应用GasBench Ⅱ－IRMS优化碳氧同位素分析方法

摘要

GasBenchⅡ－连续流稳定同位素质谱仪（IRMS）联用在线分析已成为碳酸盐碳氧同位素分析测试的常用方法，已有研究认为不同的实验条件直接影响δ13 C和δ18 O同位素测试结果的准确性。但这些报道未对该联用方法所涉及的实验条件进行综合分析。本文系统研究了GasBenchⅡ－IRMS法中各种实验条件（包括排空时间、反应温度、反应时间和色谱分离温度）对碳氧同位素测试结果的综合影响。结果表明：排空时间大于9 min时可有效消除空气对测试结果的干扰，不同的反应温度和时间对碳氧同位素分析结果均有一定影响，经条件优化确定反应温度为72℃，反应时间为60 min，色谱分离温度为60℃。在优化的实验条件下，碳氧同位素分析精度分别优于0．03‰和0．05‰，达到了国际分析测试水平。同时，选择合适的同位素数据归一化方法可以进一步保证碳氧同位素测试结果的准确性和可靠性。通过分析近4000件实际样品，对比单一标准物质校准和双标准物质校准同位素归一化方法的计算结果，发现双标准物质的校准偏差小于单一标准物质的校准偏差，因此建议采用双标准物质校准法进行样品同位素标准化计算。本研究为 GasBenchⅡ－IRMS 联用技术中实验条件的选取提供了一定的参考。同时提出，由于样品成分复杂且不均一，在分析实际样品时需要根据样品的性质进一步对实验条件进行考察。%The continuous flow technique coupled with GasBenchⅡ-Isotope Ratio Mass Spectrometry (IRMS ) became the routine method to analyse the stable carbon and oxygen isotope compositions of carbonate.Previous studies revealed that the isotope results were influenced by the various experimental conditions.However,rare studies have assessed the influences of multiple experimental conditions on the isotope results.Here,all reaction conditions including flushing time,reaction temperature,reaction time and chromatographic separation temperature have been evaluated systematically.Flushing time longer than 9 minutes can eliminate the interference of air. Different reaction temperatures and time have distinct influences on the isotope values.72℃,60 minutes and 60℃have been chosen for the reaction temperature, reaction time and chromatographic separation temperature, respectively.The analytical precisions are better than 0.03‰(forδ13C)and 0.05 (forδ18O)under the optimized conditions.In addition,different isotope normalization methods would affect the isotope results.Two isotope normalization methods have been compared,based on isotope data of about 4000 samples.The calculated results from two standard samples are more precise and reliable than those from single standard sample.The study provides a reference for experimental conditions in GasBench Ⅱ-IRMS technology,ensuring the accuracy and reliability for carbon and oxygen isotope analysis.At the same time,the experimental conditions should be further investigated in real samples analysis due to the inhomogeneous and complex sample compositions.