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ZHANG Le,REN Zhong-yuan,DING Xiang-li,WU Ya-dong,LAI Yong-wang.A Comparison of Microdrilling-TIMS/MC-ICPMS and LA-MC-ICPMS for Micro-sample Sr Isotope Measurement[J].Rock and Mineral Analysis,2014,33(5):615-624
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A Comparison of Microdrilling-TIMS/MC-ICPMS and LA-MC-ICPMS for Micro-sample Sr Isotope Measurement
Received:April 09, 2014  Revised:May 30, 2014
DOI:
Key words: Sr isotope  in-situ analysis  microdrilling  Thermal Ionization Mass Spectrometry/Inductively Coupled Plasma-Mass Spectrometry  multiple-collector Inductively Coupled Plasma-Mass Spectrometry
Author NameAffiliationE-mail
ZHANG Le State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
University of Chinese Academy of Sciences, Beijing 100049, China 
 
REN Zhong-yuan State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China zyren@gig.ac.cn 
DING Xiang-li State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
University of Chinese Academy of Sciences, Beijing 100049, China 
 
WU Ya-dong State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
University of Chinese Academy of Sciences, Beijing 100049, China 
 
LAI Yong-wang State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
University of Chinese Academy of Sciences, Beijing 100049, China 
 
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Abstract:
      Compared to the traditional strontium isotope analytical method, a micro-sample strontium isotope system study can reveal the heterogeneity of analyzed samples and is widely used in various fields of geology, such as crust-mantle interaction, genesis and evolution of magmas, open magma systems, tracing provenance of sedimentary basin and climate research. Accurate measurement of Rb-Sr isotopic ratios is the premise to apply Sr isotope in these research fields. Two detailed and widely used analysis methods for micro-sample Sr isotope measurement are microdrilling-TIMS/MC-ICPMS and LA-MC-ICPMS. These two methods have different advantages and disadvantages in sample preparation, interference correction and measurement in mass spectrometry. The greatest advantage of microdrilling-TIMS/MC-ICPMS is that this technique can acquire high quality data (external precision is better than 100×10-6, 2SD). However the tedious chemical separation is very time-consuming (about 10 days) and the chemical procedure blank must be critical to low level. The large sampling depth (100-2000 μm) and diameter (200-2000 μm) reduce the spatial resolution. However, with chemical separation this method can effectively measure samples with high Rb content. Simple sample preparation and fast analysis are the most outstanding advantages of LA-MC-ICPMS which can analyze lots of samples in a much shorter time than that of microdrilling-TIMS/MC-ICPMS. The laser spot size is mainly from 60 to 300 μm. Based on Sr contents in samples, the method of LA-MC-ICPMS improved spatial resolution, compared to microdrilling-TIMS/MC-ICPMS technique. However, without chemical separation, many kinds of interferences (e.g. Rb, Ca, Kr and REEs) hinder this technique to obtain high quality data (external precision is about 200×10-6, 2SD and accuracy is about 150×10-6). LA-MC-ICPMS is only suitable for high Sr and low Rb samples, instead of samples with high content of interferences. Further studies are required for the microdrilling-TIMS/MC-ICPMS method to improve the efficiency of chemical separation, also microdrilling technology with increasing of spatial resolution by reducing spot diameter and depth. Meanwhile, a better solution for interferences of Kr, Rb and REEs is needed for LA-MC-ICPMS in order to improve precision and accuracy of high interference samples. Instrumental sensitivity improvement is also needed to satisfy Sr isotope measurement for samples with relative low Sr content.