The technique of comprehensive two-dimensional gas chromatography (GCxGC) is reviewed. A description of technical aspects of the method illustrates how the GCxGC result is achieved through the use of dual-coupled columns and the modulation of capillary chromatographic peaks. This review presents an expanded section dealing with the relationship between the modulation phase and frequency and the resulting peak pulse profiles. Experimental results that support the appreciation and understanding of the effects that pulsing has on a chromatographic peak are provided. The main goals of GCxGC analysis are discussed with respect to analytical sensitivity and peak capacity arising from zone compression effects and fast analysis on the second column. A typical application of GCxGC is presented, along with a consideration of implementation of the GCxGC method.

The new technique of comprehensive gas chromatography (GC×GC) is applied to the analysis of Vetiver essential oil, and the complex nature of the oil components is readily displayed in a two‐dimension separation space. The GC×GC method involves the use of two directly coupled columns, with a cryogenic modulation system at their confluence; this allows coeluting peaks from the first column to be zone compressed and pulsed rapidly into the second column and separated. Greater sensitivity of detection is also obtained. Results show that the earlier eluting components from the gas chromatography analysis have similar chemical nature in respect of component polarity, being of low‐to‐moderate polarity. Later eluting compounds appear to be more popular, and are presumably of an oxygenated nature. Many of these show extensive co‐elution, with up to 6–8 overlapping compounds on the first column. These results clearly demonstrate that the complexity of essential oils is much greater than that which might be suspected from single column GC analysis, and also suggest that GC–MS analysis with peak deconvolution capabilities will still probably not be able to adequately identify the interfering components. With GC×GC, minor constituents in the presence of larger components may still be well characterized and quantitated, and from the chromatographic retention patterns their chemical nature might be indicated; this would be aided by establishing the retention behaviour of known compounds. Copyright © 2000 John Wiley & Sons, Ltd.

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