PYROLYSIS-FIELD IONIZATION MASS-SPECTROMETRY OF LOW RANK COALS

Pyrolysis-field ionization mass spectrometry (Py-FIMS) of low rank coals from the Nógrád basin in Hungary reveals several characteristic ion series. The molecular ions dominating in the spectra (and not observed in higher rank coals) proved to be due mostly to oxygen-containing compounds. Moreover thiophenes were identified in the Py-FI spectra of lignites of high organic sulfur content. Phenols, dihydroxybenzenes and thiophenes as characteristic thermal decomposition products are distinguished from evaporated "guest" compounds of the coal matrix (such as n-alkanoic acids, tocopherols, terpenoid and aromatic biomarker hydrocarbons) with the help of temperature- and time-resolved signal profiles. Temperature/time ion profiles indicate that the molecular ions of n-alkanoic acids (occurring with even carbon number predominances in the spectra) correspond partly to vaporized free acids, partly to acids formed by thermolysis of esters. Ion profiles evidence the formation of pristenes from tocopherols during pyrolysis. The Py-FIMS signals were assigned by high resolution FIMS, by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and by the GC/MS analysis of the chloroform extracts of the coals. © 1990.