Separating biologically active polymers often proves difficult due to the similarity between polymers with different biological activities. The small differences in charge and or size between polymers can give them different electrophoretic mobilities. This difference in mobility serves as a means for separation using dynamic field gradient focusing (DFGF). Separation and concentration by DFGF occurs in free-solution within a vertical, annular separation chamber filled with a low-conductivity buffer. Unlike isoelectric focusing, no pH gradient or carrier ampholytes are used in the separation.

Dynamic field gradient focusing uses two opposing forces to focus a molecule. One force, due to an electric field, is proportional to the molecule's electrophoretic mobility and decreases in intensity as the molecule moves down the chamber. Pumping buffer into the bottom of the separation chamber pushes the molecule up the chamber in opposition to the force of the electric field. The molecule will then focus at the height in the chamber where the opposing forces are equivalent. Thus, DFGF separates molecules by electrophoretic mobility and concentrates them in one step.

We use COMSOL Multiphysics, a finite element differential equation solving package, to numerically solve equations for mass and current conservation. A 2D axially symmetric mathematical model of the separation process in the preparative DFGF instrument confirms prior experimental results using Hb and BSA. The model results indicate that the preparative DFGF instrument functions as designed. The model also serves as a guide for optimizing the instrument.