Determinação simultânea de cobre e chumbo em amostras de azeite de dendê (Elaeis guineensis) por técnicas de redissolução utilizando o método de extração assistida por ultra-som

Abstract

The concentration of trace metals in vegetable oils is an important criterion for the assessment of oil qualities in regard of freshness, keeping properties, storage and their influence on human nutrition and health. In this work, an effective and simple method for the determination of copper and lead in palm oil by potentiometric stripping analysis is proposed. The metals ions were concentrated as their amalgams on the glassy carbon surface of a working electrode that was coated with a thin mercury film. An ultrasonic bath was used for the extraction of copper and lead from eleven oil samples in a mixture 1:1 (v/v) of concentrated hydrochloric acid and hydrogen peroxide. An efficient extraction of copper and lead (∼100 %) was attained after 60 min of ultrasonic pre-treatment. A good relation between the amount of sample and the time necessary for complete liberation of the metals was observed. Quantitative analysis was carried out by the method of standard additions; a good linearity was obtained in the range of the concentrations examined. Detection limits of 150 and 13 ng L-1 were found for Cu and Pb, respectively, in the original samples. The average values found for the analysed samples were in the range 1.55-16.54 µg g-1 for copper and 0.04-0.37 µg g-1 for lead. The palm oil samples were also analyzed by graphite furnace atomic absorption spectrometry (GFAAS), showing a very good correlation between the results.