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PubMed2000

Use of ion-selective electrodes for blood-electrolyte analysis. Recommendations for nomenclature, definitions and conventions. International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). Scientific Division Working Group on Selective Electrodes.

This paper will familiarize the reader with the terms used to describe the behavior of ion-selective electrodes, particularly in relation to their use in clinical chemistry for determination of blood electrolyte cations. It serves as an introduction to a series of papers dealing with important cations in blood, namely calcium, sodium, and potassium. The detailed relationships between the ion activity determined by means of ion-selective electrode potentiometry in undiluted specimens, and the total substance concentration measured by flame atomic-emission spectrometry are described by flow chart and equations. Adoption of a convention for reporting results is recommended. The Working Group on Selective Electrodes has taken into account recent revisions of IUPAC recommendations on nomenclature and selectivity coefficient determinations for ion-selective electrodes, and benefited from the experience of a member of the WG, who was also involved in the IUPAC discussions. Nomenclature for determined quantities follows previous IUPAC/IFCC joint recommendations.

Electrodes↗
PubMed1993

Preoperative electrical stimulation for cochlear implant selection. The use of ear canal electrodes versus transtympanic electrodes.

Preoperative electrostimulation tests were performed on 43 postlingually deaf and 20 prelingually deaf cochlear implant (CI) candidates. The stimulating electrode was placed at three different locations, i.e. the round window, the promontory and the ear canal and the results were compared. The evoked sensations were reported to be of auditory origin by most of the postlingually deaf CI candidates. Prelingually deaf subjects could not always distinguish clearly and reliably between "hearing" and "feeling". The percentage of stimulated ears of postlingually deaf subjects in whom hearing sensations were evoked was almost identical for the three locations of the stimulating electrode. However, in 5 out of the 7 ears without hearing sensations during ear canal stimulation (ECS), hearing sensations could be evoked during either promontory stimulation (PS) or round window stimulation (RWS). The mean threshold level for "hearing" at a stimulation frequency of 62 Hz was lowest during RWS, 7.7 dB higher during PS and 35.8 dB higher during ECS. The mean electrical dynamic range at 62 Hz was most favourable during RWS (23.9 dB), smaller during PS (15.6 dB) and smallest during ECS (10.0 dB). All differences were statistically significant. Placement of the ear canal electrode was easier, less frightening for the patient and required less time than insertion of the needle electrode for PS or RWS. Therefore we recommend the use of ECS to examine whether the CI candidate can be stimulated, and of RWS if more detailed information is required.

Adolescent↗
PubMed2003

Deep electrode insertion in cochlear implants: apical morphology, electrodes and speech perception results.

Morphological examination of the human temporal bone in the apical region supports the benefits of deep electrode insertion. Initiation of spikes on peripheral processes close to the basilar membrane would provide improved channel selectivity during electrical stimulation but recruiting of nerve fibres requires a higher current. A clinical study was performed on 10 users of the MED-EL COMBI 40 + implant to evaluate the effect of the insertion depth of the cochlear implant electrode on speech perception. All subjects were implanted with the standard COMBI 40 + electrode with an insertion depth of > 30 mm. Acute speech tests were carried out in which stimulation was restricted to the apical, middle and basal regions of the cochlea in turn, and using electrode arrangements in which contacts were either distributed over the whole length of the cochlea or concentrated at the basal end, thus mimicking an insertion depth of approximately 20 mm only. The results showed that stimulation of the apical region of the cochlea supports a significant degree of speech understanding, and that distributing the contacts over the whole length of the cochlea improves speech perception in quiet and in noise.

Adult↗
PubMed1987

[Methodologic aspects of measuring the potential differences in the gastrointestinal tract: effect of electrode placement and electrolyte concentration of the measuring electrode on the magnitude of the transepithelial potential difference].

The transepithelial electric potential difference (tPD) of the colonic mucosa was investigated in children in-vivo. The potential difference was measured by so-called "flowing"-electrodes. The current paper presents methodical considerations, for instance electrolyte concentration of the luminal electrode and position of the serosal electrode (reference-electrode), and their influence on the tPD-measurement.

