The electrospray ionisation-ion-trap mass spectrometry (ESI-MSn) of selected drug compounds with amine-containing side chains has been investigated. Certain characteristic in-source fragmentations have been observed for these molecules. Sequential product ion fragmentation experiments (MSn) have been performed in order to elucidate the degradation pathways for the [M + H](+) ions and their predominant fragment ions. These MSn experiments also show certain characteristic fragmentations with respect to the amine-containing side chains. QTOF-MS/MS has been used to support the identity of the proposed fragments. The data presented in this paper therefore provides useful information on the structure of these compounds with amine-containing side chains and can be used in the characterisation of such drugs, their structurally related metabolites and unknown molecules of pharmaceutical significance extracted from animal and plant sources, for example. Amphetamine. clenbuterol, flurazepam and methadone can be identified and determined in mixtures at low ng/ml concentrations by the application of HPLC-ESI-MS which can also be used for their analysis in saliva samples. (C) 2004 Elsevier B.V. All rights reserved.