Combination pH electrodes of special design: Temperature characteristics and performance in poorly-buffered waters

The performance of 5 combination pH electrodes with special design features has been assessed. Two electrodes were intended for measurements in low-conductivity waters, two were designed to have a rapid and stable temperature response and one electrode shared both features. The performance in low-conductivity waters was either poor or merely acceptable; better results have been obtained with separate glass and reference electrodes. The electrodes designed to have good temperature response were better in this respect than conventional combination electrodes, but the same or better performance can be obtained by use of separate glass and remote-junction reference electrodes. It should be noted that the temperature coefficients of these combination electrodes were the same as for almost all pH electrodes: any improvement was only in the rate and stability of response.     

The development of fluoride-sensitive membrane electrodes : Part I. Membranes containing thorium,lanthanum or calcium fluoride

Fluoride-sensitivc membrane electrodes of the Pungor type are described. In these electrodes, a fluoride precipitate is incorporated in a silicone rubber membrane; fluorides of thorium, lanthanum and other rare earths, and calcium have been examined. The method of preparing the precipitate is important; an excess of metal is vital for correct functioning of the final electrode. The most reliable results were obtained with calcium fluoride electrodes, though their sensitivity was less than that of the best lanthanum fluoride electrodes. With these electrodes, linear responses are obtained in the l0^-2–10^-4M fluoride range.     

Determination of transference numbers with ion-selective electrodes. Transference numbers and activity coefficients of concentrated aqueous solutions of potassium fluoride

An experimental method has been developed to determine transference numbers by simultaneous emf measurements of cells with liquid junction using cation- and anion-responsive electrodes. As a corrolary of the transference measurements, activity coefficient data have been obtained. The method is illustrated by reporting transference and activity coefficient data of aueous KF solutions at 25°C from about 0.05 to 3 m obtained with potassium selective glass electrodes and fluoride selective solid state electrodes. The activity coefficients are in good agreement with literature data, which reflects the excellent Nernstian response of these electrodes in solutions up to 3m. The transference numbers show the typical behavior expected for a non-associated 1:1 electrolyte.     

Disposable Gold Electrodes with Reproducible Area Using Recordable CDs and Toner Masks

The fabrication and characterization of very cheap disposable gold disk electrodes with reproducible area is reported. The innovation of the proposed procedure is the use of toner masks to define reproducible areas on uniform gold surfaces obtained from recordable compact disks (CD‐R). Toner masks are drawn in a laser printer and heat transferred to gold surfaces, defining exactly the electrodes area. The electrochemical behavior of these disposable electrodes was investigated by cyclic voltammetry in Fe(CN)₆^4? solutions. The relative standard deviation for signals obtained from 10 different gold electrodes was below 1 %. The size of the disk electrodes can be easily controlled, as attested by voltammetric responses recorded by using electrodes with radii varying from 0.5 to 3.0 mm. The advantages of using this kind of electrode for analytical measurements of substances that strongly adsorb on the electrode surface such as cysteine are also addressed.     

High transmittance blue-phase liquid crystal displays with slit-shaped electrode

A blue-phase liquid crystal displays (BP-LCDs) with slit-shaped pixel and common electrodes structure is proposed to increase the transmittance. It generates not only in plane field between the pixel electrodes, but also fringe field above the common electrodes. As a result, the high transmittance is obtained. The aperture ratio is also improved because of the capacitor between the pixel and common electrodes.     

Silver based mercury film electrode: Part II. The influence of aging of electrode on the electrode processes of various metal ions

The cyclic voltammetric behaviour of 8 metal ions at solid silver amalgam electrodes prepared by aging of a thin silver based mercury film electrode (SBMFE) and by deposition of silver and mercury on platinum were investigated. It was established that such electrodes behave in relation to some metals (Pb, Bi, Sn) similarly as silver electrodes i.e. the cyclic curves obtained with these electrodes at concentration 10^?3M range show a prepeak-postpeak system corresponding to deposition and dissolution of the monolayer of deposit. On the other hand under the same conditions no prepeaks were observed for cadmium, zinc and thallium. In all cases investigated the heights of anodic stripping peaks were lower on curves obtained with aged SBMFE than on those obtained with fresh SBMFE having a mercury layer 1 μm thick.     

