A method to induce and assess isotopic equilibrium of oxygen

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• 作者：Aregbe ; Y. ; Valkiers ; S. ; Gonfiantini ; R. ; Nø ; rgaard ; J. ; Taylor ; P.D.P.
• 关键词：Isotopic equilibrium of oxygen ; Gas isotope mass spectrometry ; Synthetic isotope mixtures ; Isotope amount ratio ; Oxygen ; Traceability
• 刊名：International Journal of Mass Spectrometry
• 出版年：2002
• 出版时间：March 1, 2002
• 年：2002
• 卷：214
• 期：2
• 页码：233-246
• 全文大小：191 K

文摘

As part of the preparation of a primary isotopic gas standard (PIGS) for oxygen, a study was carried out to assess the feasibility of developing a method for the preparation of a gravimetrically prepared isotope mixture of oxygen. Enriched ¹⁸O₂ and O₂ of natural isotopic composition were mixed gravimetrically. Several procedures were investigated to attain isotopic equilibrium of this mixture, i.e., the isotopic species distribution obeying the statistical probability. Pt and Ag powder were used as catalysts. Mass spectrometric measurements were carried out on the mixture before and after isotopic equilibration. The observed values for the isotope ratios J_17/16⁰ and J_18/16⁰ were compared to computed values, using standard equations, for non-equilibrated mixing and for isotopic equilibrium. As a result, isotopic equilibration of the oxygen mixture was achieved. A method is proposed to assess isotopic equilibrium via a ratio consistency factor χ(ⁱO), which is a measure of the closeness of the observed ion current ratios for the prepared mixture to the computed ion current ratios for ideal isotopic equilibrium. In this study, the value of χ(¹⁸O)=0.0006 (21) for the prepared mixture, with combined uncertainty u_c given in parentheses applying to the last two digits (χ=0 for complete equilibration). Preliminary conversion factors for oxygen ratio measurements K_conv