Full Paper Development of a Dual-Band Amperometric Detector for Determination of Ascorbic Acid and Glucose Thiago R. L. C. Paixaƒo, a Renato Camargo Matos , b Mauro Bertotti* a a Instituto de QuÌmica, Universidade de Sa ƒo Paulo, Sa ƒo Paulo, SP, Brazil, 05508-900 *e-mail: mbertott@iq.usp.br b Departamento de QuÌmica, Instituto de Cie √ncias Exatas, Universidade Federal de Juiz de Fora, MG, Brazil Received: September 24, 2002 Final version: January 3, 2003 Abstract A flow-through system cell that allows the direct and simultaneous amperometric determination of ascorbic acid and glucose to be performed is described. The electrolytic cell in a thin layer configuration is composed of a gold and a copper-modified electrode, polarized at  0.10 and 0.50 V, respectively. By using a 1 molL 1 NaOH solution as carrier electrolyte, amperometric data acquisition was performed simultaneously with a bipotentiostat and the results were analyzed by a multivariate calibration method. Measurements for two commercial pharmaceutical products were carried out without any pretreatment and showed a good correlation with data obtained by using recommended methods. The use of the device to the on-line quantitative removal of interfering species at the copper electrode is also discussed. Keywords: Glucose, Ascorbic acid, Dual-band electrode, Copper electrode 1. Introduction Owing to the crucial role of glucose in physiological processes, methods for detecting this compound in bio- logical matrices and foods are of continuous interest. In this end, approaches that allow measurements to be performed without previous sample pretreatments and at a high throughput are desired. Flow injection procedures associ- ated with suitable amperometric detectors fulfill these requirements. However, a problem usually found when noble metals such as platinum and gold are used as substrate for anodic oxidation of glucose is related to the adsorption of reaction products, which blocks the electrode surface and hinders further oxidation [1]. A strategy that minimizes this problem involves a two-step electrochemical cleaning of the electrode surface by applying a series of potential steps at values where adsorbed material is conveniently removed [2, 3]. Another very common approach for glucose sensing is based on the immobilization of an enzyme, usually glucose oxidase, on the electrode surface [4, 5]. The product of the reaction when oxygen exists in solution is hydrogen peroxide, which is then amperometrically monitored at a suitable potential. Copper electrodes is alkaline medium have also been studied as anodes for the oxidation of carbohydrates and related compounds [6 ± 9] . Because the electrochemical process is mediated by Cu(III) ions and reaction products are not adsorbed on the electrode surface, copper electrodes are well-suited as amperometric sensors for ethanol, sulfite, carbohydrates and sugars in FIA systems or after chromato- graphic and capillary electrophoresis separation [10 ± 14]. Nevertheless, a main drawback involving the use of copper electrodes is the need of previous separation due to the relatively low selectivity, which demands the use of poly- meric materials (cellulose, Nafion) as coatings on the electrode surface to restrain the reaching of interfering species to the electrode interface. This strategy is not always efficient because some relatively small electroactive mole- cules do penetrate through cellulose acetate membranes. This paper describes our efforts to develop an analytical method for determining glucose in samples that also contain ascorbic acid, an electroactive species at copper surfaces in alkaline medium. Multivariate calibration methods have been used in order to avoid the need for previous separations when two or more electroactive species exist in solution [15]. Accordingly, in this paper we describe results obtained with a dual-band electrode used as am- perometric detector in a continuous flow configuration. Current responses in the FIA system were monitored at copper-modified and gold electrodes polarized at conven- ient potentials, the simultaneous multicomponent analysis being performed by comparing the results with the ones arising from standard mixtures. Preliminary results on the on-line electrooxidation of ascorbic acid as a strategy to minimize its interference in some kind of samples are also reported. 2. Experimental 2.1. Chemicals and Samples All solid reagents were of analytical grade and were used without further purification. Ascorbic acid, sodium hydrox- 1884 Electroanalysis 2003, 15, No. 23±24 ¹ 2003 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim DOI: 10.1002/elan.200302773