为解决在电感耦合等离子体质谱法(ICP-MS)测定碘时易出现分解效率不高、碘记忆效应强、多原子离子干扰及基体效应等问题,进行了题示研究。粮食类、豆类样品(干样)去除杂物后,用水洗净,于60 ℃烘干;蔬菜、水果类样品(鲜样)用水洗净,晾干,取可食用部分,制成匀浆。取上述样品0.500 0 g置于高压密闭聚四氟乙烯内罐中,加入15 mL 10%(体积分数)氨水溶液,于200 ℃密封消解过夜。冷却后,用水将溶液转移至聚四氟乙烯比色管中,定容至25 mL,经0.45 μm混合纤维素滤膜过滤,采用ICP-MS测定滤液中碘的含量。选择与碘质量数最为接近的碲作为内标元素,以氦气碰撞模式进行分析,并通过优化氦气流量,降低了空白值,有效消除了基体效应及多原子离子产生的质谱干扰。碘的质量浓度在50.0 μg·L^-1内与对应的信号强度呈线性关系,检出限(3s)为0.005 mg·kg^-1。方法用于国家一级标准物质分析,测定值的相对标准偏差(n=12)为2.7%~6.2%,相对误差为-7.5%~6.9%。

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%.