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

A series-coupled (tandem) ensemble of two capillary GC columns using differ ent stationary phases and a pneumatically actuated low-volume valve connect ing the column junction point to an atmospheric-pressure vent line is used to adjust the ensemble separation of selected pairs of target compounds. Th e valve is normally closed, and the pressure at the column junction point a ssumes 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 en semble separation can be increased ifa pulse occurs when one of the compone nts has migrated across the column junction but the second component is sti ll 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 shif ted to either larger or smaller retention times, but the pattern of peaks ( elution order) for these components from the column ensemble will be relati vely unaffected by the pressure pulse. Multiple pulses can be used to enhan ce the separation of different component pairs, which sequentially reach th e column junction point. Performance of the valve-operated system is descri bed. Time-of-flight mass spectrometry with time-array detection is used to examine the effects of pulse duration on the separation achieved for differ ent component pairs.