C-60 and C70HPLC retention reversal study using organic modifiers

A novel equation (Guillaume Y. C. et al. Anal. Chem. 1998, 70, 608) modelin g the weak polar solute retention in reversed-phase liquid chromatography ( RPLC) was applied to fullerene molecules C-60 and C-70 In RPLC, with an org anic modifier (OM) /water mobile phase, the fullerene cluster solvation ene rgies were calculated for OM = methanol, ethanol, propanol, butanol, and pe ntanol. An enthalpy-entropy compensation revealed that the type of interact ions between fullerenes and the stationary phase was independent of both th e fullerene and organic modifier structures. The energetics of OM and OM-wa ter cluster exchange processes in the mobile phase were investigated in rel ation to the carbon atom number of the hydrophobic chain of the OM. Two lin ear correlations were found between the Gibbs free energy changes in the so lvent exchange processes which confirmed that (i) a reversal elution order existed for C-60 and C-70 when methanol was changed into ethanol, propanol, butanol, pentanol and that (ii) the mobile phase was dominant in governing selectivity changes in nonpolar solutes.