Potentiometric and Conformational Studies of the Acid-Base Properties of Fulvic Acid from Natural Waters

  • M. S. Varney
  • R. F. C. Mantoura
  • M. Whitfield
  • D. R. Turner
  • J. P. Riley
Part of the NATO Conference Series book series (NATOCS, volume 9)

Abstract

Gram quantities of reference fulvic acid (FA) have been extracted from natural waters for a systematic physico-chemical investigation of proton and metal binding properties. Electrophoretic and gel filtration chromatographic studies of FA indicate that during the course of an acid-base titration, marked conformational changes occurred with the molecular radius increasing from 0.65 nm (6.5Å) at pH 1.15 to 1.32 nm (13.2 Å) at pH 9.26. These conformational charges arise from intra-molecular electrostatic replusive forces associated with the build up of charge (Z) on the flexible FA polyanion. This in turn has a marked effect on the acid association constant (k). For this reason, the broad poly-disperse titration curves which are characteristic of FA could not be adequately explained by simple acid-base models which assume single values of k. However, by incorporating both electrostatic and conformational terms into an expanded Tanford model, we obtained a good fit to the titration data. The value of the intrinsic association constant ki (when Z = 0) derived from this model was rather acidic (log ki = 2.3−2.7) suggesting that the FA is strongly electron withdrawing. However, the combined effects of electrostatic and conformational changes is to spread the apparent constants over a wide range with the greatest number of sites having apparent log k = 4−5.

