Polysaccharides Donnan distribution

Winzor and coworkers have employed measurements of the Donnan distribution of small ions in dialysis equilibrium [14] to reinforce earlier evidence of charge-screening effects in polysaccharide anions [164,165]. These researchers used the absorption optical system of a Beckman XL-1 ultracentrifuge to monitor the distribution of ions in polysaccharide solutions... 

As shown in Eqs. (3.9) and (3.10), the concentration of migrating cations is a squared function of the adsorbate concentration in the outer volume of the solution. The Donnan distribution is a source of serious error when determining M of ionic polysaccharides by membrane osmometry. Polyanions may be freed of cations and excess HsO+ by electrodialysis. 

Donnan distribution, leading to abnormally high tt, is a most serious source of error for Mn of polyanions measured by osmometry. The Donnan effect is allegedly overcome by very dilute concentrations that never exceed 25 g L 1 for the polyanion and i = 0.3 mol L-1 for the solvent (Wagner, 1949). A 25-g L-1 polysaccharide concentration is in the semidilute-to-concentrated domain, outside the theoretical dilution limit of osmometry where a power-law dependence of tt/c, on ct is expected. 

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