Electrophoretic size separation of particles with diameters in the micron range, using polymer solutions

Polystyrene-sulfate particles ranging in size from 536 to 2,170 nm diameter were subjected to electrophoresis (10 V cm-1, 25 degrees C) in K-MES, 0.03 M ionic strength, pH 6.12, 50 mM CHAPS in liquid polymer media contained in horizontal glass tubes of 1 mm ID. The polymer media were linear polyacrylamide [0.3 to 0.9% Mr = 5 x 10(5) and 5 x 10(6), as well as a commercial solution of the latter in 4 M urea, 7.5% Na2SO4 designated as Gelamide-250] or polyvinylalcohol (0.25 to 2.5%, Mr = 6.5 x 10(5), designated PVA). In these polymer solutions, the polystyrene sulfate particles exhibit linear Ferguson plots [log(mobility) vs polymer concentration]. Their slope, KR, is directly related to the diameter of the particle when electrophoresis is conducted in Gelamide-250 or slowly 25 degrees C solubilized PVA solutions, indicating a molecular sieving mechanism. By contrast, KR is inversely related to the particle diameter when electrophoresis is conducted in linear polyacrylamide of 5 x 10(6) molecular weight or in PVA rapidly solubilized by autoclaving (121 degrees C, 1.2 kg cm-2 pressure), suggesting a particle exclusion (gel permeation) mechanism of size separation. Electrophoresis in solutions of polyacrylamide of 5 x 10(5) molecular weight exhibits the same degree of retardation for the entire size range of polystyrene particles used, i.e. a viscosity effect only and no size separation. Retardation of electrophoretic migration by either a sieving or a permeation mechanism is highly reproducible in polyacrylamide solutions, but not in PVA solutions (whether solubilization conditions favoring an apparent permeation mechanism or a sieving mechanism are applied).(ABSTRACT TRUNCATED AT 250 WORDS)