Yin Xijie, Chen Zhigang
Third Institute of Oceanography, State Oceanic Administration, Xiamen, Fujian, 361005, China.
J Mass Spectrom. 2014 Dec;49(12):1298-305. doi: 10.1002/jms.3463.
The thermal conversion/elemental analyzer-isotope ratio mass spectrometer (TC/EA-IRMS) is widely used to measure the δ(18) O value of various substances. A premise for accurate δ(18) O measurement is that the oxygen in the sample can be converted into carbon monoxide (CO) quantitatively or at least proportionally. Therefore, a precise method to determine the oxygen yield of TC/EA-IRMS measurements is needed. Most studies have used the CO peak area obtained from a known amount of a solid reference material (for example, benzoic acid) to calibrate the oxygen yield of the sample. Although it was assumed that the oxygen yield of the solid reference material is 100%, no direct evidence has been provided. As CO is the analyte gas for δ(18) O measurement by IRMS, in this study, we use a six-port valve to inject CO gas into the TC/EA. The CO is carried to the IRMS by the He carrier gas and the CO peak area is measured by the IRMS. The CO peak area thus obtained from a known amount of the injected CO is used to calibrate the oxygen yield of the sample. The oxygen yields of commonly used organic and inorganic reference materials such as benzoic acid (C6 H5 COOH), silver phosphate (Ag3 PO4 ), calcium carbonate (CaCO3 ) and silicon dioxide (SiO2 ) are investigated at different reactor temperatures and sample sizes. We obtained excellent linear correlation between the peak area for the injected CO and its oxygen atom amount. C6 H5 COOH has the highest oxygen yield, followed by Ag3 PO4 , CaCO3 and SiO2 . The oxygen yields of TC/EA-IRMS are less than 100% for both organic and inorganic substances, but the yields are relatively stable at the specified reactor temperature and for a given quantity of sample.
热转换/元素分析仪-同位素比率质谱仪（TC/EA-IRMS）被广泛用于测量各种物质的δ(18)O值。准确测量δ(18)O的一个前提是样品中的氧能够被定量或至少按比例转化为一氧化碳（CO）。因此，需要一种精确的方法来确定TC/EA-IRMS测量的氧产率。大多数研究使用从已知量的固体参考物质（例如苯甲酸）获得的CO峰面积来校准样品的氧产率。尽管假定固体参考物质的氧产率为100%，但尚未提供直接证据。由于CO是通过IRMS测量δ(18)O的分析气体，在本研究中，我们使用六通阀将CO气体注入TC/EA。CO由氦载气携带至IRMS，并由IRMS测量CO峰面积。从已知量的注入CO中获得的CO峰面积用于校准样品的氧产率。在不同的反应器温度和样品量下，研究了常用有机和无机参考物质如苯甲酸（C6H5COOH）、磷酸银（Ag3PO4）、碳酸钙（CaCO3）和二氧化硅（SiO2）的氧产率。我们获得了注入CO的峰面积与其氧原子量之间的良好线性相关性。C6H5COOH的氧产率最高，其次是Ag3PO4、CaCO3和SiO2。对于有机和无机物质，TC/EA-IRMS的氧产率均小于100%，但在指定的反应器温度和给定的样品量下，产率相对稳定。
