Desenvolvimento de métodos para a determinação de halogênios e enxofre em grãos

Abstract

In this study, the microwave-induced combustion (MIC) was evaluated for the sample preparation of different cereals and legumes (rice, maize, wheat, bean, lentil and soybean) and further chlorine and sulfur determination by ion chromatography (IC), and bromine and iodine by inductively coupled plasma mass spectrometry (ICP-MS). Samples from different countries (Germany, Brazil, Chile, USA, Indian and Uruguay) were decomposed in this study. The samples were ground and dried previous to the initial studies. For this, some parameters such as sample mass and the absorbing solution more suitable (H2O and 25, 50 or 100 mmol L-1 NH4OH) for the analytes and for the determination techniques were evaluated. For the developed method for chlorine and sulfur determination, ultrapure water was chosen as absorbing solution, while for bromine and iodine determination, 50 mmol L-1 NH4OH was efficient for this purpose. The accuracy evaluation for both methods was carried out by recovery tests, as well as by the use of reference material with similar matrix to the samples. Thus, suitable recoveries were obtained for all evaluated analytes (halogens: 97 to 105% and sulfur: 98 to 109%) with relative standard deviations always less than 16%. Low limits of detection (LODs) were obtained (Br: 0.012 mg kg-1; Cl: 9.2 mg kg-1; I: 0.006 mg kg-1 e S: 8.3 mg kg-1). In this sense, low limits of quantification (LOQs) were also obtained (Br: 0.032 mg kg-1; Cl: 16.1 mg kg-1; I: 0.009 mg kg-1 e S: 16.5 mg kg-1). The bromine, chlorine and sulfur concentrations varied in a wide range (Br: 0.231 a 55.7 mg kg-1; Cl: 33 a 909 mg kg-1; S: 640 a 4990 mg kg-1), while iodine concentrations did not present a wide variation (0.005 to 0.031 mg kg-1).