LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY INVESTIGATION OF THE REVERSED-PHASE SEPARATION OF FULLERENES AND THEIR DERIVATIVES

The separation of fullerenes and their derivatives on four commerciall y available reversed-phase columns was investigated using liquid chrom atography/mass spectrometry with atmospheric pressure chemical ionizat ion. Three octadecylsilica stationary phases were incapable of adequat ely separating the fullerenes according to the number of carbons. Howe ver, baseline resolution of nearly all the fullerenes (up to at least C96) was achieved with a 2-(1-pyrenyl)ethylsilica phase. The resolutio n of individual fullerene isomers, on the other hand, was best accompl ished with a polymeric octadecylsilica bonded phase. A proposed mechan ism for this unique ability combines the shape selectivity of polymeri c phases, previously recognized for planar polycyclic aromatic hydroca rbons, and the different ''molecular footprints'' of the isomers. This retention mechanism can also be used to explain the increasingly lowe r retention times of successively substituted fullerenes; groups bonde d to the fullerene surface appear to disrupt adsorptive interactions b etween the fullerene molecular footprints and the stationary phases.