Potassium Ion-selective Electrodes Research Articles

All‐Solid‐State Reference Electrodes with Poly(n‐butyl acrylate) Based Membranes

AbstractA new kind of all‐solid‐state reference electrode, suitable for potentiometry with ion‐selective electrodes is proposed, where a poly(n‐butyl acrylate) based membrane is coated on a glassy carbon support with conducting polymer–polypyrrole ion‐to‐electron transducing layer. These electrodes are compatible with poly(acrylate) based ion‐selective electrodes in simple disposable cells, where both indicator and reference electrode can be produced in a single fabrication process, using the same or similar methods. The composition of the membrane with lipophilic salt and Ag/AgCl system was tuned to expose nonselectivity and to obtain a stable potential, independent of solution composition. Near‐zero slopes of potentiometric characteristics were recorded in typical electrolyte solutions in the concentration range: 1 to 10−5 M, stable potentials and only slight influence of interferents: oxygen, redox reactants, H+/OH− ions and surfactants make this arrangement promising for practical applications, particularly when matched against a similar ion‐selective electrode. Tests of cells with poly(n‐butyl acrylate) based membrane potassium selective sensors and reference electrodes confirmed their analytical applicability.

Fullerene-based electrochemical buffer layer for ion-selective electrodes

In this work, C(60) fullerene is used as an electrochemical mediator for the development of an all-solid-state ISE. The unique electrochemical characteristics of the fullerenes allow for the facile ion-to-electron transduction across the ionically active polymeric ion-selective membrane and the electrochemically active glassy carbon transducer. The interfacial ion-to-electron charge transfer was investigated by Electrochemical Impedance Spectroscopy. The study of the analytical characteristics of a model potassium-selective electrode, together with the EIS studies, reveals that, indeed, the interfacial C(60) electrochemically active layer facilitates the ion-to-electron transduction, providing a stable and reversible solid-state ISE system. This finding is a significant contribution to the efforts aiming at overcoming one of the most significant drawbacks of the solid-state ISEs, that is the potential drift observed during continuous measurements, and could lead to the development of both cation- and anion-sensitive systems.

Simultaneous determination of potassium and total fluoride in toothpastes using a SIA system with two potentiometric detectors

A sequential injection analysis (SIA) system has been developed for the first time to quantify potassium and total fluoride in toothpastes and gels used to prevent both dentinal hypersensitivity and dental caries. To enable this simultaneous determination, potentiometric detection, using a conventional fluoride electrode and a tubular potassium selective electrode, formed by a PVC membrane containing valinomycin as ionophore, was carried out. A manifold that uses a three-way solenoid valve was designed. The former under binary sampling conditions, provides reproducible mixing ratios of two solutions. This fact facilitates that the system automatically generates, on-line, the calibration curves required by the analytical procedure. The calibration ranged from 1.0 × 10 −4 to 1.0 × 10 −3 mol L −1 for both potassium and total fluoride determinations. The R.S.D. (11 readings) resulted to be less than 1.5% for both determinations. Off-line studies related to the dissolution of the solid samples, the transformation of monofluorophosphate in fluoride, the elimination of organic matrix interference onto the plastic membrane of the potassium electrode, and the selection of the most adequate TISAB solution for fluoride determination, were also considered. A sampling rate of 18 samples h −1 for both determinations was attained, their precisions and accuracies being statistically indistinguishable from those achieved by atomic emission spectroscopy (for potassium determination) and by a conventional batch potentiometry (for total fluoride determination) adopted as reference techniques.

Measuring permeability with a whole cell-based biosensor as an alternate assay for angiogenesis: Comparison with common in vitro assays

Angiogenesis plays cardinal role in normal developmental processes as well as in numerous pathologies. Multiple cytokines are released and act simultaneously to activate endothelial cells in vivo. The present study investigated the relative ability of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), tumor necrosis factor-alpha (TNF-α) in modulating cell monolayer permeability, migration, proliferation and tube formation individually and in combination. While the common methods for assaying angiogenesis were conducted for studying cell migration, proliferation and differentiation, endothelial cell monolayer permeability studies were carried out using a whole cell-based biosensor. The biosensor, consisting of a confluent monolayer of human umbilical vein endothelial cells (HUVECs) on a potassium ion-selective electrode, takes advantage of cell monolayer permeability dysfunction to detect the presence of small quantities of cytokines. When a confluent monolayer of cells was formed on the membrane surface, the response of the electrode toward the marker ion, potassium, was inhibited. The response obtained after exposing this sensor to different cytokines for 1 and 3 h, can be attributed to the modulation of monolayer permeability by these cytokines. The present study demonstrated that at the concentrations experimented with, the relative change in permeability assay in the presence of cytokines compared to the control was much higher than that observed in other assays, thereby bolstering the potential of the biosensor to act as a quick screening tool for angiogenesis.