Keywords

Humic Acid Natural Water Fulvic Acid Titration Curve Molecular Radius 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. 1.
    Mantoura, R.F.C., A. Dickson and J.P. Riley, 1978: The complexation of metals with humic materials in natural waters. Est. Coast. Mar. Sci. 6, 387–408.CrossRefGoogle Scholar
  2. 2.
    Sunda, W.G. and P.J. Hanson, 1979: Chemical Speciation of Copper in River Water; Effects of total Cu, pH, Carbonate and dissolved Organic Matter. In: “Chemical Modelling in Aqueous Systems”, E.A. Jenne, ed. ACS Symposium Series 93. pp. 147–180.CrossRefGoogle Scholar
  3. 3.
    Mantoura, R.F.C., 1981: Organo-metallic interactions in natural waters. Ch. 7 in: “Marine Organic Chemistry: evolution, composition, interactions and chemistry of organic matters in seawater”, E.K. Dursma and R. Dawson, eds. Elsevier, Amsterdam.Google Scholar
  4. 4.
    Rashid, M.A. and L.H. King, 1971: Chemical characteristics of fractionated humic acids associated with marine sediments. Chem. Geol . 7, 37–43.CrossRefGoogle Scholar
  5. 5.
    Reuter, J.H. and E.M. Perdue, 1977: Importance of heavy metal-organic matter interactions in natural waters. Geochim. Cosmochim. Acta . 41, 326–334.CrossRefGoogle Scholar
  6. 6.
    Jenne, E.A., ed., 1979: “Chemical modelling in aqueous systems”. ACS Symposium Series No. 93.Google Scholar
  7. 7.
    Mantoura, R.F.C. and J.P. Riley, 1975: Analytical concentration of humic substances from natural waters. Anal. Chim. Acta . 76, 97–106.CrossRefGoogle Scholar
  8. 8.
    Schnitzer, M. and S.U. Khan, 1972: Humic substances in the marine environment. Marcel Dekker, H.Y.Google Scholar
  9. 9.
    Weber, J.H. and S.A. Wilson, 1975: The isolation and characterisation of fulvic acid and humic acid from river water. Water Res., 9, 1079–1084.CrossRefGoogle Scholar
  10. 10.
    Stevenson, F.J. and J.H.A. Butler, 1969: Chemistry of humic acids and related pigments. Ch. 22 in: “Organic Geochemistry: Methods and results”, G. Eglington and M.T.J. Murphy, eds. Springer, N.Y.Google Scholar
  11. 11.
    Bracewell, J.M., G.W. Robertson and B.L. Williams, 1980: Pyrolysis — mass spectrometry studies of humification in a peat and a peaty podzol. J. Anal. App. Pyrolysis 2, 53–62.CrossRefGoogle Scholar
  12. 12.
    Biederman, G. and L.G. Sillen, 1953: The hydrolysis of metal ions. IV Liguid junction potentials and constancy of activity factors in NaC10 — HC10 ionic medium. Ark. Kemi . 5, 425–440.Google Scholar
  13. 13.
    Determann, H., 1968: Gel chromatography — a laboratory handbook. Springer Verlag, N.Y., 195 p.Google Scholar
  14. 14.
    Andrews, P., 1970: Estimation of molecular size and molecular weights of biological compounds by gel filtration. In: “Methods of Biochemical Analysis”, D. Glick, ed. 18, 1–53.CrossRefGoogle Scholar
  15. 15.
    Tanford, C., 1961: Physical chemistry of macromolecules. Wiley, N.Y., 710 p.Google Scholar
  16. 16.
    Cameron, R.S., R.S. Swift, B.K. Thornton and A.M. Posner, 1972: Calibration of gel permeation chromatography for use with humic acid. J. Soil Sci . 23, 342–349.CrossRefGoogle Scholar
  17. 17.
    Reuter, J.H. and E.M. Perdue, 1981: Calculation of molecular weights of humic substances from colligative data: application to aqueous humus and its molecular size fractions. Geochim. Cosmochim. Acta. in press.Google Scholar
  18. 18.
    Hansen, E.H. and M. Schnitzer, 1969: Molecular Weight measurements of polycarboxylic acids in water by vapour pressure osmometry. Anal. Chim. Acta . 46, 247–254.CrossRefGoogle Scholar
  19. 19.
    Wilson, D.E. and P. Kinney, 1977: Effects of polymeric charge variations on the proton-metal ion equilibria of humic materials. Limnol. Oceanogr . 22, 281–289.CrossRefGoogle Scholar
  20. 20.
    Huizenga, D.L. and D.R. Kester, 1979: Protonation equilibria of marine dissolved organic matter. Limnol. Oceanogr., 24, 145–150.CrossRefGoogle Scholar
  21. 21.
    Rossotti, H., 1978: The Study of Ionic Equilibria: an introduction. Longman, London.Google Scholar
  22. 22.
    Perdue, E.M., J.H. Reuter and M. Ghosal, 1980: The operational nature of acidic functional group analyses and its impact in mathematical descriptions of acid-base equilibria in humic substances. Geochim. Cosmochim. Acta., 44, 1841–1851.CrossRefGoogle Scholar
  23. Sposito, G. and K.M. Holtzclaw, 1977:. Titration studies on the polynuclear, polyacidic nature of fulvic acid extracted from sewage sludge-soil mixtures. Soil Sci. Soc. Am. J . 41, 330–336.Google Scholar
  24. 24.
    Katchalsky, A. and P. Spitnik, 1947: Potentiometric titrations of polymethacrylic acid. J. Polymer. Sci . 2, 432–447.CrossRefGoogle Scholar
  25. 25.
    Pommer, A.M. and I. A. Breger, 1960: Potentiometric titration and equivalent weight of humic acid. Geochim. Cosmochim. Acta., 20, 30–44.CrossRefGoogle Scholar
  26. 26.
    Katchalsky, A. and J. Gillis, 1949: Theory of the potentiometric titration of polymeric acids. Rec. Tray. Chim. 68, 879–897.CrossRefGoogle Scholar
  27. 27.
    Fletcher, J.E., 1977: A generalized approach to equilibrium models. J. Phys. Chem . 81, 2374–2387.CrossRefGoogle Scholar
  28. 28.
    Hunston, D.L., 1975: Two techniques for evaluating small molecule-macromolecule binding in complex systems. Anal. Biochem . 63, 99–109.Google Scholar
  29. 29.
    Beck, K.C., J.H. Reuter and E.M. Perdue, 1974: Organic and inorganic geochemistry of some coastal plain rivers of the south eastern United States. Geochim. Cosmichim. Acta . 38, 341–364.CrossRefGoogle Scholar
  30. 30.
    Gamble, D.S., 1973: Na + and K+ binding by fulvic acid. Can. J. Chem . 51, (19), 3217–3222.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1983

Authors and Affiliations

  • M. S. Varney
    • 1
    • 2
    • 3
  • R. F. C. Mantoura
    • 2
  • M. Whitfield
    • 3
  • D. R. Turner
    • 3
  • J. P. Riley
    • 1
  1. 1.Department of OceanographyUniversity of LiverpoolLiverpoolUK
  2. 2.Institute for Marine Environmental ResearchNERCThe Hoe, PlymouthUK
  3. 3.Marine Biological Association, UKThe Laboratory Citadel HillPlymouthUK

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