Ultra-trace heavy metal determination in sea food by differential pulse catalytic voltammetry: application to fishes and bivalve molluscs

The paper proposes an analytical procedure regarding the voltammetric determination of chromium(VI), copper(II), lead(II), cadmium(II), zinc(II) and mercury(II) by differential pulse catalytic voltammetry (DPCV) in matrices involved in the food chain, but also employed as possible biological monitors for trace metal. The digestion of each matrix was carried out using a concentrated HCl-HNO3-H2SO4 acidic attack mixture. 0.23 mol L-1 dibasic ammonium tartrate buffer pH 4.9 + 5.9x10-2 mol L-1 NaBrO3 was employed as the supporting electrolyte. The voltammetric measurements were carried out using, as working electrodes, a stationary hanging mercury drop electrode (HMDE) [simultaneous determination of Cr(VI), Cu(II), Pb(II), Cd(II) and Zn(II)] and a gold electrode (GE) [determination of Hg(II)], a platinum electrode and Ag⎪AgCl⎪KClsat electrode as auxiliary and reference electrodes, respectively. The analytical procedure has been verified on the standard reference materials Mussel Tissue BCR-CRM 278 and Cod Muscle BCRCRM 422. For all the elements in the certified matrices, the precision as repeatability, expressed as relative standard deviation (sr) was lower than 6 %, while the trueness, expressed as relative error (e) was of the order of 5-6 %. Once set up on the standard reference materials, the analytical procedure was transferred and applied to fishes and molluscs sampled in the Po river mouth area.