SEPARATION AND MOLECULAR-WEIGHT DISTRIBUTION OF ANIONIC AND CATIONIC WATER-SOLUBLE POLYMERS BY FLOW FIELD-FLOW FRACTIONATION

A broad study is reported here on the retention and separation of anionic polystyrenesulfonate (PSS) and cationic polyvinylpyridine (PVP) water-soluble polymers by flow field-flow fractionation (FFF) using a thin hydrophobic polypropylene membrane as the accumulation wall of the FFF channel. As background, the general role and impact of polymer adsorption in size exclusion chromatography and in flow FFF are compared. Adsorption at the accumulation wall in FFF systems is described, and explanations for its self-limitation and nonbtrusion are supported by experimental data. The retention and separation of PSS and PVP standards in the molecular weight range 6500-690 000 and 28 000-240 000, respectively, are shown to be generally consistent with theory. Molecular weight distribution curves obtained for the PVP polymers by different flow FFF runs and by thermal FFF are found to be consistent. Weight and number average molecular weights and their ratios are determined for both polymer types. Overloading studies show unexpectedly improved selectivity with low (submicrogram) loading.