Observation of non-linear chromatographic peaks in comprehensive two-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC × GC) often incorporates a conventional capillary gas chromatography column in combination with a fast elution column. If this latter column has a thin stationary phase film, it may be supposed that the analyst risks loss of peak resolution due to the onset of non-linear conditions. This will normally be evidenced by overloading - or fronting - peak shapes. GC × GC methods which result from zone compression will be even more likely to exhibit overloading on the second column since the instantaneous peak concentration (CM and CS), will be significantly greater than that of the band which enters the modulation region. Two cases of overloading may be considered - that on the first column, and that on the second column. Each of these cases will lead to different two-dimensional peak shapes when the GC × GC result is converted to a two-dimensional separation space. In each instance, however, resolution of components will be degraded, although the GC × GC experiment will still not be as badly affected as a single dimensional GC analysis. When overloading conditions are obtained, the GC × GC peak pulsing phenomenon will result in the extremities of the chromatographic band showing linear conditions even though the centre of the band is non-linear.