Measurement of retention in comprehensive two-dimensional gas chromatography using flow modulation with methane dopant.

Flow modulation of methane-doped carrier gas is used to visualize the second dimension hold-up time in GC x GC continuously throughout the run. This provides an internal reference of hold-up time and presents a straightforward means of examining retention in each dimension of GC x GC. Retention factors on similar and dissimilar column pairs are examined. Stationary phase bleed is shown to be retained by the second dimension column.