Characterization of metal complexes with metallothioneins by capillary zone electrophoresis (CZE) with ICP-MS and electrospray (ES)-MS detection

The complementarity of CZE-ICP-MS and CZE-ES-MS couplings was evaluated for the characterization of metal complexes with metallothionein (MT) isoforms . The preparations characterized included the rabbit liver MT and its furth er purified MT-1 and MT-2 isoforms. The CZE-ICP-MS electrophoregrams showed the presence of several well (often baseline) separated Gaussian-shape pea ks. ES-MS was used for the identification of these signals; mass spectra ta ken at the peak apexes were complex and indicated the co-existence of sever al metal complexes (possibly with different isoforms) within each peak. Man y of these complexes could be identified on the basis of the molecular mass . The study highlights the attractive potential of CZE-ICP-MS and CZE-ES-MS when used in parallel for the characterization of metal complexes with bio molecular ligands. The inherent discrepancy between the sensitivities of IC P-MS and ES-MS is partly alleviated by the fact that the metal (detected by ICP-MS) constitutes only a small fraction of the total molecule (detected by ES-MS), and by the smaller dilution factor with the makeup sheath flow i n ES-MS than in ICP-MS.