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Metal Binding Properties of Leaf Litter Extracts: I. Discontinuous Spectrophotometric Titration with Iron and Copper¹

ABSTRACT

A spectrophotometric titration method is proposed with which the maximum Fe or Cu binding ability of leaf litter extracts and the conditional stability constants of the organo-metallic compounds can be determined. The method was checked against the dialysis method of Zunino and Martin (1977) using Cu as titrant. With Fe instead of Cu the spectrophotometric titration yields also plausible results. In the latter case, however, the results cannot be verified with dialysis experiments because of the colloidal nature of aqueous Fe(OH)₃.

The distribution between bound and free metal ions can be described by rectangular hyperbolas (Langmuir type regression models). The measurements deviate systematically from the simple Langmuir equation. These deviations can be adequately described if the heterogeneous mixture of dissolved organic constitutents is considered as a system of two independent components with distinct distribution isotherms. The errors involved in the estimation of the conditional stability constants and of the maximum binding abilities are analyzed.

¹ Contribution of the Swiss Federal Institute of Forestry Research, CH-8903 Birmensdorf, Switzerland.

² Soil Scientist, Soil Physicist, and Agronomist, respectively.

Received for publication July 9, 1979. Accepted for publication March 4, 1980.