Fleisher Adam J, Yi Hongming, Srivastava Abneesh, Polyansky Oleg L, Zobov Nikolai F, Hodges Joseph T
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA.
These authors contributed equally: Adam J. Fleisher, Hongming Yi.
Nat Phys. 2021;17. doi: 10.1038/s41567-021-01226-y.
Measurements of isotope ratios are predominantly made with reference to standard specimens that have been characterized in the past. In the 1950s, the carbon isotope ratio was referenced to a belemnite sample collected by Heinz Lowenstam and Harold Urey in South Carolina's Pee Dee region. Due to the exhaustion of the sample since then, reference materials that are traceable to the original artefact are used to define the Vienna Pee Dee Belemnite (VPDB) scale for stable carbon isotope analysis. However, these reference materials have also become exhausted or proven to exhibit unstable composition over time, mirroring issues with the international prototype of the kilogram that led to a revised International System of Units. A campaign to elucidate the stable carbon isotope ratio of VPDB is underway, but independent measurement techniques are required to support it. Here we report an accurate value for the stable carbon isotope ratio inferred from infrared absorption spectroscopy, fulfilling the promise of this fundamentally accurate approach. Our results agree with a value recently derived from mass spectrometry, and therefore advance the prospects of SI-traceable isotope analysis. Further, our calibration-free method could improve mass balance calculations and enhance isotopic tracer studies in CO source apportionment.
同位素比率的测量主要是参照过去已被表征的标准样品进行的。在20世纪50年代，碳同位素比率是以海因茨·洛温斯坦姆和哈罗德·尤里在南卡罗来纳州皮迪地区采集的一个箭石样品为参照的。从那时起，由于该样品已耗尽，可追溯到原始样品的参考物质被用于定义用于稳定碳同位素分析的维也纳皮迪箭石（VPDB）标度。然而，这些参考物质也已耗尽或被证明随着时间推移成分不稳定，这反映了千克国际原器出现的问题，进而导致了国际单位制的修订。一项阐明VPDB稳定碳同位素比率的活动正在进行，但需要独立的测量技术来支持它。在此，我们报告了通过红外吸收光谱法推断出的稳定碳同位素比率的准确值，实现了这种从根本上准确的方法的前景。我们的结果与最近通过质谱法得出的值一致，因此推进了可溯源至国际单位制的同位素分析的前景。此外，我们的免校准方法可以改进质量平衡计算，并加强在CO源分配中的同位素示踪研究。