Roughness factor evaluation of thermal arc sprayed skeleton nickel electrodes

Skeleton nickel electrodes obtained by thermal arc spraying technique were characterized by different methods including scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and electrochemical impedance spectroscopy. The skeleton electrodes reveal a highly porous structure with a surface roughness of about 270, determined from double layer capacitances obtained from impedance spectra.     

Ruthenium and ruthenium dioxide-modified graphite-ethylene/propylene/diene and graphite-Teflon composite electrodes as amperometric flow detectors. Application to the determination of methionine

The flow injection amperometric performance of solid composite graphite electrodes with ethylene/propylene/diene (EPD) or Teflon as binding agents, and with Ru or RuO2 particles as electrocatalytic modifiers has been compared. Both, Ru and RuO2 modified electrodes exhibited electrocatalytic properties on the methionine oxidation process in alkaline media. The electrodes composition and the hydrodynamic and chemical variables were optimized. Graphite-EPD (GEPD) electrodes showed a better analytical performance than graphite-Teflon (GPTFE) electrodes. Furthermore, a better sensitivity, repeatability and reproducibility was observed for RuO2-GEPD electrodes when compared with Ru-GEPD electrodes. At an applied potential of +0.50 V, a detection limit for methionine of 4.8x10(-5) mol L(-1), similar to those reported in the literature for other RuO2-modified electrodes, was obtained. The analytical applicability of RuO2-GEPD electrodes was demonstrated by determining methionine in a complex pharmaceutical formulation.     

Analytical quality solid-state composite reference electrode manufactured by injection moulding

An injection moulding method was used for fabricating solid-state reference electrodes (Ag/AgCl type) based on a polymer/inorganic salt composite. In this method, a silver/silver chloride wire was placed inside a mould into which the mixture of polymer and inorganic salt was injected. The obtained solid-state composite reference electrodes were extensively tested to study the influence of different parameters such as solution composition, the concentrations and mobility of ions and pH on the potential stability of the electrodes. These experiments revealed that the composite reference electrodes are insensitive to the matrix effect, have excellent potential readings stability and considerably reduced leakage of inorganic salt. The composite reference electrodes were compared favourably to high-quality commercial reference electrodes. It was concluded that the composite reference electrodes obtained by injection moulding are of analytical quality allowing for continuous, prolonged and intensive usage.     

Single‐Wall Carbon Nanotube Paste Electrodes: a Comparison with Carbon Paste,Platinum and Glassy Carbon Electrodes via Cyclic Voltammetric Data

A new carbon electrode material, obtained by mixing single wall carbon nanotubes (SWNTs) with a mineral oil binder is studied. Carbon nanotube pastes show the special properties of carbon nanotubes combined with the various advantages of composite electrodes such as a very low capacitance (background current) and the possibility of an easy preparation, modification and renewal. A better knowledge of the characteristics of electrode reactions at carbon nanotube paste (CNTP) electrodes was obtained studying the electron transfer rates of various redox couples under different pretreatment conditions. A critical comparison with carbon paste (CP), platinum (Pt) and glassy carbon (GC) electrodes was also carried out. Capacitance and resistance values were also calculated for all electrodes investigated. Both untreated and treated CNTP electrodes showed a low resistance while the capacitance was markedly reduced with CNTP electrodes previously treated with concentrated nitric acid. An electrochemical pretreatment on CNTP electrodes was developed which showed an excellent result towards two‐electron quinonic structure species. After this treatment the heterogeneous standard rate constants for p‐methylaminophenol sulfate (MAP) and dopamine resulted to be significantly higher (2.1×10^?2 cm/s and 2.0×10^?2 cm/s, respectively) than those obtained with the other electrodes studied. Reproducibility, stability and storage characteristics of CNTP electrodes were also reported.     

