Gums I'm working on have approximately 60-80 polysaccharide by content but Im unable to precipitate or purify the gum by using methanol ethanol or even acetone. By acetone additon i just get slurry. But not complete separation or precipitate. But before adding solvent if I add calcium chloride and then followed by solvent I get change in media and precipitaes setting down in bottom. Should I proceed with that?
If you are working with ionic polysaccharides the effect of calcium chloride is probably the screening of charges by salt whereby the polysaccharide becomes somewhat less hydrophilic. This effect is non-specific and the main parameter is ionic strength. In that case NaCl should also be effective.
A possible reason for your problems with acetone or ethanol precipitation is the high viscosity of aqueous polysaccharide solutions. In that case precipitates tend to become very sticky and difficult to handle. A way to avoid these problems is to use high dilution of polysaccharide solution, a large excess of precipitant (e.g. 5 fold on volume basis) and highly turbulent stirring (blender or homogenizer). I recommend to start with small scale trials to select optimal precipitation conditions.
Thank u Sir Peter A. M. Steeneken for your reply and yes NaCl Has also some effect as well as Barium chloride. I'm making small level trials to optimize the conditions. Rite now I want to test and established method barium hyrdoxide method for ppt. Simple solvent even 5 to 7 folds is not effective. on your recommendation i will use a high dilution too.
Ca and Ba are more effective than Na because ionic strength scales with the square of ionic charge. Please note that barium is toxic and therefore not very suitable for food applications. It may also help to work at low temperature. We used acetone at -18 degrees C pouring out slowly in aqueous solution at 4 degrees C with high speed stirring. Success with your work!
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