Five phenolic compounds, (+)-catechin, (-)-epicatechin, (-)-epigallocatechin, (-)-epigallocatechin gallate and quercetin prepared in methanol solution were investigated with respect to their electrochemical response after long time storage at screenprinted carbon and at modified with carbon nanotube electrodes. The differential pulse voltammograms for these compounds showed a shift of their potential peaks and a change in the current intensity with the storage time. The differential pulse voltammograms showed that for (+)-catechin, (-)-epicatechin and (-)-epigallocatechin the current intensity decreased slowly with the storage time. From these results it was concluded that by differential pulse voltammetry the stability and the level of the antioxidant capacity of phenolic standard solutions can be monitored. The interaction of phenolic compounds in binary solutions is also discussed.
In this work we studied the electrochemical behavior of a glassy carbon electrode modified with natural and synthetic zeolites. Iron exchanged zeolites were set up for the detection of arsenic species. The electrochemical response both in KCl and HCl 0.1 M of the electrodes after modification was investigated by cyclic and differential pulse voltammetry. The electrochemical parameters of the redox pairs Fe3+/Fe2+ and Fe2+/Fe0 were determined for the iron containing electrode and the effect of repetitive potential cycling on the formation of iron oxides was studied. The reactivity of the exchanged iron species in the zeolite and the reduction of the complex As(V)-iron generated in-situ could be demonstrated.
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