Desenvolvimento de método para determinação de halogênios e enxofre em mel por cromatografia de íons acoplada à espectrometria de massa

Abstract

A method for the indirect determination of halogens and sulfur in honey in a single analysis by ion chromatography with conductimetric detection coupled to mass spectrometry (IC-CD-MS) was developed. For this, the microwave-induced combustion (MIC) was used for the sample preparation. Employing MIC, it was possible to decompose up to 1000 mg of the sample using microcrystalline cellulose as combustion aid. However, aiming more reproducible combustions, given the variation on the moisture content of the honey samples (14 to 21%), the sample mass was kept in 800 mg. For the method optimization, the absorbing solution was evaluated by recovery test with the addition of analytical standards with known concentrations of analytes, for the choice of the most suitable solution to the retention of Br, Cl, F, I and S on its ionic forms. The 50 mmol L-1 NH4OH solution was chosen as the condition for further experiments because it showed recoveries varying from 93% to 101% for all analytes. Using the same solution were performed recovery tests with reference materials, and the recoveries varied from 94% to 103% for all analytes. The LOQs obtained were 0.45 mg kg-1 (Br), 21 mg kg-1 (Cl), 3.7 mg kg-1 (F), 0.08 mg kg-1 (I) and 9.8 mg kg-1 (S). For the comparison of the results, the concentrations of Cl and S were also determined by inductively coupled plasma optical emission spectrometry (ICP OES), and of Br and I by inductively coupled plasma mass spectrometry (ICP-MS) in six samples, and no statistical difference (t-test, confidence level of 95%) was observed. Finally, the proposed method was applied for the determination of halogens and sulfur in 19 samples from 11 countries. The concentrations of the analytes ranged from < 0.45 to 2.39 ± 0.23 mg kg-1 (Br), 21.8 ± 0.8 to 671 ± 20 mg kg-1 (Cl), and 11,3 ± 1,3 to 154 ± 4 mg kg-1 (S), while for F and I the obtained values were below the respective LOQs in all analyzed samples. In this sense, with the results that were obtained, it was possible to achieve an efficient decomposition of the samples, without volatilization losses, with digests free of interferences and compatible with multiple determination techniques.