High-precision Measurement of Strontium and Neodymium Isotopic Composition by Multi-collector Inductively Coupled Plasma-Mass Spectrometry with Microwave Digestion
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摘要: 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。Abstract:
BACKGROUNDDetermination 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. OBJECTIVESTo effectively digest samples and eliminate interferences from the experimental process. METHODSGeological 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. RESULTSThe research shows that after ten times usages Sr and Nd procedure, blanks of the resin are less than 1.0 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 AG50W-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-2a, BHVO-2, AGV-2). The acquired 87Sr/86Sr and 143Nd/144Nd ratios are consistent with those in the literature, and the instrumental internal precision 2SE (n=50) and methodological external precision 2SD (n=6) are better than 0.0015%. CONCLUSIONSThe proposed method meets the requirement of high-precision measurement of Sr and Nd isotopic composition in geological samples. -
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表 1 微波消解程序
Table 1. Program of the microwave digestion
步骤 温度
(℃)功率
(W)加热时间
(min)保持时间
(min)1 120 400 5 2 2 160 800 5 5 3 180 1200 4 10 
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表 2 MC-ICP-MS仪器工作参数
Table 2. Working parameters of MC-ICP-MS
工作参数 设定值 冷却气流量 16 L/min 辅助气流量 0.8 L/min 雾化气气压 2.6×105 Pa (via DSN) 射频功率 1100 W 每次测量积分时间 0.4194 s 每组测量次数 10 测量组数 5
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表 3 离子交换柱分离锶和钕的流程
Table 3. Procedure of Sr and Nd separation
步骤 项目 使用试剂和用量 样品引入 离心后上清液 1 洗脱基体 3 mol/L硝酸，6 mL 洗脱基体 3 mol/L硝酸，4 mL 收集锶 Milli-Q水，4 mL 样品引入 离心后上清液 2 洗脱基体 2 mol/L盐酸，10 mL 收集稀土 6 mol/L盐酸，12 mL 样品引入 离心后上清液 3 洗脱基体 0.25 mol/L盐酸，9 mL 收集钕 0.25 mol/L盐酸，6 mL 注：步骤2中样品为步骤1中前6 mL 3 mol/L硝酸淋洗液蒸干后转为2 mol/L盐酸介质的溶液，步骤3中样品为步骤2收集到的稀土馏分蒸干后转为0.25 mol/L盐酸介质的溶液。
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表 4 树脂不同使用次数的流程空白和回收率(n=5)
Table 4. Procedure blanks and recoveries of resin with different times of use (n=5)
树脂使用次数 空白(ng) 回收率(%) Sr Nd Sr Nd 0 0.47 0.34 98 91 5 0.88 0.61 52 73 10 0.92 0.63 23 50
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表 5 87Sr/86Sr和143Nd/144Nd测定结果与文献报道值对比
Table 5. Comparison of 87Sr/86Sr and 143Nd/144Nd in standard samples with the reported values
标样编号 87Sr/86Sr同位素测定 143Nd/144Nd同位素测定 fRb/Sr Sr含量
(μg)87Sr/86Sr测试值 内精度
(2SE)87Sr/86Sr平均值 外精度
(2SD)数据来源 fCe/Nd Nd含量
(μg)143Nd/144Nd测试值 内精度
(2SE)143Nd/144Nd平均值 外精度
(2SD)数据来源 BCR-2 0.137 3.21 0.705042 0.000008 0.705046 0.000008 本文 1.89 1.34 0.512642 0.000003 0.512636 0.000004 本文 5.77 0.705056 0.000007 2.40 0.512638 0.000004 6.90 0.705035 0.000009 2.87 0.512632 0.000004 8.67 0.705043 0.000008 3.60 0.512636 0.000005 10.53 0.705047 0.000006 4.37 0.512632 0.000004 13.80 0.705052 0.000006 5.73 0.512633 0.000003 - - - 0.705019 0.000008 Dominique等[16] - - - 0.512634 0.000006 Dominique等[16] BHVO-2 0.025 3.75 0.703488 0.000008 0.703504 0.000013 本文 1.54 1.16 0.512993 0.000004 0.512989 0.000005 本文 6.73 0.703518 0.000009 2.08 0.512984 0.000005 8.05 0.703504 0.000009 2.49 0.512983 0.000005 10.12 0.703521 0.000010 3.13 0.512993 0.000005 12.29 0.703498 0.000008 3.80 0.512984 0.000006 16.10 0.703495 0.000007 4.98 0.512996 0.000006 - - - 0.703487 0.000007 Dominique等[16] - - - 0.512981 0.000006 Dominique等[16] W-2A 0.103 1.85 0.706996 0.000009 0.707003 0.000010 本文 1.77 0.63 0.512503 0.000007 0.512502 0.000003 本文 3.32 0.707011 0.000009 1.14 0.512506 0.000005 3.97 0.707011 0.000007 1.36 0.512502 0.000008 4.99 0.706992 0.000008 1.71 0.512505 0.000007 6.06 0.706995 0.000007 2.07 0.512499 0.000008 7.94 0.707014 0.000010 2.72 0.512499 0.000007 - - - 0.706973 0.000006 Li等[11] - - - 0.512518 0.000004 Li等[11] AGV-2 0.102 6.28 0.704023 0.000010 0.704026 0.000006 本文 2.28 1.43 0.512776 0.000005 0.512784 0.000008 本文 11.26 0.704021 0.000009 2.57 0.512795 0.000005 13.48 0.704031 0.000011 3.08 0.512776 0.000005 16.94 0.704029 0.000006 3.87 0.512784 0.000006 20.56 0.704031 0.000006 4.69 0.512794 0.000006 26.94 0.704018 0.000008 6.15 0.512776 0.000006 - - - 0.703987 0.000009 Dominique等[16] - - - 0.512790 0.000006 Dominique等[16] 注：fRb/Sr为该标样中铷和锶含量的质量比，Sr含量(μg)为样品引入时锶的理论质量。
fCe/Nd为该标样中铈和钕含量的质量比，Nd含量(μg)为样品引入时钕的理论质量。
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