Modulation and Manipulation of Gas Chromatographic Bands by Using Novel Thermal Means

Abstract

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 in chromatography. Recent work has demonstrated an alternative approach to band accumulation. A small tube incorporating an inter-nal sleeve cooled cryogenically, placed over a gas chromatography capillary column, can be moved back-and-forward over the column to permit collection and remobilization of focused bands. The movement frequency or timing can be altered to give different operational modes and outcomes. Results demonstrate that peaks can be fully accumulated just prior to a detector then rapidly flushed into the detector, allowing considerable increase in peak height as the peak width diminishes. Applications illustrate that all or selected peaks in a chromatogram can be thus modified by the trap. Column bleed can likewise be collected and then re-eluted, leading to a novel presentation of the molecular constituents of the bleed. With multidimensional gas chromatography, heart-cuts from the first column can be trapped and focused at the head of the second column, then rapidly re-injected into the second column leading to certain advantages. Furthermore, by rapid modulation of the cold trap, a single peak can be cut into a series of separate pulses, either into a detector or into a second column. This allows unusual expression of a chromatographic peak profile, and can be incorpo-rated into a comprehensive GC experiment.