Characterization of Oxide Interference for the Determination of Rare Earth Elements in Geological Samples by High Resolution ICP-MS

The main factor which limits the analysis accuracy and precision in the determination of rare earth elements (REEs) in geological samples is the interference of polyatomic ions, especially the interferences from oxide and hydroxide of light rare earth elements and natural Ba isotopes. A method for the determination of REEs in geological samples has been developed by using high temperature and pressure digestion and performing measurements using High Resolution Inductively Coupled Plasma-Mass Spectrometry (HR-ICP-MS). The oxide interferences were studied under low, moderate and high resolution modes, in order to select the best measured isotopes and appropriate resolution. The results show that oxides of light rare earth elements Ce, Pr, Nd, Sm and Ba oxide will produce interferences under low or middle resolution modes, and the value of Gd is seriously deviated. Under high resolution mode, the interference from ¹⁵⁷Gd cannot be eliminated completely. When the Pr/Gd ratio is greater than 100, the value of Gd must be mathematically corrected. Meanwhile, interference corrections are unnecessary for light REEs oxide and hydroxide on heavy REEs and Ba on Eu.