Determination of Iodine in Plant Samples by Ammonia Sealed Digestion-Inductively Coupled Plasma Mass Spectrometry

In order to solve the problems of low decomposition efficiency, strong iodine memory effect, multi atom ion interference, and matrix effect in the determination of iodine by inductively coupled plasma mass spectrometry (ICP-MS), the study mentioned by title was carried out. After removing impurities, the grain and bean samples (dry samples) were washed with water and heated to dryness at 60 ℃. The vegetable and fruit samples (fresh samples) were washed with water and dried, and the edible portion was taken to make a homogenate. The above sample (0.500 0 g) was taken and placed in a high pressure sealed polytetrafluoroethylene inner tank, adding 15 mL of 10% (volume fraction) ammonia solution. The mixture was sealed and digested at 200 ℃ for overnight. After cooling, the solution was transferred with water to a polytetrafluoroethylene colorimetric tube, made its volume up to 25 mL, and filtered through 0.45 μm mixed cellulose filter membrane. Iodine in the filtrate was determined by ICP-MS. Tellurium which was closest to the iodine in mass number was selected as the internal standard element, using the helium collision mode for analysis, so the blank value was reduced, and the matrix effect and the mass spectrum interference caused by multi atom ions were eliminated effectively by optimizing the flow rate of helium. Linear relationship between the corresponding signal intensity and mass concentration of iodine was found within 50.0 μg·L^-1, with detection limit (3s) of 0.005 mg·kg^-1. This method was applied to analysis of the national primary standard material, with RSDs (n=12) of the determined values in the range of 2.7%-6.2%, and the relative error in the range of -7.5%-6.9%.