Electrode Cleaning Research Articles

Avaliação da limpeza de CDtrodo construídos a partir de CD de ouro gravável/fita adesiva de galvanoplastia

Os eletrodos de ouro são largamente utilizados em estudos eletroquímicos e eletroana-líticos, devido à sua elevada pureza, ampla faixa de potencial de trabalho, bem como a possibi-lidade de controle e modificação da superfície eletródica. Neste trabalho são descritos procedi-mentos para construção e limpeza de eletrodos a partir de CDs de ouro graváveis, denominados CDtrodos. Inicialmente, os CDs foram submetidos à ação de HNO3 concentrado para retirada da camada polimérica protetora e exposição da camada metálica, posteriormente, para a cons-trução dos CDtrodos, delimitou-se a área eletródica com fita de galvanoplastia. Diversos méto-dos para a limpeza da superfície do ouro foram empregados, após ataque do HNO3, tais como, aplicação de potencial fixo em solução de NaCl, ciclagens sucessivas em H2SO4 e aplicação de ultra-som, sendo que os melhores resultados foram obtidos por tratamento com H2SO4. A litera-tura tem registrado vários trabalhos empregando CDtrodo no entanto são focados na aplicação e pouco se descreve sobre a limpeza do eletrodo; nenhum trabalho foi registrado empregando a fita de galvanoplastia para delimitar a área do eletrodo. A utilização desse tipo alternativo de eletrodo é de suma importância, uma vez que o mesmo apresenta desempenho eletroquímico comparável aos eletrodos comerciais,além de grande versatilidade e baixo custo.

Electrodeposition polymers as immobilization matrices in amperometric biosensors: improved polymer synthesis and biosensor fabrication

Electrodeposition polymers can be precipitated on electrode surfaces upon electrochemical-induced modulations of the pH value in the diffusion zone in front of the electrode. The formed polymer films can be used as immobilization matrices in amperometric biosensors. In order to rationally control the thus obtained biosensor properties, it is indispensable to develop strategies for the reproducible synthesis of electrodeposition polymers as well as methods for the non-manual and reproducible sensor fabrication. Based on instrumental developments such as a specifically designed parallel synthesizer with improved stirring and temperature control, an automatic pipetting robot for the preparation of the monomer mixtures and controlled removal of polymerization inhibitors, the reproducible synthesis of libraries of electrodeposition polymers was achieved. Moreover, the polymerization process could be monitored using in-line thermocouples, and it could be shown that the chosen strategies led to reproducible polymerization reactions. By adaptation of an electrochemical robotic system integrating a Au microtiter plate and automatic electrode cleaning by means of a polishing wheel reproducible biosensor fabrication using glucose oxidase as a model enzyme could be demonstrated. These results open the route for the rational development of biosensors and control of the sensor properties by choosing specifically designed electrodeposition polymers.

Avaliação da limpeza de CDtrodo construídos a partir de CD de ouro gravável/fita adesiva de galvanoplastia

Os eletrodos de ouro são largamente utilizados em estudos eletroquímicos e eletroanalíticos, devido à sua elevada pureza, ampla faixa de potencial de trabalho, bem como a possibilidade de controle e modificação da superfície eletródica. Neste trabalho são descritos procedimentos para construção e limpeza de eletrodos a partir de CDs de ouro graváveis, denominados CDtrodos. Inicialmente, os CDs foram submetidos à ação de HNO3 concentrado para retirada da camada polimérica protetora e exposição da camada metálica, posteriormente, para a construção dos CDtrodos, delimitou-se a área eletródica com fita de galvanoplastia. Diversos métodos para a limpeza da superfície do ouro foram empregados, após ataque do HNO3, tais como, aplicação de potencial fixo em solução de NaCl, ciclagens sucessivas em H2SO4 e aplicação de ultra-som, sendo que os melhores resultados foram obtidos por tratamento com H2SO4. A literatura tem registrado vários trabalhos empregando CDtrodo no entanto são focados na aplicação e pouco se descreve sobre a limpeza do eletrodo; nenhum trabalho foi registrado empregando a fita de galvanoplastia para delimitar a área do eletrodo. A utilização desse tipo alternativo de eletrodo é de suma importância, uma vez que o mesmo apresenta desempenho eletroquímico comparável aos eletrodos comerciais, além de grande versatilidade e baixo custo.

