Cryogenic focusing of pyrolysis products for direct (splitless) capillary gas chromatography

• Published in: Journal of analytical and applied pyrolysis 1985-01, Vol.8, p.65-71
• Main Authors: Wampler, T.P., Levy, E.J.
• Format: Article
• Language: English
• ISSN: 0165-2370; 1873-250X
• DOI: 10.1016/0165-2370(85)80015-2

The progression from packed column to split capillary to direct capillary chromatography has permitted analysis with greatly improved sensitivity and resolution, allowing the study of specific components which may be present at low concentration. Pyrolysis-gas chromatography (GC) has tried to follow these trends, from pyrolysis-packed column GC to pyrolysis-split capillary GC. Split capillary GC is adequate for many pyrolysis needs because the amount of volatiles generated is usually quite large, and the high flow-rate to the splitter permits thorough sweeping of the pyrolysis chamber, which may have considerable volume. For sensitivity and reproducibility, however, it may be advantageous to perform pyrolysis-direct (splitless) chromatography. Because of the instrument volume generally involved in pyrolysis equipment, direct capillary chromatography is problematical. The flow-rate required for the column may not be adequate for efficient transfer of the pyrolysates onto the column from the pyrolysis chamber. One solution is to pyrolyze, then collect the pyrolysates onto a trap, which is backflushed to the gas chromatograph. An improvement of this system is to use the GC column itself as the trap by collecting the pyrolysates cryogenically at the head of the column. The cryogenic device is positioned at the injection port of the gas chromatograph and requires no permanent modification of the gas chromatograph. Pyrolysates are delivered from the pyrolysis chamber to the head of the direct capillary GC systems, where they are trapped at sub-ambient temperatures. After the pyrolysis and collection process, the trap is pulse heated and the GC program is begun. The resulting chromatograms retain the sharp resolution which may be sacrificed in some trapping modes while permitting the direct capillary sensitivity required by samples of low organic content such as composites, geological samples and fragments recovered in forensic work.