HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY OF C-60, C-70, AND HIGHER FULLERENES ON TETRAPHENYLPORPHYRIN-SILICA STATIONARY PHASES USING STRONG MOBILE-PHASE SOLVENTS

The HPLC separation of C-60, C-70, and higher fullerenes on a tetraphenylporphyrin-silica stationary phase is investigated using pure carbon disulfide, chlorobenzene, p-xylene, and toluene as mobile phases. Selectivity factors (cu) for C-70/C-60 separations using these solvents are determined to be 1.8, 3.2, 3.8, and 4.3, respectively. Thermodynamic studies reveal that an exothermic interaction takes place between the fullerene and porphyrin stationary phase in the presence of such solvents. Higher fullerenes (up to C-94) can be separated quickly at 90 degrees C using CS2-toluene (45:55, v/v) as the mobile phase. The high solubility of fullerenes in these solvents dramatically increases the overall potential with regard to preparative fullerene purification. The inability of an alternative protoporphyrin-silica phase to separate C-60/C-60 using the same mobile phases supports a retention mechanism based on simultaneous face-to-face and face-to-edge pi-pi interactions between the immobilized tetraphenylporphyrin and the fullerenes.