Determinação simultânea de Cd, Pb e Cu em amostras de chá (Camellia sinensis) por voltametria de onda quadrada e redissolução anódica

Abstract

This paper describes the development of a method for quantification Cd2+, Pb2+ and Cu2+ cations, in teas, performed simultaneously, using Square Wave Anodic Stripping Voltammetry carbon nanotube paste electrode modified with bismuth film. Tea is one of the most beneficial and consumed beverage through the world, being prepared from the infusion parts of the plant Camellia sinensis. Most commonly this kind of tea presents metal ions, such as Cd 2+, Pb 2+ and Cu 2+, which offers health risk, in case of being ingested above the limit. To detect these metals, it is necessary to make use of techniques with high sensitivity. The spectrometric methods are the most widely used, but they have a high cost, are laborious and expensive. The voltammetric techniques are characterized by being inexpensive and having equal sensitivity, and even greater than some spectrometric methods. The parameters of the technique used were obtained after optimization with fractional factorial design. The tea samples were prepared through digestion with heating by microwave radiation in a closed system using diluted nitric acid and hydrogen peroxide. The method was validated based on the sample certified plant tissue (forage Marandu) and applied in green and black tea samples. Recoveries of cations Cd 2+, Pb 2+ and Cu 2+ ranged from 79.3 to 107.6%, the certified sample, and 73.3 to 122.1% in the evaluated samples of teas. The detection limits obtained in the simultaneous analysis of Cd 2+, Pb 2+ and Cu 2+ were 0.16; 0.20; 0.39 ug L-1, respectively. Cu2 + was detected only in samples of tea, but the method was efficient for the simultaneous quantification of all metals in the matrix assessed after the addition and recovery.