Adolescent↗
PubMed1988

Studies on response characteristics of drug ion-selective electrodes (II)--sulpha-drug sensitive electrodes using quaternary phosphonium and arsonium compounds.

Ion-pair complexes of sulphonamide derivatives with quaternary phosphonium and quaternary arsonium have been synthesized and their electrode performances studied. It has been found that the electrode functions depend mainly on the site cation rather than on the anionic species and deteriorate in the order of cetyltrioctylammonium greater than cetyltriphenylphosphonium greater than cetyltriphenylarsonium. The electrode selectivity for different sulpha-drugs decreases in the order of sulphathiazole greater than sulphamethoxazole greater than sulphadimethoxine, sulphadoxine greater than sulphacetamide greater than sulphadiazine greater than sulphanilamide. Selectivity coefficients depend not only on the molecular connectivity index chi, but also on the electronic charge at the ionizing amide nitrogen atom sigma and pKa according to the following formula: logKij = a chi + b sigma - CpKa - d. The quaternary phosphonium type electrodes have been suggested for use in the potentiometric determinations of sulpha-drugs.

Electrodes↗
PubMed2006

Determination of surface potentials from the electrode potentials of a single-crystal electrode.

Determination of surface potentials Psi0 at the metal oxide/aqueous solution interface from measured electrode potentials of a metal oxide single-crystal electrode (SCrE) is described. The proposed method is based on the surface complexation model and evaluates the surface potential at the isoelectric point, i.e., at pHiep. This value is used for calculation of Psi0 values from the measured electrode potentials. Both 1-pK and 2-pK models produced the same result so that the procedure does not depend on the assumed mechanism of the surface charging. It is proposed to determine the pristine point of zero charge pHeln and the isoelectric point pHiep, and use these data to set the scale of surface potentials. The value of pHeln can be obtained at a sufficiently low ionic strength where pHpzc coincides with pHiep. The method is demonstrated on the example of the anatase single-crystal electrode. From the shifts of pHiep and pHpzc with respect to the pristine point of zero charge pHeln it was concluded that Cl- ions exhibit higher affinity for association with positively charged surface groups than ClO-4 ions. Also, preferential surface association of Na+ cations compared to both anions was detected. The slopes of the Psi0(pH) functions were found to be significantly lower in magnitude with respect to the Nernst equation, which is due to the high degree of counterion association at the surface caused by their relatively high concentration.

Journal Article↗
PubMed2004

Sol-gel-derived ceramic-carbon nanotube nanocomposite electrodes: tunable electrode dimension and potential electrochemical applications.

Nanocomposite electrodes made of sol-gel-derived ceramic-carbon nanotube are fabricated by doping mutliwalled carbon nanotubes (MWNTs) into a silicate gel matrix. The electrochemical behavior and potential electrochemical applications of the ceramic-carbon nanotube nanocomposite electrodes (CCNNEs) are also studied. The as-prepared CCNNEs exhibit a tunable dimension ranging from conventional electrode to nanoelectrode ensemble (NEE), depending on the amount of the MWNT dispersed in the silica sol and finally doped within the gel matrix. A high content of the MWNT (i.e., higher than 1.5 mg/mL in the sol) leads to the formation of the CCNNE characteristic of an electrode of conventional dimension, while a low content (typically lower than 0.10 mg/mL) essentially yields the CCNNE like a nanoelectrode ensemble. The NEE is demonstrated to possess good electrocatalytic activity toward the oxidation of ascorbic acid (AA), and the CCNNE of conventional dimension is found to possess remarkable electrocatalytic activity toward the oxidation of glutathione (both reduced and oxidized forms, GSH and GSSG). These properties of the CCNNEs essentially offer a new electrochemical approach for the detection of AA, GSH, and GSSG. The possible essence of the tailor-made dimensions of the CCNNEs is also presented and discussed.

Journal Article↗
PubMed2001

P-chip and P-chip bienzyme electrodes based on recombinant forms of horseradish peroxidase immobilized on gold electrodes.

