Sample stacking capillary electrophoresis with ICP-(Q) MS detection for Cd, Cu and Zn speciation in fish liver metallothioneins

Speciation of different metal isoforms present in metallothioneins (MTs) of living organisms requires both a high efficiency separation technique, e.g., CE, and a multielement, specific and highly sensitive detector (e.g. ICP-MS). To cope with naturally occurring low metal-MTs levels in biological systems and compensate for CE lack of sensitivity a large volume sample stacking (LVSS) methodology for CE-ICP-MS measurements is presented here. Two different CE-ICP-MS interfaces, including the use of a Babington and a HEN nebulizer, are investigated in detail and compared in terms of repeatability (%RSD) and limit of detection (LOD). By using the LVSS technique developed here the LODs obtained were improved 9-13 times. Finally, the proposed methodology was successfully applied to metal speciation studies of MT isoforms present in eel liver, both in control and Cd-induced groups, revealing a clear increase in Cd isoform signals by this metal exposure. Clear differences in profiles and signal intensities of the isoforms detected in both groups were also observed when Cu and Zn are monitored.