ABSTRACT
This chapter shows that size fractionation by filtration gives results which are realistic of the initial composition of the sample. Filtration is most widely used to separate the so-called “particulate” phase from the “dissolved” phase. The distinction between “dissolved” and “particulate” material was first operationally defined by Goldberg et al., who used filters with a nominal pore size of 0.5 µm. The washing technique is preferable to the concentration technique because in the former the concentration of the retained compound does not increase during filtration. In most cases, sequential filtration has been used, each filtrate obtained with a particular membrane being further fractionated with a membrane of smaller pore size. In aquatic systems many complexing agents are poly electrolytes, macromolecules, colloids, or particles most of which can be retained by ultrafiltration membranes. Low molecular weight hydrocarbons may also be leached from ultrafiltration membranes.
