CORRELATIONS BETWEEN ACIDITY AND MOLECULAR-SIZE DISTRIBUTIONS OF AN AQUATIC FULVIC-ACID

The overall acid-base properties of humic substances have been postula ted to be affected by the functional group heterogeneity and heterogen eity in molecular size leading to an ionic strength effect. In this pa per, the acidic properties of various molecular size fractions (500, 1 000, 5000, 10000 daltons as per ultrafiltration) of an aquatic fulvic acid (Radsla FA) are determined and correlated to other physicochemica l parameters such as UV, FTIR, and molecular weight determinations by gel-filtration chromatography. There was a positive correlation betwee n the size cut-off as per ultrafiltration and the molecular weight det erminations from the gel-filtration chromatography. The acid-base titr ations of the filtrates and retentates corroborate the hypothesis that ionic strength effects are significantly larger for samples with high er molecular weight moieties.