Oligo-chitosans were chemically modified with dinitrophenyl groups for selective and rapid adsorption of amitriptyline by forming pi-pi complexes. H-1-NMR was utilized not only for characterization of modified chitosans but also for monitoring the aromatic-aromatic interaction. The variation in the chemical shift of aromatic protons was followed to monitor the aromatic-aromatic interaction. Upfield shift of aromatic protons of dinitrophenyl groups supports aromatic-aromatic interactions with amitriptyline. Drug uptake test by HPLC reveals that dinitrophenyl chitosan particles (1-2 mum) at 0.4 wt% (w/v) in a saline solution (pH 6.9) adsorb 90% amitriptyline within 30 min.