Microfluidic Device Architecture for Electrochemical Patterning and Detection of Multiple DNA Sequences

Electrochemical biosensors pose an attractive solution for point-of-care diagnostics because they require minimal instrumentation and they are scalable and readily integrated with microelectronics. The integration of electrochemical biosensors with microscale devices has, however, proven to be challenging due to significant incompatibilities among biomolecular stability, operation conditions of electrochemical sensors, and microfabrication techniques. Toward a solution to this problem, we have demonstrated here an electrochemical array architecture that supports the following processes in situ, within a self-enclosed microfluidic device: (a) electrode cleaning and preparation, (b) electrochemical addressing, patterning, and immobilization of sensing biomolecules at selected sensor pixels, (c) sequence-specific electrochemical detection from multiple pixels, and (d) regeneration of the sensing pixels. The architecture we have developed is general, and it should be applicable to a wide range of biosensing schemes that utilize gold-thiol self-assembled monolayer chemistry. As a proof-of-principle, we demonstrate the detection and differentiation of polymerase chain reaction (PCR) amplicons diagnostic of human (H1N1) and avian (H5N1) influenza.

A New Method of Studying Ion Transfer at Liquid|Liquid Phase Boundaries Using a Carbon Nanotube Paste Electrode with a Redox Active Binder

We report a new method for the study of voltammetric processes at liquid vertical bar liquid interfaces, namely that of using a redox active organic oil as the binder in a carbon nanotube (CNT) paste electrode. Specifically we report voltarnmetry at the,liqui vertical bar liquid interface studied at a N,N-didodecyl-N',N'-diethylphenylenediamine (DDPD, as binder) CNT paste electrode immersed in aqueous electrolytes containing potassium salts of various anions (AsF6-, PF6_, ClO4-, SCN-, I-, NO3, Br-, Cl-, F-, and SO42-). Ion transfer across the liquid vertical bar liquid interface occurs to maintain electroneutrality upon oxidation of the DDPD, the direction of which, and the subsequent effect upon the observed voltammetric response, is found to be driven by the relative hydrophobicity of the ions involved. This method of studying liquid vertical bar liquid interfaces offers significant advantages, not least with regard to ease of electrode fabrication and cleaning and the formation of multiple three-phase boundaries (at which any voltarnmetry must occur) due to the structure of the DDPD-CNT paste vertical bar aqueous electrolyte interface.

Polymer-coated bismuth film electrodes for the determination of trace metals by sequential-injection analysis/anodic stripping voltammetry

In this work, the utility of polymer-coated bismuth film electrodes (BiFEs) was assessed for the simultaneous on-line determination of Cd(II), Pb(II) and Zn(II) by square-wave anodic stripping voltammetry (SWASV) in the sequential-injection analysis (SIA) mode. The polymeric Nafion coating was initially plated on a glassy carbon electrode forming part of the flow-through electrochemical cell. The subsequent steps of the bismuth layer generation, analyte preconcentration, voltammetric measurement and electrode cleaning were conducted on-line. For a sample volume of 1.2 mL, the limits of detection (at S/N = 3) were 2 μg L −1 for Cd(II) and Pb(II) and 6 μg L −1 for Zn(II), the coefficients of variation at 20 μg L −1 were 5.1% for Cd(II), 5.9% for Pb(II) and 6.2% for Zn(II) and the measurement frequency was between 10 and 20 h −1 (depending on the sample volume aspirated). It is demonstrated that the polymer-coated BiFEs, combined with SIA, can provide an environmentally friendly, sensitive and robust tool to perform rapid and cost-efficient on-line monitoring of trace metals by ASV, even in the presence of surface-active compounds.

Optimizing the Quadruple‐potential Waveform for the Determination of Gentamicin Sulfate by High Performance Liquid Chromatography with Pulsed Electrochemical Detection

AbstractIn this paper, a quadruple‐potential waveform was investigated and optimized for the determination of gentamicin by reversed phase ion‐pair chromatography. Instead of a relatively high positive potential, a negative potential was adopted as a potential for the cleaning of gold working electrode. By this way, the formation of gold oxide resulting from the application of high positive potential during the analyte detection and electrode cleaning was greatly reduced, and therefore, the dissolution and recession of gold working electrode was also reduced. The good condition of gold working electrode achieved by this quadruple‐potential waveform can help us to obtain a good reproducibility. In order to acquire signal‐to‐noise ratio as high as possible, several waveform parameters affecting the detection of gentamicin were carefully selected. The analytical method has been applied to the determination of two real gentamicin samples, and good results with low relative standard deviation not more than 4% were obtained.

Simple and sensitive electrode design for microchip electrophoresis/electrochemistry.

