Response Time Of Electrode Research Articles

Laboratory evaluation of the ion selective electrode for use in an automated soil nitrate monitoring system

Abstract Environmental pollution partly caused by excessive use of nitrogen fertilizer is focusing the attention of the agricultural industry towards prescription farming. It has been suggested that fertilizer application rates should be varied in response to the in situ nutrient concentrations of the soil. The time consuming nature of present methods of soil nitrate testing limits their suitability for in situ use. The nitrate ion‐selective electrode was tested in the lab for its suitability for use in an automated soil nitrate monitoring system. Tests were conducted to evaluate the parameters of soikextractant ratio, extract clarity, and electrode response time. Results indicate that with proper calibration, the electrode is suitable for in situ measurement of soil nitrate concentration and reliable readings may be obtained in less than four seconds.

Theory of transient potential response of ion-selective electrodes based on polarizable liquid ⋯ liquid interface

The theory of the transient potential response of ion-selective electrodes is presented. The mechanism of the potential response is considered using a model of the phase-boundary potential difference, and the transient potential response is considered in terms of the electrochemical principle of ion transfer, with a single ion transfer being assumed (i.e. no interference) across the boundary interface and the electric double-layer structure of the interface. The theory predicts the effect of the ion concentrations, the ion transfer kinetics and the differential capacity of the interface on the response time of ion-selective electrodes.

Potentiometric detection of organic acids in ion-exclusion chromatography using different types of liquid-membrane electrodes

Four different liquid-membrane electrodes were tested in a potentiometric flow-cell, in combination with an LC ion chromatography system (Aminex HPX-87H column). This setup was used for the determination of weak organic acids. The flow-through detector was of the wall-jet type. Conditions were established to achieve the best separation and detection characteristics. The sensitivity, selectivity and response time of the different electrodes were compared. Calibration curves and detection limits were measured for several organic acids, and compared with conductometric, and with low-wavelength UV detection. The detection limits were improved by inserting a post-column ion-suppressor system between the column and the detector. Several biological samples were analyzed to demonstrate the possibilities of the potentiometric detector.

The use of total ionic strength adjusting buffers in determining fluoride concentration in soil solutions by ion selective electrometry

Abstract Total ionic strength buffers based on citrate at pH 7.5 and cyclohexylenediaminetetra‐acetic acid (CDTA) at pH 5.2 were evaluated for use when determining fluoride (F) concentration in soil solutions. Both buffers achieved acceptable recoveries of F added to ultra‐filtered (0.025 μm) solutions. Recovery of F added to unflltered and 0.22 μm filtered solution was low when the CDTA buffer was used. This effect was attributed to the adsorption of F by micro‐particulate materials present in these samples. The use of this buffer would need to be restricted to samples in which micro‐particulates were not present. The performance of the citrate buffer was not affected by the presence of microparticulates; however, electrode response times, and departure from Nernstian response at low F concentrations, were greater when this buffer was employed. Fluoride was found to be present at low concentrations in the soil solution of the 60 virgin highly weathered soils tested. The F concentration in 75% of the surface samples was <3 μM, while all subsoil samples had soil solution F concentrations <1 μM.

Micellar acid—base potentiometric titrations of weak acidic and/or insoluble drugs

The effect of various surfactants [the cationics cetyl trimethyl ammonium bromide (CTAB) and cetyl pyridinium chloride (CPC), the anionic sodium dodecyl sulphate (SDS), and the nonionic polysorbate 80 (Tween 80)] on the solubility and ionization constant of some sparingly soluble weak acids of pharmaceutical interest was studied. Benzoic acid (and its 3-methyl-, 3-nitro-, and 4-tert-butyl-derivatives), acetylsalicylic acid, naproxen and iopanoic acid were chosen as model examples. Precise and accurate acid-base titrations in micellar systems were made feasible using a microcomputer-controlled titrator. The response curve, response time and potential drift of the glass electrode in the micellar systems were examined. The cationics CTAB and CPC were found to increase considerably the ionization constant of the weak acids (delta pKa ranged from -0.21 to -3.57), while the anionic SDS showed negligible effect and the nonionic Tween 80 generally decreased the ionization constants. The solubility of the acids in aqueous micellar and acidified micellar solutions was studied spectrophotometrically and it was found increased in all cases. Acetylsalicylic acid, naproxen, benzoic acid and iopanoic acid could be easily determined in raw material and some of them in pharmaceutical preparations by direct titration in CTAB-micellar system instead of using the traditional non-aqueous or back titrimetry. Precisions of 0.3-4.3% RSD and good correlation with the official tedious methods were obtained. The interference study of some excipients showed that a preliminary test should be carried out before the assay of formulations.

