EELS-ESI IDENTIFICATION OF HETEROGENEOUS SUSPENSIONS OF AQUATIC MICROPARTICLES

Submicron mineral particles in freshwaters represent an important prop ortion of the total particle number. These microparticles are frequent ly associated to macromolecular organic matter and have a high specifi c surface area; they might thus be strong heavy metal and nutrient sca vengers in aquatic systems. Their non-artefacted characterization at t he level of individual particles represents a promising challenge, whi le preservation of the undisturbed state of natural fragile specimens is a prerequisite. We have used a TEM-EELS-ESI procedure which allows the identification of mineral microparticles in individual model suspe nsions of iron oxides, aluminum oxides and clays in the presence of po lysaccharides, at concentrations typical of natural levels. As expecte d, core-loss ionization edge intensities measured by this method are l imited by the thickness of particles. Heterogeneous mixtures of the fo rmer microparticles/macromolecules were prepared in order to mimic nat ural specimens. Under optimum analytical conditions, it was possible t o extract the very nature of these entities, to reveal low electron-de nsity polysaccharides and even to identify microparticles masked withi n complex aggregates.