A tandem column ensemble with an atmospheric pressure junction-point vent for high-speed GC with selective control of...

A series-coupled (tandem) ensemble of two capillary GC columns using different stationary phases and a pneumatically actuated low-volume valve connecting the column junction point to an atmospheric-pressure vent line is used to adjust the ensemble separation of selected pairs of target compounds. The valve is normally closed, and the pressure at the column junction point assumes the value that would occur in the absence of any other connections. The valve can be opened for brief periods of time, thus producing pulses of atmospheric pressure at the column junction point. If a component pair is separated by the first column but coelutes from the column ensemble, the ensemble separation can be increased if a pulse occurs when one of the components has migrated across the column junction but the second component is still on the first column. All of the mixture components that are on the same column during the time that the valve is open (pulse duration) will be shifted to either larger or smaller retention times, but the pattern of peaks (elution order) for these components from the column ensemble will be relatively unaffected by the pressure pulse. Multiple pulses can be used to enhance the separation of different component pairs, which sequentially reach the column junction point. Performance of the valve-operated system is described. Time-of-flight mass spectrometry with time-array detection is used to examine the effects of pulse duration on the separation achieved for different component pairs.