We study the interaction of single-walled carbon nanotubes and organic amines with sizable alkyl groups from the first principles. Adsorption energy is calculated, and amine affinities for the typical semiconducting and metallic nanotubes are compared. We discuss role of the amine in nanotube debundling. Our results support the idea of using alkylamines as nanotube purifying agents in addition to ultrasonic treatment. (c) 2005 Elsevier B.V All rights reserved.