Characterization of Large Synthetic Polycyclic Aromatic Hydrocarbons by MALDI- and LD-TOF Mass Spectrometry

Abstract

Polycyclic aromatic hydrocarbons (PAHs) with high molecular weights represent a class of compounds which are difficult to analyze with conventional analytical methods because of their insolubility. In this paper, we describe their characterization by laser desorption mass spectrometry (LDMS). The huge PAHs show a fragmentation pathway which is unknown so far. It can be explained by the loss of cyclic C6-units and a subsequent rehydrogenation of the resulting radical sites of the measured fragments. With these findings we are able to detect structure defects in a PAH induced by rearrangement reactions during synthesis. Since the analysis of large PAHs by LDMS is generally hindered by the formation of fragments we also developed an improved method of sample preparation analogous to matrix assisted laser desorption/ionization (MALDI) mass spectrometry. By this method, the isotopic distribution of the PAH molecular ions can now be measured without interfering signals of fragments to enable a reliable identification.