Redispersion Tests

Redispersibility. For an oral suspension that settles on storage, a redispersibility test might be required. Time required to achieve resuspension by a particular procedure should be defined. 

Redispersibility testing. Redispersibility testing will be required for injectable suspensions that settle on storage. 

The redispersion microreactor is applied for the liquid-liquid polycondensation to yield an OLED material by multiple Suzuki coupling. As the initial test reaction, the following single Suzuki coupling is currently being explored in the liquid-liquid system made from water/ dioxane/toluene. 

Work with the objective of comparing oxo-ions with oxide particles in order to test the validity of this reasoning has been reported by Chen et al. who used a catalyst that initially contains Fe oxo-ions, [HO-Fe-0-Fe-OH] +. These sites were first converted to Fc203 particies by a simpie chemical treatment. This was followed by another treatment, which redispersed these Fc203 particies back to oxo-ions. The change in particle size was monitored by a spectroscopic method based on the observation that in zeolites metal ions and oxo-ions, that are attached to the wall of a cage, give rise to a typical IR band caused by the perturbation of the vibrations of the zeolite lattice. 

Oral Solutions and Suspensions Formation of precipitate, clarity for solutions, pH, viscosity, microbial bioburden, extractables, and polymorphic conversion when applicable. Additional tests for suspensions include redispersability, rheological properties, mean size, and distribution of particles. 

The most important parameters for the physical stability of suspensions are the relative volume of sediment (= volume of sediment/total volume) and the redispersability. They are tested after 1 -4 weeks have elapsed. 

Producing bland fluid lecithins is possible by redispersing the de-oiled lecithin in clean oils that have been properly refined and deodorized. Lecithin flavors are not typically a problem in food applications because lecithins are used in most foods at low levels. Laboratory tests have shown that in finished food formulations, lecithins can either accentuate or reduce the flavor intensity of salt, acids, and some spices. However, lecithin flavors can penetrate bland dairy-based systems. Studies have shown that 0.25% de-oiled lecithin could be detected in cottage cheese (31). 

Table 5.8 Typical physical properties of acrylic redispersible powers. Source Tsai, M.C., Burch, M.J. and Lavelle, J.A., Solid grade acrylic cement modifiers, in Polymer Modified Hydraulic Cement Mixtures, ASTM STP 1176 (eds L.A. Kuhlam and D.G. Walter), Table 1 published by the American Society for Testing and Materials, Philadelphia, PA, 1993...

It is a pharmacopoeial requirement that suspensions should be redispersible if they settle on storage. However, the pharmacopoeias do not offer a suitable test that can be used to characterize this aspect of the formulation. In an attempt to remedy this situation, Deicke and Stiverkrtip (1999) have devised a mechanical redispersibility tester, which closely simulates the action of human shaking. The crystal habit may also affect the physical stability of the formulation Tiwary and Panpalia (1999) showed that trimethoprim crystals with the largest aspect ratio showed the best sedimentation volume and redispersibility. 

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