Sampling of humic and colloidal phases in liquid samples

Humic and colloidal phases represent a key fraction of natural dissolved organic matter, which have been difficult to separate and characterize. This chapter examines the current methods for separating humic substances and aquatic colloids from liquid samples, a key step in understanding the environmental significance of such material. Separation methods examined include dialysis, centrifugation, ion exchange, gel filtration, ultrafiltration, cross-flow ultrafiltration, and field-flow fractionation. Each method is critically appraised in terms of advantages, disadvantages, and future direction. In addition, methods of characterizing humic and colloidal samples are evaluated, including spectroscopic techniques, imaging techniques, scattering techniques and others such as analytical pyrolysis and stable isotope analysis. A recommendation is made on the most promising method for separating humic and colloidal material from environmental water samples.