Electrochemical pretreatment

Brewis et al. used TOF-SIMS to determine the surface composition of hydrocarbon polymers after electrochemical pretreatment with nitric acid alone or in the presence of silver ions [58J. AgNO was generated by electrolysis of a 0.1 M solution of silver nitrate in 3.25 M nitric acid in the anode compartment of a... 

J. Nicole, D. Tsiplakides, S. Wodiunig, and C. Comninellis, Activation of catalyst for gas-phase combustion by electrochemical pretreatment, J. Electrochem. Soc. 144(12), L312-L314 (1997). 

For instance, in our laboratory, we have recently successfully coupled ex situ STM experiments with electrochemical treatment of Pt single crystals, and we have been able to assign certain changes in surface morphology to electrochemical pretreatment [Strmcnik et al., 2008]. 

Wash effluents from nitration installation can cause problems due to the high nitrophenol concentrations, their high toxicity to sewage bacteric and their general resistance to biodegradation. Electrochemical pretreatment tests in the laboratory showed a reduction in toxicity, and improvement of the color smell, etc. The electrochemical pretreatment is also attractive because of the absence of solid waste coproducts and its ease of operational control, [135]. 

Owing to these characteristics, PG has been extensively used for the adsorption of DNA and its derivatives. DNA was successfully adsorbed on PG by dry-adsorption at 100 °C [67]. The electrodes were stored in TriS buffer at 4 °C without loss of DNA, showing that DNA was firmly adsorbed on PG. It was demonstrated that the adsorbed ODN was also able to be hybridized with its complementary strand, suggesting that although DNA bases are compromised in the adsorption, they are still available for hybridization [67]. A composite film of DNA and the polyanionic perfluorosulfonated ionomer Nation was cast on PG by the layer-by-layer procedure performed by dry-adsorption [68]. In another approach, the PG surface was electrochemically pretreated at - 1.7 V for 60 s. DNA was then wet-adsorbed at the pretreated electrode surface from solutions containing 0.2 M NaCl, 10 mM Tris- HCl, pH 7.4, for 1 min followed by rinsing the electrode with distilled water [69,70]. 

Dai HP, Shin KK (1988) Voltammetric behavior of ahzarin S adsorbed on electrochemically pretreated glassy carbon electrodes. Electrochim Acta 43 2709-2715. 

Solid electrode performance can be affected by the electrode s previous history. A freshly polished electrode surface is virtually free of functional groups. To what extent its electrochemical behaviour changes in use depends very much on the electrode material and electrochemical pretreatment procedures [98]. 

Several types of carbon are in common use as electrodes. The most used of these is glassy carbon (GC) [100] it is the most reproducible but very difficult to machine as it is hard and brittle. One thus tends to be confined to the dimensions and shapes which come from the manufacturer. Each manufacturer has his own fabrication method (or more than one). A common problem is that small holes can appear in the middle of the piece of GC if this occurs, there is no option but to machine more away. Additionally, the GC is not always homogeneous. In the authors opinion, the best glassy carbon is Tokai. While it is not always possible to use this because of geometrical considerations, better reproducibility will be obtained with it, especially after electrochemical pretreatment [101]. 

Preparations of carbon fibers are similar to those of GC, with two important exceptions caused by the small fiber diameter. Fibers are mounted quite differently from GC, particularly for in vivo applications that require a small overall electrode diameter. In addition, fibers can experience much higher current densities during electrochemical pretreatment, which can qualitatively alter ECP effects. 

Figure 10.15 Voltammetry at a cylindrical carbon fiber electrode (1) before and (2) after electrochemical pretreatment (A) 0.1 mM dopamine and (B) 1.0 mM ascorbic acid, pH 7 solutions, scan rate = 0.1 V/s. [Adapted from Ref. 6.]...

J. Wang, X. Cai, C. Jonsson and M. Balakrishnan, Adsorptive stripping potentiometry of DNA at electrochemically pretreated carbon paste electrodes, Electroanalysis, 8 (1996) 20-24. 

Acetylcholineesterase and choline oxidase Prepared by mounting a carbon fiber (200 pm diam) in a glass capillary with silver paste and epoxy resin, electrochemically pretreating the electrode from 0 to 1.2 V for 15 min, and dipping the electrode in 11% PVA-Styryl pyridinium solution containing AChE and ChO. The calibration graph was rectilinear from 0.2 to 1 mM of ACh. The response time was 0.8 min. [76]... 

Electrode surface activation can be improved simply by electrochemical pretreatment. Determination of nitroaromatic compounds in water and soil spiked samples have been reported at electrochemically activated carbon-fiber microelectrodes. No interference was found from compounds such as hydrazine, phenolic compounds, carbamates, triazines or surfactants. The detection limit obtained can be approximately 0.03 iigml-1 for all the nitroaromatic compounds (Agui et al. 2005). Chen and coworkers reported an effective field-deployable tool for detecting nitroaromatic compounds with an electrochemically pre-anodized screen-printed carbon electrode (SPE) (Chen et al. 2006). 

Platinum, gold and carbon are the most frequently employed materials for solid electrodes. Platinum has a high background current, but it also exhibits the highest degree of reproducibility of the obtained voltammet-ric curves. Carbon must not be porous and for this reason the pores must be filled, e.g., with paraffin. The so-called Glassy carbon [9] with a very low porosity is recommended. The electrode surface must in all cases be respected, this makes a mechanical or an electrochemical pretreatment necessary before each recording of a voltammetric curve. 

In an earlier report, which Woodard et al. [493] do not cite, Vasquez et al. [650] also studied the effect of electrochemical pretreatment of a carbon electrode on its adsorption behavior. In contrast to Woodard et al. [493], these authors endorsed the donor-acceptor complex proposal ... 

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