Full Paper Differentiation of Detection of Ascorbic Acid and Dehydroascorbic Acid Using Hydrodynamic Amperometry and Anodic Stripping Voltammetry on Modified Aluminum Electrodes M. H. Pournaghi-Azar,* H. Dastangoo, R. Fadakar Electroanalytical Chemistry Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz, Iran *e-mail: Pournaghiazar@tabrizu.ac.ir Received: April 21, 2009 Accepted: September 9, 2009 Abstract An electroanalytical strategy for the simultaneous determination of ascorbic acid (AA) and dehydroascorbic acid (DHA), is described. A palladized Al electrode is used for hydrodynamic amperometry of AA. While the decrease of anodic stripping voltammetry current of the K 2 UO 2 [Fe(CN) 6 ]-Pd/Al electrode prepared in the presence of DHA was the principal of the DHA determination. The calibration graph for both methods was linear over the concentration range 1 – 50 mM. The detection limit was found to be 0.5 mM. Some fresh fruit juices and vegetables of trace level of AA and DHA were analyzed as the typical example of application. Keywords: Ascorbic acid, Dehydroascorbic acid, Uranyl hexacyanoferrate, Modified aluminum electrode, Fruit juice, Vegetable, Vitamins DOI: 10.1002/elan.200900213 1. Introduction Ascorbic acid (AA), vitamin C, is used clinically in the treatment and prevention of scurvy [1]. Ascorbic acid/ ascorbate are a vital component in the diet of humans. Ascorbate is known to take part in several biological reactions and is present in mammalian brain [2]. Ascorbate is possibly the primary antioxidant in human blood plasma. In addition, AA is found in high concentration in some pharmaceuticals. In specialized cells, vitamin C is directly transported as AA via sodium-dependent vitamin C transporters (SVCT) [3]. However, most cells transport vitamin C in its oxidized form, dehydroascorbic acid (DHA), via facilitative glucose transporters (Glut), including Glut1 [4]. Once inside cells, DHA is reduced and accumulated as AA [5]. Although AA does not penetrate the blood – brain barrier (BBB), its oxidized form DHA, enters the brain by means of facili- tative transport [6]. It is hypothesized that DHA would improve outcome after stroke because of its ability to cross the BBB and augment brain antioxidant levels. Some researches have suggested that administration of DHA may confer protection from neuronal injury following an ischemic stroke [6]. Though the literature is replete with the different types of methods for the analysis of such diversified products, efforts continue in the search of better methods according to their simplicity, rapidity, sensitivity, selectivity and utility. Besides spectrophotometric methods, which have been reviewed from time to time including that by Araya et al. [7] the nonspectrophotometric methods have been reviewed [8]. In general, traditional methods, such as titration [9, 10], spectrophotometry [7], chemiluminescence and enzymatic measurements [8] require long analysis times, favoring AA degradation, can give overestimations because of other oxidizable species, or finally are unable to independently measure both AA and DHA. Furthermore colored samples are hard to work with and the methods are not suited for determination of trace AA. A selective electrochemical determination of AA has been a major target of electroanalytical research. It is almost too difficult to determine AA electrochemically by direct oxidation on a conventional electrode because of its large overpotential and surface fouling by the oxidation products. A carbon electrode, when subjected to an appropriate pretreatment procedure, exhibits minimal propensity for surface fouling. However, the kinetic of electron transfer is quite sluggish. This last characteristic of electrochemical irreversibility means that AA will be oxidized only at potentials considerably removed from its standard redox potential. It has been demonstrated that AA can undergo mediated oxidation via a homogeneous process by electro- generated ferricinium derivatives [11]. In addition some chemically modified electrodes with various conductive polymers [12 – 15] and active mediators [16 – 28] immobi- lized at the electrode surface for the catalytic oxidation of AA have been used. Simultaneous measurement of both AA and DHA using high-performance liquid chromatography (HPLC) in blood serum has proven difficult owing to detection problems. Full Paper Electroanalysis 2010, 22, No. 2, 229 – 235  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 229