Determinação de halogênios por cromatografia de íons e ICP-MS em sulfato de bário após decomposição por piroidrólise

Abstract

In this work pyrohydrolysis is proposed as pretreatment of barium sulfate and subsequent determination of F, Cl, Br and I by ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS). After the evaluation of experimental parameters the following conditions were used: 300 mg of barium sulfate, temperature of 1000 ° C, time of 20 minutes, 200 ml min-1 of air, 1.0 ml min-1 of water and 10 ml of NH4OH 100 mmol l-1 as absorbing solution. Using these conditions, the concentration of F and Cl was 6.62 ± 0.23 and 2103 ± 31 μg g-1, respectively, with relative standard deviation lower than 3%, and for Br and I the concentration was lower than the limit of quantification (LOQ) for IC (Br: 1.09 e I: 1.25 μg g-1) and ICP-MS (Br: 0.150 e I: 0.086 μg g-1). Recoveries for spiked samples were 98.1 ± 1.2, 98.2 ± 1.1, 97.0 ± 6.3 and 104 ± 2% for F, Cl, Br and I, respectively, suggesting the suitability of pyrohydrolysis to volatilization and subsequent determination of these elements. The methods of fusion, microwave-induced combustion (MIC), alkaline extraction, halogen extraction with water and extraction with ultrasound were also evaluated. The results for Cl by pyrohydrolysis and fusion were in agreement, however, the results obtained for F and Cl by MIC and extractions showed lower concentrations when compared to pyrohydrolysis and for Br and I was lower of the limit of detection (LOD) (Br: 0.048 e I: 0.023 μg g-1), suggesting that further experiments are required for these methods. Accuracy was evaluated using a certified reference material of marine sediment, MESS-1, with certified value for Cl (8200 ± 700 μg g-1) and the agreement to certified value was 93%. Therefore, the pyrohydrolysis can be used for the determination of halogens after their release from barium sulfate for further determination by IC and ICP-MS. In addition, this method is relatively inexpensive, allowing the separation of analytes from the matrix and reduced interference in the determination step by IC or ICP-MS.