Size exclusion chromatography (SEC) has been used to separate single wall carbon nanotubes (SWNT) dispersed by chemical modification in organic solvents and by DNA in aqueous solution. The chromatographic detection includes size sensitive detectors, multi-angle light scattering (MALS) and intrinsic viscosity (IV), which can provide information on the size and shape of the SEC fractions. The dispersions were also characterized by small angle neutron scattering (SANS) and atomic force microscopy (AFM). Chemical modification was accomplished by covalent attachment of octadecyl amine to acid treated SWNT and by covalent attachment of butyl groups through free radical grafting. Both covalent attachment methods produced dispersions that contained impurities or clusters of SWNT. The DNA dispersions produced the best dispersions, being predominately single nanotubes.