Mercury(II) ion-selective electrodes based on heterocyclic systems

Mercury ion-selective electrodes (ISEs) were prepared with a polymeric membrane based on heterocyclic systems: 2-methylsulfanyl-4-(4-nitro-phenyl)-l-p-tolyl-1H-imidazole (I) and 2,4-diphenyl-l-p-tolyl-1H-imidazole (II) as the ionophores. Several ISEs were conditioned and tested for the selection of common ions. The electrodes based on these ionophores showed a good potentiometric response for Hg2+ ions over a wide concentration range of 5.0 x 10(5-) - 1.0 x 10(-1)M with near-Nernstian slopes. Stable potentiometric signals were obtained within a short time period of 20 s. The detection limits, the working pH range of the electrodes were 1.0 x 10(-5) M and 1.6-4.4 respectively. The electrodes showed better selectivity for Hg2+ ions over many of the alkali, alkaline-earth and heavy metal ions. Also sharp end points were obtained when these sensors were used as indicator electrodes for the potentiometric titration of Hg2+ ions with iodide ions.     

A contactless conductivity detector for capillary electrophoresis: effects of the detection cell geometry on the detector performance

The effect of the gap between the electrodes and of their width on the behavior of a capacitively wired contactless conductivity detector was studied. The results obtained have indicated that the detector response can be qualitatively described by a model based on the concept of the effective electrode width which is a complex parameter determined by the gap between the electrodes, the frequency of the input signal and the conductivity of the test solution. The detector sensitivity and the effect on the separation efficiency depend on the difference between the effective and geometric electrode widths. Higher detection sensitivities have been attained for detectors with wide electrodes operating at lower frequencies, however, better separation efficiencies have been achieved using detectors with narrow electrodes and higher operational frequencies. The noise increases with decreasing gap between the electrodes and increasing frequency, especially with detectors employing narrow electrodes.     

Self-assembled monolayer of an iron(III) porphyrin disulphide derivative on gold

A novel iron(III) porphyrin disulphide derivative have been successfully immobilised on gold surfaces by self-assembly. The redox response of the modified electrodes was compared with the obtained for a similar iron porphyrin in solution, confirming the immobilisation of the metalloporphyrin. The gravimetric data obtained by electrochemical quartz crystal microbalance (EQCM) during adsorption allowed an estimation of the electrode coverage, providing further evidence for the formation of the porphyrin SAM. The modified electrodes were also measured by conventional and imaging ellipsometry. The electrocatalytic activity of the two modified electrodes was tested for the reduction of the molecular oxygen.     

Antibody response of polymer membrane electrodes incorporating antigenic ionophores

An investigation of the antibody sensing properties of potentiometric polymer membrane electrodes incorporating antigens shows that at least two categories of such electrodes are possible. When the immobilized antigen has no ionophoric character of its own, antibody response can be obtained only upon conjugation of the antigen to an ionophore. The second category, corresponding to a new class of electrodes, yields potentiometric antibody response in the absence of a conjugated ionphore. These effects are illustrated with electrodes for antidigoxin, anti-DNP, and antiquinidine, respectively.     

Electric capacity of electrochemical capacitors with composite electrodes based on the aluminum–active carbon system

The electric capacity of electrochemical capacitors with composite electrodes obtained by laser microstructuring was studied. The obtained electrodes allowed control of the contribution of the resistance of the electrode material and electrolyte to the total equivalent series resistance of the electrochemical capacitor. This allowed us to determine their effect on the resulting characteristics of the capacitors. The dependences of the specific electric capacity on the parameters of the composite structure of electrodes were studied, and the optimum parameters were found.     

