Non-mass-dependent O-17 anomalies generated by a superimposed thermal gradient on a rarefied O-2 gas in a closed system

作者：Sun Tao; Bao Huiming^*

来源：Rapid Communications in Mass Spectrometry, 2011, 25(1): 20-24.

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 Delta O-17 value, a measure of the O-17 anomaly, can be up to -0.51 parts per thousand (standard deviation (s.d.) 1 sigma = 0.03) in one of the temperature compartments. The magnitude of the O-17 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 H2O 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.

• 出版日期2011-1-15