Development and Field Tests of an Automated Pyrolysis Insert for Gas Chromatography.


Pitt Con, 1997

Gary A. Schultz1 and Steven M. Colby2: 1Rohm and Haas Company, Analytical Research Department, Spring House, PA; 2Scientific Instrument Services, Inc., Ringoes, NJ

We report on the development of a new automated pyrolysis system for the introduction of sample into a gas chromatograph. The computer controlled device adapts onto injection ports with minimal modification of existing equipment. The height of the port is increased by approximately 1 inch. This permits the use of autosamplers and therefore allows for the systematic and reproducible analysis of a large number of samples. Reproducibility is improved through the use of a tightly wound Pt coil instead of a Pt boat and quartz wool slug as the heat source. This dramatically improved the temperature uniformity of the sampling volume. The software control system is fully integrated with HP ChemStationTM software and also regulates a cryotrap for collection of analyte at the head of the capillary column. This greatly improves the chromatographic separation. It also allows for gradual increases in pyrolysis temperature. Volatile species can therefore be thermally extracted before pyrolytic temperatures are reached. The control system determines the split ratio within the injector and makes it possible to purge volatile solvents before heating of the analyte. One of the greatest advantages to coupling an autosampler with a pyrolysis system is the ability to reproducibly deposit discrete, known sample quantities onto a pyrolysis filament contained within the injection inlet of a GC. This property is demonstrated in a polymer analysis application. It is shown that the absolute peak areas for the monomers can be used to quantitatively determine polymer composition. We report the results of field trials in which this automated pyrolyser is used in a quality control laboratory to measure batch to batch reproducibility in a plant setting.