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

Abstract

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 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%. CONCLUSIONS The proposed method meets the requirement of high-precision measurement of Sr and Nd isotopic composition in geological samples.

Keywords

• microwave digestion
• elution curve
• strontium
• neodymium
• column residuals
• multi-collector inductively coupled plasma-mass spectrometry