PREPARATIVE-SCALE LIQUID-CHROMATOGRAPHY AND CHARACTERIZATION OF LARGEFULLERENES GENERATED IN LOW-PRESSURE BENZENE FLAMES

Soot generated in a premixed benzene/oxygen/argon low-pressure flame w as extracted sequentially with dichloromethane, toluene, CS2 and 1,2-d ichlorobenzene. Quantifications by HPLC were performed for C-60, C-70, C-76, C-78, and C-84 by means of external standards using a monomeric octadecylsilica (ODS) bonded stationary phase and acetonitrile/toluen e (55:45) as a mobile phase. Toluene was found to be the most suitable solvent for all the cases studied here. After the partial removal of smaller fullerenes with preparative HPLC, the presence of fullerenes u p to C-104 was shown by means of HPLC-APCI-MS using a heated nebulizer interface. The macroscopic isolation of C-86 C-90, C-92, C-94, and C- 96 was performed using a two-step HPLC separation with a 2-(1-pyrenyl) ethylsilica stationary phase and toluene as eluent preceded by the par tial removal of C-60 and C-70 With a poly(divinylbenzene) HPLC column. UV-vis spectra were measured, and the presence of a C-90 adduct could be discerned. Based on the results of this work, the estimated ratios C-60:C-70:C-76:C-78: C-84 in the investigated flame-generated soot ar e 100:100:4:3:6 while the corresponding values for C-84:C-86:C-90:C-92 :C-94:C-96 are 100:0.5:5:0.5:1.25:1.