Extending the dynamic range of electrochemical sensors using multiple modified electrodes

Multiple electrodes, combined with a chemometric strategy to calibrate the measurement response, have been used for the determination of an analyte across a broader dynamic range than is possible with a single electrode. The model system used for the detection of copper comprised electrodes modified with a self-assembled monolayer. The electrodes were modified with the copper-complexing species (3-mercaptopropionic acid, thioctic acid, and the peptides cysteine and Gly-Gly-His) and copper was determined over concentrations ranging from nanomolar to millimolar using voltammetric analysis. We have demonstrated that by combining the calibration functions from the four electrodes a better estimate (i.e. with smaller variance) of the concentration of the analyte is obtained. Measurement uncertainty is expressed for independently prepared electrodes, which allows the possibility of commercial production and factory calibration. The principles of using multiple electrodes modified with recognition elements with different affinities for the target analyte to extend the dynamic range of sensors is a general one that could be applied to other analytes.     

Nanocomposite Carbon‐PDMS Material for Chip‐Based Electrochemical Detection

This paper presents an alternative approach to create low‐cost and patternable carbon electrodes suitable for microfluidic devices. The fabrication and the electrochemical performances of electrodes made of Polydimethylsiloxane doped with commercially available carbon black (C‐PDMS) are described. Conductivity and electrochemical measurements performed on various carbon to PDMS ratios showed that electrodes with suitable electrochemical properties were obtained with a ratio of 25 %.     

Enhanced electrolytic generation of oxygen gas at binary nickel oxide–cobalt oxide nanoparticle-modified electrodes

This study addresses the enhancement of the oxygen evolution reaction (OER) on glassy carbon, Au, and Pt electrodes modified with binary catalysts composed of nickel oxide nanoparticles (nano-NiO_x) and cobalt oxide nanoparticles (nano-CoO_x). Binary NiO_x/CoO_x-modified electrodes (with NiO_x initially deposited) show a high catalytic activity and a marked stability which far exceeds that obtained at the individual oxide-modified electrodes. This enhancement is demonstrated by a marked negative shift (more than ca. 600 mV) in the onset potential of the OER compared to that obtained at the unmodified electrodes. The modified electrodes show a significantly higher long-term stability, over a period of 5 h of continuous electrolysis, without any significant loss of activity towards the OER in alkaline medium. The influence of the solution pH, the loading level, and sequence of deposition of each oxide on the electrocatalytic activity of the modified electrodes is addressed with an aim to maximize the catalytic activity of the modified electrodes towards the OER. SEM imaging is used to disclose the size and morphology of the fabricated nano-NiO_x and nano-CoO_x binary catalysts at the electrode surface.     

Effect of lipophylic salts on ise detection limit: application to calixarene-based highly efficient potassium-selective electrodes

A new interpretative model for interpolation of potentiometric data from liquid membrane ion selective electrodes has been formulated; the model allows one to achieve information about partitioning equilibria establishing at the membrane-analysed solution interface of hydrophilic cations present in the membrane as counterions of exchanger lipophylic anions. The fundamental importance of such equilibria is related to their contribution to the detection limit of the electrodes. The soundness of the proposed model was positively verified by employing it in the characterization of new K(+)-selective electrodes based on a calixarenic ionophore. Although the validity of interpolation based on our model does not significantly differ from that obtained with the simpler model providing the inclusion of a constant parameter in the logarithmic argument of Nicolski-Eisenman's equation, the information obtained resulted to be analytically suitable for optimising the membrane composition and, as a consequence, the performance of the electrodes.     

Low-voltage blue-phase liquid crystal display with single-penetration electrodes

A blue-phase liquid crystal display (BPLCD) with single–penetration (S-P) electrodes is proposed to reduce the operating voltage. X-shape inclined-electric field is induced by the S-P electrodes with 2 ~ 3 μm height, which can lower the operating voltage by ~45%, and improve the transmittance compared with BPLCD with conventional in-plane electrodes. Moreover, the wide viewing angle and very small image distortion index can be obtained in this structure with a half-wave biaxial film. The proposed structure shows simple etching control and easy one-drop filling process of blue-phase liquid crystal compared with dual-convex-penetration electrodes.