Miniature glucose biosensor with extended linearity

A rapid and simple method for the preparation of a miniature glucose sensor (enzyme electrode) has been developed. Glucose oxidase is immobilized by glutaraldehyde in albumin gel on a cellulose diacetate membrane. This membrane is directly attached to an H 2O 2 detecting electrode and covered with an external polyvinyl chloride membrane. The response time of the glucose electrode thus prepared is about 2 min, the calibration graph is linear for 0–30 mM glucose, and the sensor can be used repeatedly at room temperature for at least 10 days with small deterioration in response.

Bioelectrochemical responses of the polyaniline uricase electrode

The catalytic activity of the polyaniline uricase electrode is very sensitive to uric acid. At a very low concentration of the substrate, such as 1. 2 × 10 −6 mol dm −3, uric acid can be determined reliably by using a polyaniline uricase electrode. The response current increases linearly with increasing concentration of uric acid in the region of 1.2 × 10 −6 to 1.2 × 10 −3 mol dm −3. The reaction rate of the enzyme electrode is affected quite significantly by potential: the response time of the enzyme electrode at 0.35 V (vs. SCE) is about 40 s. The effect of the solution pH on the electrode reaction is rather complicated, the reaction rate increasing with rising temperature. The activation energy of the enzyme-catalyzed reaction is 29.9 kJ/mol.

Copper(II) ion-selective sensor with electrolytically plated chalcogenide coating

The performance characteristics of a copper(II) ion-selective electrode, based on the copper selenide formed by cathodic deposition of selenium directly onto a copper substrate, are reported. The deposition is carried out at a constant current of 2 mA/cm 2 from 0.1 M Na 2SeO 3 solution whose pH is adjusted to between 6 and 4 with either sulphuric or hydrochloric acid. The electrodes exhibit a linear Nernstian response down to 10 −5 M copper(II) in non-buffered medium. Data on the electrode response time and pH dependence are also presented.

Novel solvent systems for the preparation of phase‐inversion cellulose acetate size exclusion membranes: Voltammetric investigations

AbstractNovel solvent systems have been developed for the casting of size exclusion electrode modifications by the phase‐inversion process. Solvent systems studied were (solvent/nonsolvent): pyridine/2‐octanol, pyridine/cyclohexanol, acetone/2‐octanol, tetrahydrofuran/aqueous Mg(ClO4)2, and tetrahydrofuran/toluene. These were compared to modifications made from the solvent system acetone/aqueous Mg(ClO4)2. The membranes were cast onto Pt microelectrodes embedded in glass. Cyclic voltammograms were recorded once per min after immersing the membrane‐modified electrode into a solution containing an electroactive species. Modified electrode response time to a concentration perturbation is correlated with the percent nonsolvent and percent polymer in the casting solution. The magnitude of the current from a solution of a 1500 dalton polyethylene glycol ferrocene carboxylate ester solute, and good casting reproducibility. This formulation is recommended for permselective coating applications; applications to biosensors are envisioned.

A one-side hydrophilic polypropylene membrane prepared by plasma treatment

The surface on one side of a hydrophobic polypropylene (PP) membrane was modified with a gaseous plasma of 60 W discharge power in the presence of ammonia gas at 0.9 Torr pressure. Results of contact angle measurements indicate that one side of the hydrophobic membrane was modified; it became hydrophilic while the other side remained hydrophobic. Data from ESCA (electron spectroscopy for chemical analysis; X-ray photoelectron spectroscopy) and ATR-IR (attenuated total reflectance infrared) spectral analysis showed that the hydrophilicity was mainly derived from the amino groups on the modified surface. The modified PP membrane was coupled to urease and used to construct a urea sensor, which gave electrode response time only half that of the conventional urea sensor. The enzyme electrode gave a potential change of 30 mV per decade of increase in analyte concentration. The response of this electrode remained stable during continuous use for up to 12 days.

