Electrochemical Pseudo-Titration of Water-Soluble Antioxidants Philippe Tacchini, a Andreas Lesch, b Alice Neequaye, a GrØgoire Lagger, a, c Jifeng Liu, d Fernando CortØs-Salazar, b Hubert H. Girault* b a EDEL Therapeutics SA, PSE-B, EPFL, CH-1015 Lausanne, Switzerland b Laboratoire dElectrochimie Physique et Analytique, Station 6, Ecole Polytechnique FØdØrale de Lausanne, CH-1015 Lausanne, Switzerland tel: + 41216933145; fax: + 41216933667 c Service dEnseignement ThØrapeutique pour Maladies Chronique, FacultØ de MØdecine, UniversitØ de Genve, CH-1205 Genve, Switzerland d Department of Chemistry, Liaocheng University, No.1 Hunan Road, Liaocheng, Shandong Province, 252059, China *e-mail: hubert.girault@epfl.ch Received: October 30, 2012 Accepted: December 18, 2012 Published online: March 4, 2013 Abstract An amperometric test for the antioxidant power (AOP) of biological and food samples is presented. The gist of the method is to measure by linear sweep voltammetry the anodic current produced during the oxidation of the labile species present in the sample and then rationalizing this signal with a mathematical treatment that allows the pseudo-titration of antioxidants (AOs) around a given threshold potential. As a result, the AOP of the sample is cal- culated. This method allows the discrimination of the most biologically relevant AOs that react rapidly and at low oxidation potentials, from less reactive AOs that are oxidised slowly and at much higher oxidation potentials. This methodology was applied for measuring the AOP of blood, saliva, and natural drinks like orange juice. Keywords: Antioxidants, Electrochemical pseudo-titration, Antioxidant power DOI: 10.1002/elan.201200590 Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/elan.201200590 Dedicated to Professor Erkang Wang on the Occasion of His 80th Birthday 1 Introduction The reaction of oxidation consisting of a transfer of elec- tron(s) from one species to another, often corresponds to a structural and functional damage of the oxidised spe- cies. In biological systems, reactive oxygen species (ROS; hydroxyl radical COH, hydrogen peroxide H 2 O 2 , superox- ide O 2 C  , etc.) and reactive nitrogen species (RNS; nitro- gen dioxide CNO 2 , peroxynitrite ONOO  , etc.) responsi- ble for the oxidation of several target molecules, includ- ing proteins, cellular membranes, cells, DNA or RNA play a relevant role in the development of several diseas- es such as Alzheimer, Parkinson and cancer [1–7]. For in- stance, it has been shown recently that the oxidation of copper (I) ions complexed with b-amyloid peptides leads to the formation of b-amyloid agglomerates which precip- itate as plaques in the brain and contribute to the genera- tion of Alzheimer diseases [8]. Likewise, in other fields such as in alimentation, an oxidised product is often equal to a damaged product. In order to overcome oxida- tion and oxidative stress conditions, a series of species known as antioxidants (AOs) have evolved to prevent ox- idation and/or to protect living cells, human tissues or food sources from oxidative species by inactivating them within redox reactions. The AO species and their regulatory mechanisms, in- cluding catalytic cellular enzymes, scavengers, metal che- lators responsible for controlling oxidation represent the AO defence system. AOs are a complex family of com- pounds, including hydrophilic and lipophilic molecules that act as neutralisers of oxygen or nitrogen radicals, as repairing machines of damaged membranes and preven- tive antioxidants [9]. AOs are present at different concen- trations and locations in the human body. They include endogenous species that are produced by the cells and exogenous ones, mostly from dietary origins. The most common water-soluble AOs present in blood and saliva are uric acid (UA; endogenous), ascorbic acid (AA, vita- min C; exogenous) and glutathione (GSH; endogenous), while their hydrophobic counterpart is tocopherol (vita- min E; exogenous) [10–12]. The cellular and extra-cellular (i.e. in biological fluids such as blood and saliva) AOs concentration is tightly regulated and ideally maintains within an optimum phys- iological range. Thus, the ability of measuring the AOP in a simple, rapid and economic manner is important and SPECIAL ISSUE 922  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2013, 25, No. 4, 922 – 930 Full Paper