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Soil Science Society of America Journal Abstract -

Spectrofluorometric Investigation of Trace Metal Complexation by an Aqueous Chestnut Leaf Litter Extract1


This article in SSSAJ

  1. Vol. 51 No. 3, p. 612-619
    Received: Apr 11, 1986

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  1. P. Blaser and
  2. Garrison Sposito2



Fluorescence spectroscopy was investigated as a method for quantitating trace metal complexes with the organic ligands in a water extract of chestnut (Castanea sativa L.) leaf litter. Copper(II) and aluminum(III) were selected as environmentally significant metals with which to characterize the method as applied to the leaf litter extract. Solutions of Cu or Al mixed with the extract exhibited fluorescence that decreased in relative intensity as the total metal concentration and/or the pH increased. Data were obtained in the pH range 5 to 8 for total Cu concentrations up to 160 mmol m−3 and in the pH range 4 to 8 for total Al concentrations up to 100 mmol m−3. The fluorescence intensity data for Cu were comparable to those obtained in previous studies for solutions of Cu and soluble humic materials. A conventional equation was used to calculate an overall stability coefficient for metal complexation by the leaf litter extract. The pH-dependence of this stability coefficient was modeled mathematically in terms of pH-independent conditional stability constants through a new application of the Scatchard quasiparticle model. The quasiparticle species Cu(OH)nH0.9L (n = 0 or 1; L = organic ligands) were sufficient to model the Cu data with the two pH-independent conditional stability constants, cβ0/0.9 = 1012.6 and cβ1/0.9 = 105.3. For the Al data, the conditional stability constants cβ0/0 = 108.55 and cβ2/0 = 10−1.8 were obtained for the quasiparticle species Al(OH)nL (n = 0 or 2). These stability constants can be used in computer speciation programs to estimate organic complexation of Cu(II) or Al(III) by the leaf litter extract, but otherwise have no molecular chemical significance.

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