CHARACTERIZATION OF AQUATIC COLLOIDS AND MACROMOLECULES .2. KEY ROLE OF PHYSICAL STRUCTURES ON ANALYTICAL RESULTS

Parts 1 and 2 of this series are tutorial feature articles exceptionally published as Critical Reviews for editorial reasons. They intend to give to the nonspecialist an overview of the major aspects of the characterization of aquatic colloids in relation to their physical and chemical properties. For this reason, there is a close link between parts 1 and 2, which in reality form one single paper. In these papers, the words colloids and macromolecules refer to any organic or inorganic entity in the size range of 1 nm to 1 mu m. In aquatic systems, they form inherently unstable suspensions due to their propensity to undergo conformational changes, aggregate, and then sediment. These factors should be considered carefully in the development of any procedure for the characterization of colloidal material. They are discussed in part 1 of the series. Part 2 describes some important characterization procedures commonly reported in the literature by discussing critically their limitations based on the above-mentioned properties and behavior of colloids. The following analytical steps and methods are covered: (i) sampling and sample storage and handling in relation to problems of microbial activity, colloid aggregation, adsorption, and flotation; (ii) fractionation by filtration, centrifugation, end field-flow fractionation techniques; and (iii) characterization by electron microscopy and light scattering techniques.