title: Acquisition and processing of data for isotope-ratio-monitoring mass spectrometry.
abstract: Methods are described for continuous monitoring of signals required for precise analyses of 13C, 18O, and 15N in gas streams containing varying quantities of CO2 and N2.  The quantitative resolution (i.e. maximum performance in the absence of random errors) of these methods is adequate for determination of isotope ratios with an uncertainty of one part in 10(5); the precision actually obtained is often better than one part in 10(4).  This report describes data-processing operations including definition of beginning and ending points of chromatographic peaks and quantitation of background levels, allowance for effects of chromatographic separation of isotopically substituted species, integration of signals related to specific masses, correction for effects of mass discrimination, recognition of drifts in mass spectrometer performance, and calculation of isotopic delta values.  Characteristics of a system allowing off-line revision of parameters used in data reduction are described and an algorithm for identification of background levels in complex chromatograms is outlined.  Effects of imperfect chromatographic resolution are demonstrated and discussed and an approach to deconvolution of signals from coeluting substances described.
authors.affiliation: Department of Geological Sciences, Indiana University, Bloomington 47405, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Ricci
authors.forename: D A
authors.initials: DA
authors.lastname: Merritt
authors.forename: K H
authors.initials: KH
authors.lastname: Freeman
authors.forename: J M
authors.initials: JM
authors.lastname: Hayes
mesh_terms: D000473:Alkanes / Q000032:analysis; D002245:Carbon Dioxide / Q000138:chemical synthesis / Q000737:chemistry*; D002247:Carbon Isotopes; D002623:Chemistry Techniques, Analytical / Q000295:instrumentation / Q000379:methods*; D008401:Gas Chromatography-Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D007477:Ions; D009584:Nitrogen / Q000737:chemistry; D009587:Nitrogen Isotopes; D016011:Normal Distribution; D010103:Oxygen Isotopes; D012984:Software
chemical_list: D000473:Alkanes; D002247:Carbon Isotopes; D007477:Ions; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D002245:Carbon Dioxide; D009584:Nitrogen