Abstract
Osmotic pressure measurements for aqueous solutions of a gellan gum and standard samples, such as three kinds of pullulans and a dextran, were made to determine number average molecular weights Mn and osmotic second viral coefficients A 2 using a Hewlett-Packard high speed membrane osmometer. From the measurements of the standard samples, some technical problems for the osmometry of aqueous solutions were discussed. It was found that the values of Mn obtained for the standard samples were close to but somewhat smaller than the Mw values determined by sedimentation equilibrium measurements. Osmometry of the polyelectrolyte of gellan gum was carried out at 40°C in tetramethyl ammonium nitrate solution using the sample converted into tetramethyl ammonium salt. The Mn values of the sample obtained were 5.4 × 10 4 and 5.5 × 10 4 in 0.05 and 0.075 mol/dm 3 tetramethyl ammonium nitrate solutions respectively. The A 2 values obtained were rather large due to the Donnan effect.
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