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.