Cyclic voltammetry catecholamines

Electrochemical oxidation of some catecholamines such as dopamine, L-dopa, and methyldopa has been studied using cyclic voltammetry. The catecholamines undergo intramolecular cyclization to form the corresponding o-quinone derivatives. The significant differences in the electrochemical behaviour of the catecholamines have been attributed to the effects of the side-chain carboxyl group.253 Electron-transfer reactions of 2,-deoxyguanosine-5,-monophosphate (dGMP) in phosphate buffers by cyclic... 

Another voltammetric method, sinusoidal voltammetry (SV), was also employed. This was a frequency-based electrochemical method, which was found to be more sensitive than the usual constant potential (DC) amperometric detection method. SV has been achieved to detect on-chip separated catecholamines. This method is very similar to fast-scan cyclic voltammetry (CV), except that a... 

In the 1980s electrochemical studies provided a fundamentally new mechanistic insight into the early stages of the melanization processes. Cyclic voltammetry of several catecholamines identified and clarified the cascade of chemical steps that precede the final polymerization of the respective 5,6-indolequinones. These studies allowed the identification of each electron-transfer process and determination of the rate constants of the coupled chemical (nonoxidative) reactions. 

Jones SR, Mickelson GE, CoUins LB, Kawagoe KT, Wightman RM (1994) Interference by pH and Ca2+ ions during measurements of catecholamine release in slices of rat amygdala with fast-scan cyclic voltammetry. J Neurosci Methods 52 1—10. 

The earliest experiments of this type employed voltammetry as a detection scheme. Fast-scan cyclic voltammetry can be used to discriminate between released substances with different oxidation/reduction properties. Voltammetric measurements of absolute concentrations released from single vesicles undergoing exocytosis have proven to be difficult however, because the amount of transmitter released is only at zeptomole levels and because the events occur on the millisecond time scale [13]. Furthermore, although elicited by chemical stimulation, these events do not occur at precise times. Although several neurotransmitters have been identified on the basis of characteristic voltammograms, it is difficult to distinguish catecholamines with this technique. However, fast-scan cyclic voltammetry has been used to identify the seaeted catecholamines norepinephrine and epinephrine [14]. 

The oxidation of a number of catecholamines including adrenaline, noradrenaline, a-methylnoiadrenaline, dopamine and isoprenaline has been studied by electrochemical techniques [106, 107]. In 1 m sulphuric acid, adrenaline was reversibly oxidised to adrenaline quinone (43) and it was shown by cyclic voltammetry that under these conditions negligible cyclisation to adrenochrome occurred [106]. At pH 3, however, there was considerable cyclisation, and, as well as the adrenaline-adrenaline quinone (43) couple, the leucoadrenochrome (13)-adrenochrome and the 5,6-dihydroxy-A-methyl-indole (44)-A-methylindole-5,6-quinone (45) couples could be detected and... 

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