of Sparteine hydroiodine

Currently, there are many different methods of quantitative determination of alkaloid Sparteine amounts such as gravimetry, acidimetry, argentometry (including the use of ion-selective electrode), iodometry, extraction photometry, colorimetry, amperometry, potentiometry, direct ionometry with ion-selective electrode, thin layer chromatography, high-performance liquid chromatography and high pressure gas chromatography, also infrared and Nuclear magnetic resonance spectroscopy, chromatography-mass-spectrometry. It has been analyzed that most of the well-known methods are too insensitive, indiscriminate or too expensive, time-consuming and inaccessible. An application for analysis of amperometric titration techniques using both analytical reagent heteropolianions (GPA) Kehhina structure - standard solution 12-molibdophosphoric heteropolyacid and method of direct potentiometric determination using ISE for determining the choice amounts or amounts of alkaloids qinolizidine series in extracts are very promising, relatively simple in execution, express and sufficiently sensitive.

Methods for the determination of anionic surfactants

Methods for the determination of synthetic anionic surfactants published in the past two decades are considered, and their advantages and disadvantages are demonstrated. Spectrophotometric and potentiometric (with the use of ion-selective electrodes) techniques, including flow injection analysis versions, are used for the determination of anionic surfactants. Chromatographic techniques (primarily, high-performance liquid chromatography) are most frequently used for the separation, preconcentration, and determination of anionic surfactants in complex mixtures. Spectrofluorimetry, voltammetry, and immunoassay did not find wide application.

Extended artificial neural networks: Incorporation of a priori chemical knowledge enables use of ion selective electrodes for in-situ measurement of ions at environmentally relevant levels

A novel artificial neural network (ANN) architecture is proposed which explicitly incorporates a priori system knowledge, i.e., relationships between output signals, while preserving the unconstrained non-linear function estimator characteristics of the traditional ANN. A method is provided for architecture layout, disabling training on a subset of neurons, and encoding system knowledge into the neuron structure. The novel architecture is applied to raw readings from a chemical sensor multi-probe (electric tongue), comprised of off-the-shelf ion selective electrodes (ISEs), to estimate individual ion concentrations in solutions at environmentally relevant concentrations and containing environmentally representative ion mixtures. Conductivity measurements and the concept of charge balance are incorporated into the ANN structure, resulting in (1) removal of estimation bias typically seen with use of ISEs in mixtures of unknown composition and (2) improvement of signal estimation by an order of magnitude or more for both major and minor constituents relative to use of ISEs as stand-alone sensors and error reduction by 30-50% relative to use of standard ANN models. This method is suggested as an alternative to parameterization of traditional models (e.g., Nikolsky-Eisenman), for which parameters are strongly dependent on both analyte concentration and temperature, and to standard ANN models which have no mechanism for incorporation of system knowledge. Network architecture and weighting are presented for the base case where the dot product can be used to relate ion concentrations to both conductivity and charge balance as well as for an extension to log-normalized data where the model can no longer be represented in this manner. While parameterization in this case study is analyte-dependent, the architecture is generalizable, allowing application of this method to other environmental problems for which mathematical constraints can be explicitly stated.

Application of nanoparticles in the potentiometric ion selective electrodes

Among the various analytical techniques available, the use of ion-selective electrodes is a wellestablished routine analytical technique. Good ion-selective electrodes (ISEs) possess many advantages over traditional methods for analysis and provide accurate, reproducible, fast, and regular selective determination of various ionic species. Modification of ISEs with nanoparticles has shown interesting ability toward various ions and biological molecules. In this article we review some of developments about applications of nanoparticles in the construction of ISEs in recent years.

Renal excretion of water and electrolytes and plasma monovalent cations in hypertensive patients under psychoemotional stress

Изменение водо- и ионовыделительной функции почки и физико-химического состояния одновалентных катионов плазмы крови у больных гипертонической болезнью при психоэмоциональной нагрузке Dynamics of water and ion renal excretion and physicochemical monovalent cations in hypertensive patients under psychoemotional stress I.E. Ganelina, N.A. Kruchinina, M.N. Maslova, A.A. Panov, E.E. Poroshin Object. To study the influence of psychoemotional stress (PES) on renal mechanisms blood pressure regulation and on the activity of plasma Na + and K + in hypertensive patients. Design and methods. Eighteen males with normal blood pressure and 20 males with hypertension (mean age in both groups - 57 ± 3 years) underwent PES [1], and all of them developed the rise in blood pressure, increased diuresis, natriuresis, renal excretion of K + , osm, clearance of Na-C Na and osm–Cosm. We assessed the levels of Na + and K + in the flame photometer Flafo-40 (Germany), we performed osm-cryoscopy on the thermoelectric milliosmometre (MT-1) to assess the activity of Na + and K + in plasma with the use of ion-selective electrodes ISE-M-K and ISE- M-Na. Results. After PES, SAP and DAP reduced in normotensive and hypertensive patients, however, it was about 12 % remaining above the initial level in both groups. After PES, normotensive subjects increased kidney excretion compared to the initial level: diuresis for 15 %, , U Na V for 15 %, U К V for 18 %, U osm V for 14 %, C Nа for 17 %, C osm for 15 %, i.e. their reabsorption remained low. After PES diuresis, renal excretion of ions, CNa, Cosm are decreased in comparison to baseline level: diuresis, U Na V; U osm V, CNа, C osm were higher for 1-1,3 %. The baseline levels of Na + and K + activity and their activity coefficients were higher in patients in comparison with healthy subjects for 12 %, and the activity coefficient of K + was decreased at PES for 9 %. Conclusion. After PES reabsorption of water, Na + , C Na , Cosm is decreased in normotensive subjects, while in hypertensive patients it significantly increases, despite high blood pressure. The high activity of Na + , and its activity coefficient in patients with hypertension may be associated with a decrease in the proportion of free water in blood plasma.

코발트전극과 자동시험장치를 이용한 파프리카 양액 내 무기인산 측정

The need for rapid on-site monitoring of hydroponic macronutrients has led to the use of ion-selective electrodes, because of their advantages over spectrophotometric methods, including simple methodology, direct measurement of analyte, sensitivity over a wide concentration range, and low cost. Stability and repeatability of response can be a concern when using multiple ion-selective electrodes to measure concentrations in a series of samples because accuracy might be limited by drifts in electrode potential. A computer-based measurement system could improve accuracy and precision because of both consistent control of sample preparation and easy calibration of sensors. Our goal was to investigate the applicability of a cobalt-based electrode used in conjunction with a laboratory-made automated test stand for quantitative determination of in hydroponic solution. Six hydroponic solutions were prepared by diluting highly concentrated paprika hydroponicsolution to provide a concentration range of 1 to 300 ppm -P. A calibration curve relating electrode response to phosphate in paprika hydroponic solution titrated to pH 4 with 0.025M KHP was developed based on the Nikolskii-Eisenman equation with a coefficient of determination () of 0.94. The laboratory-made test stand consisting of three cobalt-based electrodes measured phosphate concentrations similar to those obtained with standard laboratory methods (a regression slope of 0.98 with = 0.80). However, the y intercept was relatively high, 30 ppm, probably due to the relatively large amount of variation present among multiple measurements of the same sample. Further studies on the high variation in EMFs obtained with cobalt electrodes during replicate measurements were required for P estimations comparable to those obtained with standard laboratory instruments.