Modified voltammetric procedures

Microphotometer 768 Microwave oven 97 Migration current 592, 596 Mixed indicators 267, (T) 268 Mobile phase 13, 217, 218, 222 Mobilities, ionic (T) 520 Modified voltammetric procedures 611 Modulation 791... 

In another work, Parra and coworkers proposed a method based on chemically modified voltammetric electrodes for the identification of adulterations made in wine samples, by addition of a number of forbidden adulterants frequently used in the wine industry to improve the organoleptic characteristics of wines, like, for example, tartaric acid, tannic acid, sucrose, and acetaldehyde (Parra et ah, 2006b). The patterns identified via PCA allowed an efficient detection of the wine samples that had been artificially modified. In the same study, PLS regression was applied for a quantitative prediction of the substances added. Model performances were evaluated by means of a cross-validation procedure. 

Yu, H. Z., Luo, C. Y., Sankar, C. G., Sen, D. (2003). Voltammetric procedure for examining DNA-modified surfaces quantitation, cationic binding activity, and electron-transfer kinetics. Anal Chem 75, 3902-3907. 

Use of modified gold electrodes is not the only approach to achieve cytochrome c electrochemistry. Indeed, a number of studies have been reported on a variety of electrode surfaces. In 1977, Yeh and Kuwana illustrated (23) well-behaved voltammetric response of cytochrome c at a tin-doped indium oxide electrode the electrode reaction was found to be diffusion-controlled up to a scan rate of 500 mV sec Metal oxide electrodes were further studied (24, 25) independently in Hawkridge and Hill s groups. The electrochemical response of cytochrome c at tin-doped indium oxide and fluoride-doped tin oxide was very sensitive to the pretreatment procedures of the electrode surface. At thin-film ruthenium dioxide electrodes, variation of the faradaic current with pH correlating with the acid-base protonation of the electrode surface was observed. 

The electrode preparation, the enzyme immobilization procedure was described as follows. About two mg of acid treated MWCNTs was ultrasonicated in 1 pL of N, N dimethylformamide (DMF) until a black suspension was obtained. About 15 pi of this MWCNTs suspension was casted on the working area of SPE surface and dried in an oven at 80 °C for 30 min. About 10 pi of AChE solution (0.132 U) was dropped on the MWCNTs modified electrode surface and dried at room temperature under a current of air and used. Hydrodynamic voltammetric studies results shows that significant response was observed at MWCNT-SPE towards 2mM thiocholine, whereas the response was poor at the unmodified electrode (Fig. 2). The linear response of the MWCNT-SPE modified sensor was found to be between 5 pM - 430 pM (r2 = 0.999) with a sensitivity of 6.018 mA/M. In contrast, the response of AChE/SPE modified electrode was only 5 % and thus this result further reveals the contribution of MWCNTs in improving the sensitivity. 

As it was mentioned in Section 8.1, an experiment is included in order to illustrate the selection procedure. Each model was developed for specific experimental conditions. Sometimes, a description can be modified, extended, and corrected in order to cover other experimental conditions. Thus, a model initially developed with the purpose of describing a film formed under potentiostatic conditions can be adapted, via mathematical derivations, to potentiodynamic conditions. In the present experiment, the film considered was generated under potentiodynamic conditions by the use of voltammetric techniques. As a consequence, only the models developed for potentiodynamic conditions were considered [56-58]. 

The theoretical treatments for the different voltammetric methods (e.g., polarography, linear sweep voltammetry, and chronopotentiometry) and the various kinetic cases generally follow the procedures described previously. The appropriate partial differential equations (usually the diffusion equations modified to take account of the coupled reactions producing or consuming the species of interest) are solved with the requisite initial and boundary conditions. For example, consider the EfCi reaction scheme ... 

Procedures suitable for the incorporation of chemical or biochemical substances or ion-exchange sites onto an electrode surface have been developed in various laboratories. " Such modified surfaces can then be used to perform a variety of functions. They have, for instance, been employed to preconcentrate analytes prior to voltammetric analysis and hence impove sensitivity. For example, dimethylglyoxime has been used to preconcentrate nickel and EDTA to preconcentrate silver." If this preconcentration can be achieved in an environment conducive to rapid electron transfer, then sensitivity will be enhanched even further. Alternatively electrocatalysts have been attached to electrode surfaces, and by speeding up what would otherwise be a sluggish electron transfer process, increased sensitivity has been attained. However, this approach yields no added selectivity and a large background must usually be tolerated. 

We have developed nanoparticle label-based electrochemical immunoassay of OP exposure biomarkers, OP-ChE (44). The principle and procedure of this method is shown in Figure 5. Here, zircomia (Zr02) NPs, electrochemically deposited on the electrode surface, which functioned as the capture antibodies in the sandwich immunoassay. The zirconia- NP- modified electrode is then exposed to the sample solution and the ChE-OP in the sample is captured by the Zr02 nanoparticles. The QD-tagged, anti-AChE conjugate is introduced to form the sandwich-like complex on the sensor surface. The captured QDs are then dissolved by a drop of acid to release cadmium ions. This is followed by square wave voltammetric (SWV) [abbreviation already introduced but unexplained] detection of the released cadmium ions at an in situ plated mercury/bismuth film electrode. 

We have reviewed the family of dealloyed Pt-based nanoparticle electrocatalysts for the electroreduction of oxygen at PEMFC cathodes, which were synthesized by selective dissolution of less-noble atoms from Pt alloy nanoparticle precursors. The dealloyed PtCua catalyst showed a promising improvement factor of 4-6 times on the Pt-mass ORR activity compared to a state-of-the-art Pt catalyst. The highly active dealloyed Pt catalysts can be implemented inside a realistic MEA of PEMFCs, where an in situ voltammetric dealloying procedure was used to constructed catalytically active nanoparticles. The core-shell structural character of the dealloyed nanoparticles was cmifirmed by advanced STEM and elemental line profile analysis. The lattice-contracted transition-metal-rich core resulted in a compressive lattice strain in the Pt-rich shell, which, in turn, favorably modified the chemisorption energies and resulted in improved ORR kinetics. 

Responses obtained at mediator modified electrodes can be complicated if some of the analyte diffuses through to the bare electrode surface. Conventional voltammetric stripping procedures introduce another step into conventional voltammetry, namely, preconcentration of the analyte on or into the electrode surface. Similarly, with preconcentrating modified electrodes (Figure 5.7, iii) the analytical performance depends on ... 

This technique involves the accumulation of the analyte at the electrode surface from diluted solutions, via favorable interaction with the electrode modifier, and its subsequent electrochemical detection. This enables to lower the detection limit and to increase the sensor sensitivity owing to effective concentration of the analyte. This is especially useful to enable quantitative determinations when they are not achievable by direct electrochemical measurement performed in the native medium. Compared to stripping voltammetric techniques, this one is based on chemical accumulation rather than on an electrolytic one, thus being basically independent on potentials. The typical experimental procedure involves successive steps (Fig. 16.19a) that must be optimized to get the best performance. The analyte is first accumulated at open-circuit under constant stirring (to enhance mass transport rates). The electrode is then removed from the preconcentration medium, rinsed with pure water, and immersed into the analysis cell containing an appropriate electrolyte, where the electrochemical quantification is carried out (analyte desorption is usually required, especially when the electrode modifier is an... 

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