Enhanced resolution comprehensive two-dimensional gas chromatography applied to the analysis of roasted coffee volatiles

The present research is based on the full exploitation of the separation power of a 0.05mm internal diameter (ID) capillary, as a comprehensive two-dimensional (2D) GC (GC×GC) secondary column, with the objective of attaining very high-resolution second dimension separations. The aim was achieved by using a split-flow system developed in previous research [P.Q. Tranchida, A. Casilli, P. Dugo, G. Dugo, L. Mondello, Anal. Chem. 79 (2007) 2266], and a dual-oven GC×GC instrument. The column combination employed consisted of a polar 30m×0.25mm ID column connected, by means of a T union, to a detector-linked high-resolution 1.1m×0.05mm ID apolar analytical column and to a 0.33m×0.05mm ID retention gap; the latterwas connected to a manually operated split valve. As previously demonstrated, the use of a split valve enables the regulation of gas flows through both analytical columns, generating the most appropriate gas linear velocities. Comprehensive 2D GC experiments were carried out on Arabica roasted coffee volatiles (previously extracted by means of solid-phase microextraction) with the splitvalve closed (equal to what can be defined as conventional GC×GC) and with the split-valve opened at various degrees. The reasons why it is absolutely not effective to use a 0.05mm ID column as second dimension in a conventional GC×GC instrument will be discussed and demonstrated. On the contrary, the use of a 0.05mm ID column as second dimension, under ideal conditions in a split-flow, twin-oven system, will also be illustrated and discussed.