title: Non-mass-dependent (17) O anomalies generated by a superimposed thermal gradient on a rarefied O(2) gas in a closed system.
abstract: 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.
authors.affiliation: Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803-4101, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Sun
authors.forename: Huiming
authors.initials: H
authors.lastname: Bao
mesh_terms: D004867:Equipment Design; D013058:Mass Spectrometry / Q000379:methods*; D010100:Oxygen / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000737:chemistry*; D011312:Pressure; D013696:Temperature
chemical_list: D010103:Oxygen Isotopes; D010100:Oxygen