ION-SELECTIVE ELECTRODE DETERMINATION OF SOLUTION K IN SOIL SUSPENSIONS AND ITS SIGNIFICANCE IN KINETIC STUDIES

The feasibility of using a K ion-selective electrode (K-ISE) to monitor changes in solution K concentration in soil suspensions with time, under shaking conditions, was investigated and its significance in kinetics studies of K adsorption was discussed. Factors that affect the efficiency of the K-ISE method include the response time of the electrode, influence of suspended soil particles, shaking speed, and ionic strength of the system. The response time of the K-ISE decreased with increasing K concentration. Moreover, for a system with a solution K concentration greater than 10 mg K L−1, errors resulting from response delays were negligible when, under shaking conditions, observation time intervals were greater than 30 s. The influence of suspended soil particles on the K-ISE method was negligible for soil suspensions with a solution/soil ratio of 50:1 (vol/wt). Shaking significantly influenced K-ISE determination of solution K concentration. The degree of the influence of shaking on the determination of solution K appeared to be related to ionic factors of the systems. Shaking had much less influence on the soil suspensions, the filtrates and mixed CaCl2-KCl solutions than on pure KCl solutions. Satisfactory results were obtained by taking into account the response time, suspended soil particle and shaking speed factors and by adjusting the ionic strength of the calibration system (KCl standard solution series). Key words: Potassium ion-selective PVC membrane electrode, batch technique, kinetics, calibration system, electrode response time, suspended soil particle, shaking speed, ionic strength

Operation and methodology of an alanine ion-selective electrode dosimetric system: I. Electrode characteristics and data analysis

A new electrochemical technique for high-dose dosimetry, employing an ion-selective electrode (ISE), consists of measuring the ammonia content of an aqueous sample after dissolving irradiated solid α-alanine. The operational principles, readout procedure, as well as data analysis are presented here and discussed. For direct calibrations, a modified Nernst equation produces the best fit to the experimental data. Time stability of the response parameters is shown to be very good. The background reading varies linearly with alanine concentration in the sample. The temperature coefficient of the readout system may be +1.3 mV C −1 (+4% C −1), so a thermostatic isolated set-up is recommended. The electrode response time is 1–3 min, depending on the concentration level.

Shorter response times and improved selectivity for potentiometric electrodes

The response times of potentiometric electrodes of the coated-wire variety are shortened by the addition of non-selective charge carriers to the ion-selective membrane. As a charge carrier, ferrocene was effective in decreasing the response time by a factor of 2–3, e.g. from 19 to 6 s. The optimum amount of ferrocene in the polymer film was 1.5% (w/w). As an unexpected benefit, the selectivity of the electrodes containing ferrocene improved by up to two orders of magnitude.

Effect of potassium chloride additions on pH measurements of dilute sulphuric acid standards

Considerable controversy surrounds the common practice of adding a neutral salt (usually KCl) to solutions in order to increase the accuracy of pH measurement and shorten electrode response times. In this study, we demonstrate theoretically, and confirm experimentally, that KCl additions always change the pH of water samples of low solute content when compared with unspiked water samples. However, small KCl-induced pH changes (0.01–0.03 pH units) often go unnoticed, especially when they are equal to, or less than, the precision of the pH measurement. The results of four titrations of 5.00 (± 0.05)× 10–5M H2SO4 with KCl, repeated with and without stirring, confirm that spiking with KCl and stirring of samples of low solute content improves measurement precision and mean response time, but at the cost of accuracy. Spiking with 0.01, 0.10 and 0.19 M KCl results in pH errors of 0.02, 0.06 and 0.09 pH units, respectively, compared with the pH of unspiked 5.00 × 10–5M H2SO4. For these reasons we do not recommend KCl additions or stirring of water samples of low ionic strength during studies emphasising the accuracy of pH measurement.

