 The solvent is evaporated and the residue (the toluene-soluble soot fraction) redissolved in toluene and subjected to column chromatography.C60 elutes first with a purple color and C70 is next displaying a reddish-brown color.In nanotube processing the established purification method for removing amorphous carbon and metals is by competitive oxidation (often a sulfuric acid / nitric acid mixture).