Glassy Carbon Disk Research Articles

Voltammetric information from arrays of individually controlled electrodes: their potential for industrial process measurements

The construction, control and operation of an array of electrodes used to obtain voltammetric information in a wall- jet geometry is described for flow-stream analysis. The array consisted of a ring-disk arrangement, where the ring is composed of eight radially-spaced 1-mm glassy carbon disks. The ring array surrounds a 3-mm glassy carbon disk in the centre, impinged by a perpendicular 0.3-mm inlet diameter jet. Independent electrode control and monitoring were achieved through a computer-based multi-electrode potentiostat, designed to operate with single reference and counter electrodes. The flow cell was characterised through variation of the inlet jet separation from the planar ring-disk array and control of inlet volume flow-rate. Optimum conditions were chosen with stability as the primary criterion. A jet separation of 7.25 mm and a flow-rate of 1.5 cm3 min−1 ensured wall jet behaviour at the central electrode and planar behaviour at the ring array. These conditions were maintained throug hout subsequent experiments which demonstrated the feasibility of utilising the array of electrodes for voltammetric monitoring of simple mixtures of metal ions, with or without prior separation. The potential of this approach for industrial process monitoring is discussed with a view of maximising information recovery and enhancing data reliability.

Effects of dopant and solvent on the properties of polypyrrole: Investigations with cyclic voltammetry and electrochemically in situ conductivity

A new method for electrochemically in situ conductivity measurements based on a reusable glassy carbon disc—carbon fibre array double electrode is described. Using this technique and cyclic voltammetry, we have investigated the effects of the doping anion and solvent on the electrochemical properties of polypyrrole film. The electroactivity and potential dependent conductivity of polypyrrole film are strongly affected by solvent and the doping anion's solubility in the solvent, and also by the history of electrochemical treatments in different electrolyte solutions. It is very interesting that NO − 3 doped polypyrrole can completely keep its conducting state (doped state) at a reasonably negative potential ( eg −0.8 V vs. sce) in acetonitrile solutions.

Ion-specificities of sulfite and phosphate ion enzyme sensors.

A sulfite ion enzyme sensor was prepared by cross-linking sulfite oxidase with bovine serum albumin using glutaraldehyde on the flat end of a platinum disk electrode silanized with 3-aminopropyltrimethoxysilane. Similarly, a phosphate ion enzyme sensor was made by coimmobilizing purine nucleoside phosphorylase and xanthine oxidase on the flat end of a glassy carbon disk electrode. A sulfite sensor was based on the amperometric detection (0.6 V vs. Ag/AgCl) of hydrogen peroxide produced by an enzymatic reaction; the current response was linearly related to the sulfite concentration over the range of 5×10-75×10-4 M. This sensor was highly selective for sulfite, except for a small response to nitrite, thiocyanate and thiosulfate. A phosphate sensor gave a response when inosine (5 mM) was added to a 0.1 M borate buffer solution (pH 7.5) containing phosphate. This sensor was based on the amperometric detection (0.5 V vs. Ag/AgCl) of uric acid produced by two successive enzymatic reactions. The current response was linearly related to the phosphate concentration over a range of 5×10-72×10-5 M at 37±0.2°C. This sensor was essentially specific for phosphate.

Highly sensitive high-performance liquid chromatography detection of catecholamine with interdigitated array microelectrodes

Interdigitated array (IDA) microelectrodes in which both the band width and gap are 2 μm were fabricated and applied to the electrochemical detectors used in flow injection analysis (FIA) and high-performance liquid chromatography (HPLC). The steady-state limiting current measured by FIA consists of the one-third power flow dependent current and the flow independent current. This flow independent current is caused by redox cycling. When an IDA electrode is used, the current density is about ten times greater than with an ordinary glassy carbon disk electrode. The high current density and low background noise allowed the detection of 100 pM (2 fmol) of dopamine by HPLC measurement. It was found that the peak current and sample concentration had a linear relationship over a wide range (from 100 pM to 10 μM).

