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Determination of conditional stability constants of cadmium‐humic acid complexes in freshwater by use of a competitive ligand equilibration‐solvent extraction technique
Author(s) -
Van Ginneken Luc,
Blust Ronny
Publication year - 2000
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620190206
Subject(s) - chemistry , cadmium , extraction (chemistry) , ligand (biochemistry) , stability constants of complexes , titration , iodide , solvent , pyridine , humic acid , inorganic chemistry , chromatography , organic chemistry , aqueous solution , fertilizer , biochemistry , receptor
A technique for determining organic complexation of cadmium in freshwater using competitive ligand equilibration coupled with solvent extraction was evaluated. The method involves a competitive equilibration of the sample with potassium iodide and pyridine followed by extraction of the mixed cadmium‐iodide‐pyridine complex into a benzene phase. The final distribution of the metal is measured by gamma ray spectrometry. The method's suitability was verified by performing extractions on the model ligand 8‐hydroxyquinoline‐5‐sulfonic acid (sulfoxine), which forms well‐characterized complexes with cadmium. The speciation results so obtained were in excellent agreement with results calculated with a chemical speciation model. The method was applied to study complexation of cadmium with two commercially available humic acids in reconstituted freshwater at relatively high cadmium concentrations to mimic polluted freshwaters. The obtained titration data were fitted to a one‐site Langmuir adsorption model, yielding values of 10 6.59 and 10 6.52 for the respective conditional stability constants, and 0.57 and 0.90 μM for the respective ligand concentrations.