Preparation of Chemically Modified Carbon Electrodes by Anodization in 1-Alkanols and Their Application to Electrochemical Analysis

Abstract

Anodization of a glassy carbon (GC) in a 1-alkanol in a cycled or constant potential mode serves as a useful tool for preparing a chemically modified GC electrode. By this treatment, 1-alkanol molecules are fixed on the GC surface via ether linkage. As the 1-alkanol in the anodic modification, CH₃(CH₂)_nOH (1 : n=0-7), HO(CH₂)_nOH (2 : n=1-5), and HO(CH₂CH₂O)_nR (3 : n=1-4, R=H; 4 : n=1-3, R=CH₃) are utilized. The surface of a GC electrode anodized in the 1-alkanol remarkably reflects the identities of the modifiers. Some of the modified GC electrodes exhibit surface characteristics useful for electroanalytical application as follows : (1) the surface of the GC electrode anodized in 3 or 4 is hydrophilic and resists protein adsorption. An HPLC system equipped with an electrochemical detector employing the GC plate anodized in triethylene glycol as a working electrode has proven to provide a useful analytical method for a protein-containing sample; (2) in the course of anodization of the GC electrode in 2, the diol molecules are first fixed on the surface via ether linkage with one of hydroxyl groups, and the remaining terminal hydroxyl groups in some of the fixed molecules are then oxidized to carboxyl groups. Thus, the GC electrode anodically modified with 2 has carboxyl groups on the surface, which allow dopamine to be voltammetrically discriminated from ascorbic acid in a large excess; (3) when the GC electrode is anodized in triethylene glycol containing HOCH₂CH₂SO₃Na, carboxyl groups are effectively introduced on the surface. On the basis of the formation of an amide bond formation through chemical reaction between the functional groups and amino compounds, electrochemical catalysts such as 2, 2, 6, 6-tetramethylpiperidinyl-1-oxyl (TEMPO) and catechol are immobilized on the surface of the GC electrode. The obtained electrodes shows stable voltammetric and electrochemically catalytic performance probably because the catalytic molecules are confined on the electrode surfaces via a hydrophilic linker instead of a hydrophobic one.