Multitechnique Determination of Halogens in Soil after Selective Volatilization Using Microwave-Induced Combustion

A method for digestion of soils with high inorganic matter content (ranging from 50 to 92%) by microwave-induced combustion (MIC) is proposed for the first time for further halogens (F, Cl, Br, and I) determination by ion chromatography (IC) and also by inductively coupled plasma mass spectrometry (ICP-MS). Microcrystalline cellulose (100-500 mg), used as a combustion aid, was mixed with sample and water or NH₄OH solutions (10-100 mmol L^-1) were investigated for analytes absorption. The use of cellulose (400 mg) was mandatory to volatilize the halogens from soils with high inorganic matter. It was possible to use diluted absorbing solutions (up to 100 mmol L^-1 NH₄OH) for halogens retention, providing limits of quantification in the range of 0.06 (I) to 60 (Cl) μg g^-1. Accuracy was evaluated using certified reference materials (CRMs), spiked samples, and pyrohydrolysis method. Recoveries for halogens after spiked samples were in the range of 94 to 103% and the results after digestion of CRMs by MIC were in agreement better than 95% to certified values. Blanks were low, relative standard deviation was below 8% for all soils and no statistical difference was observed for results by pyrohydrolysis and MIC methods showing the feasibility of the proposed method for further halogens determination in soil samples.