Potassium Electrode Research Articles

Enhancing biocompatibility of some cation selective electrodes using heparin modified bacterial cellulose

Bacterial cellulose (BC) and heparin-modified bacterial cellulose (HBC) were utilized to enhance the biocompatibility of highly thrombogenic PVC-based potassium and calcium membrane electrodes. Three types of membrane electrodes were prepared: (1) conventional PVC electrode (control), (2) PVC-based electrode sandwiched with bacterial cellulose membrane (BC-PVC), and (3) PVC-based electrode sandwiched with heparin-modified bacterial cellulose membrane (HBC-PVC). The potentiometric response characteristics of the modified potassium and calcium membrane electrodes (BC-PVC and HBC-PVC) were compared with those of the control PVC-based potassium and calcium selective electrode, respectively. Response characteristics of the modified membrane electrodes were comparable to the control PVC membrane electrode. The platelet adhesion investigations indicated that (BC) and (HBC) layers are less thrombogenic compared to PVC. Therefore, use of BC or HBC would enable the enhancement of the biocompatibility of PVC-based membrane electrodes for potassium and calcium while practically maintaining the overall electrochemical performance of the PVC sensing film.

Sensitive voltammetric determination of thymol in essential oil of Carum copticum seeds using boron-doped diamond electrode

Essential oil of Carum copticum seeds, obtained from a local shop, was extracted and content of thymol was analyzed using square-wave voltammetry at boron-doped diamond electrode. The effect of various parameters, such as pH of supporting electrolyte and square-wave voltammetric parameters (modulation amplitude and frequency), was examined. In Britton–Robinson buffer solution (pH 4), thymol provided a single and oval-shaped irreversible oxidation peak at +1.13 V versus silver/silver chloride potassium electrode (3M). Under optimal experimental conditions, a plot of peak height against concentration of thymol was found to be linear over the range of 4 to 100μM consisting of two linear ranges: from 4 to 20μM (R2=0.9964) and from 20 to 100μM (R2=0.9993). The effect of potential interferences such as p-cymene and γ-terpinene (major components in essential oil of C. copticum seeds) was evaluated. Thus, the proposed method displays a sufficient selectivity toward thymol with a detection limit of 3.9μM, and it was successfully applied for the determination of thymol in essential oil of C. copticum seeds. The Prussian blue method was used for validation of the proposed electroanalytical method.

Calibration-free ionophore-based ion-selective electrodes with a Co(II)/Co(III) redox couple-based solid contact.

A high electrode-to-electrode reproducibility of the emf response of solid contact ion-selective electrodes (SC-ISEs) requires a precise control of the phase boundary potential between the ion-selective membrane (ISM) and the underlying electron conductor. To achieve this, we introduced previously ionophore-free ion exchanger membranes doped with a well controlled ratio of oxidized and reduced species of a redox couple as redox buffer and used them to make SC-ISEs that exhibited highly reproducible electrode-to-electrode potentials. Unfortunately, ionophores were found to promote the loss of insufficiently lipophilic species from the ionophore-doped ISMs into aqueous samples. Here we report on an improved redox buffer platform based on equimolar amounts of the much less hydrophilic Co(III) and Co(II) complexes of 4,4'-dinonyl-2,2'-bipyridyl, which makes it possible to extend the redox buffer approach to ionophore-based ISEs. For example, K(+)-selective electrodes based on the ionophore valinomycin exhibit electrode-to-electrode standard deviations as low as 0.7 mV after exposure of freshly prepared electrodes for 1 h to aqueous solutions. Exposure of freshly prepared ISE membranes to humidity prior to their first contact to electrolyte solution minimizes the initial (reproducible) emf drift. This redox buffer has also been successfully applied to sodium, potassium, calcium, hydrogen, and carbonate ion-selective electrodes, which all exhibit the high selectivity over interfering ions as expected for ionophore-doped ISE membranes.

Rubber-based substrates modified with carbon nanotubes inks to build flexible electrochemical sensors

The development of a solid-contact potentiometric sensor based on conducting rubbers using a carbon nanotubes ink is described here. Commercial rubbers are turned into conductive ones by a simple and versatile method, i.e. painting an aqueous dispersion of single-walled carbon nanotubes on the polymer surface. On this substrate, both the working ion-selective electrode and the reference electrode are built in order to form an integrated potentiometric cell. As a proof-of-principle, selective potassium electrodes are fully characterized giving comparable performances to conventional electrodes (sensitivity, selectivity, stability, linear range, limit of detection and reproducibility). As an application of the rubber-based electrodes, a bracelet was constructed to measure potassium levels in artificial sweat. Since rubbers are ubiquitous in our quotidian life, this approach offers great promise for the generation of chemical information through daily objects.