Potassium-Selective Electrodes with Stable and Geometrically Well-Defined Internal Solid Contact Based on Nanoparticles of Polyaniline and Plasticized Poly(vinyl chloride)

Solid contact potassium-selective electrodes with the internal ion-to-electron transduction layer composed of plasticized poly(vinyl chloride) (PVC) and 2-20% (m/m) of polyaniline (PANI) nanoparticles, with the mean particle size of 8 nm, have been studied in this paper. UV-vis measurements in pH buffer solutions between pH 0 and 12 show that the electrically conducting emeraldine salt (ES) form of PANI has exceptionally good pH stability. Membranes of PANI nanoparticles were mainly in the ES form even at pH 12, in contrast to electrochemically prepared PANI(Cl) films, which are converted completely to the nonconducting form already at pH 6. Long-term UV-vis measurements with the PANI membranes in contact with aqueous buffer solution at pH 7.5 showed no degradation of the ES form. The PANI nanoparticles are homogenously mixed in the PVC-based solid contact (SC) layer. Only the uppermost part of the SC layer is to a minor extent dissolved in the outer potassium-selective PVC membrane. This enabled the preparation of geometrically well-defined inner SC layers, thus improving the reproducibility of the solid contact electrodes and resulting in good mechanical strength between the inner and outer membranes.

Fabrication and Characterization of Potassium Ion-Selective Electrode Based on Porous Silicon

Porous-silicon (PS)-based potassium ion-selective microelectrode (K+ISME) was fabricated by using a microelectronic planar process and an electrochemical anodization etching technique. The apparent sensing area of the K+ISME is 100times100 mum 2. The response time t95% is 20 and 31 s when the concentration change is from low to high and vice versa, respectively. The potentials are constant at pH 2-8. The calibration curve for the K +ISME is linear within a wide range of pK=2.0~6.0. Its average slope during six months is 56.5 mV per decade, which is close to the Nernst response. The detection limit was found to be on the order of 5times10-7 M. The potentiometric selectivity coefficients (Ki,j pot) of the K+ ISE were 1.8 for NH 4 +, 3.6 for Li+, 4.1 for Na+, 4.5 for Mg2+, and 4.8 for Ca2+, respectively. Good performances of the K+ISME are attributed to large specific surface area and excellent adhesion between sensing membrane and the surface of PS

이온선택성 전극을 이용한 토양추출물의 질산 및 칼륨이온 측정

Automated sensing of soil macronutrients would allow more efficient mapping of soil nutrient spatial variability for variable-rate nutrient management. The capabilities of ion-selective electrodes for sensing macronutrients in soil extracts can be affected by the presence of other ions in the soil itself as well as by high concentrations of ions in soil extractants. Adoption of automated, on-the-go sensing of soil nutrients would be enhanced if a single extracting solution could be used for the concurrent extraction of multiple soil macronutrients. This paper reports on the ability of the Kelowna extractant to extract macronutrients (N, P, and K) from US Corn Belt soils and whether previously developed PVC-based nitrate and potassium ion-selective electrodes could determine the nitrate and potassium concentrations in soil extracts obtained using the Kelowna extractant. The extraction efficiencies of nitrate-N and phosphorus obtained with the Kelowna solution for seven US Corn Belt soils were comparable to those obtained with IM KCI and Mehlich III solutions when measured with automated ion and ICP analyzers, respectively. However, the potassium levels extracted with the Kelowna extractant were, on average, 42% less than those obtained with the Mehlich III solution. Nevertheless, it was expected that Kelowna could extract proportional amounts of potassium ion due to a strong linear relationship (

Biosensor incorporating cell barrier architectures for detecting Staphylococcus aureus alpha toxin

