Interference of Pb leaching from the pH electrode on Cd¯metallothionein complex

The electrochemical behaviour of CdMT complexes from commercially available rabbit liver (MTRL) and isolated from the mussel (Mytilus galloprovincialis) digestive gland (MTDG) was studied by pH-titration, using a differential pulse anodic stripping voltammetry (DPASV). When the conventional combined pH electrode is directly immersed in the supporting electrolyte uncontrolled leaching of lead from the glass of the pH electrode occurs. The lead contamination of the studied system is considerable, since the study is performed at the trace level of the order of 10-8 mol dm-3 of both metal and ligand. During the pH-titration the dissociation of the CdMT complex is not caused only with pH but also with the uncontrolled leaching of Pb2+ ions which disables the determination of the dissociation stability constant of CdMT complex.