用电感耦合等离子体质谱（ＩＣＰ－ＭＳ）研究了直接测定９９．９９９％Ｅｒ２Ｏ３中１４个稀土杂质的含量．采用基体匹配法扣除Ｅｒ对Ｈｏ和Ｔｍ元素的基体峰背景干扰，选择同位素Ｅｒ１６２为内标，可显著提高测量精度和准确度。 Ｈｏ和Ｔｍ元素的测定下限分别为 ４．０ μｇ／ｇ和 １．２μｇ／ｇ，其余稀土元素的测定下限均＜０．２μｇ／ｇ；加标回收率 ９５％～１０５％；相对标准偏差为４．３％～１０．０％． The direct determination of 14 rare earth impurities in 99.999% Er2O3 was studied by inductively coupled plasma mass spectrometry (ICP-MS). Substrate matching method was used to deduce the matrix background interference of Er on Ho and Tm elements. Selecting isotope Er162 as the internal standard can significantly improve the measurement accuracy and accuracy. The lower limits of determination of Ho and Tm were 4.0 μg / g and 1.2 μg / g respectively, and the limits of determination of other rare earth elements were all less than 0.2 μg / g. The recoveries were 95% -105%. The relative standard deviations 4.3% ~ 10.0%.