Second dimension column ensemble pressure tuning in comprehensive two-dimensional gas chromatography

A pressure tunable (PT) coupled column ensemble has been implemented for the second dimension (²D) separation in comprehensive two dimensional gas chromatography (GC×PTGC). This process requires two columns to be connected by a pressure junction, as a replacement for a single narrow bore, short column in ²D. Various ²D₁ and ²D₂ columns may be selected to provide complementary selectivity (polarity) compared to the ¹D column. The tunable residence time arising from differential pressure drop in each ²D column results in a tunable fractional contribution of each column in the ²D separation. A sample mixture comprising different chemical classes, including alkanes and alcohols, is used to identify the feasibility and extent of selectivity tuning possible in GC×PTGC. The column length is also varied due to the imposed challenge of wraparound in the PT coupled column system as pressures are adjusted in the ²D separation. Different experimental parameters, stationary phase materials and column lengths have been applied to investigate and understand the separation behaviour of the ²D PT coupled column GC×GC system. Results are discussed considering analyte retention time, peak width, linear velocity and the contribution of each ²D column. A specific and unexpected example of GC×GC separation was demonstrated where the peak positions of polar and apolar compounds could almost swap their ²D retention position by application of PT. Kerosene was analysed as an example of complex sample analysis by GC×PTGC system. This process is shown to be a practical approach for altering different stationary phase selectivities in a single ²D arrangement in GC×GC.