Immobilization of glucose oxidase on a carbon surface derivatized by electrochemical reduction of diazonium salts

Glassy carbon disk electrodes grafted with superficial 4-phenylacetic groups through electrochemical reduction of the corresponding diazonium salt were used for glucose oxidase covalent immobilization. Protein attachment was confirmed by means of X-ray photoelectron spectroscopy and the activity of the enzyme modified electrode was ascertained by performing enzymatic electrocatalysis. The present method does not cause any roughening of the electrode surface and concomitant increase of a background current thus allowing precise measurements using transient electrochemical techniques such as cyclic voltammetry. As diazonium salts (which upon reaction provide the anchoring site) can be synthesized with various substituents, it is conceivable that customized attachment of enzymes and biochemical reagents could be designed.

Comparison of colloidal gold electrode fabrication methods: the preparation of a horseradish peroxidase enzyme electrode

In order to prepare biosensing electrodes which respond to hydrogen peroxide, horseradish peroxidase has been adsorbed to colloidal gold sols and electrodes prepared by deposition of these enzyme-gold sols onto glassy carbon using three methods: evaporation, electrodeposition and electrolyte deposition. In the latter method the enzyme-gold sol is applied to the surface of a glassy carbon disk electrode followed by an equal volume of 2 mM CaCl 2. The electrolyte causes the sol to precipitate on the electrode surface, producing an immobilized enzyme electrode. Satisfactory electrodes which gave an electro-chemical response to hydrogen peroxide in the presence of the electron transfer mediator ferrocenecarboxylic acid were produced by all three methods. Evaporation of horseradish peroxidase-gold sols produced electrodes with the best reproducibility and the widest linear amperometric response range. These electrodes can also easily be stored in a dry state. Although not as good as evaporation, electrodeposition also produced satisfactory electrodes. Electrodeposition provides the added advantage that it lends itself to the preparation of multi-enzyme/multi-analyte electrodes by the adsorption of different enzymes to separate gold sols, followed by sequential electrodeposition only discrete areas of multichannel electrode.

Voltammetry of vanadyl sulfate hydrates in the absence of a deliberately added liquid phase

Charge-transfer processes in solid samples of VOSO 4· χ H 2O (χ = 3 or 5) were studied using an ultramicroelectrode as the indicator and a 3 mm diameter glassy carbon disk as a quasi-reference electrode. The use of the solid matrix facilitated the electron transfer process in the V(IV)/V(V) couple. In contrast to solution-phase systems, reversible cyclic voltammograms were obtained, and the electrode surface did not undergo rapid poisoning. Voltammetry indicated that the electrode process was diffusion controlled for χ = 5, but a surface-confined pathway predominated when χ = 3. From constant potential chronoamperometry with solid samples of VOSO 4·5 H 2O, the apparent diffusion coefficient of charge propagation was 3 × 10 −7 cm 2 s −1, and the population of trapping sites was 1 mol dm −3. The redox conductivity of the solids was related to their crystallographic structures. The possibility of the existence of a liquid microphase in these solids is discussed.

A Microcomputer Controlled System for Potentiometric Stripping Analysis

ABSTRACT The construction of an inexpensive microcomputer controlled potentiometric stripping analysis system is described. The system allows both cathodic or anodic preconcentration of metal ions, and the deposited material may be stripped either chemically or galvanically. The interface circuits and the units comprising the system are described and the main features of the control software are also presented. The system has been designed to support operation with a rotating glassy carbon disk as a working electrode and it can be used for the determination of several heavy metals at ppb concentration range. The system is flexible, expandable and suitable for general studies on the technique, allowing the development of new operating modes by simple modifications on the hardware and software.

