Date of Award

Spring 1983

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

Abstract

The purpose of this study is to develop methodologies for the investigation of the metal ion binding properties of natural humic substances. Humic materials are prevalent in soil and water and their important metal ion detoxification and transport properties are the major justification for this work. The primary emphasis is the determination of the complexing capacity of a sample for a particular metal ion under fixed conditions.

The initial part of the investigation involves the application of chelating ion exchange to remove and quantify humic-chelated trace metal ions from water samples. Amine, dithiocarbamate and 8-hydroxyquinoline chelating agents immobilized on porous glass beads are compared to Chelex 100. In the presence of humic materials, modeled with isolated soil-derived fulvic acid (SFA), the removal of metal ions with Chelex is significantly hindered while the stronger immobilized chelates still perform adequately.

A fluorescence titration technique is also described which can be used to determine complexing capacities (C(,L)) and 1:1 conditional stability constants (K) of fluorescing ligands with paramagnetic metal ions at the micromolar level. Titrations of the model compound L-tyrosine prove the validity of the technique. Fluorescence data for SFA with Cu('2+) at pH 5, 6 and 7 compares well with results for the same material using different techniques. The binding of Cu('2+) to SFA is much stronger than Co('2+) and Mn('2+) which are similar. Co('2+) and Mn('2+) also bind to fewer sites. Rayleigh scattering data collected with fluorescence indicates Cu('2+) is more effective at precipitating and aggregating SFA than Co('2+) and Mn('2+).

The natural fluorescence of humic substances in both marine and freshwaters is also quenched upon complexation to Cu('2+) ion. The fluorescence technique is therefore applied to several samples to determine K and C(,L) values. Scattering and fluorescence trends were similar for all samples except an estuarine sample which demonstrated a high degree of scattering with the addition of Cu('2+). Pore water obtained from several estuarine sediment cores contained a high organic matter content but a low C(,L) value, probably due to competition from other ions. A multiple correlation study of several parameters for the freshwater samples showed a statistically significant trend between UV absorbance and C(,L) values.

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