High-speed column switching is used after a partial separation on a nonpolar capillary column to selectively transfer groups of sample components to either a polar or nonpolar capillary column for the final separation. A separate flame ionization detector and measurement channel is used to monitor each of the columns used for the final separation. Design and operation of the bifurcation system is discussed. By changing the pressure at the bifurcation point, the pressure drops along the initial column and the final separation columns are altered. This changes the residence times of the sample components on the columns and permits adjustment of the selectivity of the final separation occurring on the polar column. The combination of column bifurcation and tandem-column tunable selectivity allows for the complete high-speed separation of some moderately complex mixtures containing compounds of different functional group classes.
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Akard et al. (1993) studied this question.