Adsorption and bioelectrocatalytic activity of native horseradish peroxidase (HRP) and its recombinant forms on polycrystalline gold electrodes were studied. Recombinant forms of HRP were produced by a genetic engineering approach using an E. coli expression system. According to direct mass measurements with a quartz crystal microbalance, all the forms of HRP formed monolayer coverage of the enzyme on the gold surface. However, only gold electrodes modified with the recombinant HRP forms (non-glycosylated) exhibited high and stable current response to H2O2 due to its bioelectrocatalytic reduction based on direct electron transfer (ET) between gold and the active site of the enzyme. Introduction of a six-His tag either at the C-terminus or at the N-terminus of the enzyme molecule additionally increased the strength of the enzyme binding with the gold surface and the efficiency of direct ET. Immobilization of recombinant forms of HRP containing histidine functional groups on the surface of the gold electrode was used both for the development of a P-chip, a biosensor for hydrogen peroxide determination based on direct ET, and for the development of a bienzyme biosensor electrode for the determination of L-lysine based on co-immobilized recombinant forms of HRP and L-lysine-alpha-oxidase.

Adsorption↗
PubMedDate not supplied

Longitudinal variations of characteristic frequencies of skeletal muscle fibre potentials detected by a bipolar electrode or multi-electrode.

We aimed to reveal reasons for longitudinal variations of characteristic frequencies of electromyographic signals detected by surface longitudinal multi-electrodes. Since the terminal phases were reduced in bipolar recordings, we tested whether the frequency variations reflected the effects of the excitation origin and extinction as in monopolar recordings. A precise and fast convolution method to calculate the signals detected by a multi electrode was suggested. The contribution of different electrode poles was introduced in the impulse response. When a longitudinal multi-electrode with an even number of poles was positioned above the end-plate of asymmetrical fibres, the signal mainly reflected the processes of the excitation extinction This increased the signal mean and median frequencies Although the effects of origin and extinction of the excitation were significantly reduced in the spatially filtered signals, the frequency variations along the fibre reflected these intrinsic features of any skeletal muscle fibre of finite length.

Electromyography↗
PubMedDate not supplied

Calculations of two-dimensional electric field and potential distributions aroun electrodes in conducting media.

Tumor cells can be killed by heating to 42.5degreesC. It is convenient to localize heating by passing electric current at 500 kHz through tissue between a pair of electrodes. It is desirable to determine, for a given electrode-tissue configuration, what the resulting field and, therefore, current distribution will be. A computer program FFEARS was used to calculate electric field and potential distributions in two dimensions for three simple cases.

Computers↗
PubMed2005

Development of rotating liquid membrane disk electrode and rotating liquid membrane ring-liquid membrane disk electrode and evaluation of characteristics of ion transfer reactions at the rotating aqueous/organic solution interface.

A liquid membrane disk electrode, LMDE, and a liquid membrane ring-liquid membrane disk electrode, LMRE-LMDE, were developed by placing a gelled polyvinyl chloride thin membrane impregnated with 2-nitrophenyl octyl ether, NPOE-LM, on the surface of a glassy carbon, GC, disk or ring electrode. The voltammogram for the ion transfer at the interface between an aqueous solution, W, and NPOE-LM was recorded by setting the developed electrode in W and rotating at a rate, omega, between 0 and 4000 rpm. The sensitivity of the ion-transfer current at the WINPOE-LM interface, I, was enhanced to be more than 100 times better than that at the WINPOE (solution) interface when LMDE was rotated at omega higher than 200 rpm. The reversibility of the ion transfer reaction could be evaluated based on the dependence of I on omega of LMDE, and the reaction product at LMDE could be identified at LMRE when the rotating LMRE-LMDE system was adopted.

Journal Article↗
PubMed1989

Safety and ECT Stimulus Electrodes: I. Heat Liberation at the Electrode-Skin Interface.