The determination of N,N-dimethyl-4-aminoazobenzene and its reduction products by anodic voltammetry at a glassy carbon electrode

The oxidation of N,N-dimethl-4-aminoazobenzene at a rotating and stationary glassy carbon disk electrode in a medium of 40% (v/v) acetic acid was studied in the framework of a systematic study of methods for determing the efficiency of the destruction of the genotoxic derivatives of this substance; conditions were found for the determination using direct current and differential pulse voltammetry. Analogous conditions were used to determine aniline, N,N-dimethylaniline and N,N-dimethyl-p-phenylendiamine as model substances representing possible products of the reductive splitting of genotoxic azocompounds. The determination limit of the method is less than 1 . 10-5 mol l-1 and its selectivity is completely satisfactory for controlling the efficiency of the destruction.

Electrode processes of plutonium ions in phosphate media

The electrolytic behaviour of plutonium ions in a mixture of phosphate and nitrate solutions was studied by flow-coulometry with column electrodes of glassy carbon(GC)-fibers and voltammetry with a GC disc electrode, and compared with that in phosphate-free media. The redox processes, PuO 2 2+ /PuO 2 + and Pu4+/Pu3+, were demonstrated to be reversible even in the phosphate media and their half wave potentials shifted more negatively due to the formation of PuO2(H2PO4)+ and Pu(HPO4)2. The rate of the irreversible reduction of PuO 2 + to Pu3+ increased in the presence of phosphoric acid and the quantitative reduction was attained with the column electrode even at +0.35 V vs. saturated KCl-Ag/AgCl. The reduction process of PuO 2 + was elucidated considering an intermediate Pu(IV)-species, PuO2+, which decomposed into Pu4+ by a post-chemical reaction. Analytical advantages of the use of phosphate media are discussed.

Amperometric detection at a carbon-fibre array ring/glassy-carbon disk electrode in a wall-jet cell

A wall-jet cell incorporating a carbon fibre array ring/glassy-carbon disk electrode has been constructed, and characterized by the cyclic voltammetry and flow-injection techniques. The ring (composed of several microdisks) and glassy-carbon disk electrode, can be used separately for different purposes, e.g., detection in solution without a supporting electrolyte, collection/shielding detection with dual-electrode and voltammetric/amperometric detection with series dual-electrode. The electrode shows better collection and shielding effects than the usual ring—disk electrode in quiescent solution and the series dual-electrode in a thin-layer flow-through cell. The detection limit at the ring electrode is comparable with that at a conventional-size electrode, and has been used in the mobile phase without a supporting electrolyte, proving to be a promising detector for normal-phase liquid chromatography.

Wear property and structure of nitrogen implanted glassy carbon

A study has been made of the correlation between wear resistance and crystalline structure of ion implanted glassy carbon. Nitrogen ions were implanted in glassy carbon with fluences ranging from 5 × 1014 to 5 × 1016 ions/cm2 at an energy of 150 keV. The target temperature during ion implantation was maintained constantly at −70, 25, and 200 °C. Wear tests were carried out with the system of glassy carbon and polishing silk disk on which water including diamond slurry was poured, using a conventional polishing machine. The surface layer structure was investigated by means of laser Raman spectroscopy. Nitrogen implantation causes the wear resistance to improve, and the reduction of wear rate is dependent on the ion fluence and the target temperature during ion implantation. As the fluence increases and the target temperature is lower than room temperature, the wear rate decreases drastically. Raman spectra show that the structure of ion implanted layers becomes what is called amorphous-like as the fluence increases and the target temperature is lowered. In conclusion, the wear resistance of glassy carbon is improved owing to the change in structure followed by nitrogen implantation at a relatively high fluence and low target temperature.

Copper determination in urine by flow injection analysis with electrochemical detection at platinum disk microelectrodes of various radii

The incorporation of platinum disk microelectrodes of various radii (2.5-50 microns) in a well-jet flow cell offers reduced limits of detection for the determination of copper in urine by flow injection analysis compared with standard methods based on a conventional sized glassy carbon disk macroelectrode (radius 1.5 mm), in a thin-layer cell. The radius of the platinum disk microelectrode was found to be critical with respect to both the limit of detection and flow rate dependence. An optimal radius value of 28 microns was found with detection limits increasing with both larger and smaller electrode radii. In contrast, as theoretically expected, a diminished flow rate dependence was observed the smaller the radii of the platinum disk microelectrodes. Sample cleanup and preparation is conveniently achieved by the use of Sep-Pak cartridges and formation of a copper dithiocarbamate complex. The metal complex is easily oxidized at platinum disk microelectrodes in acetonitrile, which was the solvent used in the flow injection method of analysis.

