Spectroscopic investigation of organic matter-metal complexes
Literature was reviewed on the nature of organic matter in soil in the presence and absence of trace metal ions (especially copper) and on the techniques, notably EPR and visible spectroscopy, used to study this material. The humic acid (HA) fractions used in this study were prepared by pyrophosphate extraction of a peaty loam soil and an alcohol/aqueous alkali fractional precipitation technique. They were examined by a variety of chemical and physical techniques (ash and trace element content, elemental analysis, potentiometric titrations, visible, IR, NMR and EPR spectroscopy) and found to have properties more similar to fulvic acids than HAs. An EPR study of copper-HA complexes for each fraction showed the presence of up to three complexes, one of which was similar to copper type I proteins. EPR spectroscopy was also used to calculate a stability constant for Cu 2+ -HA and to investigate the binding of Cu(H20)6+, Cubisglycine and Cu t+-HA' to montomorillonite and imogolite. At least two types of copper binding sites were found on these minerals. Visible spectroscopy studies of Cu 2+-HA solutions were carried out and adsorption isotherms were produced; the Freundlich equation was more suitable than the Langmuir equation for describing this reaction. Competition between simple organic acids and HA was also studied by visible spectroscopy and maximum binding ability values were calculated.