Direct Mass Spectrometric Analysis of Solid Coal Samples Using Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

The direct analysis of complex organic solid samples, such as coal, still represents a challenge for mass spectrometric researchers. In this work, we present an approach to analyze various carbonaceous samples with different degrees of coalification (one peat and five coals) using laser desorption/ionization in negative ion mode (LDI(-)) and ultrahigh resolving Fourier transform ion cyclotron resonance mass spectrometry. This preparation and analysis method enables a characterization of reactive organic molecules in their native state, without a need for excessive sample preparation or processing. By combining ultrahigh resolving mass spectrometry with different chemometric analyses, an in-depth characterization of the analyzed peat and coal samples was possible, and a correlation between the mass spectra and the degree of coalification of each sample could be verified. As a proof of concept, various analytical standard molecules were analyzed at increasing laser powers to demonstrate that the detected coal-related molecules are actually contained in the samples and were not simply formed by fragmentation reactions during the LDI process. Overall, the direct analysis method presented is a time-saving alternative to analyze complex organic solid samples of all kinds by mass spectrometry.