Longitudinal Modulation Studies for Augmentation of Injection and Detection in Capillary Gas Chromatography

A longitudinally modulated cryogenic system (LMCS) was used for detection and injection enhancement in capillary gas chromatography. Several modes of operation were evaluated, including discrete and continuous modulation. This later operating mode was also used to study column bleed profiles obtained over a wide temperature program range. It was found that the trapped-then-remobilized bleed profile matches closely to that seen in normal gas chromatography, except that the concentrated pulses of bleed constituents have a greatly increased response. In addition, this procedure appears to have potential for understanding the molecular make-up of column bleed. The LMCS was also evaluated as a reinjection device in capillary gas chromatography. Increases in efficiencies of up to 210% arising from reduced peak widths were observed under some operating conditions, thus offering a mechanism for routine narrow injection bandwidths in capillary chromatography.