Two Different Configurations of Flow Field-Flow Fractionation for Size Analysis of Colloids

Abstract

Flow field-flow fractionation (F.FFF) is a technique for measuring the size of species in the colloidal range (1 nm to 1 μm) which makes the use of the formation of a molecular or colloidal polarization layer at the surface of a filtering membrane. The species to be analyzed are introduced into a flow of liquid passing through a channel with porous walls (of pore size less than that of the colloids to be analyzed) which allow a certain controlled flow to pass through. The remaining fraction of the flow passes through the system, carrying the colloids to a nonspecific detector. The transit time of the colloids through the channel is found to be a function of their size and the permeation rate through the porous membrane. This chromatographic system can be calibrated by using known colloids, such as standard latex particles or fractionated polymer samples, and then used to determine the size of unknown colloids. Here we present results obtained in two different systems, an asymmetric module with a rectangular channel having a single flat membrane and a module based on a hollow ultrafiltration fiber with a radial symmetry. The common feature of the two systems is that there is only one fluid inlet. Measurements are reported for the mean size of various samples of real colloids, such as dextran macromolecules, emulsion paints, and milks, and a comparison is made with measurements using hydrodynamic chromatography (HDC), and photon correlation spectrometry (PCS).