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Pressure‐monitored headspace analysis combined with compound‐specific isotope analysis to measure isotope fractionation in gas‐producing reactions
Author(s) -
Mundle Scott O. C.,
Vandersteen Adelle A.,
LacrampeCouloume Georges,
Kluger Ronald,
Sherwood Lollar Barbara
Publication year - 2013
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6625
Subject(s) - chemistry , isotope analysis , isotope , chromatography , fractionation , isotope fractionation , measure (data warehouse) , radiochemistry , analytical chemistry (journal) , data mining , ecology , quantum mechanics , computer science , biology , physics
RATIONALE Processes that lead to pressure changes in closed experimental systems can dramatically increase the total uncertainty in enrichment factors (ε) based on headspace analysis and compound‐specific isotope analysis (CSIA). We report: (1) A new technique to determine ε values for non‐isobaric processes, and (2) a general approach to evaluate the experimental error in calculated ε values. METHODS ε values were determined by monitoring the change in headspace pressure from the production of CO 2 in a decarboxylation reaction using a pressure gauge and measuring the δ 13 C values using CSIA. The statistical error was assessed over shorter reaction progress intervals to evaluate the impact of experimental error on the total uncertainty associated with calculated ε values. RESULTS As an alternative to conventional compositional analysis, calculation of CO 2 produced during the reaction monitored with a pressure gauge resulted in rate constants and ε values with improved correlation coefficients and confidence intervals for a non‐isobaric process in a closed system. Further, statistical evaluation of the ε values as a function of reaction progress showed that uncertainty in data points for reaction progress ( f ) at late stages of the reaction can have a significant impact on the reported ε value. CONCLUSIONS Pressure‐monitored headspace analysis reduces the uncertainty associated with monitoring the reaction progress ( f ) based on estimating substrate removal and headspace dilution during sampling. Statistical calculations over shorter intervals should be used to evaluate the total error for reported ε values. Copyright © 2013 John Wiley & Sons, Ltd.