SYNCHRONOUS FLUORESCENCE-SPECTRA OF METAL-FULVIC ACID COMPLEXES

Synchronous quenching spectra, the difference between synchronous scans of ligand fluorescence before and after metal addition, have distinct and readily identifiable patterns for divalent transition metals [Cu(II), Pb(II), Ni(II), Co(II), Mn(II)], Mg(II), and Al(III) binding to fulvic acid (FA). Quenching spectra of Fe(III) resemble those of other transition metals at pH 5.0 but differ at pH 7.5. Principal component analyses of the spectra acquired at varying total metal concentrations demonstrate that multiple fluorescent binding sites for divalent transition metals are present in FA solutions at pH 7.5. No evidence was found for multiple binding sites at pH 5.0. Quenching spectra of solutions of two metals show that Al(III), but not Mg(II), competes with Cu(II) for binding sites in the FA. Al(III) also appears to displace Mg(II) bound to FA.