Fulvic metal complexing

ESR examination of nonchemically isolated fulvic acids showed that Mn2+ was the primary paramagnetic species observable (60, 61). Most likely, the soluble-colloidal fraction we identified in the speciation studies consisted primarily of such complexes. Because the ESR spectral characteristics of Mn in fulvic acid complexes are quite similar to Mn(H20)62+, Alberts et al. (62) suggested that the metal-fulvate interaction was weak. Stronger interaction would be expected to lead to changes in peak shape. This view leaves unexplained the ability of the complexes to survive the isolation procedure s long ultrafiltration steps, because weak interactions are usually associated with reversible complexation. 

Many studies have been carried out concerning the stability constants of humic and fulvic acid complexes.188 190,191 Stability constants vary considerably with pH and ionic strength213 and this, together with the variable nature of the ligands involved, accounts for the range of values reported for individual metal ions in the literature. However, the stabilities of divalent metal complexes generally follow the well-known Irving-Williams order Mg < Ca < Mn < Co < Zn = Ni < Cu < Hg. 

Cabaniss, S. E. 1992. Synchronous fluorescence spectra of metal-fulvic acid complexes. Environmental Science and Technology 26 1133. 

Schnitzer, M., and E. H. Hansen. 1970. Organo-metallic interactions in soils. 8. An evaluation of methods for the determination of stability constants of metal-fulvic acid complexes. Soil Science 109 333-340. 

Sposito, G., Holtzclaw, K. M., and Baham, J. (1976). Analytical properties of the soluble, metal-complexing fractions in sludge-soil mixtures II. Comparative structural chemistry of fulvic acid. Soil Sci. Soc. Am. J. 40, 691-697. 

Jambu, R, Dupuis,T., and Garais, M. (1975a). Use of differential thermal-analysis to characterize fulvic acid metal complexes and humic acid metal complexes. 2. Application to natural organometallic complexes. J. Therm. Anal. 8(2), 231-237. 

Provenzano, M. R., and Senesi, N. (1998). Differential scanning calorimetry of river aquatic fulvic acids and their metal complexes. Fresenius Environ. Bull. 7(7-8), 423—428. 

Sposito, G., Bingham, F.T., Yadav, S.S. and Inouye, C.A. (1982) Trace metal complexation by fulvic acid extracted for sewage sludge II. Development of chemical models. Soil Sci. Soc. Am.J., 46, 51—56. 

Adamic and Bartak [6] used high pressure aqueous size exclusion chromatography with reverse pulse amperometric detection to separate copper(II) complexes of poly(amino carboxylic acids), catechol and fulvic acids. The commercially available size exclusion chromatography columns were tested. Columns were eluted with copper(II) complexes of poly(aminocarboxylic acids), citric acids, catechol and water derived fulvic acid. The eluent contained copper(II) to prevent dissociation of the labile metal complexes. Reverse pulse electrochemical measurements were made to minimise oxygen interferences at the detector. Resolution of a mixture of DTP A, EDTA and NTA copper complexes was approximately the same on one size exclusion chromatography column as on Sephadex... 

Schnitzer, M. Hansen, E. H. Organo-metallic Interactions in Soils 8. An Evaluation of Methods for the Determination of Stability Constants of Metal-Fulvic Acid Complexes, Soil. Sci. 1970, 109, 333-340. 

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