Complexation of Cu(II) with a soil humic acid: Response characteristics of the Cu(II) ion-selective electrode and ligand concentration effects

Alanah Fitch*, F. J. Stevenson, Y. Chen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Scopus citations

Abstract

A study was made of parameters affecting the binding of Cu(II) to a soil humic acid, using the Cu(II) ion-selective electrode (ISE). A concentration effect was observed, both in estimates for total Cu(II) bound (maximum binding capacity) and apparent stability constant for binding at the strongest site (K1*). Log K1* values (pH 4, ionic strenth of 0.005) ranged from 6.3 at a humic acid concentration of 0.06 mg/ml to 7.0 at a concentration of 0.25 mg/ml. A still higher value (8.2) was obtained using an approach that permitted measurements to be made at low concentrations of the metal ion (pCu 8). An evaluation of the Cu(II) ISE revelaed that the electrode exhibited Nernstian response in the presence of humic acid, and that extension of the linear portion of the ISE standard curve to lower free Cu(II) concentrations (i.e. pCu 6 to near pCu 8) could be used for estimating free and bound forms of Cu(II). Extrapolation to the lower values permits study of the binding of Cu(II) to the stronger sites, a factor of some importance to natural systems where percent saturation of organic material is expected to be low.

Original languageEnglish
Pages (from-to)109-116
Number of pages8
JournalOrganic Geochemistry
Volume9
Issue number3
DOIs
StatePublished - 1986

Keywords

  • Langmuir equation
  • metal-organic complexes
  • potentiometric titration
  • Scatchard plot
  • soil organic matter chemistry

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