微波消解-多接收电感耦合等离子体质谱高精度测定锶钕同位素组成

High-precision Measurement of Strontium and Neodymium Isotopic Composition by Multi-collector Inductively Coupled Plasma-Mass Spectrometry with Microwave Digestion

应用多接收器电感耦合等离子体质谱仪(MC-ICP-MS)测定地质样品中锶、钕同位素组成时,化学前处理流程冗长、复杂,且容易出现样品未完全溶解的现象。本文采用微波消解法消解样品,在保证消解效果的前提下有效地缩短了溶样时间,在此基础上研究了锶、钕化学分离和质谱测试流程,重点考察了树脂柱的回收率和记忆效应。结果表明:树脂经10次使用后的锶、钕流程空白均低于1.0 ng,但回收率明显下降,分别由原来的98%和90%降到20%和50%,若待测样品中锶、钕含量较低,所接收的锶、钕则达不到质谱仪测试范围,因此建议锶特效树脂使用次数不超过5次,AG50W-X8稀土柱和Ln树脂使用次数不超过10次。整套流程应用于国际地质标准样品(BCR-2、W-2a、BHVO-2、AGV-2)的锶、钕分离,MC-ICP-MS所得的87Sr/86Sr、143Nd/144Nd测定值与文献报道值一致,仪器的内精度2SE(n=50)和方法的外精度2SD(n=6)均优于0.0015%,表明该流程可以满足地质样品中锶、钕同位素高精度测定的要求。

BACKGROUND： Determination of strontium（ Sr） and neodymium（ Nd） isotopic composition in geological samples by Multi-collector Inductively Coupled Plasma-Mass Spectrometry（ MC-ICP-MS） needs a lengthy and complex chemical preparation procedure. Moreover,samples cannot be dissolved completely.OBJECTIVES： To effectively digest samples and eliminate interferences from the experimental process.METHODS： Geological samples were dissolved by microwave digestion. The processes of Sr,Nd chemical separation and mass spectrometry analyses were studied. In particular,the recovery and memory effect of resin column were investigated.RESULTS： The research shows that after ten times usages Sr and Nd procedure,blanks of the resin are less than1. 0 ng. However,the recovery decreases significantly from 98% to 20% and 90% to 50%,respectively. If the analyzed samples contain low concentrations of Sr and Nd,which are insufficient for mass spectrometry analysis,it is suggested that Sr special effect resin should be used no more than 5 times and AG50 W-X8 and Ln resin should be used no more than 10 times. The entire procedure is applied in the separation of Sr and Nd of international standard geological samples（ BCR-2,W-2 a,BHVO-2,AGV-2）. The acquired87 Sr/86 Sr and143 Nd/144 Nd ratios are consistent with those in the literature,and the instrumental internal precision 2 SE（ n = 50） and methodological external precision 2 SD（ n = 6） are better than 0. 0015%.CONCLUSIONS： The proposed method meets the requirement of high-precision measurement of Sr and Nd isotopic composition in geological samples.