EVALUATION OF STATIONARY PHASES FOR THE SEPARATION OF BUCKMINSTERFULLERENES BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The high-performance liquid chromatographic separation of the buckmins terfullerenes C60 and C70 was studied using different chromatographic systems. Normal-phase (silica), non-aqueous reversed-phase (C18-bonded silica and graphitized carbon black) and charge-transfer complexation with dinitrobenzoylpherrylglycine (DNBPG) and ,5,7-tetranitro-9-fluor enylideneaminooxy)propionic acid (TAPA) were considered as retention m echanisms. Mobile phases of different compositions, but all based on h ydrocarbons (toluene, hexane, heptane) as the main solvent, were used. Although it was found that the adsorption of the fullerenes on all th e other phase systems is exothermic, their interactions with the charg e-transfer phases exhibit an unusual endothermic behavior. The retenti on times of C60 and C70) on these phases increase with increasing temp erature. The adsorption enthalpy and entropy derived from the Van 't H off plots confirm this rare temperature dependence. The adsorption ent halpy is positive whereas the adsorption entropy is strongly positive.