Comparison of stepwise and single-step pyrolysis GC/MS for natural complex macromolecular organic matter

Pyrolysis gas chromatography-mass spectrometry is a useful technique for the analysis of complex organic matter. However, the pyrolysis temperatures must be carefully chosen to maximize the information obtained and, in parallel, minimize byproducts. One solution to accomplish this is the stepwise pyrolysis method, which has been employed to analyze complex mixtures of natural samples. Here, we compared the stepwise pyrolysis method to a suite of single-step pyrolysis runs using the same temperatures by employing a humic acid standard sample, to evaluate the advantage of the stepwise pyrolysis method. In addition, we conducted in-situ heating experiments of the humic acid under infrared microspectroscopy to observe changes in the functional groups during the stepwise pyrolysis process. Results showed that O-bearing components were released at relatively low temperatures, whereas aromatic components were released at higher temperatures, indicating that the stepwise method effectively separates labile and refractory fractions. As such, the stepwise method would be useful for analyzing limited amounts of samples, such as for extraterrestrial materials as well as for payload instruments onboard space missions.