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Multi-method Study on Aquatic Humic Substances from the "Rio Negro" - Amazonas State/Brazil: Emphasis on Molecular-Size Classification of their Metal Contents

1999; Brazilian Chemical Society; Volume: 10; Issue: 3 Linguagem: Inglês

10.1590/s0103-50531999000300002

1678-4790

Júlio César Rocha, Ézio Sargentini, Ilda Antonieta Salata Toscano, André Henrique Rosa, P. Burba,

Heavy metals in environment

The aquatic humic substances investigated in this study were conventionally isolated from Rio Negro waters - Amazonas State/Brazil by means of the collector XAD 8. Molecular spectroscopy investigations of these humic substances using ¹H-NMR and 13C-NMR indicated the presence of high aromaticity with few substituents, small amounts of carboxylic carbon, and an aliphatic/aromatic ratio of 1:1. The relatively high UV-VIS absorbance E350/E450 ratio suggested the presence of relatively large proportions of aliphatic structures. Moreover, using a five-stage tangential-flow ultrafiltration (UF) device, the molecular-size distribution of the isolated humic substances was characterized. The fractionation patterns showed that metal traces remaining in humic substances after their XAD 8 isolation have different size distributions. For instance, Mn, Cu, Cd and Ni quantified by ICP-AES were preferably found in the high molecular-weight fractions (10-100 kDa).