The electrochemical behavior and amperometric determination of tyrosine and tryptophan at a glassy carbon electrode modified with butyrylcholine

A monolayer butyrylcholine (BuCh) modified glassy carbon electrode (BuCh/GCE) was first prepared by electrochemical method. X-ray photoelectron spectroscopy, in situ UV-Vis spetroelectrochemistry, and electrochemical techniques were used for characterization of the electrode surface. It was demonstrated that the BuCh was hydrolyzed to choline (Ch) and butyric acid during the electrochemical planting process. Both Ch and butyric acid products were immobilized onto the carbon surface forming a covalently planted Ch monolayer, which immobilized the butyric acid in the monolayer by a special adsorption mechanism. This provided a novel example of two-component digitally mingled monolayer modified electrode. The electrochemical activity of the BuCh/GCE was primarily tested for electrochemical catalyses of amino acids. It was found that tyrosine (Tyr) and tryptophan (Trp) could be catalytically oxidized with diffusion-controlled characteristics at this electrode, which could be applied for analytical sensitivity in practical sample. In static solutions, the linear ranges of the differential pulse voltammetry peak current at the electrode were 4 x 10(-6)-1 x 10(-4) M Tyr and 2 x 10(-6)-6 x 10(-5) M Trp with detection limits of 4 x 10(-7) M Tyr and 6 x 10(-7) M Trp, respectively. The BuCh/GCE sensor was stabile and reproducible for at least month operation. The electrochemical activity of the BuCh/GCE was compared with similarly prepared Ch, acetylcholine and propionylcholine-modified electrodes. (C) 2004 Elsevier B.V. All rights reserved.