Diffusion coefficient and capacity factor in capillary electrokinetic chromatography with replaceable charged polymeric pseudophase

Apparent diffusion coefficients, D-app,D-i, were determined in solutions wi th a polycationic additive - poly(diallyldimethylammonium) - acting as a ps eudostationary phase for electrokinetic chromatography. They were determine d for six small neutral analytes at five concentrations of the polymeric ad ditive (between 0 and 4% w/w) by a stopped migration method. The apparent d iffusion coefficients decrease with increasing polymer concentration only w ithin 40% maximum, an effect that cannot be associated with the macroscopic viscosity of the polymer solution (which increases by a factor of 10). The change of the apparent diffusion coefficients is related to the interactio n of the neutral analyte molecules with the polyelectrolyte chain. Applying the model of analyte partitioning between "free" solution and polymer, cap acity factors and partition constants were derived from the slope of the 1/ D-app,D-i vs. polymer concentration curves. Partition constants determined by this method (ranging between 40 and 170) agree with those obtained by el ectrokinetic chromatography.