Quantitative analyses of fullerene and polycyclic aromatic hydrocarbon mixtures via solvent‐free matrix‐assisted laser desorption/ionization mass spectrometry

Abstract

AbstractWe explore the feasibility of reliable quantitative matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) analyses via solvent‐free sample preparation, as this procedure provides the unique convenience of being applicable also to insoluble samples. As quantitative MALDI measurements are even more complicated for species ionized by cation attachment, we investigated model systems, such as polycyclic aromatic hydrocarbons (PAHs) and fullerenes, which undergo photoionization and do not require additional cationizing salts. Our quantitative approach rests upon applying the standard‐addition method in MALDI for the quantitative characterization of binary mixtures. Two different systems are tested. Set 1 is composed of hexakis(dodecyl)hexabenzocoronene and hexakis(dodecyl)hexaphenylbenzene, which represent the product and precursor of a cyclodehydrogenation reaction, and Set 2 is a mixture of C60 and C70 fullerenes. In Set 1, severe anomalies could be detected due to a strong influence of the matrix/analyte ratio on the correlation between signal intensity and analyte amount. This can be related to the strong intermolecular interactions among the hexabenzocoronene (HBC) aromatic cores hampering the desorption step and to intermolecular charge transfers, which influence the ionization probability. Minor interferences to the quantitative MALDI characterization are encountered in the analysis of C60 and C70 fullerenes. The spherical shapes of C60 and C70 buckyballs prevent strong aggregation. Thus, no molecule‐dependent anomalies in their desorption‐photoionization behaviour are recognized. Copyright © 2008 John Wiley & Sons, Ltd.