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 (C_M and C_S), 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.