Alpha toxin is a common virulent factor of Staphylococcus aureus and is believed to play crucial roles in pathogenicity induced by S. aureus. Alpha toxin is also known to induce permeability to endothelial cell monolayers in vitro due to the formation of interendothelial gaps. The present study is directed towards measuring alpha toxin using a whole-cell-based biosensor. The biosensor, consisting of a confluent monolayer of human umbilical vein endothelial cells (HUVECs) on a potassium ion-selective electrode, takes advantage of cell permeability dysfunction to detect the presence of small quantities of alpha toxin. When a confluent monolayer of cells was formed on the membrane surface, the response of the electrode toward the marker ion, potassium, was inhibited. Upon exposing this sensor to varying concentrations of alpha toxin for 20 min, an increase in sensor response to potassium was observed. The response thus obtained was indirectly related to the concentration of alpha toxin. The detection limit of this sensor for alpha toxin was found to be 0.1 ng/ml. Cell monolayers were stained with silver nitrate to quantify the formation of intercellular gaps as well as to study the effect of this toxin on HUVECs morphology. A strong positive correlation was observed between the response obtained from the biosensor and the area of the intercellular gaps. Silver staining also revealed the tendency of cells to round up upon being exposed to alpha toxin.

Interactions of bovine lactoferricin with acidic phospholipid bilayers and its antimicrobial activity as studied by solid-state NMR

Bovine lactoferricin (LfcinB) is an antimicrobial peptide released by pepsin cleavage of lactoferrin. In this work, the interaction between LfcinB and acidic phospholipid bilayers with the weight percentage of 65% dimyristoylphosphatidylglycerol (DMPG), 10% cardiolipin (CL) and 25% dimyristoylphosphatidylcholine (DMPC) was investigated as a mimic of cell membrane of Staphylococcus aureus by means of quartz crystal microbalance (QCM) and solid-state 31P and 1H NMR spectroscopy. Moreover, we elucidated a molecular mechanism of the antimicrobial activity of LfcinB by means of potassium ion selective electrode (ISE). It turned out that affinity of LfcinB for acidic phospholipid bilayers was higher than that for neutral phospholipid bilayers. It was also revealed that the association constant of LfcinB was larger than that of lactoferrin as a result of QCM measurements. 31P DD-static NMR spectra indicated that LfcinB interacted with acidic phospholipid bilayers and bilayer defects were observed in the bilayer systems because isotropic peaks were clearly appeared. Gel-to-liquid crystalline phase transition temperatures (Tc) in the mixed bilayer systems were determined by measuring the temperature variation of relative intensities of acyl chains in 1H MAS NMR spectra. Tc values of the acidic phospholipid and LfcinB-acidic phospholipid bilayer systems were 21.5 °C and 24.0 °C, respectively. To characterize the bilayer defects, potassium ion permeation across the membrane was observed by ISE measurements. The experimental results suggest that LfcinB caused pores in the acidic phospholipid bilayers. Because these pores lead the permeability across the membrane, the molecular mechanism of the antimicrobial activity could be attributed to the pore formation in the bacterial membrane induced by LfcinB.

An Electrogravimetric Study of an All-Solid-State Potassium Selective Electrode with Prussian Blue as the Electroactive Solid Internal Contact

Due to their fragility, classical ion-selective electrodes (ISEs) can be replaced by a new generation of chemical sensors. In this work, all-solid-state potassium selective electrodes, based on a plasticized poly(vinyl chloride) (PVC) membrane and a Prussian blue film as the solid internal contact, were prepared and characterized. First of all, potentiometric measurements revealed a non-Nernstian response of the electrode. Then, ac electrogravimetric measurements were carried out in KCl solutions under various polarization potentials. It was clearly found that potassium ions enter the PVC membrane regardless of the potential applied. Moreover, small quantities of solvent also enter the membrane at certain studied potentials. Electroacoustic measurements have been also carried out in order to check the validity of Sauerbrey’s law for the quartz crystal microbalance by estimating the electrical characteristics of the quartz resonator under our experimental conditions.

Ac-Electrogravimetry study of an all solid state potassium selective electrode with polypyrrole as the solid internal contact

The performances of all solid state potassium selective electrodes with polypyrrole film as solid internal contact were evaluated. Potentiometric measurements revealed near Nernstian responses close to values already given in the literature for classic ISEs. In addition, ac-electrogravimetry was used in order to study the ions and solvent motions at the membrane/electrolyte interface. We have found that potassium ions enter the selective membrane firstly but solvent molecules and anions are also participating in the phenomenon.