The Lantibiotic NAI-107 Binds to Bactoprenol-bound Cell Wall Precursors and Impairs Membrane Functions

The lantibiotic NAI-107 is active against Gram-positive bacteria including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. To identify the molecular basis of its potency, we studied the mode of action in a series of whole cell and in vitro assays and analyzed structural features by nuclear magnetic resonance (NMR). The lantibiotic efficiently interfered with late stages of cell wall biosynthesis and induced accumulation of the soluble peptidoglycan precursor UDP-N-acetylmuramic acid-pentapeptide (UDP-MurNAc-pentapeptide) in the cytoplasm. Using membrane preparations and a complete cascade of purified, recombinant late stage peptidoglycan biosynthetic enzymes (MraY, MurG, FemX, PBP2) and their respective purified substrates, we showed that NAI-107 forms complexes with bactoprenol-pyrophosphate-coupled precursors of the bacterial cell wall. Titration experiments indicate that first a 1:1 stoichiometric complex occurs, which then transforms into a 2:1 (peptide: lipid II) complex, when excess peptide is added. Furthermore, lipid II and related molecules obviously could not serve as anchor molecules for the formation of defined and stable nisin-like pores, however, slow membrane depolarization was observed after NAI-107 treatment, which could contribute to killing of the bacterial cell.

Performance Evaluation of ZnO Coated Film on Al and Ag Electrodes for Potassium Sensing Applications

Performance Evaluation of ZnO Coated Film on Al and Ag Electrodes for Potassium Sensing Applications

Endocochlear Potential and Potassium Concentration Recording in Minipig Cochlea

ObjectiveTo record the endocochlear potential (EP) and calculate potassium concentration [K+] in Minipig cochleae. MethodsWe used multi-barreled electrodes to measure the EP and the potential, [K+]. EP and potassium electrode recording were made in 9 cochleae from 5 minipigs to get normal EP values. ResultsThe average EP value in the cochlea from the minipigs was 77.3 ± 14mV. The average [K+] for the minipigs was 147.1 ± 13mM. ConclusionsThe EP and potential, [K+] in minipigs are lower than in the human and rodents. This may be the reason why porcine ABR thresholds are slightly higher than humans and rodents.

The vagus and the heart: revisiting an early contribution to a still on-going dispute

The vagus and the heart: revisiting an early contribution to a still on-going dispute

New Calibration Methods to Eliminate the Non-Ideal Effect of Drift and Hysteresis in All-Solid-State Potassium Electrode

The object of this study is to develop a non-ideal effects calibration method combining of hardware and software, and apply this calibration methods to an all-solid-state potassium electrode. In the hardware method, the calibration circuit owning drift and hysteresis calibration functions are developed to improve the accuracy of the measurement system. The experimental results show that both drift and hysteresis of all-solid-state potassium electrode can be reduced by a calibration circuit. In the software method, a three-time-constant model is used to simulate drift behaviors, and the drift of the all-solid-state potassium electrode is reduced by the software method. The measurement conditions of drift and hysteresis are set as below; the drift time is last for 12 h, the hysteresis loop is 10-3 M → 10-1 M → 10-3 M → 10-5 M → 10-3 M KCl solutions, and the total loop time of hysteresis measurement is 5 min. Simulation of drift behaviors are in 10-2 M and 10-5 M KCl solutions. In addition, the alternated current (AC) impedance analyzer is used to measure the transfer impedance of the sensing membrane. The experimental results obtained by the AC impedance analyzer are used to explain the relationship between the hysteresis and transfer impedance of the sensing membrane.

Microdischarge extreme ultraviolet source with alkali metal vapor for surface morphology application

We have characterized a discharge-produced potassium plasma extreme ultraviolet (XUV) source. Potassium ions produced strong broadband emission around 40 nm with a bandwidth of 8 nm (full width at half-maximum). By comparison with atomic structure calculations, the broadband emission is found to be primarily due to 3d–3p transitions in potassium ions ranging from K2+ to K4+. The current-voltage characteristics of the microdischarge suggest that the source operates in a hollow cathode mode and consequently the emitting ions may be localized on the potassium electrode surface at the hole into the capillary. To understand the spectral behavior from the potassium plasmas we compared the spectra from the discharge-produced plasma with that from a laser-produced plasma. The spectra from the different (electric and laser) plasmas at the same electron temperature (12 eV) were almost the same. This compact capillary XUV source with a photon energy of 30 eV is a useful XUV emission source for surface morphology applications.

