Electrospray ionization mass spectrometry was used to investigate the complexation of plutonium(III) and americium(III) by DOTA in aqueous solution. As for europium(III) complexation, data obtained show the pre-sence of a single extremely stable ion ML -in negative ion mode. The kinetic stability of gas phase ions has been investigated by both in-source and in-ion trap collision induced dissociation for lanthanides(III) and actinides(III) species and provides valuable information on the system. Keywords Electrospray ionization mass spectrometry Á DOTA Á Plutonium(III) Á Americium(III) Á Europium(III)