Lasers in organic petrology and organic geochemistry, II. In-situ laser micropyrolysis-GCMS of coal macerals

The development and preliminary results of a novel laser micropyrolysis-gas chromatography, mass spectrometry (LMPy-GCMS) system are described. Short exposures of near-infra red (IR) laser radiation focused through a microscope's optics onto a specific, targeted maceral within a polymaceralic organic-rich shale or coal are used to release the thermal evaporation and pyrolysis products from the maceral. The products from multiple exposures on a single maceral type are collectively analyzed online using GCMS. This technique is intended to provide a means of chemically characterizing individual, microscopic organic entities (> 25 μm) in coals and shales without the need to physically separate them from each other (e.g. density gradient centrifugation) or from their mineral matrix (e.g. bulk analysis of kerogen concentrates). Molecular characterization of individual macerals is important in predicting the technological properties of coal and the petroleum generation potential of petroleum source rocks.Different macerals respond differently when exposed to focused near-IR laser radiation due to differences in their heat capacity and heat conduction. The thermal products released during irradiation of macerals (ulminite, alginite, sporinite and fusinite) representing the huminite, liptinite and inertinite maceral groups are presented. Under the appropriate heating, collecting, and trapping conditions, the thermal products liberated are considered representative of the macromolecular structure of the macerals. Structural elucidation of macerals in coals and shales could significantly benefit from concerted efforts of this and other in-situ micro-analytical techniques.