A simple and sensitive electrode design for microchip capillary electrophoresis/electrochemistry (CE-EC) is presented. The system employs metal microwires as the working electrodes for electrochemical detection. Two general approaches for integration of electrodes in microchip CE-EC are commonly used, end-channel and microfabrication. The end-channel approach allows electrode cleaning and the use of chemically modified electrodes; however, the designs generally lack portability and the ability to incorporate multiple electrodes. Microfabrication allows the incorporation of multiple electrodes on-chip and is easily made portable; however, it requires the use of expensive metallization and clean room facilities, and integration of more than one electrode material is challenging. The reported approach aligns a solid metal microwire through the separation channel allowing integration of multiple electrodes and the use of different electrode materials without sacrificing the portability. A detection limit of 100 nM for dopamine was achieved without the use of a decoupler as a result of a higher collection efficiency with the new design.

Performance of glass RPC with industrial silk-screen-printed electrodes

In this paper we describe the performance of several Glass RPCs, where the water-based graphite coating is replaced by a synthetic coating applied using the screen printing technique. As expected, the performance of the detectors is good and reproducible due to the accurate control of the coating resistivity value. The resistance of the coating to the action of mechanical and chemical agents permits an easy electrode cleaning and mounting with respect to the RPC coated with the graphite varnish. This coating, together with the use of float glass as electrode material, allows an industrial production, where the detector characteristics can be tailored as a function of the experiment requirements.

Self-contained microelectrochemical immunoassay for small volumes using mouse IgG as a model system.

A self-contained, microelectrochemical immunoassay on the smallest volumes reported to date (1 microL for the antigen, 1 microL for the secondary antibody-enzyme conjugate, and 200 nL for the electrochemically detected species) has been developed using mouse IgG as a model system in a sandwich-type enzyme-linked immunosorbant assay, which takes less than 30 min to both complete the assembly of immunoassay components onto the antibody-modified surface and detect enzymatically generated species (excluding time for electrochemical cleaning of electrodes). These studies demonstrate the advantage of the close proximity of electrodes to modified surfaces and their application in the analysis of small volumes. Using a 50 microm diameter x 8 microm deep cavity with individually addressable electrodes on a microfabricated chip, the primary antibody was selectively and covalently attached at a gold, recessed microdisk (RMD) at the bottom of the microcavity to the free end of SAMs of either 11-mercaptoundecanoic acid or 11-mercapto-1-undecanol using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride. Nonspecific adsorption to the surrounding material, polyimide, of the microcavity device was eliminated. Electrochemical desorption was used to confine the immunoassay activity at the RMD. Enzymatic conversion of the substrate p-aminophenyl phosphate top-aminophenol is detectable in less than 30 s using cyclic voltammetry at a gold, tubular nanoband electrode, which is on the wall of the microcavity and immediately adjacent to the modified RMD. A third electrode, also within the region of the microcavity, served as the pseudoreference/auxiliary electrode. Calibration curves obtained for 1-microL solutions of 5-100 ng/mL of IgG and for 200 nL-solutions of 5 microM to 4 mM of PAPR gave detection limits of 4.4 nM (6.4 ng/mL) or 880 fmol (129 pg) for PAPR and 56 fM (9 pg/mL) or 56 zmol (9 fg) for IgG. It is expected that the device may be suitable for analysis with volumes down to tens of picoliters.

Sono-Cathodic Stripping Voltammetry of Lead at a Polished Boron-Doped Diamond Electrode: Application to the Determination of Lead in River Sediment

Ultrasonically-assisted cathodic stripping voltammetry at a boron-doped diamond electrode, has been developed for the detection of lead. At concentrations above 3 µM, linear sweep voltammetry was used to give the analytical signal from a cathodic strip of electrodeposited PbO2; linearity was observed from 3–100 µM, with 3 µM being the lower detection limit. Square-wave voltammetry was then employed for the cathodic stripping step, to lower the detection limits of the technique while retaining linearity to the order of 10–8 M. The procedure involves ultrasonic electrode cleaning, cathodic preconditioning and sono-anodic deposition of PbO2. This novel analytical tool is mercury-free, oxygen insensitive and highly specific towards lead, yet still offers scope for further elemental diversity, particularly for the detection of copper and iron. The square-wave sono-cathodic stripping voltammetry technique was combined with an ultrasonically assisted acid digestion protocol to successfully determine the lead content of a contaminated sample of river sediment, offering significant time saving over the currently used analytical procedure.

