Eletrodo Modificado com Pectina para Determinação de Cobre por Voltametria de Redissolução Anódica

Pectin is a polysaccharide containing predominantly residues of galacturonic acid that is largely present in the cell wall of plants[1].From a chemical point of view, the pectin can act as a sequestering agent for metal ions, due to the presence of multiple carboxylate-binding sites in its structure[1].In this work was developed acarbon paste electrodes (CPE) modified with pectin (CPE/PEC) to the copper determination in bioethanol. Electrodes of carbon paste were confectioned with graphite, mineral oil Nujol and pectin as modifier (0 to 25% m/m) and cyclohexane. The pectin has extracted by the albedo from orange peel using acid hydrolysis (citric acid 1.0 M)and absoluteethanol. Electrochemicalexperiments were realized using CPE/PEC as work electrode, Ag/AgCl (KCl 3.0 M) and platinum wire as reference and auxiliary electrodes, respectvely. Voltammetric techniques were employed, such as, ciclic voltammetry (CV) and linear sweep anodic stripping voltammetry (LSASV)in hidroalchoolic solution containing nitric acid (HNO3)/potassium nitrate (KNO3) as supporting electrolyte. The results obtained by CV showed the CPEmodified withpectin improves the anodic peak resolution of copper oxidation up to 10% (m/m) of modifier. Using the modified CPE with 10% of pectin was evaluated the concentration ofKNO3/HNO3 and the etanol/water proportion by CV. It was observed that the peak resolution better it was obtained in a hidroalchoolic solution of etanol/water (50/50 v/v) contained 2.0×10-3M KNO3and 2.0×10-4M HNO3. Employing theLSASV was studiedthe equilibrating time (2.5 to 80s),electrodeposition potencial (-0.1 to 0.8 V), electrodeposition time(20 to800 s) and scan rate (10 to 500mVs-1)in the potencial range from -0.5 to 1.5 V. Scan rate study indicated the anodic peak currents were found increase linearly with the square root of the scan rate in range from 10 to 150 mV s-1, indicating that the electron transfer reactions is controlled by diffusion processes. The best oxidation current of copper were observed in equilibration time of 10 s,electrodeposition potentialof -0.4V, time of electrodeposition of300sand scan rate of 100mVs-1. The figures of merit for the developed method were evaluated using analytical curves. Hidroalcoolic solutions were prepared and the analytical curve showed linear range from 4.0×10-5to 1.0×10-3M (Ipa= 1.1×10-5 + 1.3×10-1C), limit of detection of 2.0×10-5M,amperometric sensitivity of 1.3×10-1A mol-1L and correlation coefficient of 0.998. The results indicated that the analytical method proposedusing linear sweep stripping voltammetry showed good analytical performance indicating that the proposed electrode can be applied to the detection and determination of copper in bioethanol samples.