Fluorescence studies of the microstructure of humic acid

Chapter I introduces humic acid substances and their origins. Methods of extraction, isolation, purification, concentration, and fractionation of humic substances are discussed. The chemical and physical characteristics of humic acid are explained, using various procedures to determine those characteristics.; Chapter II discusses the investigation of five dissolved humic acids by monitoring the fluorescence behavior of a pyrene probe added to the solutions. The results indicate that cations have the property of increasing intramolecular micellization in these humic acids. The proposed mechanism involves enhanced shielding of the probe rather than its expulsion into the aqueous bulk. The observations suggest that a series of events take place that are comparable to the clouding behavior of nonionic detergent solutions. The microorganization progresses through the equivalent of "intramolecular clouding" to the customary intermolecular analogue, leading to a separate humic acid phase.; Chapter III introduces an association index based on the fluorescence anisotropy of a diphenyloxazole probe as a quantitative parameter for the estimation of the association of humic acid with nonpolar organic compounds. The association indices of humic acid size fractions suggest the existence of an intermolecular component in the association process, leading to pseudomicellar behavior that depends on the polydispersity of the humic acid solution.