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Square-Wave Voltammetry of Sodium Copper Chlorophyllin on Glassy-Carbon and Paraffin-Impregnated Graphite Electrode

Electrochemical oxidation of sodium copper chlorophyllin (CHL) has been investigated at a glassy-carbon (GC) and paraffin-impregnated graphite electrode (PIGE) using square-wave voltammetry (SWV). Square-wave voltammograms of other two chlorin-type compounds, namely chlorin e6 and chlorophyll a, have been studied as well. The measurements were performed in the pH range between 7 and 11. The square-wave frequency was changed between 8 and 1000 Hz. The oxidation of studied chlorins is a complex, pH-independent, reversible or quasireversible process, followed by the chemical transformation of the product. The product of the EC reaction of CHL is an electroactive π-π dimer, which strongly adsorbs on the electrode surface and undergoes further oxidation at more positive potential. The electrooxidation of the adsorbed dimer is a pH-independent irreversible process with the formation of an electroinactive film. The voltammetric behaviour of chlorin e6 on PIGE was qualitatively similar to that of CHL. The SW voltammograms of chlorin e6 recorded on GCE and of chlorophyll a recorded on PIGE consisted of only one peak. The SW responses of studied compounds strongly depend on the stabilization of the reaction intermediate by adsorption to the electrode surface.

chlorophyll a; chlorin e6; electrochemical oxidation; sodium copper chlorophyllin; square-wave voltammetry

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