Electrochemical Studies of Alkyl Gallates Behaviour in SDS/Water/EtOH Solutions

Abstract

In this paper the results of electrochemical oxidation of propyl and lauryl gallates in various sodium dodecyl sulphate solutions using the cyclic voltammetry method with a glassy carbon electrode are presented. The dependences of peak current and peak potential on the surfactant concentration were determined in the aqueous buffer and 1:1 v/v buffer+ethanol solutions, pH=4, 7, 11. On the basis of the obtained results the effects of pH, surfactant concentration and ethanol on the oxidation reaction kinetics were discussed. The distinct effect on the peak potential and peak current of both gallates is due to the pH change from 4 to 7; the lower pH, the higher value of oxidation potential. The increasing surfactant concentration caused the noticeable increase of peak potential and the decrease of peak current of propyl gallate in the aqueous solution. These changes were observed up to the critical micelle concentration and above this value the parameters became almost constant. The addition of ethanol reduced the dodecyl sulphate concentration effect on propyl gallate oxidation. The water insoluble lauryl gallate was investigated in the aqueous system with the dodecyl sulphate content above the critical micelle concentration (solubilization in micelles) and in the buffer+ethanol solvent containing different amounts of surfactant. Here the changes of oxidation parameters with the increasing surfactant concentration were much less pronounced than those for propyl gallate.

Keywords:

• Antioxidants
• alkyl gallates
• micellar solution
• cyclic voltammetry