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Determination of metal–organic complexation in natural waters by SWASV with pseudopolarograms
Author(s) -
Lewis B. L.,
Luther G. W.,
Lane H.,
Church T. M.
Publication year - 1995
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.1140070213
Subject(s) - chemistry , anodic stripping voltammetry , zinc , seawater , stability constants of complexes , metal , ionic strength , analytical chemistry (journal) , electrochemistry , titration , metal ions in aqueous solution , inorganic chemistry , electrode , aqueous solution , chromatography , organic chemistry , oceanography , geology
Abstract A novel electrochemical method is described for the examination of metal–organic complexation in natural waters. The technique is based upon the comparison of square wave anodic stripping voltammetry (SWASV) ‘pseudopolarograms’ (current vs. deposition potential plots) for natural samples with those obtained for metal complexation with selected ‘model’ binding ligands at constant ionic strength. For electrochemically active zinc species in seawater, the pseudopolarogram approach allowed the estimation of thermodynamic stability constants ( K ML ) within a stability constant window of approximately 10 4 –10 6 M −1 up to ≥ 10 15 M −1 . For a natural rainwater sample, the pseudopolarogram indicated only one zinc class, probably a mixture of ‘free’ and/or inorganically complexed species. In an application to a coastal seawater sample, three species were identified: (1) weakly complexed, log K ZnL = 4.14 ± 0.92 M −1 ; (2) moderately complexed, log K ZnL = 7.77 ± 0.62 M −1 ; (3) strongly complexed, log K ZnL = 11.45 ± 0.95 M −1 . Results are compared to those obtained using complexometric titration with SWASV at a thin mercury film–glassy carbon rotating disk (TMF–GCRD) electrode. The latter detected a single strong complexing ligand (or ligand class), with [ L ′] = 15.25 ± 0.04 n M and log K ′ ZnL ≥ 10.9 M −1 .