溶样方法对电感耦合等离子体质谱法测定铝土矿中稀土元素的影响

Influence of sample dissolution method on determination of rare earth elements in bauxite by inductively coupled plasma mass spectrometry

对电感耦合等离子体质谱法（ICP-MS）测定痕量稀土元素的条件进行了优化,并讨论了敞开式混合酸多次分解法、封闭溶样法、碱熔法3种溶样方法对ICP-MS测定铝土矿中稀土元素的影响。结果表明：采用敞开式混合酸多次分解法和碱熔法溶解样品后,均可实现ICPMS对铝土矿样品中稀土元素的测定;敞开式混合酸多次分解法与ICP-MS相结合测定稀土元素的方法检出限为0.003～0.028μg/g,较碱熔法0.010～0.066μg/g低;敞开式混合酸多次分解法与ICP-MS相结合测定稀土元素的相对标准偏差（RSD）为1.1%～2.8%,碱熔法为2.8%～5.6%,这说明敞开式混合酸多次分解法与ICP-MS相结合方法的测定精密度较高。敞开式混合酸多次分解法具有操作简便,对仪器污染小的优点,但对于个别类型铝土矿样品（如一水硬铝石型铝土矿）不能够完全溶解,从而导致ICP-MS对个别铝土矿样品中稀土元素的测定结果偏低;碱熔法能将所有类型铝土矿样品全部溶解,因此碱熔法与ICP-MS相结合可测定所有类型铝土矿样品中的稀土元素,但该法溶样时试剂用量大、流程复杂,易带来大量的基体,会给仪器带来污染。因此采用ICP-MS对铝土矿中稀土元素进行测定时,建议先采用敞开式混合酸多次分解法进行溶样,如果能将样品溶解完全,则直接采用ICP-MS进行测定,如不能,则需要重新采用碱熔法对样品进行处理后再采用ICP-MS进行测定。将混合酸多次分解法和碱熔法2种溶样方法分别与ICP-MS结合应用于铝土矿实际样品中稀土元素的测定,加标回收率分别为92%～110%、90%～103%。

The conditions for determination of trace rare earth elements by inductively coupled plasma mass spectrometry（ICP-MS）were optimized.The influence of three sample dissolution methods（including multi-decomposition with mixed acid in open environment,dissolution in closed system and alkali fusion）on the determination of rare earth elements in bauxite by ICP-MS was discussed.The results showed that the determination of rare earth elements in bauxite sample by ICP-MS could be realized using two methods above,i.e.,multi-decomposition with mixed acid in open environment and alkali fusion.For the method of multi-decomposition with mixed acid in open environment combined with ICP-MS,the detection limits of rare earth elements were 0.003-0.028μg/g,which was lower than that of alkali fusion method（0.010-0.066μg/g）.Their corresponding relative standard deviation（RSD）was 1.1%-2.8% and 2.8%-5.6%,respectively.It indicated that the determination precision of multi-decomposition with mixed acid in open environment combined with ICP-MS was relatively high.Moreover,multi-decomposition with mixed acid in open environment had some advantages such as simple operation and low pollution to instrument.However,little bauxite sample（such as diasporic bauxite）could not be fully dissolved,resulting in lower determination results of rare earth elements.For alkali fusion method,all types of bauxite samples could be fully dissolved,so it was applicable for determination of rare earth elements in all types of bauxite samples.Nevertheless,this method had some disadvantages such as large dosage of reagents for sample dissolution,complex procedure,introduction of much matrix and pollution to instrument.Therefore,during the determination of rare earth elements in bauxite by ICP-MS,the method of multi-decomposition with mixed acid in open environment was preferentially recommended for sample preparation.If the sample was fully dissolved,the solution could be directly determined by ICP-MS.If the sample could not be fully dissolved,the sample should be retreated by alkali fusion and determined by ICP-MS.The two sample dissolution methods,such as multi-decomposition with mixed acid in open environment and alkali fusion,were combined with ICP-MS and applied to the determination of rare earth elements in bauxite actual samples.The recoveries were 92%-110% and 90%-103%,respectively.