Determination of bromine and iodine in shrimp and its parts by ICP-MS after decomposition using microwave-induced combustion

Abstract

A digestion method based on microwave-induced combustion (MIC) was developed for bromine and iodine determination in shrimp and its parts (shells and head, and tissue) by inductively coupled plasma mass spectrometry (ICP-MS). Ammonium nitrate solution was used as an igniter for combustion and vessels were pressurized with O₂ at 20 bar. Solutions of (NH₄)₂CO₃ (50 or 100 mmol L⁻¹) and NH₄OH (25, 50, 75 or 100 mmol L⁻¹) were evaluated as absorbing media for Br and I. Better results were obtained for Br and I determination using 50 mmol L⁻¹ NH₄OH as absorbing medium. Using this solution, blanks were always negligible and memory effects were virtually absent. The accuracy of the proposed MIC method was evaluated using a reference material (NIST 8414) with agreement better than 99% for both analytes. The limits of detection by MIC and further ICP-MS determination (Br: 0.12 μg g⁻¹; I: 0.001 μg g⁻¹) were better than those obtained when the extraction procedure was used. Additionally, a microwave-assisted alkaline extraction method was also evaluated using 0.11 mol L⁻¹ TMAH as extractant solution. However, alkaline extraction was only feasible for shrimp tissue and not for whole shrimp or shells. Decomposition using MIC allowed the determination of Br and I by ICP-MS in shrimp and the respective distribution of these elements in shells and head, and in tissue avoiding the use of concentrated digestion or extraction solutions.