Métodos de preparo de amostras para a posterior determinação de halogênios em solos contendo elevados e baixos teores de matéria orgânica empregando técnicas de cromatografia e de espectrometria atômica

Abstract

In this work, four sample preparation methods were evaluated for further determination of F and Cl by ion chromatography (IC) and Br and I by inductively coupled plasma mass spectrometry (ICP-MS) in soils with variable organic matter content (in the range of 8 to 96%). The following sample preparation methods were evaluated: microwave-induced combustion (MIC), quartz combustion tube followed by pyrohydrolysis (QTC-P), microwave-assisted acid wet digestion using a single reaction chamber (MAWD-SRC) and microwave-assisted extraction using a single reaction chamber (MAE-SRC). All the methods were applied for three soil groups based on the organic matter content: i organic matter content lower than 10%; ii) organic matter content about 50% and iii organic matter content higher than 95%. The results obtained after soils digestion by MIC were used as reference values for optimization of other sample preparation methods evaluated. According to the obtained results, it was possible to observe that for combustion methods (MIC and QTC- P), the use of cellulose was necessary for soils containing organic matter lower or about 50% for quantitative recoveries of F, Cl, Br and I. On the other hand, for soils containing higher organic matter content ( , the use of cellulose was not necessary and quantitative results were obtained for all the halogens for both combustion methods. Regarding to the MAWD-SRC and MAE-SRC methods, the determination of F in all groups of soils was not possible due to the interferences observed using IC. The application of MAWD-SRC method using only H2O2 as decomposition solution allowed Cl, Br and I determination in soils with high content of organic matter However, the determination of Cl was not possible for soils containing low organic content soils extraction by MAE-SRC, it was possible to observe that quantitative results were only obtained for Cl, Br and I in soil used for method optimization (organic matter higher than 95%). When MAE-SRC was applied for the extraction of other soils in the same group (group “C”), lower agreement (in the range of 70 to 80%) were obtained for analytes in comparison to those obtained by the reference method (MIC).