Peak-bridges due to in-column analyte transformations as a new tool for establishing molecular connectivities by comprehensive two-dimensional gas chromatography-mass spectrometry

Comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) has been shown to permit for the unprecedented chromatographic resolution of volatile analytes encompassing various families of organic compounds. However, peak identification based on retention time, two-dimensional mapping, and mass spectrometric fragmentation only, is not a straightforward task yet. The possibility to establish molecular links between constituents is of crucial importance to understand the overall chemistry of any sample, especially in natural extracts where biogenetically related isomeric structures are often abundant. We here present a new way of using GC × GC that allows searching for those molecular connectivities. Analytical investigations of essential oil constituents by means of GC × GC-MS permitted to observe in real time the thermally-induced transformations of various sesquiterpenic derivatives. These transformations generated a series of well-defined two-dimensional peak bridges within the 2D-chromatograms connecting parent and daughter molecules, thus permitting to build a clear scheme of structural relationship between the different constituents. GC × GC-MS appears here as a tool for investigating chromatographic phenomena and analyte transformations that could not be understood with conventional GC-MS only.