A flame-generated, fullerene-rich material (J. B. Howard et al., Nature 352, 139 (1991)) has been characterized by liquid chromatography coupled on-line to ionspray mass spectrometry. Charge-transfer complexation, using a post-column addition of either an electron donor or acceptor, was utilized as a pre-ionization technique. Analyses in the positive-ion mode showed that the thermally metastable constituents of the flame-generated material, tentatively identified previously (J. F. Anacleto et al., Rapid Commun. Mass Spectrom. 6, 214 (1992)) as fullerene isomers on the basis of atmospheric pressure chemical ionization muss spectrometry, yielded mass spectra consistent with their identification as fullerene adducts with highly uiuaturated moieties CnH2n−4 with n = 5, 6, and 7. The molecular radical cations of these adduct species were susceptible to facile fragmentation yielding the molecular ions of the corresponding fullerenes. The negative-ion mode experiments failed to provide any information regarding the identity of these metastable constituents.