Electrodes pre-treatment

Oliveira, S.C.B., Oliveira-Brett, A.M. Boron doped diamond electrode pre-treatments effect on the electrochemical oxidation of dsDNA, DNA bases, nucleotides, homopolynucleotides and biomarker 8-oxoguanine. Electrochim. Acta 648, 60-66 (2010)... 

It should also be noted that the platinum surface is very sensitive to the presence of species in solution and to electrode pre-treatments (anodization, pre-reduction). Damjanovic etal reported a very strong dependence of the reaction pathway on the purity of the solution. They concluded that the oxygen reduction reaction occurred without hydrogen peroxide intermediate formation on a pre-reduced platinum electrode, and therefore that the production of hydrogen peroxide was effective only on sites affected by the presence of adsorbed impurities. 

Analyte BDD electrode, pre treatment Method Matrix (pmol L ),... 

Table 1 shows that the physicochemical properties of the support material were modified by the pre-treatment process. The particle sizes. Dp, which are summarized in the Table 1 were calculated from the X-ray diffraction patterns of prepared catalysts and a commercial catalyst(30 wt% Pt-Ru/C E-TEK) by using Scherrer s equation. To avoid the interference from other peaks, (220) peak was used. All the prepared catalysts show the particle sizes of the range from 2.0 to 2.8nm. It can be thought that these values are in the acceptable range for the proper electrode performance[7]. For the prepared catalysts, notable differences are inter-metal distances(X[nm]) compared to commercial one. Due to their larger surface areas of support materials, active metals are apart from each other more than 2 3 times distance than commercial catalyst. Pt-Ru/SRaw has the longest inter-metal distances. 

Electrodes of 2 x 2 cm2 geometric area were used in the experiments. In the case of platinum, a pretreatment by fast triangular potential scans (200-300 V/s between 0.05 V and 1.5 V RHE) followed by heating up to 900 K in a 3 x 10 6 mbar 02 atmosphere was carried out. Electrodes, pre-treated in this way, can be emersed with a thin liquid film, which can easily be evaporated in the vacuum chamber. The heat treatment drastically reduces contamination of the platinum electrode by carbon. The roughness factor is usually in the order of three. 

It is immediately evident from Figure 3b that pre-treatment of the electrode surface is essential for a direct electrochemical study of proteins. The reason for the success achieved using an electrode on which 4,4/-bipyridyl has been pre-adsorbed is shown in Figure 4. 

Takamura et al. have reported an electrochemical method for the determination of chlorpromazine with an anodically pretreated vitreous carbon electrode [164]. Optimal conditions for the pre-treatment were attained by the anodic oxidation of vitreous carbon electrodes in 0.5 mM phosphate buffer (pH 6.7) at 1.6 V V5. S.C.E. for 2 minutes. This was found to enhance the oxidation peak of the cyclic voltammogram for chlorpromazine by a factor of simeq 30. The peak current at +0.75 V was directly proportional to the concentration of chlorpromazine over the range of 0.2-40 pM and the detection limit was 0.1 pM. 

Takamura et al. have determined chlorpromazine by the use of differential pulse voltammetry incorporating rotating glassy-carbon disc electrodes [170]. The determination was carried out after pre-treatment of vitreous carbon by anodic oxidation for two minutes in 0.5 M phosphate buffer (pH 6.3) at 1.6 V vs. Ag/AgCl reference electrode. The determination was made with the use of 50 mV pulses at 2 seconds intervals, a rotation rate of 2500 rpm, and a scan rate of 5 mV/sec. 

After the mechanical pre-treatment, the electrode can be subjected to a chemical and/or electrochemical pre-treatement. Chemical treatment consists mainly of etching of a few layers of the metal, including possible contaminants. A well-known etching solution for gold is the so-called piranha solution. Other reported solutions are kali, which is a concentrated KOH solution to remove fats and oils and etch off a layer of platinum. 

Finally, electrochemical pre-treatment is performed to obtain a reproducible surface. This is done mainly by cycling the applied potential over the entire potential window limited by the hydrogen and oxygen evolution reaction. Such a treatment has two functions first, removal of adsorbed species and, second, altering the microstructure of the electrode, the latter being caused by the repetitive dissolution and deposition of a metal mono-layer in the scanning procedure. 

