Flocculation effect of xanthan gum in pharmaceutical suspensions.

The particulate structure in suspensions of magnesium carbonate, aluminum hydroxide, calcium carbonate, and zinc oxide was assessed by sedimentation volume studies, measurement of particle size by an electronic particle sizer, and visualization by microscopy. The results of the particle-size measruement did not always agree with results from the other techniques. magnesium carbonate, aluminum hydroxide, and zinc oxide were flocculated in water. The addition of xanthan gum increased flocculation of magnesium carbonate and aluminum hydroxide and apparently caused partial deflocculation of zinc oxide suspensions. Calcium carbonate suspensions were deflocculated in water, and xanthan gum did not significantly change the properties. Studies with sodium chloride showed that flocculation cannot be attributed to changes in double-layer repulsion. Flocculation in the suspensions studied appeared to be consistent with a bridging mechanism.