Effective Method for the Covalent Introduction of the 2-(2-Carboxymethoxyethoxy)ethoxy Group on a Glassy Carbon Electrode by Anodization in Triethylene Glycol

Abstract

The effects of supporting electrolytes used for anodizing a glassy carbon (GC) electrode in triethylene glycol on the extent of the 2-(2-carboxymethoxyethoxy)ethoxy group introduced on the anodized electrode surface were investigated. To evaluate these influences, cyclic voltammetry of phosphate buffer (pH 7.0) solutions of epinephrine as a cationic marker, and 3,4-dihydroxyphenylacetic acid and ascorbic acid as anionic markers was carried out at GC electrodes anodized in the glycol containing LiClO4, LiBF4, Mg(ClO4)2, H2SO4, CH3SO3H, CH3CH2SO3Na, or HOCH2CH2SO3Na. By comparing the extent to which the electrode reaction of the cation was conserved, while those of the anions were regressed, HOCH2CH2SO3Na was shown to be the supporting electrolyte of choice for anodization to introduce a molecule with a terminal carboxyl group on the electrode surface most effectively. The modified electrode obtained with the supporting electrolyte allows compounds existing as cationic and neutral species at pH 7.0 (norepinephrine, dopamine, 3-methoxytyramine, and catechol) to show voltammetric responses, and prevents those existing as anionic species (vanillo-mandelic acid and uric acid) from entering electrochemical reactions.