Desenvolvimento de métodos para a determinação de halogênios e enxofre em cogumelos comestíveis

Abstract

In this study the microwave-induced combustion (MIC) was evaluated for the sample preparation of edible mushrooms and further halogens and sulfur determination by ion chromatography (IC). Dry and fresh samples were decomposed. For this, some parameters such as sample mass, combustion aid mass (microcrystalline cellulose) and the absorbing solution (H2O and 50 mmol L -1, 100 mmol L-1 or 150 mmol L-1 NH4OH) were evaluated. The most suitable conditions for mushrooms preparation by MIC were: 500 mg of sample mixed with 50 µL of 6 mol L-1 NH4NO3 for dry mushrooms and 800 mg of sample mixed with 800 mg of cellulose for fresh mushrooms. Ammonium hydroxide (100 mmol L -1) was selected as absorbing solution. The bromine and iodine concentrations were less than limits of detection (LODs) obtained by IC (Br: 6 mg kg-1 and I: 24 mg kg-1). Thus, inductively coupled plasm mass spectrometry (ICP-MS) was used for Br and I determination, and the LODs were considerably lower (Br: 0.066 mg kg-1 and I: 0.014 mg kg-1) than those obtained by IC. It was also not possible the determination of fluorine by IC, in view that the concentrations were below than LOD (23 mg kg-1) for this method. The accuracy of the proposed methods using MIC for sample preparation and further halogens and sulfur determination by IC or further bromine and iodine determination by ICP-MS was evaluated by recovery tests using standard solution. A reference material was used for accuracy evaluation of the method for chlorine and sulfur by IC and, bromine and iodine by ICP-MS. Recoveries when used the standard solution ranged from 95% to 103% for halogens and sulfur determination by IC, and of 105% and 109% for bromine and iodine determination by ICP-MS. When used the reference material, recoveries of 102% and 94% for chlorine and sulfur by IC and, of 87% and 86% for bromine and iodine by ICP-MS, respectively, were obtained. The relative standard deviations were always lower than 9%. Both methods presented suitable accuracy and precision. The proposed methods were applied for the determination of halogens and sulfur in the following mushrooms species: Champignon (white and brown), Shiitake and Shimeji. The chlorine and sulfur concentrations ranged from 523 mg kg-1 to 13053 mg kg-1 , and from 2452 mg kg-1to 6399 mg kg-1, respectively. In turn, bromine and iodine concentrations ranged from 2.49 mg kg-1 to 5.50 mg kg-1 and from < 0.014 mg kg-1 to 0.047 mg kg-1 , respectively. The concentration of fluorine not was detected in the samples.