Effect of strong ligand on mercury analysis by cold vapour atomic absorption spectrometry

V. Wernert; J.-J. Ehrhardt; P. Behra

doi:doi:10.1051/jp4:20030555

Numéro		J. Phys. IV France Volume 107, May 2003


Page(s)		1365 - 1368
DOI		https://doi.org/10.1051/jp4:20030555

J. Phys. IV France 107 (2003) 1365
DOI: 10.1051/jp4:20030555

Effect of strong ligand on mercury analysis by cold vapour atomic absorption spectrometry

V. Wernert^{1, 2}, J.-J. Ehrhardt³ and P. Behra^{1, 4}

¹ Institut de Mécanique des Fluides et des Solides, UMR 7507 du CNRS, Université Louis Pasteur, 2 rue Boussingault, 67000 Strasbourg, France
² Universität Karlsruhe (TH), Engler-Bunte-Institut, Engler-Bunte-Ring 1, 76131 Karlsruhe, Germany
³ Laboratoire de Chimie Physique et Microbiologie de l'Environnement, UMR 7564 du CNRS, Université Henri Poincaré, 405 rue de Vandoeuvre, 54600 Viller-les-Nancy, France
⁴ École Nationale Supérieure des Ingénieurs en Arts Chimiques et Technologiques, Laboratoire de Chimie Agro-lndustrielle, UMR 1010, INRA/INP-ENSIACET, 118 route de Narbonne, 31077 Toulouse cedex 4, France

Abstract
The influence of ligands (halogens, sulphur-containing ligands and organic ligands) on the determination of Hg by cold vapour atomic absorption spectrometry (CVAAS) was studied. The principle of the cold vapour technique is to break the Hg-ligand structure under oxidative and pH stress to generate Hg(II) as Hg ²⁺ cation which is then reduced to atomic Hg(O) by Sn(II). The presence of chemical species, which can strongly complex Hg ²⁺ or Sn ²⁺, can partially or totally inhibit the Hg or Sn can partially or totally inhibit the Hg reduction. The aim of this study was to evaluate the effect of ligands (Cl ^-, I ^-, S ^2-, SO ₃^2-, S ₂O ₃^2-, S ₂O ₃^2-, cysteine, EDTA) on the Hg detection by CVAAS for different ligand concentration ([L]) and pH. The conditional constants, K ', taking into account both complex formation and redox equilibrium were calculated. The log K ' decreases strongly in the presence of strong ligands (I ^-, S ^2- and S ₂O ₃^2-) due to the formation of very stable complexes even at low pH ( $\rm pH < 1$ ). These assumptions were verified experimentally. In fact the presence of strong ligands strongly decreased the Hg signal. The decrease depended on L and Sn(II) concentrations and pH. The reduction kineties decreases as the ligand concentration increases, the Sn(Il) concentration decreases and the pH decreases for I ^- and increases for S ^2- and S ₂O ₃^2-.