AbstractThe complementarity of ICP sector-field double-focussing (SF-DF) MS and electrospray MS detection in capillary zone electrophoresis (CZE) was studied for the identification and determination of metal complexes with metallothionein (MT) induced in the liver of a rat exposed to intravenously administered Cd2+. The MT fraction investigated was isolated by size-exclusion chromatography, preconcentrated by lyophilization and desalted. CZE-ICP MS allowed the separation of four mixed-metal complexes with one or more MT isoforms. Isotope dilution analysis was developed for the accurate quantification of the MT content in each of the species and the determination of the stoichiometry of the metal complex. A multi-isotope spike (33S,106Cd, 65Cu, 70Zn) was supplied on-line in the makup flow (6 l min−1) of a self-aspirating total consumption micronebulizer that served as the interface. The characterization of the MT fraction was completed by electrospray MS, allowing the determination of the molecular masses of the complexes formed and the identification of the ligands as MT-1 and MT-2 isoforms.