Gas Sensing Metrology Group, Chemical Sciences Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA.
Surface and Trace Chemical Analysis Group, Materials Measurement Science Division, Materials Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA.
Anal Bioanal Chem. 2018 Jul;410(17):4153-4163. doi: 10.1007/s00216-018-1064-0. Epub 2018 May 25.
Isotope ratio measurements have been conducted on a series of isotopically distinct pure CO gas samples using the technique of dual-inlet isotope ratio mass spectrometry (DI-IRMS). The influence of instrumental parameters, data normalization schemes on the metrological traceability and uncertainty of the sample isotope composition have been characterized. Traceability to the Vienna PeeDee Belemnite(VPDB)-CO scale was realized using the pure CO isotope reference materials(IRMs) 8562, 8563, and 8564. The uncertainty analyses include contributions associated with the values of iRMs and the repeatability and reproducibility of our measurements. Our DI-IRMS measurement system is demonstrated to have high long-term stability, approaching a precision of 0.001 parts-per-thousand for the 45/44 and 46/44 ion signal ratios. The single- and two-point normalization bias for the iRMs were found to be within their published standard uncertainty values. The values of C/C and O/O isotope ratios are expressed relative to VPDB-CO using the [Formula: see text] and [Formula: see text] notation, respectively, in parts-per-thousand (‰ or per mil). For the samples, value assignments between (-25 to +2) ‰ and (-33 to -1) ‰ with nominal combined standard uncertainties of (0.05, 0.3) ‰ for [Formula: see text] and [Formula: see text], respectively were obtained. These samples are used as laboratory reference to provide anchor points for value assignment of isotope ratios (with VPDB traceability) to pure CO samples. Additionally, they serve as potential parent isotopic source material required for the development of gravimetric based iRMs of CO in CO-free dry air in high pressure gas cylinder packages at desired abundance levels and isotopic composition values. Graphical abstract CO gas isotope ratio metrology.
采用双进样同位素比质谱（DI-IRMS）技术，对一系列具有不同同位素特征的纯 CO 气体样品进行了同位素比测量。研究了仪器参数、数据归一化方案对样品同位素组成计量溯源性和不确定度的影响。利用纯 CO 同位素标准物质（IRMs）8562、8563 和 8564，实现了与维也纳 PeeDee 贝壳（VPDB）-CO 标度的溯源。不确定性分析包括与 IRMs 值以及我们测量的重复性和再现性相关的贡献。我们的 DI-IRMS 测量系统具有很高的长期稳定性，对于 45/44 和 46/44 离子信号比，其精度接近 0.001 parts-per-thousand。IRMs 的单点和两点归一化偏差均在其公布的标准不确定度值范围内。C/C 和 O/O 同位素比值的值分别用[Formula: see text]和[Formula: see text]表示，相对于 VPDB-CO 的变化范围为(-25 至+2) ‰和(-33 至-1) ‰，单位为 parts-per-thousand（‰或 per mil）。对于这些样品，获得的[Formula: see text]和[Formula: see text]值分别在(-25 至+2) ‰和(-33 至-1) ‰之间，其标称组合标准不确定度分别为(0.05, 0.3) ‰。这些样品可用作实验室参考，为纯 CO 样品中具有 VPDB 溯源性的同位素比值赋值提供基准点。此外，它们还可用作在高压钢瓶包装中的 CO 自由干燥空气中开发 CO 同位素比质量基准 IRMs 所需的潜在母同位素源材料，以达到所需的丰度水平和同位素组成值。
