Application of water nuclear magnetic resonance relaxation times to study of metal complexes of the soluble soil organic fraction fulvic acid

Abstract

The binding of the paramagnetic metal ions Mn2+, Cu2+, and Fe3+ to the acid soluble organic fraction of soils, fulvic acid, has been examined. The measurements use effects on paramagnetic ion induced longitudinal (T1) and transverse (T2) relaxation in the proton magnetic resonance signal of solvent water. The effects of the fulvic acid sample are compared to model ligand effects. Evidence is developed to suggest that Mn2+ forms outer sphere complexes with fulvic acid. On the contrary, Cu2+ and Fe3+ appear to form inner sphere complexes.