MODULATION AND MANIPULATION OF GAS-CHROMATOGRAPHIC BANDS BY USING NOVEL THERMAL MEANS

The maturity of the gas chromatography technique belies the continuing search for improved operating methods. Cryogenic methods, applied in many forms, have been used for many years to trap volatile compounds i n chromatography. Recent work has demonstrated an alternative approach to band accumulation. A small tube incorporating an internal sleeve c ooled cryogenically, placed over a gas chromatography capillary column , can be moved back-and-forward over the column to permit collection a nd remobilization of focused bands. The movement frequency or timing c an be altered to give different operational modes and outcomes. Result s demonstrate that peaks can be fully accumulated just prior to a dete ctor then rapidly flushed into the detector, allowing considerable inc rease in peak height as the peak width diminishes. Applications illust rate that all or selected peaks in a chromatogram can be thus modified by the trap. Column bleed can likewise be collected and then re-elute d, leading to a novel presentation of the molecular constituents of th e bleed. With multidimensional gas chromatography, heart-cuts from the first column can be trapped and focused at the head of the second col umn, then rapidly re-injected into the second column leading to certai n advantages. Furthermore, by rapid modulation of the cold trap, a sin gle peak can be cut into a series of separate pulses, either into a de tector or into a second column. This allows unusual expression of a ch romatographic peak profile, and can be incorporated into a comprehensi ve GC experiment.