Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) has been applied to the neutral 1.4 nm sized cluster [Cd32Se14(SePh)(36)(L)(4)] upon targeted exchange of the neutral ligands L by various anionic ligands in solution. Use of SePh-as a 'charging ligand' leads to virtually monodisperse ion beams constituted of the intact cluster as tetra-and tri-anions. An electrostatic model is employed which is consistent with the proposed charge distribution of four excess charges being localized at the corner sites of the tetrahedron. The experimental results suggest a general applicability of charged ligand exchange to obtain monodisperse cluster ion beams. © 2005 Elsevier B.V. All rights reserved.