Osmotic pressure, molecular weight polysaccharides

Molecular weights of polysaccharides in solution can also be measured by osmotic pressure and light scattering. Osmotic pressure yields the number average molecular weight, which can be usefully used with Mw from sedimentation equilibrium as a measure of polydispersity Preston and Wik [28] have done this for example with hyaluronic acid. The ratio Mw/Mn the polydispersity index is often given as a measure of polydispersity, and can be related to the width of a molecular weight distribution via the well-known Herdan [96] relation ... 

The molecular weight of the methylated polysaccharide used in structural determinations of a complex specific somatic polysaccharide has been determined by osmotic pressure measurements in chloroform solution as being 12,000.111... 

Methods for the determination of the molecular weight of a polysaccharide include gel-filtration (Andrews, 1970), ultracentrifugation, light scattering, and osmotic pressure determinations (Banks and Greenwood,... 

Molecular weights of polysaccharides may be determined by measuring the osmotic pressure of dilute solutions. The osmotic pressure at infinite dilution, obtained by extrapolating a number of measurements at various low concentrations, is a fimction of the molecular weight as shown by the modified van t Hoff formula. 

The number average molecular weight of a polysaccharide may be calculated from its osmotic pressure in solution, according to the Van t Hoff formula, but any association of the molecules in solution will give spurious high values. This may be overcome by using a limiting value of osmotic pressure/concentration extrapolated to zero concentration. Alternatively, a modified Van t Hoff expression ... 

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