QUANTITATIVE APPROACH TO HUMIC-ACID ASSOCIATIONS

An association index based on the fluorescence anisotropy of a dipheny loxazole probe is introduced as a quantitative parameter for the estim ation of the associations of humic acid with nonpolar organic compound s. The variations of the index were consistent with the behavior of di ssolved humic acids in response to solution conditions. These included salt concentration, pH, humic acid concentration, probe concentration , and type of humic acid. The evidence provided further support for th e formation of humic pseudomicelles that have the ability to sequester hydrophobic species in the solution environment. The molecular parame ters governing this behavior include size and flexibility. The associa tion indices of humic acid size fractions suggest the existence of an intermolecular component in the association process, leading to pseudo micellar behavior that depends on the polydispersity of the humic acid solution.