Capillary zone electrophoresis of rigid submicron-sized particles in polyacrylamide solution: Selectivity, peak spreading and resolution

Submicron-sized rigid particles can be separated in a size-dependent fashion by electrophoresis in free solution. Yet it has remained unknown whether the presence of polymers in the solution confers an advantage in size-dependent separation of submicron particles and their resolution. The present study addresses that question, using capillary zone electrophoresis of carboxylate modified polystyrene latex microspheres of 55, 140 and 215 nm radius in solutions of linear polyacrylamide in the M r range of 0.4·10 6 to 1.14·10 6. Selectivity of particle separation increases in direct relation to the polymer concentration in the concentration range of 0 to 1% (w/v). Selectivity was found to increase with M r of the polymer for the particle sets of 55/140 (nm/nm) and 140/215 (nm/nm) but to decrease with polymer M r for the 55/215 (nm/nm) set. Peak spreading is a complex and, in the case of the largest particle, non-monotonic function of polymer concentration, with a minimum at concentrations around the entanglement threshold, c*. Consequently, resolution of the 55/215 and 140/215 (nm/nm) sets also exhibits a maximum around the entanglement threshold while resolution for the 55/140 (nm/nm) set increases with a rise of polymer concentrations above c*. Within the range of optimally resolving polymer concentrations there also occurs a maximum of resolution for all particle sets at a field strength in the range of 150 to 250 V cm −1.