DETERMINATION OF BROMINE AND IODINE IN MILK POWDER SAMPLES USING HIGH-RESOLUTION CONTINUUM SOURCE MOLECULAR ABSORPTION SPECTROMETRY IN A GRAPHITE FURNACE: A STUDY OF INTERFERENCES

Milk is widely recognized as an important source of nutrients, but can also represent a source of exposure to halogens and information about their concentrations is important. Halogens play an important role in metabolism and their excess or absence can cause serious damages to human organism. Deficiency or excess intake of I can lead to disorders commonly related to thyroid gland. With regard to Br, it can be combined with hemoglobin causing hematologic diseases. In this sense, the determination of Br and I in milk powder is of great importance. However, is not a simple task mainly due to problems related to sample preparation step, such as analytes losses by volatilization and contamination. Alternatively, Br and I can be determined by high-resolution continuum source molecular absorption spectrometry using graphite furnace (HR-CS-GF MAS) using direct solid sampling, avoiding problems related to sample preparation. In this study, absorption of CaBr and BaI at 625.315 and 538.308 nm for Br and I, respectively were chosen for determination in milk powder samples by HR-CS-GF MAS. All experiments were carried out with an Analytik Jena ContrAA 700 high-resolution continuum-source atomic absorption spectrometer. Parameters, such as the temperature program, the amount of chemical and permanent modifier and the interferences by Cl presents in the milk powder samples were investigated. For the proposed method, 10 µL of standard solution or 1 mg of milk powder + 10 µL of solution containing the modifier and element molecule forming were weight and/or pipetted into the graphite tube. Optimized temperatures for pyrolysis and vaporization were 900 and 1900 oC and 600 and 1900 oC, for CaBr and BaI, respectively. However, CaBr and BaI molecular absorption signals obtained for milk powder samples were lower than when only standard solutions containing Br and I were used, probably due to interferences from sample. Then, a systematic study was performed for evaluation of interferences from Cl (which is present in high concentration in milk powder) on molecular absorption of CaBr e BaI. These experiments were performed using 100 ng of analytes (Br or I), chemical modifier and 0 to 2500 ng of Cl. Non-spectral interferences were observed in the presence of Cl (from 2.5 to 2500 ng) for CaBr e BaI molecular absorption, indicating that Br and I can not be determined in samples that containing Cl, even when presents in very low concentration, such as 2.5 ng.