Donnan dialysis matrix normalization for the voltammetric determination of metal ions

The efficacy of Donnan dialysis for removal of interferences by surfactants, complexing agents, and electroactive organic compounds on anodic stripping voltammetry and differential pulse polarography is demonstrated. Up to at least 0.05% gelatin and 0.005% Triton X-100 do not alter the rate of dialysis of Cd(II), Pb(II), Zn(II), and Cu(II). As the ion-exchange membrane is not permeable to the surfactants, subsequent voltammetric determinations can be performed by a working curve method. Recoveries of metals from a variety of real samples were generally above 90%. The presence of humic acid (50 mg l^-1) does not alter the transport of Cu(II), Pb(II), or Cd(II) from pH 3 solution but does at pH 8. The transport is related to the free and labile-complexed ion concentration which suggests that Donnan dialysis can be used for speciation as well as for enrichment and matrix normalization.