Flow-field-flow-fractionation as a new tool for fractionating aquatic colloids

The flow-field-flow-fractionation (Flow-FFF) is a sensitive and gentle technique for the size measurement and separation of macromolecular and particulate matter. Its theoretical fractionation power extends across a broad size spectrum ranging from about 1 nanometer to several micrometers. In a first step the optimal working conditions for applications on environmental aquatic colloids have been evaluated. Subsequently, a calibration procedure using certified polystyrene latex microspheres of different sizes was carried out. The influence of electrolytes on the fractionation process was tested with several experiments carried out in ground water. To control the fractionation process, most of the eluates were collected and examined by scanning electron microscopy (SEM). The results show that excellent fractionation results are obtained for particles with diameters between 30 nm and 500 nm. For bigger particles the fractionation becomes increasingly inexact (e.g. broad elution peaks), thus the resolution is deteriorated. Based on these results the size distribution of a commercial humic acid before and after coagulation was determined.