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Rapid Commun Mass Spectrom

Title:		Compatibility of electron ionization and soft ionization methods in gas chromatography/orthogonal time-of-flight mass spectrometry
Author(s):		Hejazi L; Ebrahimi D; Hibbert DB; Guilhaus M;
Address:		"School of Chemistry, The University of New South Wales, Sydney 2052, Australia"
Journal Title:		Rapid Commun Mass Spectrom
Year:		2009
Volume:		23
Issue:		14
Page Number:		2181 - 2189
DOI:		10.1002/rcm.4131
ISSN/ISBN:		1097-0231 (Electronic) 0951-4198 (Linking)
Abstract:		"Orthogonal acceleration time-of-flight (oa-TOF) mass spectrometry (MS) was coupled to gas chromatography (GC) to measure ion yields (ratio of ion counts to number of neutrals entering the ion source) and signal-to-noise (S/N) in the electron ionization (EI) mode (hard ionization) as well as in the soft ionization modes of chemical ionization (CI), electron capture negative ion chemical ionization (NICI) and field ionization (FI). Mass accuracies of the EI and FI modes were also investigated. Sixteen structurally diverse volatile organic compounds were chosen for this study. The oa-TOF mass analyzer is highly suited for FI MS and provided an opportunity to compare the sensitivity of this ionization method to the more conventional ionization methods. Compared to the widely used quadrupole mass filter, the oa-TOF platform offers significantly greater mass accuracy and therefore the possibility of determining the empirical formula of analytes. The findings of this study showed that, for the instrument used, EI generated the most ions with the exception of compounds able to form negative ions readily. Lower ion yields in the FI mode were generally observed but the chromatograms displayed greater S/N and in many cases gave spectra dominated by a molecular ion. Ion counts in CI are limited by the very small apertures required to maintain sufficiently high pressures in the ionization chamber. Mass accuracy for molecular and fragment ions was attainable at close to manufacturer's specifications, thus providing useful information on molecular ions and neutral losses. The data presented also suggests a potentially useful instrumental combination would result if EI and FI spectra could be collected simultaneously or in alternate scans during GC/MS"
Keywords:		Electrons Gas Chromatography-Mass Spectrometry/instrumentation/*methods Ions/*chemistry Mass Spectrometry/*instrumentation/methods Organic Chemicals/chemistry;
Notes:		"MedlineHejazi, Leila Ebrahimi, Diako Hibbert, D Brynn Guilhaus, Michael eng Evaluation Study England 2009/06/17 Rapid Commun Mass Spectrom. 2009 Jul; 23(14):2181-9. doi: 10.1002/rcm.4131"