| Spectroelectrochemistry is a cross subject of modern spectra technique and electrochemical technique. It is a method that can give much information from an electrochemical cell. It provides very powerful means for studying the electrochemical phenomena, elucidating electrochemical reaction mechanisms, identifying the intermediate compounds or instantaneous state in the reaction process and the properties of products, and determining the kinetic and thermodynamic parameters of electron-transfer processes. It is a key to design high qualitative thin-layer electrochemical cell through utilizing this technique. In this paper, an improved long optical path thin-layer spectroelectrochemical cell has been testified. The investigation revealed that the electrochemical cell is practically usable and suitable not only for thermodynamic studies but also for kinetic studies.Adrenaline and its oxidative product adrenochrome are widely used in medicine. It is very important to study the electrochemistry properties of them for their appling in medicine and electroanalytical. In this paper, the electrochemical oxidation of adrenaline in different pH value media was investigated on graphite and platinum plate electrode in the improved long optical path thin-layer spectroelectrochemical cell by using electrochemical and UV-VIS spectroelectrochemical technique. The thin-layer cyclic voltammocharacter of adrenaline in different pH value media had been firstly investigated on graphite and platinum electrode by using cyclic voltammetry. On this basis, The electrochemical oxidation reaction kinetics parameters (DO,DR, ks0/,β) ofadrenaline to adrenalinequinone in 1.0MH2SO4and glacial acetic acid were determined by using single-potential step chronoabsormetry. Then the apparent rate constant of the electrochemical oxidation of adrenaline in media of pH=2.5-7.0 Mcllvaine buffer solution and pH=7. 48 KRPB solution were studied. The relationship of pH value and /robs was deduced in theory as well . The mechanism of the electrochemical oxidation of adrenaline was studied by using this way.The investigation has revealed: In the medium of strong acid , the electrochemical oxidation reaction kinetics parameters (D O, DR) of adrenaline to adrenalinequinone are relevant to the media , but not to the electrode material. Therefore they do not change according to the electrode material in the same media. However, the kinetics parameters (DO, DR,kS0/,β) are higher in 1. OMH2SO4 than in glacial acetic acid on the same electrode in different media, which revealed that the electrochemical oxidation of adrenaline is easier in 1. OMH2SO4, than in glacial acetic acid. It also revealed that the electrochemical oxidation reaction capacity degrades with the viscidity increasing. The heterogeneous electron transfer rate constants and the transfer constants of the graphite electrode is bigger than that of the platinum electrode in the same pH value, which revealed that the graphite electrode is oxidized easier than on the platinum electrode.In the medium of weak acid and neutral solution, the apparent rate constant of the electrochemical oxidation of adrenaline to adrenochrome was affected apparently with changing the solution pH value on graphite and platinum electrode. The mechanism of the electrochemical oxidation of adrenaline is different if thepH value changed, and the dehydrate reaction of non-color adrenochrome was affected, then the reaction of non-color adrenochrome to adrenochrome was affected differently. Generally, increasing the pH value is good for the produce of non-color adrenochrome and then the produce of adrenochrome, however, the low pH value is good for the dehydrate reaction rate of non-color adrenochrome, but the high is bad, so the apparent rate constant will be bigger if the pH value increase as a whole, but in the middle the change is very slow. When the pH value is between 4.0 and 6.0, there is a line relationship between the pH value and logkobs, which in line with the result of the deduction in the app... |
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