Calculations reveal that the electroconvulsive therapy (ECT) stimulus cannot cause burn injury to brain tissue, but poor electrode-skin contact is a risk for skin burn. This article reviews factors that influence skin temperature, including electrical charge, skin impedance, topographic conformity between electrode and skin, electrode surface area, and thermal diffusivity of electrode material.

Journal Article↗
PubMed1994

Gold foil electrodes: a two-center study of electrode reliability.

Using the routine techniques employed at our two centers for recording pattern electroretinograms and a variety of methods, we investigated the reliability of the gold foil electrode over repeated uses. We found no significant difference between the pattern electroretinograms recorded with new electrodes and those that had had such extensive use in patients that they were believed unsuitable for further clinical use. We therefore continue to recommend the gold foil electrode for repeated use.

Electrodes↗
PubMedDate not supplied

Computer programs for calibrating control electrode voltages and for conditioning working electrodes for a neurochemical voltammetry system.

Two computer programs are described which are used to set voltages, calibrate the system, and cyclically condition electrodes electrically in an electrochemical system. This voltammetry system is normally used for measurement of monoamines in neurochemical studies. The system uses an Apple II, a potentiostat, and a DAS-5 interface between the two. The calibration program is used to establish the numerical values needed by the DAS-5 interface from the computer to yield desired potentiostat voltages, to calibrate the potentiostat, and to set output voltages of the system to be safe for the electrode and neural tissue before the potentiostat is turned on. Another program is used to condition electrodes as required in some cases to establish discriminably different oxidation potentials for different electroactive compounds (monoamines and ascorbate).

Animals↗
PubMed1989

The strap-electrode: a stimulating and recording electrode for small nerves.

A method is described for the construction of a strap-electrode that can be used for stimulation as well as recording of small nerves. The electrode can be applied to nerves of various diameters by adjusting the strap diameter with a teflon sleeve. Shunting is minimized by using dental rubber-dam placed under the nerve and enveloping the electrode and nerve with a silicon polymer. The arrangement is very resistant against straining forces. Stable nerve recordings and stimulus thresholds were obtained for several hours.

Electrodes↗
PubMed2004

Application of thin film mercury electrodes and solid amalgam electrodes in electrochemical analysis of the nucleic acids components: detection of the two-dimensional phase transients of adenosine.

The optical diffractive (DOE)-based sensor was used to the study of the optical roughness of different carbon/graphite electrodes modified by mercury film (MFEs) and solid amalgam-alloy electrodes (S-MeAEs). The electrode surfaces were visualised by an optical metallurgical microscope. The adsorption of adenosine at the MFEs and S-MeAEs has been investigated by capacitance measurement. Some kinetics aspects, such as the influence of the surface morphology, nature of the substrate and thickness of the mercury film and amalgam-alloy on the formation of two-dimensional (2D) physisorbed adenosine adlayer on the MFEs and S-MeAEs, were studied.

Adenosine↗
PubMed2006

How to assess the limits of ion-selective electrodes: method for the determination of the ultimate span, response range, and selectivity coefficients of neutral carrier-based cation selective electrodes.

The span and range of an ion-selective electrode (ISE) has been identified by IUPAC as a potential or activity difference between the upper and lower detection limits of the electrode. Once the span is known, the ultimately attainable detection limit of the ISE can be calculated using its theoretical response slope. In this paper, we propose an original method for the determination of the ultimate span and response range of ISEs. The simple measurement of span is recommended to aid the fast screening of novel ionophores and help to focus optimization processes to the most promising candidates. The measurement of span is combined with a generally applicable procedure for the determination of the three seminal parameters of ISEs: the response slope, the ultimate selectivity coefficients, and detection limit. In the proposed procedure, following the span measurement, two subsequent exponential dilution experiments are completed in which the responses of the electrode for the primary and the interfering ions are tested using a solution of a discriminated ion and deionized water as diluting electrolytes in consecution. The advantages and the practical usefulness of the proposed methods and procedures are demonstrated through the evaluation of the performance characteristics of novel and well-characterized ionophore-based potassium and calcium sensors.

Calcium↗