Susceptibility of Campylobacter jejuni to organic acids and monoacylglycerols

Organic acids can be used as feed supplements or for treatment of poultry carcasses in processing plants. The antimicrobial activity of nineteen organic acids and two monoacylglycerols in cultures of Campylobacter jejuni CCM 6214(T) (ATCC 33560) was determined using a SYBR Green-based real-time PCR assay. The IC(50) was a concentration at which only 50 % of a bacteria specific DNA sequence was amplified. Caprylic, capric and lauric acids were the most efficient antimicrobials among the compounds tested (IC(50) < or = 0.1 mg/mL). In a weakly acidic environment (pH 5.5), the antimicrobial activity was more pronounced than at pH 6.5. At pH 5.5, oleic and fumaric acid also had clear antimicrobial activity, as did monocaprylin. The antimicrobial activity of acetic, butyric, stearic and succinic acid was low. In cells treated with fumaric acid, the potential of potassium and tetraphenylphosphonium ion-selective electrodes changed, indicating an increase in cytoplasmic and outer membrane permeability, respectively. No changes in membrane permeability were observed in cells treated with capric acid or monocaprin. Transmission electron microscopy revealed separation of the inner and outer membrane in cells treated with capric and fumaric acid, as well as cytoplasmic disorganization in cells exposed to capric acid.

Potassium ion-selective polyaniline solid-contact electrodes based on 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether ionophore

New ion-selective electrodes for potassium were developed and tested employing 18-crown-6-ether, dibenzo-18-crown-6-ether, and 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether ionophores in PVC membranes with a polyaniline solid contact between the membranes and the Pt substrate. We compared the response characteristics of the solid-contact electrodes (SCEs) based on these ionophores and various plasticizers. Among the three ionophores, 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether-based SCE produced the best results exhibiting a high reproducibility with negligible drifts in the standard potential with a response slope (RS) of 58.2 mV/decade: the detection limit (DL) of the potassium ion was 10−5.80 M with linearity over five decades. This is a significant improvement for the response slope and detection limit compared to SCEs with valinomycin, 2,3-naphtho-15-crown-ether, and dibenzo-15-crown-5-ether ionophore, which showed 53–56 mV/decade of RS and 10−5.3 M of DL. The response slope, detection limit, and selectivity were compared with other K+ ISEs reported until present. Finally, the new SCE was applied to determine potassium ions in artificial human serum with satisfactory results. However, the detection limit for the artificial serum was slightly diminished yielding a value of 10−5.19 M (6.5 × 10−3 mM) which is still good. Electrodes with polypyrrole in place of polyaniline exhibited comparable results.

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.

All-Solid-State Separated Potassium Electrode Based on SnO2/ITO Glass

An all-solid-state potassium electrode based on tin oxide /indium tin oxide (ITO) glass is developed in this paper. The sensing membrane of the electrode is prepared by mixing poly(vinyl chloride) (PVC), bis(2-ethylhexyl) sebacate (DOS), valinomycin (VAL), and potassium tetrakis(p-chlorophenyl) borate (KTpClPB). The mixed solution is dissolved in tetrahydrofuran (THF). Then, it is dropped on the sensing window of /ITO glass. In addition, the wire, which is coated PVC membrane containing powder, is used as a miniaturized reference electrode in this study. The optimum experiment of the potassium sensor is conducted by observing the characteristics of sensitivity and selectivity in different weight ratios. After the optimum experimental trials, the best weight ratio of the potassium sensor is PVC:DOS:VAL:KTpClPB = 33:66:4:2. In this optimum condition, the sensitivity is /decade with linear concentration range between and . The low detection limit of the sensor reaches to , and response time is . Moreover, the sensor is slight interfered by sodium, calcium, and magnesium ions. The pH variation does not affect its electromotive force in the range between pH 6 and pH 12. The sensor possesses reusable properties showing that it can be repeated, measuring 30 times.

Astrocyte membrane responses and potassium accumulation during neuronal activity

Older studies suggest that astrocytes act as potassium electrodes and depolarize with the potassium efflux accompanying neuronal activity. Newer studies suggest that astrocytes depolarize in response to neuronal glutamate release and the activity of electrogenic glial glutamate transporters, thus casting doubt on the fidelity with which astrocytes might sense extracellular potassium rises. Any K(+)-induced astrocyte depolarization might reflect a spatial buffering effect of astrocytes during neuronal activity. For these reasons, we studied stimulus-evoked currents in hippocampal CA1 astrocytes. Hippocampal astrocytes exhibited stimulus-evoked transient glutamate transporter currents and slower Ba(2+)-sensitive inward rectifier potassium (K(ir)) currents. In whole-cell astrocyte recordings, Ba(2+) blocked a very weakly rectifying component of the astrocyte membrane conductance. The slow stimulus-elicited current, like measurements from K(+)-sensitive electrodes under the same conditions, predicted small bulk [K(+)](o) increases (<0.5 mM) following the termination of short-stimulus trains. These currents indicate the potential for astrocyte spatial K(+) buffering. However, Ba(2+) did not significantly affect resting [K(+)](o) or the [K(+)](o) rises detected by the K(+)-sensitive electrode. To test whether local K(+) rises may be significantly higher than those detected by glial recordings or by K(+) electrodes, we assayed EPSCs and fiber volleys, two measures very sensitive to K(+) increases. We found that Ba(2+) had little effect on neuronal axonal or synaptic function during short-stimulus trains, indicating that K(ir)s do not influence local [K(+)](o) rises enough, under these conditions to affect synaptic transmission. In conclusion, our results indicate that hippocampal astrocytes are faithful sensors of [K(+)](o) rises, but we find little evidence for physiologically relevant spatial K(+) buffering during brief bursts of presynaptic activity.

