Determination of Iodine in Compound Minerals, Potassium Iodide and Potassium Iodate Monomers by Inductively Coupled Plasma Mass Spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) in the national standard GB 5009.267-2020 had a wide range of applications and covered all food products. However, it required tetramethylammonium hydroxide (TMAH) extraction for 3-4 h, which took a long time and was not suitable for the analysis of compound minerals and iodide monomers (such as potassium iodide and potassium iodate). Therefore, the study mentioned by title was proposed. 0.2 g of the compound mineral sample was dissolved in 10 mL of 4% (volume fraction) nitric acid solution by ultrasound for 5-10 min and diluted to 50 mL. An aliquot (2.5 mL) was taken, and 5 mL of 10% (volume fraction, the same below) TMAH solution was added. The mixture was made its volume up to 50 mL with water. 0.2 g of potassium iodide or potassium iodate monomer sample was dissolved directly in 10% TMAH solution and made its volume up to 50 mL with water. The solution was diluted 500 times with 1% (volume fraction, the same below) TMAH solution for determination of 1.05% (mass fraction) potassium iodide monomer samples and 1.3% (mass fraction) potassium iodate monomer samples, and 5 000 times with 1% TMAH solution for determination of 10% (mass fraction) potassium iodide monomer samples. Iodine in the above solution was determined by ICP-MS. As shown by the results, the improved extraction method greatly shortened the time. Linear relationship between the signal intensity ratio of iodine to internal standard tellurium and mass concentration of iodine was found in the range of 10.0-50.0 μg·L^-1, with detection limit (3s) of 0.02 μg·g^-1. Test for recovery was made by standard addition method, giving results in the range of 84.0%-106%, with RSDs (n=6) of the determined values less than 9.0%. The method was applied to the analysis of actual compound minerals and samples of potassium iodide and potassium iodate monomers, and the determined results were consistent with the theoretical values (claimed values).