Characterization of aquatic humic and fulvic materials by cylindrical internal reflectance infrared spectroscopy

Cylindrical internal reflectance (CIR) techniques have been applied to humic and fulvic acids that were size fractionated by using hollow-fiber ultrafiltration methods with cutoffs of 0.1 mu m and 100,000, 30,000, 10,000, 3,000, and 500 molecular weight. The dissolved organic carbon and major cation contents were compared with the CIR spectra to estimate the active carboxylate units in each size fraction. Comparison of infrared spectra at various pH values for aquatic humics and for model polycarboxylate compounds (polymaleic acid and polyacrylic acid) indicated that the principal metal binding functionalities are carboxylate groups.