Compared to genosensors based on GEC, the novelty of this approach is in part attributed to the simplicity of its design, combining the hybridization and the immobilization of DNA in one analytical step. The optimum time for the one-step immobilization/hybridization procedure was found to be 60 min [66]. The proposed DNA biosensor design has proven to be successful in using a simple bulk modification step, hence, overcoming the complicated pre-treatment steps associated with other DNA biosensor designs. Additionally, the use of a one-step immobilization and hybridization procedure reduces the experimental time. Stability studies conducted demonstrate the capability of the same electrode to be used for a 12-week period [66]. 

The above FIA systems are based on monitoring the anodic decomposition of hydrogen peroxide at a platinum electrode set at 600-700 mV vs a Ag/AgCl electrode. However, at such high potentials other electroactive species, notably ascorbic acid, uric acid and hypoxanthine, will also be oxidised unless appropriate sample pre-treatment is taken. 

While the subject of this chapter may seem counter to the title of the book, metal dissolution is vital in numerous aspects of metal deposition, counter electrode processes, pre-treatment protocols and electropolishing. This chapter outlines the current state of understanding of metal dissolution processes and discusses in some detail an electropolishing process that has now been commercialised using a Type III ionic liquid. 

An example of the selectivity of diamond electrodes is the detection of dopamine in the presence of 1000-fold excess of ascorbic acid (typical of the composition of neural extracellular fluid). On an H-terminated diamond, potentials of the dopamine (DA) and ascorbic acid (AA) oxidation peaks on potentiodynamic curves are very close each other the peaks cannot be resolved (Fig. 32). To impart selectivity to diamond electrode, it was subjected to anodic pre-treatment (discussed in Section 6.2). The treated electrode exhibited a substantial shift in the positive direction for the peak potential for AA oxidation, thus making it possible to discriminate between the DA... 

Pre-treatment of the electrode substrate, which involves polishing, sonicating, and rinsing. The electrode can be pohshed using diamond pastes or alumina, followed by ultrasonic cleaning in water, acetone, or ethanol, and is then rinsed to obtain a clean surface. 

Electrodeposition onto solid electrodes or mercury cathodes is a long established pre-treatment capable of large concentration factors, and provided the cathode potential is carefully controlled it is also of considerable selectivity. When atomic absorption is used as the finish, selective deposition is not usually required. There have been recent reports of electrodeposition of trace metals from water samples directly onto special graphite furnace tubes [8] and this technique should prove to be just as applicable to the analysis of reagents, where the chemical conditions can be more carefully controlled. The utility of electrodeposition for electrothermal atomisation... 

Many authors pointed out that an oxidative pretreatment of the carbon surfaces is necessary to enhance the adsorptive accumulation of DNA [ 15,16,23]. The enhanced adsorptive accumulation is attributed to increased surface roughness and hydrophilicity following such treatment. This pre-treatment consists of the application of + 1.6 V/ + 1.8 V for a short period of time (1-3 min) in acidic media. The application of high potentials in acidic media (e.g. acetate buffer pH 4.7) seems to increase the hydrophilic properties of the electrode surface through the introduction of oxygenated functionalities accomplished with an oxidative cleaning [31]. 

The solid oxide fue( cell (SOFC) have been under development during several decades since it was discovered by Baur and Preis in 1937, In order to commercialise this high temperature (600 - 1000°C) fuel cell it is necessary to reduce the costs of fabrication and operation. Here ceria-based materials are of potential interest because doped ceria may help to decrease the internal electrical resistance of the SOFC by reducing the polarisation resistance in both the fuel and the air electrode. Further, the possibility of using less pre-treatment and lower water (steam) partial pressure in the natural gas feed due to lower susceptibility to coke formation on ceria containing fuel electrodes (anodes) may simplify the balance of plant of the fuel cell system, and fmally it is anticipated that ceria based anodes will be less sensitive to poising from fuel impurities such as sulphur. 

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