Depolarizer, voltammetry

B. Chronopotentiometry (Formerly called Voltammetry at Constant Current). These terms were applied by Delahay et al (Refs 4 5) to measurements in which the course of polarization of an electrode (immersed in an unstirred soln) under forced constant current was followed potentiometrically as a function of time. The potential-time curve recorded in the presence of a depolarizer is characterized by a transition time, during which the rate of change of potential is relatively small. This... 

Suitable working electrodes for voltammetry are those that can be driven to take up a new potential in response to an applied external voltage, a process known as electrode polarization. Reduction or oxidation of an electrochemically active species at a working electrode results in depolarization of the electrode. The word depolarizer is therefore sometimes used to describe an electrochemically active species. In voltammetry, the working electrode may be fabricated from metals such as gold or platinum, various forms of carbon, or metallic mercury. 

Define half-wave potential, depolarizer, DME, residual current, and voltammetry. 

Within its working window, an electrode can be depolarized by electroactive substances which are dissolved in the electrolyte. The electrochemical reaction on the electrode surface causes concentration gradients perpendicular to the electrode surface. The current is proportional to these concentration gradients. This relationship depends on the electrode geometry, on the hydrodynamic conditions in the solution (whether it is stirred, or not) and on the voltammetric technique. However, in all cases, the current reaches a maximum, or a limiting value, which is proportional to the bulk concentration of the reactant. This is called the concentration polarization of the working electrode. It is the basis of all analytical applications of voltammetry. 

As expected from the push-pull and dialysis data, measurement of electroactive substances in extracellular fluid has indicated that the composition of the primary detectable species are ascorbate and dihydroxy-phenylacetlc acld[31,32]. These measurements were made in the caudate nucleus, a region of the brain known to contain large amounts of dopamine, in the hope that this substance would be determined. The first report of the release of dopamine which was confirmed by voltammetry came as a result of injecting potassium at a distance remote from the electrode into this caudate nucleus region[33]. The basis of this experiment is that the potassium would cause the depolarization of many neurons resulting in an increased extracellular concentration of dopamine. This is indeed the observed result. 

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