Bl. Lewis et al., DETERMINATION OF METAL-ORGANIC COMPLEXATION IN NATURAL-WATERS BY SWASV WITH PSEUDOPOLAROGRAMS, Electroanalysis, 7(2), 1995, pp. 166-177
A novel electrochemical method is described for the examination of met
al-organic complexation in natural waters. The technique is based upon
the comparison of square wave anodic stripping voltammetry (SWASV) 'p
seudopolarograms' (current vs. deposition potential plots) for natural
samples with those obtained for metal complexation with selected 'mod
el' 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 s
tability constant window of approximately 10(4)-10(6) M(-1) up to grea
ter than or equal 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 co
mplexed, log K-ZnL = 4.14 +/- 0.92 M(-1); (2) moderately complexed, lo
g K-ZnL = 7.77 +/- 0.62 M(-1) (3) strongly complexed, log K-ZnL = 11.4
5+/-0.95 M(-1). Results are compared to those obtained using complexom
etric titration with SWASV at a thin mercury film-glassy carbon rotati
ng disk (TMF-GCRD) electrode. The latter detected a single strong comp
lexing ligand (or ligand class), with [L'] = 15.25 +/- 0.04 nM and log
K-ZnL(') greater than or equal to 10.9 M(-1).