Tunable secondary dimension selectivity in comprehensive two-dimensional gas chromatography

In this paper two tunable two-dimensional gas chromatography setups are compared and described in which the secondary dimension consists of two different capillary columns coupled in series. In the first setup the selectivity of the second dimension can be tuned by adjusting the effective column length of the first secondary dimension column, simply by sliding it stepwise back or forward through the GC × GC modulator. In the second setup, in which the first secondary dimension column is installed in a separate GC-oven (oven-2), the overall selectivity of the second dimension can be tuned by adjusting the oven-2 temperature offset with respect to the main oven. The contribution of the first secondary dimension column to the overall secondary dimension separation can be decreased by applying a higher temperature offset. A real-life sample, the headspace of a coffee powder, was used to demonstrate the added value of tunable GC × GC by solving coelutions of some specific aroma compounds. Besides optimizing the overall GC × GC separation, by altering the second dimension column selectivity, these set-ups also offer enhanced possibilities for qualitative analysis. By stepwise altering the selectivity of the second dimension, classes of compounds showing similar retention behavior could be discriminated.