表面热电离同位素稀释质谱法的计算及质量分馏效应校正  

Calculation Methods and Mass Fractionation Correction of Spiked Isotopic Ratios with Thermal Ionization Isotope Dilution Mass Spectrometry

作　　者：颜妍 崔建勇[1] 张天睿 汤书婷[1] 朱键铭 YAN Yan;CUI Jian-yong;ZHANG Tian-rui;TANG Shu-ting;ZHU Jian-ming(Beijing Research Institute of Uranium Geology,Beijing 100029)

机构地区：[1]核工业北京地质研究院

出　　处：《质谱学报》2019年第5期492-498,I0005,共8页Journal of Chinese Mass Spectrometry Society

摘　　要：表面热电离同位素稀释质谱法(ID-TIMS)是国际公认的基准方法之一。本文以稀释分析锶同位素为例,详细介绍了其计算和推导过程,提出基于指数近似模式的稀释分析同位素分馏校正的方法。该方法适用于校正含有两对参考比值的元素静态多接收稀释分析同位素比值的质量分馏,与指数校正方法和对数校正方法相比,计算过程更简单。还讨论了稀释剂同位素比值准确度对稀释分析同位素比值的影响及其质量分馏的校正方法,通过数学迭代计算质量分馏系数,得到稀释剂测量的质量分馏系数和准确的同位素比值。采用建立的质量分馏校正方法稀释分析NBS987,结果表明,在误差范围内与其参考值(87 Sr/86 Sr=0.710 237±8(1σ))一致。Isotope dilution thermal ionization mass spectrometry(ID-TIMS)combined with the advantage of thermal ionization mass spectrometry in isotope measurement with isotope dilution technology is one of primary method of measurement.ID-TIMS has the following advantages:1)high accuracy;2)quantitative recovery of measured elements is not required in the process of experiment.Mass fractionation effect is difficult to obtain accurately and it is the main factor affecting the accurate determination of isotope composition.Taking the analysis of strontium isotope ratio as an example,the whole calculation and derivation process were introduced.The method for mass fractionation correction based on exponential approximation was proposed.It could achieve the goal of obtaining isotopic ratio and element content at the same time by weighing one sample and was suitable for isotope with two internal reference isotopic ratios in static multicollector measurements mode.The exponential approximation was similar to the linear correction law formula transformed from the complex exponential correction mode,the calculation method was simple compared to those using Power law and Exponential law.In addition,the influence of isotope ratio in spike on the isotope ratio of dilution analysis was also be discussed.By changing the proportion of standard samples to spikes,a series of strontium isotope ratios in standard samples could be obtained through calculation.The results showed that with the increased of mixing 84 Sr/86 Sr ratio,the deviation between the calculated 87 Sr/86 Sr in standard samples and the true value increased gradually.Therefore,mass fractionation correction for the isotope ratio of spike was necessary.Theoretically,if isotope ratio of spike was true value,the formula calculated 87 Sr/86 Sr of standard samples should be consistent,regardless of the mixing 84 Sr/86 Sr ratio.According to this theory,several standard samples were weighed with different proportions of spike,then the mixing isotopic composition and isotopic compositi

关 键 词：表面热电离同位素稀释质谱法(ID-TIMS) 质量分馏 校正 

分 类 号：O657.63[理学—分析化学]