Separation and characterization of cationic, anionic, and nonionic water-soluble polymers by flow FFF: Sample recovery, overloading, and ionic strength effects

The flow field-flow fractionation (FFF) separation, characterization, and molecular weight distribution of a wide variety of synthetic water-soluble polymers is reported. Cationic polyvinylpyridine (PVP) anionic polystyrene sulfonate (PSS), and neutral polyacrylamide (PAAm) polymers of molecular weight from a few thousands to several millions were separated by flow FFF and their molecular weight distribution evaluated by software. The good correspondence of the molecular weight distribution curves extrapolated from two different FFF techniques, flow FFF and thermal FFF, either for narrow PVP samples with molecular weight 28,000, 110,000, and 240,000 or for the broad-disperse component of nominal molecular weight above one million demonstrates consistency with theory. Some critical issues in the separation and characterization of polyelectrolytes by flow FFF, such as the recovery of the polymer sample, and the effect of the injected load and of ionic strength on the retention parameters, are also discussed here. Study of the recovery of sample shows that under the experimental conditions used, the absolute recovery of the PVP polymers of molecular weight 240,000 is close to 100%, and the proportionate recovery of either polystyrene sulfonate or polyacryalmide samples is always obtained. The change in retention time (and the parameters derived from it) with injected mass for polyelectrolytes is related to intermolecular electrostatic interactions. The changes are found to be suppressed with an increase of ionic strength. The polymer equivalent Stokes diameter measured by flow FFF for polyelectrolytes at ionic strength from 10−7 to 0.15 M shows a dependence expected for charged polymers. © 1997 John Wiley & Sons, Inc. J Micro Sep 9: 479–495, 1997