Multi-component elemental and molecular analysis of lanthanides by capillary electrophoresis–electrospray mass spectrometry (CE–ESI-MS)

Electrospray mass spectrometry is a method of choice for individual elemental and molecular analysis of uncomplexed or complexed metal ions in solution. The multi-component elemental and molecular analysis of lanthanides is however hindered by the existence of isobaric interferences, therefore a previous chemical separation is required before mass spectrometric analysis. The whole lanthanide series has been separated by capillary electrophoresis using partial complexation and detected by electrospray mass spectrometry. The multi-component capability of coupled capillary electrophoresis–electrospray mass spectrometry for elemental and molecular analysis has been shown by adjusting the degree of declustering and molecular fragmentation in the mass spectrometer interface region. Three different modes have been defined as a function of the fragmentation potential applied (high, low and intermediate fragmentation potentials). For a high fragmentation potential, the system operates as an elemental detector: spectra representing mainly singly charged lanthanide oxide or lanthanide metal ion are observed. These spectra can be related to the dissociation energies of the lanthanide oxide bond and to the lanthanide electronic properties. For a low fragmentation potential, the system operates as a molecular detector: structural information on the mixed complexes formed in the capillary during the electrophoretic separation are obtained. The intermediate fragmentation potentials enable the study of the different steps of declustering.