Determination of cell electroporation in small-volume samples by using a mini potassium-selective electrode

The increase of the cell membrane permeabilitycaused by strong electric pulses (electroporation) iswidely used in cell biology, biotechnology, and medicine[1]. For optimization of practical applications and theo-retical models, it is important to know whether cells havebecome electroporated under the inXuence of certainelectric Weld treatment and, if so, how many cells havebeen electroporated. In many cases, electroporated cellsstill remain viable; thus, viability tests (e.g., by cloningeYciency) cannot be used for the determination of cellmembrane electroporation [2].The exposure of cells to an electric pulse leads to anincrease in membrane permeability to various species(electropermeabilization). A membrane that is imperme-able to certain tracer molecules (e.g., propidium iodide,sucrose) can, at the same time, be permeable to smallerspecies (e.g., mannitol, Na

Rapid quantitative turbidimetric spot test analysis of potassium in blood serum

A spot test quantitative turbidimetric method was developed for the determination of potassium in blood serum. The precipitation of potassium is done in basic medium with the classical analytical reagent sodium tetraphenylborate. The measurement of the turbidity is directly performed in this solution without further dilution using a micro-turbidimetric cell developed in this work. Blood serum was mixed with the buffer and the analytical reagent solution. The turbidity is measured in a spectrophotometer at 700 nm. The calibration curve is a straight line in the working concentration range, presenting a correlation coefficient equal to 0.9998. The analytical results obtained with this method were compared with those obtained through the use of a potassium ion selective electrode. Complete agreement was achieved between the two methods at the 99% confidence level. The observed mean RSD was 3.8%.

Neutral-carrier-type potassium ion-selective electrodes based on polymer-supported liquid-crystal membranes for practical use.

Polymer-supported liquid-crystal membranes have been designed for neutral-carrier-type potassium ion-selective electrodes, aiming for practical applications of high-performance liquid-crystalline membrane ion sensors. Two types of polymer-supported liquid-crystal membranes were tested for their usefulness; one is microporous poly(tetra fluoroethylene) (PTFE) membranes impregnated by thermotropic liquid-crystalline compounds, and another is poly(methyl methacrylate) (PMMA) membrane dispersing the same liquid-crystalline compounds. Both of the polymer-supported liquid-crystal membranes containing a liquid-crystalline benzo-15-crown-5 neutral carrier as well as a lipophilic anion excluder work well as ion-sensing membranes for potassium ion-selective electrodes, the ion selectivities of which can be switched by the measurement temperatures. Specifically, PTFE-impregnated liquid-crystal membranes are better than the PMMA-dispersed ones in the sensitivity and selectivity of the resulting ion electrodes. A potassium ion assay in blood sera has proved that neutral-carrier-type ion-selective electrodes based on the polymer-supported liquid-crystal membranes are reliable for practical uses.

Microfabricated ISEs: critical comparison of inherently conducting polymer and hydrogel based inner contacts

A rigorous side by side comparison of miniature planar potassium-selective electrodes with hydrogel and potassium hexacyanoferrate(II)/(III) doped polypyrrole (PPy/FeCN) based inner contacts is presented. The planar electrodes were manufactured by screen printing as four- and five-site arrays on ceramic substrates. These electrode arrays were incorporated into a flow-through cell, which could accommodate nine electrode sites. Two identical flow cells were connected in series and the effect of the inner contacts on the analytical performance of the respective electrodes has been critically evaluated. The time necessary to reach steady state conditions has been determined and the effect of experimental parameters (temperature, ambient light intensity, CO 2, and O 2 concentration of the sample) on the potential stability of the electrodes was analyzed. At controlled temperature, the drift of the planar potassium electrodes with hydrogel and PPy/FeCN solid contact were 0.11±0.02 mV h −1 and 0.03±0.007 mV h −1, respectively. The experimental data proved that there is no aqueous film formation between the PPy/FeCN film and the potassium-selective solvent polymeric membrane.

Potassium and tetraphenylphosphonium ion-selective electrodes for monitoring changes in the permeability of bacterial outer and cytoplasmic membranes

A tetraphenylphosphonium ion (TPP +)-selective electrode, originally developed as a membrane potential indicator, is useful for measuring increases in the permeability of bacterial outer membranes induced by antimicrobial agents. The combination of this electrode with a potassium ion-selective electrode enabled us to determine changes in the permeability of bacterial outer and cytoplasmic membranes simultaneously. Outer membrane permeabilization induced by antimicrobial agents, chlorhexidine and polyhexamethylene biguanide (PHMB), as monitored with the TPP + electrode, correlated closely with the ability of the agents to release lipopolysaccharide (LPS) from the outer membrane.

