Determinação de ácido ascórbico em amostra de alimentos utilizando um sensor amperométrico baseado em nanotubos de carbono e 4-nitroanilina adsorvida em sílica gel modificada com óxido de zircônio

Abstract

The present work describes the development of a multi-walled carbon nanotube paste electrode (MWCNTPE) based on 4-nitroaniline (4-NA) adsorbed on silica gel modified with zirconium oxide (SZ) for the determination of ascorbic acid (AA). The MWCNT/SZ4NA film was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and fourier transform infrared spectroscopy (FTIR). The activation process of the nitro group present in 4-NA generated in situ the electroactive species R-NHOH/R-NO in the modified electrode after cycles in the potential range between 0.5 and -1.0 vs. Ag/AgCl in the first scan in 0.1 mol L-1 phosphate buffer, pH 7.0 with a scanning speed of 0.02 V s-1. After the activation process the developed sensor presented efficient electrocatalytic activity front the oxidation of AA in an observed catalytic peak potential in 0.3 V vs. Ag/AgCl. After optimizing the operating conditions, this sensor provided a linear response range of 0.5 - 3.0 μmol L-1, with limit of detection, quantification and sensitivity of 0.15 μmol L-1, 0.48 μmol L-1 and 7.60 (mA L mmol-1), respectively. This sensor was applied for the amperometric determination of AA in food samples. The results were consistent with those obtained with the standard titration procedure.