动能歧视模式电感耦合等离子体质谱法测定地球化学样品中15种稀土元素

Kinetic Energy Discrimination-Determination of Rare Earth Elements in Geochemical Samples by ICP-MS

勘查地球化学样品中稀土元素含量较低,基体效应和多原子离子干扰严重,准确测定难度较大。采用HNO3+HF+H2SO4消解样品,王水复溶的方式提取残留物,一方面确保样品消解完全,另一方面使Ba沉淀,降低Ba的氧化物对轻稀土元素的干扰。同时研究发现在动能歧视模式(KED)下仪器的氧化物干扰可以降至最小,测定结果的准确度优于标准模式(STD)测定结果,而且提高了信噪比,降低了方法的检出限。在KED模式下优选出干扰较小的同位素作为测定同位素,以Rh作为内标元素,将样品溶液稀释至1 000倍,基体效应和仪器的稳定性得到了有效的改善,方法经过6个国家一级标准物质的验证,测定结果与认定值相符,精密度(RSD,n=12)均小于15%。

The content of rare earth elements is generally low in geochemical samples so that the interference comes from the matrix effection and the polyatomic ions are serious,which leads to the difficulty for accurate determination.The samples are digested by HNO3+HF+H2SO4,and the residue was extracted by Aqua regia.On one hand,the sample solution was ensured.for complete dissolution;on the other hand,Ba was precipitated so as to exclude the interference of Ba oxides reduces for rare earth elements.The results showed that the oxide interference of the instrument was minimized under the kinetic energy discrimination(KED)mode so that the accuracy was much better than that obtained by using the standard mode(STD),the signal-to-noise ratio(SNR)was improved and the detection limit was greatly reduced.In the KED mode,the isotopes with less interference are selected as the measurement isotopes by using Rh as internal standard element,the sample solution was then diluted to 1000times so that the matrix effect and long-term stability of the instrument were effectively improved.This method was corroborated with Rocks,Stream sediments and soils certified reference materials,the results were within the allowable error ranges of the certified values and relative standard deviations were less than 15%(n=12).