Estudo eletroanalítico do ácido úrico e da guanina sobre eletrodo de carbono vítreo

Abstract

The main objective of this work was to demonstrate the electrochemical activity of UA and GUA, in different aqueous media, on the glassy carbon electrode (GCE), through different voltammetric techniques, namely cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). The results were exploited for simultaneous detection and quantification of these species using DPV. Furthermore, the experimental results will be used to prepare teaching material for theoretical and practical classes in electrochemistry and electroanalytical subjects offered at the Department of Chemistry at UFRPE. The results clearly indicated that both molecules are easily electro-oxidized through complex, multi-step mechanisms. The oxidation of UA occurred from a main anodic process (peak 1a), with the loss of two electrons and two protons, generating a quinonoid diimine, which partially underwent electroreduction (peak 1c) and/or reacted with water generating allantoin. GUA underwent electro-oxidation in N7 (peak 1a), forming an electroactive dimer (peak 2a) and/or 8-oxoguanine, reversibly electroreduced (peak 3c/3a). Both AU and GUA showed that their anodic processes were controlled from mass transport via diffusion. Under suitable conditions, UA and GUA were detected and quantified simultaneously at neutral pH, using DPV. The limits of detection (LOD) and quantification (LOQ) for UA were LOD = 0,51 μmol L-1 and LOQ = 1,70 μmol L-1 and for GUA they were 0.82 μmol L-1 and 2.73 μmol L-1.