Electrocatalytic reduction of CO 2 on modified electrodes with alkylcyclam-metal complex Langmuir-Blodgett films

Two amphiphilic nickel(II) complexes with the long-alkyl-substituted 1,4,8,11-tetraazacyclodecane cyclam were synthesized, i.e. nickel tetrakis( N-hexadecyl)cyclam and nickel N-hexadecyclam. Monolayers of these complexes were immobilized onto glassy carbon (GC) disc electrodes using the Langmuir-Blodgett (LB) technique, and the electrocatalytic activities of these electrodes were examined by cyclic voltammetry in aqueous solutions saturated with nitrogen or carbon dioxide. The redox waves of the LB films of the nickel alkylcyclams observed in nitrogen were shifted in the anodic direction relative to those of nickel cyclams in a homogeneous solution. In carbon dioxide, the increase in the reduction current on these electrodes compared with that in nitrogen was observed at more negative potentials than - 1.3 V vs. a saturated calomel electrode in a solution with a constant pH value. This result shows that the LB films of these complexes possess sufficient electrocatalytic activity to reduce carbon dioxide despite their small amounts when compared with the amounts of homogeneous catalyst.

Improvement of wear properties of glassy carbon surface layer modified by ion implantations

A study has been made of the improvement in wear resistance of glassy carbon by ion implantation. The substrates used were glassy carbon plates and the implanted elements were Li, N, O, F, K and Zn. The ion implantations were performed with doses of 5–10 × 10 16 ions/cm 2 at energies of 25–150 keV and at approximately room temperature. Wear tests were carried out with the system of glassy carbon and polishing silk disc, using a conventional polishing machine. The surface composition and structure of the implanted glassy carbon were investigated by means of secondary ion mass spectroscopy and laser Raman spectroscopy. Oxygen implantation results in enhancement of the wear rate in the initial stages of wear testing, while on the contrary ion implantations of elements other than oxygen causes the wear rate to decrease. The durability of wear resistance depends on the implanted elements and the energies used as these make the surface structure and composition change. These results suggest that one of the important causes for improving the wear resistance is the amorphization of glassy carbon due to ion implantation. In conclusion, ion implantation can lead to the improvement in wear resistance of GC by selecting the proper ions and energies.

Electrochemical behaviour of tellurium and silver telluride at rotating glassy carbon electrode

Electrodeposition of tellurium and silver is performed at rotating glassy carbon disc electrodes. First the mechanism of deposition of tellurium is investigated, and a well defined wave may be observed close to − 0.4 V/ sce. On the plateau of this wave a small peak may be noticed at − 0.7 V/ sce, and is due to reduction of Te(0) into Te(—II), but a chemical reaction occurs simultaneously between Te(—II) and Te(IV), reaching the electrode by convection and diffusion, to lead again to Te(0), and consequently the thickness of the deposit increases. Conversely, with a non-rotating electrode, the Te(IV) species reach electrode only by diffusion and in lesser amounts than in the above case; so the peak at − 0.7 V/ sce is large since the tellurium deposit dissolves by reduction int Te(—II). The electrodeposition of silver telluride Ag 2 Te is investigated with several concentration ratio of Ag(I) and Te(IV). One may observe the progressive changes in the shape and magnitude of the oxidation peaks of Ag and Te. For a Ag(I)Te(IV) ratio close to 0.8 it has been observed that quasi pure Ag 2 Te is obtained. The elementary composition of the deposit was confirmed by X-ray analysis.

