Liquid chromatography/mass spectrometry investigation of the reversed-phase separation of fullerenes and their derivatives

The separation of fullerenes and their derivatives on four commercially available reversed-phase columns was investigated using liquid chroma¬tography/mass spectrometry with atmospheric pressure chemical ionization. Three octadecyl-silica stationary phases were incapable of ade¬quately separating the fullerenes according to the number of carbons. However, baseline resolution of nearly all the fullerenes (up to at least C96) was achieved with a 2-(1-pyrenyl) ethylsilica phase. The resolution of individual fullerene isomers, on the other hand, was best accomplished with a poly¬ meric octadecylsilica bonded phase. A proposed mechanism for this unique ability combines the shape selectivity of polymeric phases, previously recognized for planar polycyclic aromatic hydro¬ carbons, and the different "molecular footprints" of the isomers. This retention mechanism can also be used to explain the increasingly lower retention times of successively substituted fullerenes; groups bonded to the fullerene surface appear to disrupt adsorptive interactions between the fullerene molecular footprints and the stationary phases.