Effect of oxygen electrode response on K L a measurement

A study on the effect of oxygen electrode response on K L a measurement was carried out by simulation. As oxygen electrode response time increases, the estimated K L a decreases when we did not consider the electrode response time. And K L a estimation by slope method is closer to real one than curve fitting method.

The influence of the Luggin capillary on the response time of a reference electrode

Modelisation et simulation du temps de reponse d'une electrode de reference. Schema equivalent

The rapid measurement of fluoride concentrations in stored human saliva by means of a differential electrode cell

For the purpose of rapid measurement, the performance of a differential cell, consisting of a combination pH electrode and a F − electrode and used at low pH (1.2), was compared with the use of a single F − electrode at pH 5.0. The differential cell proved to be as accurate and consistent as the single electrode: its response time was 2 min for a saliva volume of 50 μl; the response time of the single electrode was 20 min with a saliva volume of 1000 μl. Analysis of salivary supernatant fluid provided an unreliable guide to the original salivary F − concentrations but if fresh whole saliva was acidified to pH 1.2 immediately upon collection, the original baseline values were repeatedly obtained when measurements were made at intervals over a storage period of 14 days at 4 °C. Immediate acidification thus provides a satisfactory method for collecting samples from separate populations and then transporting them at leisure to a laboratory for direct measurement at pH 1.2 with the differential cell.

PERFORMANCE OF TRANSCUTANEOUS PO2 AND PCO2 DUAL ELECTRODES IN ADULTS

Three commercially-available combined PO2-PCO2 electrodes were assessed in vitro, and in adults breathing air, hypoxic and hypercapnic mixtures, for speed of response, correlation with end-tidal gas tensions and drift. Differences in the 90% response time of the individual electrodes were more marked in vitro than in vivo. Changes in end-tidal gas tensions were reflected by proportionate changes in transcutaneous oxygen and carbon dioxide (PtcO2 and PtcCO2) but, in the individual subject, PtcO2 and PtcCO2 were generally poor indicators of the end-tidal values. During steady-state recordings, the PtcO2 signal drifted upwards by more than 12 mm Hg during 140 min in vivo recording in all three electrodes, without changes in either PtcCO2 or end-tidal values. The dual electrodes tested provide non-invasive estimates of qualitative, but not quantitative, change in blood-gas tensions and are likely to have only a limited role to play in adult anaesthetic practice.

Extended sensitivity for the calcium selective electrode

Sensitivity of calcium-selective electrodes heretofore has been limited to calcium concentrations above 10 −8 m in the absence of competing ions. We describe the use of calcium buffers to stabilize the free calcium in the reference electrode. Electrode calibration is linear to 10 −8 m and is curvilinear to 10 −11 m in the presence of 0.1 m ionic strength. Selectivity with respect to competing cations magnesium, potassium, sodium, and hydrogen is preserved. Electrode response time is less than 2 s for small changes in calcium activity. Response range is linear over 9 log units of calcium activity. Potential-time stability is less than 10 mV/h at saturation currents. Although the silver-silver chloride terminals are photosensitive throughout the visible and near-ultraviolet regions, housing the reference and indifferent in opaque barrels avoids false photovoltaic response.

Determination of the stoichiometry of redox-linked proton translocation from the kinetics of pulse experiments: A simulation study

We have previously published a simple kinetic model to analyse possible pitfalls in kinetic measurements of H +/O ratios in mitochondria [(1984) FEBS Lett. 178, 187-192]. While this model demonstrated how relative electrode response times may affect the results, it did not adequately describe the kinetics of proton back-diffusion across the membrane. Here this model is further developed and improved, and shown to give a good quantitative description of both oxygen-pulse type experiments as well as of experiments where the reaction is started by photolysis of the cytochrome c oxidase-CO complex. Simulations based on this model reveal that the extrapolation procedure used by Lehninger et al. [e.g. (1984) J. Biol. Chem. 259, 4802-4811] to estimate the H +/O ratio will tend to yield overestimated values. This is mainly due to the back-diffusion of protons into the mitochondria, which is not correctly accounted for by this extrapolation. Electron transport Proton transport Mitochondria