An amperometric method for measuring cyanide in CIP/CIL circuits

A silver rotating disc electrode has been used to measure the ionic cyanide (CN − (aq)) concentration in gold leaching circuits amperometrically. When the electrode is held at 0.1 V vs SHE the current flow is proportional to the cyanide concentration. In laboratory solutions the correlation coefficient ranged from 0.9999 at 30 °C to 0.9995 at 50 °C. The method is free from interference from the anions expected at gold plants, except sulphide, which, if present, can be removed by precipitation with lead(II). Cyanide bound up in stable metal complexes decreases the available CN −, and is not measured by the method. Other than by complexation, the metals ions studied did not interfere with the method. CN − (aq) converted to HCN (aq) at low pHs is also not measured except on addition of a pH buffer. The results are consistent with those from a silver nitrate titration, that also does not measure HCN (aq) or strongly complexed cyanide. Laboratory and field trials have shown that the method will work in leaching slurries without filtration, but regular electrode cleaning is required to ensure accurate results.

Sonoelectrochemically modified electrodes: ultrasound assisted electrode cleaning, conditioning, and product trapping in 1-octanol/water emulsion systems

Electrode processes for three types of water soluble redox systems in the presence of power ultrasound have been studied in a non-conventional environment: the 1-octanol/water microemulsion. The capability of ultrasound both to emulsify instantly a liquid/liquid system in the absence of stabilizing agents and to generate a high flux of material towards the electrode surface is shown to provide new tools for the control of electrochemical redox processes. First, the electrochemical reduction of Ru(NH 3) 3+ 6 has been studied. This is known to be a fast and reversible process at a glassy carbon electrode in aqueous 0.1 M KCl even in the presence of ultrasound. The addition of 1-octanol does not significantly affect this redox process up to a very high 1-octanol content in the emulsion system, although a thin film or adsorbed layer of 1-octanol is believed to be present at the electrode surface. Surprisingly, the limiting current and voltammetric characteristics of the reduction process remain nearly unaffected, until, at a critical ratio of ca. 50 vol% 1-octanol, the voltammetric response suddenly disappears, attributed to loss of conductivity in the bulk liquid. Second, and in contrast, the reduction and deposition of Pb 2+ from aqueous 0.1 M HClO 4 at a glassy carbon electrode is strongly affected even by small quantities of 1-octanol, again consistent with a thin layer of 1-octanol being permanently present at the electrode/emulsion interface. With increasing quantities of added 1-octanol the reduction process is gradually shifted several hundred mV to more negative potentials whereas the anodic lead stripping response is first shifted to more positive potentials and finally disappears. Third, the reduction of cobalticinium, CoCp + 2 (Cp= η 5−C 5H 5), in aqueous 0.1 M KOH under silent conditions results in the formation of nearly insoluble, neutral cobaltocene which precipitates at the glassy carbon electrode surface. In the presence of 1-octanol the neutral product dissolves in the organic liquid and allows voltammetric experiments to be conducted without loss of electrode activity due to blocking. The efficiency and the mechanism of this product ‘trapping’ process in the presence of 1-octanol is discussed.

Determination of copper(II) by anodic stripping voltammetry using a flow-through system

Copper(II) has been determined using anodic stripping voltammetry in a flow-through system. The working electrodes consisted of thin mercury films plated on a glassy carbon macrolectrode or microelectrode. Two flow-through cells, based on the wall-jet configuration and the thin-layer configuration, respectively, accommodated the working electrodes. Depending on the type of analysis, the flow system could operate on the flow injection mode or continuous flow mode during the preconcentration period. The sequence of operations (mercury plating, metal preconcentration, stripping and electrode cleaning) were remotely controlled. The procedures developed were applied to the quantification of CuII in different matrices (tap water, acidified sea-water and pharmaceutical tablets).

Four potential step differential amperometry in a single pulse sequence mode

AbstractA new type of four potential step differential amperometry in a single pulse sequence mode is proposed on the basis of four potential step differential normal voltammetry. The charging current tends to be eliminated, and the background current is set at zero after the differentiation and addition of the sampling currents on these four potential steps. The signal‐to‐noise ratio is enhanced by utilizing a series of pulses. In addition, since the potential returns to its initial point, it is advantageous for electrode cleaning and the study of solid electrode and adsorption systems. This provides an alternative approach for electrical current‐type electrochemical sensors, electrochemical detection in liquid chromatography, and electrode kinetics studies.

