Analytical Sciences

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

Hatsuo MAEDA, Takehiro KITANO, Cheng Zhu HUANG, Kazunori KATAYAMA, Yuji YAMAUCHI and Hidenobu OHMORI

Graduate School of Pharmaceutical Sciences, Osaka University, Yamada-oka, Suita, Osaka 565-0871, Japan

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 (vanillomandelic acid and uric acid) from entering electrochemical reactions. (Keywords: Anodization, surface modification, glassy carbon electrode, charge selectivity, cyclic voltammetry, catecholamine, ascorbic acid)

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