Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803-4101, USA.
Rapid Commun Mass Spectrom. 2011 Jan 15;25(1):20-4. doi: 10.1002/rcm.4825.
Cryogenic or heating methods have been widely used in experiments involving gas purification or isolation and in studying phase changes among solids, liquids, or gases for more than a century. Thermal gradients are often present in these routine processes. While stable isotopes of an element are known to fractionate under a thermal gradient, the largely diffusion-driven fractionation is assumed to be entirely mass-dependent. We report here, however, that distinct non-mass-dependent oxygen isotope fractionation can be generated when subjecting rarefied O(2) gas in a closed system to a simple thermal gradient. The Δ(17) O value, a measure of the (17) O anomaly, can be up to -0.51‰ (standard deviation (s.d.) 1σ = 0.03) in one of the temperature compartments. The magnitude of the (17) O anomalies decreased with increasing initial gas pressures. The authenticity of this phenomenon is substantiated by a series of blank tests and isotope mass-balance calculations. The observed anomalies are not the result of H(2) O contamination in samples or in isotope ratio mass spectrometry. Our finding calls attention to the importance of thermal gradient-induced isotope fractionation and to its implications in laboratory procedures, stable isotope geochemistry, and the physical chemistry of rarefied gases.
低温或加热方法在涉及气体净化或分离的实验中以及在研究固体、液体或气体之间的相变方面已经被广泛应用了一个多世纪。在这些常规过程中经常存在温度梯度。虽然已知元素的稳定同位素在温度梯度下会发生分馏，但这种主要由扩散驱动的分馏被认为完全是质量依赖的。然而，我们在这里报告，当在封闭系统中对稀薄的 O(2)气体施加简单的温度梯度时，可以产生明显的非质量依赖的氧同位素分馏。Δ(17)O 值是衡量 (17)O 异常的指标，在其中一个温度隔室中可以达到 -0.51‰（标准偏差 (s.d.) 1σ=0.03）。(17)O 异常的幅度随初始气体压力的增加而减小。通过一系列空白测试和同位素质量平衡计算证实了这一现象的真实性。观察到的异常不是样品中 H(2)O 污染或同位素质谱质量分析的结果。我们的发现引起了对温度梯度诱导同位素分馏的重要性及其在实验室程序、稳定同位素地球化学和稀薄气体物理化学中的意义的关注。
