动能歧视模式ICP-MS测定地球化学样品中14种痕量元素

应用传统ICP-MS法测定勘查地球化学样品中Ag、Cd等痕量元素,基体效应和多原子离子干扰严重,准确测定的难度较大。本文基于当前ICP-MS消除干扰技术,分析了ICP-MS标准模式(STD)及动能歧视模式(KED)测定地球化学样品中Ag、Cd等14种痕量元素的有效性,通过比较这两种模式的测定效果,在此基础上确定了各元素的有效测定模式。结果表明:在KED模式下,基体元素如Zr、Nb氧化物的产率降低,基本上消除了Zr、Nb氧化物对痕量元素Ag、Cd的多原子离子干扰。KED模式提高了信噪比,降低了方法检出限,如Ag、Cd的检出限分别为0. 004mg/kg、0. 005mg/kg,其他12种元素的检出限也低于多目标地球化学调查76种元素分析方案中的检出限。测定痕量元素的准确度显著优于STD模式。实验中采用简单的硝酸-氢氟酸-高氯酸消解样品,残渣用王水复溶,结合KED模式下优选出干扰较小的同位素作为测定同位素,以Rh作为内标校正仪器产生的信号漂移,将样品溶液稀释至1000倍,基体效应降低至最小。本方法经国家一级标准物质的验证,测定结果与认定值相符,可为勘查地球化学提供高质量数据。

Determination of 14 Trace Elements in Geochemical Samples by ICP-MS Using Kinetic Energy Discrimination Mode

BACKGROUND:Traditional inductively coupled plasma-mass spectrometry (ICP-MS) determination of trace elements such as Ag and Cd in geochemical samples is seriously affected by the matrix effect and multiple polyatomic ions, making it difficult to measure these elements accurately.
OBJECTIVES:To compare the results of ICP-MS standard mode (STD) and kinetic energy discrimination mode (KED), and determine the valid determination modes of each element.
METHODS:The samples were digested by HNO₃-HF-HClO₄, and the residue was dissolved in aqua regia. Under the KED mode, the isotopes with less interference were selected as the determination isotopes. Rh was used as the internal standard element to correct the signal drift, and the sample solution was diluted by 1000. Under these conditions, the matrix effect was minimized.
RESULTS:The productivity of matrix elements such as Zr and Nb oxides was reduced, and the interference of oxides on Ag and Cd was minimized under the KED mode. The KED mode improved the signal-to-noise ratio and reduced the detection limits of this method with Ag and Cd, detection limits of 0.004mg/kg and 0.005mg/kg, respectively. The detection limits of the other 12 elements were also lower than those of 76 element analysis schemes in a multi-objective geochemical survey. The accuracy of determination of trace elements was significantly better than that of the STD mode.
CONCLUSIONS:The method has been verified by the first-class national reference material and the analytical results are in good agreement with the certified values. The method provides high-quality data for exploration geochemistry.