A method for separating metallic carbon nanotubes and semi-conducting carbon nanotubes includes providing a suspension containing a plurality of individual metallic carbon nanotubes and semi-conducting carbon nanotubes in a liquid, for which the dielectric constant .epsilon..sub.L meets the requirement: .epsilon..sub.M>.epsilon..sub.L>.epsilon..sub.H, wherein .epsilon..sub.M is the dieletric constant of the metallic carbon nanotubes and .epsilon..sub.H is the dielectric constant of the semi-conducting carbon nanotubes. A a non-homogeneous electric alternating field is applied to the suspension to create spatially separate species of the metallic carbon nanotubes and the semi-conducting carbon nanotubes. At least one of the separate species is then removed.