Comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC · GC-TOF) was applied for the analysis of complex metabolite profiles from mouse spleen. The resulting two-dimensional chromatograms proved that mass spectral quality and sensitivity were largely improved by the enhanced resolution and zone compression, which are features of GC · GC operation, when compared to classical one-dimensional GC-TOF methods. The improved peak capacity of GC · GC allowed for peaks to be detected that could previously not be separated in one-dimensional GC. A measure of the combined power of chromatographic and mass spectral deconvolution resolution is called ''analytical purity'', with higher values indicating less pure peaks. GC · GC-TOF lead to the detection of 1200 compounds with purity better than 0.2, compared to 500 compounds with purity up to 2.5 in one-dimensional GC-TOF. The compounds identified include many of the compounds previously reported in NMR studies and other methods on mammalian tissues. Spleen samples of several obese NZO mice and lean C57BL/6 control strains were analyzed in order to demonstrate the applicability of GC · GC-TOF for biomarker identification.
The hyphenation of gas chromatography and mass spectrometry (GC/MS) revolutionized organic analysis. In GC/MS coupling, usually electron impact ionization is applied, and molecules are identified by their fragment pattern. Although mass spectrometry in principle is a separation method, it is used predominantly as a spectrometric technique. However, if soft (i.e., fragmentation-free) ionization techniques are applied, the inherent separation character of MS is emphasized, which has similarities to a GC boiling point separation. By combining polar column GC separation and fast soft ionization time-of-flight mass spectrometry technology, a comprehensive separation of complex petrochemical samples can be obtained (GC x MS approach). Compounds of comparable physical-chemical properties are characteristically grouped together in a two-dimensional retention time-m/z representation. This resembles the separation characteristics of comprehensive two-dimensional gas chromatography (GC x GC) and, thus, represents a novel multidimensional separation approach. In this work, a gas chromatograph equipped with a polar separation column was coupled to a home-built laser ionization time-of-flight mass spectrometer. Laser-based, single-photon ionization was used for universal soft ionization and resonance-enhanced multiphoton ionization for selective ionization of aromatic compounds. A novel capillary-jet inlet system was used for the coupling. Multidimensional comprehensive analysis of complex petrochemical hydrocarbon samples using gas chromatography coupled to mass spectrometry with soft and selective photo ionization sources is first demonstrated.
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