Electrochemical study of methylene blue incorporated into mordenite type zeolite and its application for amperometric determination of ascorbic acid in real samples

Methylene blue (MB) was incorporated into mordenite zeolite by ion exchange reaction in aqueous phase. The dye is strongly retained and not easily leached from the zeolite matrix. The solid was characterized by XRD prior to using it for the electrode preparation. This compound was incorporated into a carbon paste electrode for cyclic voltammetric and amperometric measurements. Methylene blue immobilized on the support underwent a quasi-reversible electrochemical redox reaction. In various electrolyte solutions and changing the pH between 2.0 and 7.0, the midpoint potential remained practically constant, i.e. 153.7 +/- 0.8 mV. This is not the usual behavior of MB, because in solution phase its midpoint potential changes considerably as the pH changes. The electrode made with this material was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry was linearly dependent on the ascorbic acid concentration. At a fixed potential under static conditions, the calibration plot was linear over the ascorbic acid concentration range 2.0 x 10(-5) to 8.0 x 10(-4) M. The detection limit of the method is 1.21 x 10(-5) M, low enough for trace ascorbic acid determination in various real samples. (C) 2003 Elsevier B.V. All rights reserved.