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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Pyrolysis Conditions on Py/gc/ms Results of Low Organic Matter Soils and Forages: Temperature, Program, Sample Size, Split Ratio, and Fingerprints

item Reeves Iii, James
item Francis, Barry
item McCarty, Gregory

Submitted to: Pittsburgh Conference
Publication Type: Abstract Only
Publication Acceptance Date: March 11, 1999
Publication Date: N/A

Technical Abstract: Pyrolysis-gas chromatography mass spectrometry is widely used to study the composition of a wide range of materials, including forages and soils. Due to the high organic matter content in most samples, relatively small samples are used (i.e., 0.5 mg or less) combined with high split ratios (100 to one or higher) to avoid overloading the mass spectrometer (MS). In addition, the pyrolysis conditions used were often developed when pyrolysis units of limited programmability were the norm. In the course of studying low organic matter soils (total C contents of 0.6 to 3.4%), a new investigation was undertaken for optimizing pyrolysis conditions. Results showed that splitless GC operation was required to obtain sufficient signal from the MS, and that under splitless conditions residues on pyrolysis tubes from fingerprints and dust were detectable, requiring extreme care, including special cleaning of pyrolysis tubes and quartz wool, to produce accurate results, free from external contaminates. Results using a variety of pyrolysis conditions indicate that the maximum amount of information is obtained by using a programmed pyrolysis run. For example, for soils, it was found that information from carbohydrates and lignin is best obtained at pyrolysis temperatures close to 600o C as standardly used for forages, while information from humic substances is better obtained at temperatures near 1000o C. To obtain information on both fractions a programed run from 200 to 1000o C was found to be most advantageous. Similar investigations have now also been undertaken utilizing forages.

Last Modified: 4/22/2015
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