Targeted multidimensional gas chromatography using microswitching and cryogenic modulation

A new method is described that allows fast target analysis in multidimensional gas chromatography by using a microswitching valve between two GC columns, with cryogenic trapping and rapid re-injection of trapped solutes in the second dimension. The essence of the procedure is that heart-cut fractions from the first column (D-1) can be selectively transferred to column 2 (D-2), where a moveable cryogenic trap first focuses the transferred solute(s) at the head of the second column and then permits their facile rapid analysis on D-2. Since D-2 is a short narrow-bore column, which exhibits very fast analysis (on the order of a few seconds elution), peak responses (heights) are significantly enhanced (by up to 40-fold). Additionally, by using a D-2 phase of a selectivity different from that used for ID, it is possible to also separate components that are not resolved on the first column and to increase the resolution for other compounds. The heart-cut valve isolates the section(s) of solutes of interest from the first column separation, and this provides a considerable simplification to the chromatogram-in addition to the separation and sensitivity advantages. By using this method, multidimensional gas chromatography with multiple heart-cuts can be completed within the same time as the primary column separation. Since the described method permits non-heart-cut fractions to be transferred to a monitor detector, normal detection of these fractions is still permitted. By modulation of the cryotrap, it is also possible to achieve comprehensive two-dimensional gas chromatography for the heart-cut fractions; however, only those compounds passed to the second, separation column, which passes through the cryotrap, will be subjected to GC x GC analysis. The technique and the various modes of operation are described in this paper.