Prospecção de metais em diferentes etapas do consumo de café comercial por espectrometria de emissão óptica com plasma induzido por micro-ondas

Abstract

Coffee consumption is always a subject discussed in various spheres of society today and over time. Since its discovery in Africa of the years of mass dissemination, the fruit of coffee has always had its clashes, with claims of improvement in intellectual and physical performances to the risks of its consumption, such as addiction, for example. What is indisputable is its growing consumption and all the economy in its surroundings, which through various products and innovations never fall into oblivion, becoming one of the most popular beverages in the world, second only to water. In view of this, it is evident that a more detailed control of its composition becomes inevitable, especially in an elementary character. Thus, the objective of this work was to present results for the determination of metals in samples of conventional coffee and espresso at different stages of their consumption. For this, afollow-up of the concentration of the analyses was performed in the different fractions (total coffee powder, infusion, and infusion powder). The determinations were made using the microwave-induced plasma optical emission spectrometry (MIP OES) technique. For the preparation of solid fractions (powder and sludge), a digester block with reflux system was used. The best decomposition conditions were optimized from a factorial planning: 750 mg of sample with the addition of 2.0 mL and 5.0 mL of H2SO4 and HNO3, respectively, at 300°C for 3 h. For the liquid fraction (infusion), 0.2 mL of HNO3 and 3.0 mL of H 2 O2to 120°C were used for 10 mL samples. The accuracy was verified by a mass balance between the concentrations of the fractions of the samples (total powder, infusion powder and infusion) and by the analyte addition tests. Both presented recoveries between 81 119%, for Al, B, Cu, Ca, K, Mg, Mn, Pb, Se and Zn considered satisfactory, proving the accuracy of the method. The optimization of the method allowed the determination of these elements, evidencing their behavior to the coffee infusion process. The results obtained showed that there is 50% of the transfer of Pb concentration from coffee powder to coffee infusion, while for B the transfer was 74%. Through multivariate statistical methods, similarity in the elemental composition of the samples in their solid fraction was observed. Thus, it can be seen that the proposed method was able to reliably determine 12 elements and extract as much information as possible from the samples obtained.