In-Plume Thermodynamics of the MALDI Generation of Fluorofullerene Anions

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2005-02, Vol.109 (4), p.714-719
• Main Authors: Streletskii, Alexey V., Ioffe, Ilya N., Kotsiris, Sotirios G., Barrow, Mark P., Drewello, Thomas, Strauss, Steven H., Boltalina, Olga V.
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp046243l

The mechanism of formation of fluorofullerene (FF) negative ions derived from the compounds C60F18, C60F36, and C60F48 was studied by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (ToF) mass spectrometry (MS). A combined experimental/theoretical approach provides compelling evidence of nondissociative, thermodynamically controlled electron transfer from matrix-derived negative ions to the FF analyte as the main secondary-ionization process. Consistent with this thermochemical model, analyte parent molecular ion yield and degree of fragmentation for a particular MALDI experiment was found to depend on the nature of the matrix material (the five matrices investigated were sulfur, trans-2-[3-{4-tert-butylphenyl}-2-methyl-2-propenylidene]malononitrile, 9-nitroanthracene, 2,6-bis((furan-2-yl)methylene)cyclohexanone, and 2,6-bis((thiophen-2-yl)methylene)cyclohexanone). For mixtures of C60F n compounds with different n values and therefore different electron affinitites, unwanted electron-transfer reactions, which can lead to the suppression of C60F n - ions with low n values, were successfully blocked for the first time by judicious choice of the matrix. Therefore, reliable qualitative MS analysis of FF mixtures with wide ranges of composition is now possible.