Model compound interactions characterizing aquatic humic substances

Abstract

An attempt was made to simulate XAD-8 isolates of Orange County groundwater and Biscayne Aquifer groundwater using mixtures of single ligands. Mixtures of catechol, glycine, phthalic acid and salicylic acid were used to simulate potentiometric and complexometric titrations. Concentrations used for the mixtures were based on carboxylic acidity, dissolved organic carbon, and assumed values for phenolic acidity and nitrogen content. Potentiometric titrations were reproduced with mixtures of the ligands; however, complexometric titrations at pH 6.2 and pH 7.5 could not be duplicated. A stronger ligand was required to fit the pH 6.2 titrations, and higher carboxylic contents were needed for pH 7.5. At pH 6.2 70 percent of the binding sites were attributed to phthalic acid-type groups and 20 percent to catechol-type groups. At pH 7.5 greater than 98 percent was attributed to phthalic acid-type groups.