Avaliação de métodos analíticos para a determinação de metais em amostras de difícil decomposição

Abstract

In recent decades the increase in public interest in both environmental protection and the quality of life and health of the population is increasingly driving studies on the presence of metals in food samples and the control of toxic pollutants in environment (ex.: environmental samples). Thus, a new sample preparation method microscale, for the determination of metals in certified food samples by spectrometric techniques have been developed. In this study, we used to minivials digestions produced with inert material base PTFE that have good resistance to the action of strong oxidizing reagents, and suitable for the purpose it proposes. Subsequently, samples were taken analysis by spectrometric techniques for the determination of Cd, Mg and Na. According to the results we observed good agreement between the values obtained and the certified values for the analytes under study, which proves the correctness of the proposed method. RSD values lower than 8.0% for all analytes were also obtained showing good accuracy. Two other methods were developed and applied in coal and ash samples for the determination of total metals spectrometric techniques. These studies of sample preparation were performed on a system that works under reflux. For the study, a statistical program was used (Statistica 6.0), which seeks to relate the influence of each parameter studied in relation to the analytical signal of each element, allowing better optimization of the method, seeking a compromise condition for the variables in study. The first method developed was carried out a partial decomposition of the samples and the determination of Fe, Cu, and Zn were determined by F AAS and Na by F AES. Tests for accuracy by adding and analyte recovery were performed and the results ranged from 93 to 105% recovery for coal and 99 to 115% for ashes, confirming the accuracy of the proposed method for determination of the respective analytes. Another method under development for coal samples and ashes, targeting a full breakdown of these samples showed good preliminary results. When using H2SO4 and HNO3 at high temperatures it was possible to achieve efficient decomposition, resulting in a clear sample without waste at the end of the process. The accuracy of this method was confirmed by the determination of the studied metals (Al, Cu, Cr, Fe and Mn) for MIP-OES in coal CRM. The results indicated a good accuracy of the method, in view of the equivalence of results with CRM certified values as well as the application of the Student t test. The proposed methods are presented as simple procedures, fast and safe, suitable for the preparation of biological samples as well as coal and ash for later determination of the respective elements by atomic spectrometry techniques.