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 chromatography/mass spectrometry with atmospheric pressure chemical ionization. Three octadecylsilica stationary phases were incapable of adequately 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 polymeric octadecylsilica bonded phase. A proposed mechanism for this unique ability combines the shape selectivity of polymeric phases, previously recognized for planar polycyclic aromatic hydrocarbons, 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.