Electrochemical methods microelectrodes

A. Brunet, C. Privat, O. Stepien, M. David-Dufilho, J. Devynck, and M.A. Devynck, Advantages and limits of the electrochemical method using Nafion and Ni-porphyrin-coated microelectrode to monitor NO release from cultured vascular cells. Analusis 28, 469 (2000). 

Part—III exclusively treats Electrochemical Methods invariably and extensively used in the analysis of pharmaceutical substances in the Official Compendia. Two important methods, namely potentiometric methods (Chapter 16) deal with various types of reference electrodes and indicator electrodes, automatic titrator besides typical examples of nitrazepam, allopurinol and clonidine hydrochloride. Amperometric methods (Chapter 17) comprise of titrations involving dropping-mercury electrode, rotating—platinum electrode and twin-polarized microelectrodes (i.e., dead-stop-end-point method). 

Electroreduction of Cd(II)-nitrilotriace-tic acid and Cd(II)-aspartic acid systems was studied on DME using SWV [73]. The CE mechanism in which the chemical reaction precedes a reversible electron transfer was established. Also, the rate constants of dissociation of the complexes were determined. Esteban and coworkers also studied the cadmium complexes with nitrilotriacetic acid [74, 75] and fulvic acid [76]. The complexation reaction of cadmium by glycine was investigated by different electrochemical methods using HMDE and mercury microelectrode [77, 78]. 

The small area of a microelectrode, with its proportionately low capacitance, allows its use at very short time scales compared to the time scale used with a classical voltammetric electrode. As we have seen earlier in this chapter, when microelectrodes are used at short time scales, the current follows the behavior expected for diffusion in one dimension. Thus, the development of high-speed voltammetric methods with microelectrodes was a logical step, and has greatly expanded the scope and capabilities of electrochemical techniques [41]. Rapid electrochemical methods allow evaluation of the larger rate constants of rapid heterogeneous and/or homogeneous reactions. For example, theories of hetero-... 

Hrabetova S, Nicholson C. Biophysical properties of brain extracellular space explored with ion-selective microelectrodes, integrative optical imaging and related techniques. In Michael AC, Borland LM (Eds), Electrochemical Methods for Neuroscience. CRC Press/ Taylor Francis, Boca Raton, FL, 2007 167-204. 

Refs. [i] Bard AJ, FaulknerLR (2001) Electrochemical methods, 2nd edn. Wiley, New York, chaps. 5, 6, 9, 11, 12 [ii] Bard AJ, Mirkin MV (eds) (2001) Scanning electrochemical microscopy. Marcel Dekker, New York [Hi] Oldham KB, Myland JC (1994) Fundamentals of electrochemistry. Academic Press, New York, chap. 8 [iv] Zoski CG (1996) Steady-state voltammetry at microelectrodes. In Vanysek P (ed) Modern techniques in electro analysis. Wiley, New York... 

Electrical/electrical microelectrode methods under optical (microscopic) control. This class covers the conventional electrochemical methods, that is, application of an electrical signal (e.g. potential) to the electrode to induce a reaction. The role of optics here is twofold ... 

Bard AJ, Faulkner LR. Controlled potential microelectrode techniques. Potential Sweep Methods. In Electrochemical Methods Fundamentals and Applications. New York Wiley and Sons, 1980 213-248. 

Classical DC polarography uses a linear potential ramp (i.e., a linearly increasing voltage). It is, in fact, one subdivision of a broader class of electrochemical methods called voltammetry. Voltanunetric methods measure current as a function of applied potential where the WE is polarized. This polarization is usually accomplished by using microelectrodes as WEs electrode... 

Electrochemical methods for NO determination offer several features that are not available with spectroscopic approaches. Perhaps the most important is the capability of microelectrodes to directly measure NO in single cells in situ, in close proximity to the source of NO generation. Figure 2 shows sensors that have been developed for the electrochemical measurement of NO. One is based on the electrochemical oxidation of NO on a platinum electrode (the classical Clark probe for detection of oxygen) and operates in the amperometric mode [17]. The other is based on the electrochemical oxidation of NO on conductive polymeric porphyrin (porphyrinic sensor) [24]. The Clark probe uses a platinum wire as a working electrode (anode) and a silver wire serves as the counterelectrode (cathode). The electrodes are mounted in a capillary tube filled with a sodium chlo-ride/hydrochloric acid solution separated from the analyte by a gas-permeable membrane. A constant potential of 0.9 V is applied, and direct current (analytical signal) is measured from the electrochemical oxidation of NO on the platinum anode. In the porphyrinic sensor, NO is catalytically oxidized on a polymeric metalloporphyrin... 

The electrochemical methods that have evolved for neurochemical applications have several advantages that make them ideally suited to the task for which they are intended the methods are selective, sensitive, and rapid. Nevertheless, the key advantages that will be highlighted in this chapter are derived from the micrometer physical dimensions of the microelectrodes themselves (Fig. 1). Today, the majority of in vivo electrochemistry is conducted in the brain with microelectrodes constructed with individual, or a... 

The ability to place a Kne microelectrode in the plane of a monomolecular film at the air/water interface opened the possibility of investigating phenomena intrinsic to this class of chemical systems. While the list given in the following is perhaps not complete as the development of the 2D electrochemical methods continues, it outlines the main areas of research and suggests some future directions. 

The properties and applications of microelectrodes, as well as the broad field of electroanalysis, have been the subject of a number of reviews. Unwin reviewed the use of dynamic electrochemical methods to probe interfacial processes for a wide variety of techniques and applications including various flow-channel methods and scanning electrochemical microscopy (SEM), including issues relating to mass transport (1). Williams and Macpherson reviewed hydrodynamic modulation methods and their mass transport issues (2). Eklund et al. reviewed cyclic voltammetry, hydrodynamic voltammetry, and sono-voltammetry for assessment of electrode reaction kinetics and mechanisms with discussion of mass transport modelling issues (3). Here, we focus on applications ranging from measnrements in small volumes to electroanalysis in electrolyte free media that exploit the uniqne properties of microelectrodes. 

A site-specific electrochemical method for the fabrication of polypyrrole, polyaniline, and a derivate of polythiophene nanowire frameworks on microelectrode junctions (Alam et al. 2005). 

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