Use of secondary equilibria for the separation of small solutes by field-flow fractionation

Abstract

The dynamic range and selectivity of field-flow fractionation (FFF) can be increased by using secondary chemical equilibria (SCE). SCE are established by adding a macromolecular additive or aggregate, which strongly interacts with the field, to the carrier solution. In this study an oil-in-water (O/W) microemulsion was used as the carrier solution in a sedimentation FFF apparatus. The microemulsion droplets (referred to as the support) interact with the field and are retained relative to the bulk water. Small solutes that partition or bind to the microemulsion droplets are also retained relative to solutes that do not interact with the support. In this way it is possible to separate somewhat polar compounds, such as ascorbic acid and sodium benzoate, which prefer bulk water, from apolar solutes, such as toluene, which prefers the support. In addition, the study of retention times in this system allows one to calculate the average microemulsion droplet radius. It appears that SCE-FFF could be a useful way to obtain important information on the physicochemical properties of a variety of colloidal supports.