Determination of potassium ions in pharmaceutical samples by FIA using a potentiometric electrode based on ionophore nonactin occluded in EVA membrane

A simple and rapid method was developed for the K + ions determination employing a flow injection system using a flow-through electrode based on the naturally-occurring antibiotic ionophore nonactin occluded in a polymeric membrane. The nonactin ionophore was trapped in poly(ethylene- co-vinyl acetate) (EVA) matrix (40% w/w in vinyl acetate) and dispersed on the surface of a graphite-epoxy tubular electrode. The plasticizer-free all-solid-state potassium-selective electrode showed a linear response for K + concentrations between 5.0×10 −5 and 5.0×10 −2 M ( r=0.9995) with a near-Nernstian slope of 51.5 mV per decade, when Tris–HCl buffer (pH 7.0;0,1 M) was employed as a carrier. The potentiometric-FIA system allows an analytical frequency of 120 samples per hour with a precision of 3.6%. The relative standard deviations (R.S.D.) for K + determination in pharmaceuticals samples, without any previous treatment, were lower than 4.0%, comparable to those obtained by flame photometry. Ammonium is the main analytical interference and the electrode response time was 5 s at 25 °C. The useful lifetime of the tubular sensor is longer than 3 months in continuous use.

A Solid-State Potassium Selective Electrode Based on Potassium Zinc Ferrocyanide Ion Exchanger

Preparation, characterization, and application of a novel long life potassium selective electrode based on a pure tablet of K2Zn3[Fe(CN)6]2 ion exchanger are described. A sensor based on this exchanger displays a useful analytical response with excellent reproducibility, good precision, low detection limit (6 × 10−5 M), and applicability over a wide range of potassium ion concentration (10−4–1.0 M). It also offers the advantages of simple construction, low cost, fast respoónse time (<30 s), wide pH working range (pH 4–8) and significantly high radiation (up to 106 Gy) and thermal stability (up to 100°C). The sensor was successfully applied to the determination of potassium content in some pharmaceutical preparations. The results show a good recovery with the data obtained by the standard ICP emission spectrometry method, the average is 91.5 ± 1% with the standard deviation of 1.5%.

Silver Hexacyanoferrate Film Directly Modified Electrode as a Potentiometric Sensor for Potassium Ion

A chemically modified electrode (CME) was fabricated by direct modification of a silver electrode with a thin film of silver hexacyanoferrate. The modified electrode was used as a potentiometric sensor for the determination of potassium ion. The sensor exhibits a response to potassium ion in a wide concentration range from 8.0 × 10−5 to 1.0 M with a low detection limit of 4.0 × 10−5 M. The potassium-selective electrode has a relatively short response time. It has a good sensitivity with a near-Nernstian slope of 53–57 mV/decade and good selectivity in the presence of possible interferences. The electrode response is highly sensitive to some controllable parameters mainly the thickness of electroactive film which is controlled by the charge passed in the cell during the deposition of the film. Stability of the directly modified electrode and its potentiometric response were also investigated during long-term usage, which were indicative of the possibility of the potassium-selective electrode for using in a long period.

Application of Double Matrix Membrane Technology for Ion-Selective Electrodes

Double matrix membrane technology (DMM) is an excellent technique for creating inexpensive and robust electrochemical electrodes. In this report the use of DMM-electrodes to measure different ions (namely Ca2+, Mg2+, Cl−) is described. The ion-selective membranes are basing on PVC and stabilized by deposition on a porous matrix. The authors determined the following characteristics of the ion-selective electrodes (ISEs): sensitivity; detection limit; linear range and selectivity coefficients. When changing the analyte concentration response time was lower than 30 s (Ca2+, Cl−) or 1 min (Mg2+). In the case of the determination of the selectivity coefficients it was considered in which concentrations the interfering ions naturally occur in physiological matrices, e.g., blood. In case of the chloride-selective electrode the discrimination of ascorbic acid and salicylate was investigated. The coefficients were evaluated by using the fixed interference method (FIM). The reproducibility of electrochemical characteristic was determined by investigating 120 mass-produced ammonium-selective electrodes. Furthermore, it was discovered that DMM-based potassium-selective electrodes may be stored stable for at least 4.5 years.