Towards a quantitative free flow electrophoresis and its application to particle size separations

The possibility to quantify free-flow electrophoresis (FFE) data was explor ed in application to 6 negatively charged polystyrene size standards in the size range of 73 to 762 nm diameter. Peak fraction numbers in FFE were sho wn to be proportional to mobilities of the particles, determined by capilla ry zone electrophoresis in the identical buffer. Standard deviations of pea k fraction numbers demonstrate a high degree of intra-experimental reproduc ibility while inter-experimentally, a variability of 1 to 5 peak fraction n umbers within 28 fractions was found. A relative mobility (R-f) scale for p eak identification in FFE based on the free mobility of the dye, SPADNS, al lowed for the utilization of the entire electrophoretic migration path but failed to improve the precision of fraction numbers in view of the substant ial zone spreading of the dye. Mobility differences between particles increased upon lowering the ionic st rength of the electrophoretic buffer. Peak width increased with particle si ze in inverse relation to ionic strength.