Concepts and preliminary observations on the triple-dimensional analysis of complex volatile samples by using GC×GC-TOFMS

The high-resolution two-dimensional comprehensive gas chromatography (GC×GC) separation of a complex sample of an essential oil is reported, with tentative identification of selected separated components provided by time-off-light mass spectrometry (TOFMS). The GC×GC technique allows orthogonal separation mechanisms on the two columns to achieve separation of components that otherwise are unresolved on a single column, as is demonstrated for the pairs of components borneol and terpinen-4-ol, and cis-caryophyllene and β-farnesene. Peak compression and a short second column used in GC×GC lead to generation of fast second-dimension GC peaks and higher detection sensitivity, by about 25 times, as compared to conventional GC elution. This allows many more compounds to be recognized when using the GC×GC approach. Additionally, rapid mass spectral methods are required if accurate data and reliable searchable spectra are to be obtained for the fast peaks; this is achieved with TOFMS. This leads to a three-dimensional analytical technique. Application of the technique to the complex essential oil sample containing a range of chemical compound classes shows that superior separation and more accurate peak assignment results. Once peaks are identified within the two-dimensional separation space, it is conceivable that mass spectrometry might no longer be required for the routine analysis of such samples, instead relying on the precision of flame ionization detection to give quantitative analysis; however, the support of mass spectral characterization will be invaluable in validating the GC×GC approach.