Food Safety and Environmental Stewardship Program

Total dissolved iodide (I−) and iodine (I2) are determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) using iodine vapor generation. I− is determined directly after filtration. It is oxidized in situ to I2 with potassium nitrite in sulfuric acid in a simplified continuous-flow manifold. A standard nebulizer separates I2, which is quantitated by ICP-AES at 206.16 nm. The instrument detection limit for I− is 0.04 μg/mL. Recoveries from seawater, saltwater, and freshwater standard reference materials ranged from 86.5 to 118.6%, averaging 98.2%. I2 is analyzed by ICP-AES without the iodine vapor generation reagents. For samples containing both I2 and I−, total iodine is determined with oxidizing reagents, I2 alone is determined without oxidizing reagents, and I− is calculated from the difference. The analysis is specific for the 2 species (I− and I2). Stability of I2 in environmental samples was briefly investigated. This method demonstrates good accuracy and precision for samples of environmental interest and is especially well suited to small samples. It requires no additional apparatus for iodine generation or sample introduction.