Determination of the H3 Factor in Hydrogen Isotope Ratio Monitoring Mass Spectrometry

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• 作者：Alex L. Sessions ; Thomas W. Burgoyne ; and John M. Hayes
• 刊名：Analytical Chemistry
• 出版年：2001
• 出版时间：January 15, 2001
• 年：2001
• 卷：73
• 期：2
• 页码：200 - 207
• 全文大小：110K
• 年卷期：v.73,no.2(January 15, 2001)
• ISSN：1520-6882

文摘

The H₃ factor, K, is a parameter required in high-precision, mass spectrometric analyses of hydrogen isotopic abundances. When H₂ is used as the sample gas,R* = R - Ki₂, where R* is the true HD/H₂ ratio, R is theobserved (mass 3)/(mass 2) ion-current ratio, and i₂ isthe ion current at mass 2. Four different methods for thedetermination of K were defined and tested under conditions characteristic of isotope ratio monitoring systems.Three of these were peak-based. The fourth employedsteady flows of H₂ from a conventional inlet system.Results obtained using the latter method were moreprecise (standard deviation of K = 0.1 versus ~0.6 ppmmV^-1 for the peak-based methods). However, use of theresulting values of K for correction of isotope ratiomonitoring GC/MS results led to systematic errors aslarge as 9”, whereas use of the peak-based values ledto no systematic errors. Values of K were only weaklydependent on the pressure of He, declining ~5% for each10-fold increase in P_He. Small variations in partial pressures of H₂O and CH₄, potential contaminants underisotope ratio monitoring conditions, had no significanteffect on values of K.