Fulvic acid complexes

Numerous experimental systems verified the theory of surface electrode reactions. Reductions of methylene blue [92], azobenzene [79, 82] alizarine red S [93], probucol [94], molybdenum(V)-fulvic acid complex [95], molybdeniun(VI)-1,10 phenanthroline-fulvic acid complex [96], indigo [97], and reduction of vana-dium(V) [98] at a mercury electrode are some of the examples for surface electrode... 

Goodman, B.A. Cheshire, M.V. (1987) Characterization of iron-fulvic acid complexes using Mossbauer and FPR spectroscopy. Sci. Total Fnviron. 62 229-240 Goodman, B.A. Lewis, D.G. (1981) Mossbauer spectra of aluminous goethites (a-FeOOH). J. Soil Sci. 32 351-363 Goodman, B.A. (1988) An introduction to physical and chemical principles. In Studd, J.W. Goodman, B.A. Schwertmann, U. (eds.) Iron in soils and day minerals. D. Reidel Publ. Co., Dordrecht, Holland, NATO ASI Sen 217 19-36... 

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. 

The fluorescence properties of two fulvic acids, one derived from the soil and the other from river water, were studied. The maximum emission intensity occurred at 445-450 nm upon excitation at 350 nm, and the intensity varied with pH, reaching a maximum at pH 5.0 and decreasing rapidly as the pH dropped below 4. Neither oxygen nor electrolyte concentration affected the fluorescence of the fulvic acid derived from the soil. Complexes of fulvic acid with copper, lead, cobalt, nickel and manganese were examined and it was found that bound copper II ions quench fulvic acid fluorescence. Ion-selective electrode potentiometry was used to demonstrate the close relationship between fluorescence quenching and fulvic acid complexation of cupric ions. It is suggested that fluorescence and ion-selective electrode analysis may not be measuring the same complexation phenomenon in the cases of nickel and cobalt complexes with fulvic acid. 

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. 

Tiseanu, C.-D., Kumke, M. U., Frimmel, F. H., Klenze, R., and Kim, J.-I. (1998).Time-resolved fluorescence spectroscopy of fulvic acid and fulvic acid complexed with Eu3+—A comparative study. /. Photochem. Photobiol. A Chemistry 117,175-184. 

Larive, C. K., Rogers, A., Morton, M., and Carper, W. R. (1996). 113Cd NMR binding studies of Cd-Fulvic acid complexes Evidence of fast exchange. Environ. Sci. Technol. 30, 2828-2831. 

Plankey BJ, Patterson HH. 1987. Kinetics of aluminum-fulvic acid complexation in acidic waters. Environ Sci Technol 21 595-601. 

Develop a pseudo-second-order rate law for the formation of Al-fulvic acid complexes according to the reaction in Eq. 2.44 and the parallel reaction ... 

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. 

Senesi et al. (1977), using the methods of electron spin resonance and Mossbauer spectroscopy in conjunction with chemical methods, established that at least two and possibly three forms of binding of Fe occur in humic materials. Ferric iron is firmly bound and protected in tetrahedral or octahedral coordination this form of binding of iron is resistant to chemical complexing and reduction. Fe adsorbed on the outer surfaces of humic materials is less firmly bound. The iron-fulvic acid complexes studied contain from 5.5 to 50.1% Fe, but a large part of the iron is bound to the surficial octahedral position. 

Indeed, the metal humic acid complexation constants obtained for trace metals correlate reasonably well with the hydroxide and carbonate stability constants of the metals (Turner et al., 1981). Humic and fulvic acid complexation is therefore most likely to be significant for those cations that are appre-... 

Mixed ligand complexes may also exert a significant influence on metal speciation and concentration in natural waters. Fulvate-phosphate complexes of Cu", Pb", Cd" and Zn" are more stable than the metal-fulvic acid complexes. Incorporation of these species into models in order to estimate free metal ion concentrations gave estimates which were in excellent agreement with concentrations determined experimentally using ion-specific electrodes. However, mixed ligand complex formation with humic and fulvic acids has not received widespread attention, despite these results and their potential importance. 

Fluorescence Spectroscopic Studies of Al—Fulvic Acid Complexation in Acidic... 

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