Impedance spectroscopy of lithium electrodes: Part 3. The importance of Li electrode surface preparation

The influence of surface preparation on the impedance spectroscopy of Li electrodes in propylene carbonate solutions was investigated. Three methods were compared: (a) electrode preparation in a glove-box atmosphere including several atmospheric gases (e.g. O 2, CO 2); (b) electrode cleaning by anodic stripping; (c) surface preparation by shearing in solution. The surface films initially formed on Li electrodes prepared in the gas phase were analysed by surface-sensitive Fourier transform IR spectroscopy (ex situ, external reflectance mode). The data obtained from the impedance measurements and the related calculations and modelling of the Li/solution interphase formed in the various experiments seem to indicate that the first two methods lead to the formation of a highly porous interphase. Hence, the third method is preferred for electrode surface preparation since the interphase thus formed is more compact and ordered, and therefore the data obtained should be more reproducible.

A Fully Programmable Electronic Coulometer for Charge and Electrolysis Duration.

ABSTRACT A fully programmable, current quantized, electronic coulometer totalizing 6-decades of charge (99,999.9 coulombs) and 6-decades of duration, (99 hours 59 minutes 59 seconds) for electrolysis. On the front panel: two 6-digit 7-segment-LED displays with relevant 12 BCD thumbwheels for monitoring and program setting of charge and duration respectively; charge and time resets and loading-command buttons; current polarity indication; “program-fulfilled”-cutout relay with buzzer. Zero-current detector excludes wrong totalizing due to process interruptions, e.g. electrode cleaning. This coulometer outputs charge and time BCD signals for slave indicators and data processing. It is specially meant for organic electrochemical synthesis. Electrolysis current range: 0.005A to 1.00A of either polarity.

Scanning tunneling microscopy of laser-activated carbon electrodes used in studies of electrochemical charge-transfer reactions

Carbon electrodes form the basis of a variety of electroanalytical sensors, in part due to their low cost, wide potential range, and suitability for modification. A major research effort is underway in many laboratories to understand better the properties of carbon electrodes regarding electrocatalytic activity and other factors such as background current and electron transfer activity. One method of improving the performance of these electrode materials involves the application of pulses from a Nd:YAG or N2 laser, either during or prior to electrochemical use. Both electrochemical and spectroscopic probes indicate dramatic changes to the surface of the electrodes after the pulses. Raman spectroscopy of the electrode surface indicates damage to the carbon lattice, with an increase in intensity of the Raman band at 1360 cm−1. This band is active in crystallites of finite size, and indicates increased exposure of graphitic edge plane. Also, there is a dramatic increase (≥106×) in heterogeneous charge-transfer rates measured with redox benchmark probes [Fe(CN)6−3/−4, dopamine]. Mechanisms of electrode activation by the laser pulses can involve roughening of the electrode surface, or ablation or cleaning of the electrode. Scanning tunneling microscope (STM) images of graphite and glassy carbon surfaces before and after delivery of laser pulses of various energies show a roughening of the surface from the laser treatment, with the appearance of new features of submicron size. The graphite electrodes show a highly disrupted surface, with jagged features and high roughness factors, determined from the STM images. None of the types of features observed in the laser-activated regions of graphite electrodes have been previously observed in our laboratory, in the course of dozens of experiments involving the imaging of different samples and grades of fresh or mechanically damaged graphite electrodes.

The INCO-voltammetric cell: A new approach to flotation modelling

A new electrochemical cell was developed so that the impact of conditions during liberation could be related to mineral hydrophobicity. Mineral electrodes were polished in situ in the test electrolyte and allowed to achieve their rest potentials after aeration of the electrolyte. The procedure was designed to represent a grinding-flotation system and the hydrophobicity of chalcopyrite, pentlandite and pyrrhotite electrodes was found to be dependent on the following factors: (1) rate of increase in anodic potential following cleaning of the electrode; (2) presence of iron which causes galvanic coupling effects; and (3) pH variations during electrode cleaning; as well as other relevant variables (e.g. xanthate dosage). The cell produced more reliable predictions of mineral hydrophobicity than the simple potential scanning procedures which involved the arbitary choice of initial and final polarization potential. The observations made using the new cell favourably compared with flotation data. Mineral selectivity was a function of polarization of the particle surfaces and the rate of increase in the anodic potential of the pulp.

Computerised flow potentiometric stripping analysis

Computerised flow potentiometric stripping analysis simplifies automated electroanalytical determination of several trace elements. It facilitates changing of samples and cleaning of electrodes. It also makes deoxygenation of the samples unnecessary and permits the use of a fresh mercury film surface for each analysis.