Application of a polymer solid electrolyte for the vapor-phase electrocatalysis of dioxygen reduction by some cobalt porphyrins

An electrochemical cell suitable for the study of dioxygen reduction electrocatalysis by films of cobalt metalloporphyrins on electrodes in the absence of liquid electrolytes is described. The glassy carbon disk of a (stationary) ring-disk electrode is coated with either an electropolymerized film of cobalt tetra( o-aminophenyl)porphyrin or an adsorbed multimolecular layer of a dicobalt cofacial porphyrin, Co 2 FTF4. Then the disk, the ring (serving as an auxiliary electrode), and a peripheral silver wire (serving as a pseudo-reference electrode) are coated with a thin film of an ionically conducting polymer: poly(ethyleneoxide) containing a 16:1 ether oxygen/Li + concentration of lithium triflate. Bathing this solid state cell in moist, acidic or neutral bathing gases containing dioxygen produces electrocatalytic currents for dioxygen reduction. The fraction of the reduction leading to H 2O 2 was determined with a twin electrode sandwich modification of the above cell in which a Au film electrode atop a Nucleopore membrane is contacted to the top surface of the PEO 16·Li(CF 3SO 3) film. No H 2O 2 was produced in the case of the Co 2FTF4 catalyst in a neutral bathing gas; this electrocatalysis was also quite stable.

The rhodium complex of a tris(bipyridine) ligand?Its electrochemical behaviour and function as mediator for the regeneration of NADH from NAD+

The tris-bipyridine ligand3a and its stoichiometric Rh3+ complex have been prepared. Cyclovoltammograms of the complex at pH 7.4 using a glassy carbon disk electrode reveal a strong reduction peak at −620 mV and two weak reduction peaks at more negative voltage. The reduction potential of the new complex is shifted by 300 mV to more positive values as compared to [Rh(bipy)3]3+. There is no reversible reoxidation peak of the Rh(I) complex formed due to the decomplexation of one of the three bipyridine units in the course of the transition Rh(III)→Rh(I). The Rh(III) complex of3a was also studied with respect to its function as a possible redox mediator for the electrochemical regeneration of NADH from NAD+. The preparative electrolysis of the Rh3+ complex of3a in the presence of NAD+ yields a selective formation of NADH, whereas NAD dimers were not detected. On the other hand, a significant acceleration of this reaction compared to [Rh(bipy)3]3+ was not observed.

Structurally heterogeneous electrode films of acrylamide/vinylpyridine gels: Dynamics of ferricyanide mediated electrooxidation of ascorbic acid and their dependence on the electrode film structure and composition

A novel electrode coating material was synthesized by bulk, radical copolymerization of acrylamide, bisacrylamide and vinylpyridine in aqueous solutions. Highly swelled, porous gels were obtained. Sections of the copolymeric gels, a fraction of a micrometer in thickness, were cut with a microtome and deposited on glassy carbon disk electrodes. Electrochemical measurements involving chronocoulometry, cyclic voltammetry and rotating disk methods were used to characterize these electrode coatings in terms of their physical structure and ion-exchange properties. After ion-exchange incorporation of ferricyanide ions, mediated electrooxidation of ascorbic acid was investigated in an acidic electrolyte. The kinetics of the processes involved in this electrocatalysis were analyzed according to the Savéant-Andrieux theory. All electrocatalytic systems behaved according to the R + S case. Detailed analysis of the electrocatalysis data allowed us to relate the key parameters determining the system's performance to the structure and the composition of the gel films. Self-segregation of vinylpyridine groups during polymerization of a gel in acidic solution was revealed and related to its superior ion-exchange properties and the high catalytic activity of the bound ferricyanide ions.

ChemInform Abstract: Oxidation of Hydrogen at Platinum‐Polypyrrole Electrodes.

AbstractPt particles are incorporated into the polymer matrix by two different methods: 1) electrochemical deposition of Pt on a polypyrrole coated glassy carbon disc, and 2) precipitation of Pt particles during the polymerization of pyrrole on a glassy carbon disc.