Determination of potassium in fatty acid methyl esters applying an ion-selective potassium electrode

AbstractAn easy and inexpensive method of potassium determination in fatty acid methyl esters (FAME) applying an ion-selective potassium electrode (ISE-K) is presented. FAME are considered alternative fuel for diesel engines. Simple apparatus and procedure were developed to avoid contact of ester samples with the sensitive ISE-K membrane, which can damage the ISE membrane surface in long time operation. Using different FAME samples with a wide range of known potassium content a calibration curve was constructed. Among all samples, ISE-K satisfactory predicted potassium content in FAME as identified by the AAS reference method.

Array of potentiometric sensors for simultaneous analysis of urea and potassium

Urea biosensors based on urease immobilized by crosslinking with BSA and glutharaldehyde coupled to ammonium ion-selective electrodes were included in arrays together with potassium, sodium and ammonium PVC membrane ion-selective electrodes. Multivariate calibration models based on PCR and PLS2 were built and tested for the simultaneous determination of urea and potassium. The results show that it is possible to obtain PCR and PLS2 calibration models for simultaneous determination of these two species, based on a very small set of calibration samples (nine samples). Coupling of biosensors with ion-selective electrodes in arrays of sensors raises a few problems related to the limited stability of response and unidirectional cross-talk of the biosensors, and this matter was also subjected to investigation in this work. Up to three identical urea biosensors were included in the arrays, and the data analysis procedure allowed the assessment of the relative performance of the sensors. The results show that at least two urea biosensors should be included in the array to improve urea determination. The prediction errors of the concentration of urea and potassium in the blood serum samples analyzed with this array and a PLS2 calibration model, based on nine calibration samples, were lower than 10 and 5%, respectively.

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.

Potential Uses of Ion‐Selective Potassium Electrodes in Soil Fertility Management

Mapping horizontal spatial variability in soil‐potassium (K) fertility is driving renewed interest in measuring soil K with ion selective K electrodes (ISE‐K). The objectives of this study were 1) to develop a rapid and inexpensive ISE‐K protocol for soil solution phase [K+], 2) to compare this protocol to published methods for assessment of soil K intensity and capacity, and 3) to explore electrode sensitivity to environmental variables including temperature and soil moisture content. Using 32 agricultural soils with a wide range in plant‐available K, we evaluated two combination electrodes, a glass electrode (ISE‐KGls) similar to that used in earlier soil applications and a PVC membrane flat‐surface electrode (ISE‐KPVC) that is being considered for on‐the‐go real‐time sensing of soil K. A 15‐s agitation 30‐min settling proved sufficient to equilibrate K concentrations in a 1:1 H20 soil/water w/v extraction. The ISE‐K readings in slurries, supernatants, and filtrates were equivalent and did not differ from atomic adsorption spectrophotometer (AAS) filtrate analyses. Among all soils, ISE‐K accurately predicted solution‐phase [K+] differences as identified by three common reference methods used with AAS, but individual ISE‐K measured values were higher than any AAS‐measured value. To prevent interference by Na+ and NH4 +, NaCl had been added as an ionic strength adjuster (ISA) and the added Na+ displaced K+ off exchange surfaces, elevating soil solution [K+]. On naturally leached soils, the ISA may be less important as concentrations of Na+ and NH4 + tend to be low. Results from ISE‐K measurements in soils equilibrated at 20% gravimetric moisture without ISA support this contention. These ISE‐K values closely tracked AAS‐measured soil solution [K+] (regression coefficient = 0.93; r2 = 0.76). Among soils, ISE‐K measured values were not well correlated with NH4OAc or NaBPh4 extractable K, an expected result given differences in soil mineralogy and associated buffering capacity. In general, electrode output varied predictably with changes in ambient temperatures and gravimetric soil moisture indicating appropriate corrections in [K+] measurements could be made if these parameters were simultaneously monitored. The ISE‐KGls retained calibration more consistently than the ISE‐KPVC, and the ISE‐KPVC proved less durable, especially for measurements made in soil slurries. The rapid extraction of soil solution K coupled with ISE‐K technology is sufficiently precise and accurate for both research and routine use. However, general application of this technology either in the commercial testing lab or on‐the‐go in the field will require that soil fertility management guides be revised to include interpretive information for soil solution‐phase [K+].

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.