Suspension redispersability

Oral solutions and suspensions Appearance, precipitation, pH, color, odor, redispersibility (suspensions), and clarity (solutions)... 

T Assay/Inspection, Potency, Degradation Products, Preservative Assay, pH, Dissolution, Redispersibility (suspension only), Mean size and Distribution of Particles (as appropriate)... 

Stirred Vessels Gases may be dispersed in hquids by spargers or nozzles and redispersed by packing or trays. More intensive dispersion and redispersion is obtained by mechanical agitation. At the same time, the agitation will improve heat transfer and will keep catalyst particles in suspension if necessaiy. Power inputs of 0.6 to 2.0 kW/m (3.05 to 10.15 np/1,000 gal) are suitable. 

Suspensions are generally evaluated with respect to their particle size, electrokinetic properties (zeta potential), and rheological characteristics. A detailed discussion on the methods/techniques and relevant instrumentation is given in Sec. VII. A number of evaluating methods done specifically with suspension dosage forms, such as sedimentation volume, redispersibility, and specific gravity measurements, will be treated in this section. 

A Delgado, V Gallardo, A Parrera, F Gonzalez-Ca-ballero. A study of the electrokinetic and stability properties of nitrofurantoin suspensions. II Flocculation and redispersion properties as compared with theoretical interaction energy curves. J Pharm Sci 79 709-718, 1990. 

The pyrogenic flame hydrolyzed silica Aerosil 200, a commercial product from Degussa, was used as a dispersion in doubly distilled water (1). The precipitated silica was prepared by hydrolysis of orthosilicic acid tetraethylester in ammoniacal solution according to the method of Stober, Fink and Bohn (11). The prepared suspension was purified by repeated centrifugation, separation from solvent and redispersion of the sediment in fresh water. Finally, the water was evaporated and the wet silica dried at 150°C for about half an hour. 

Colloidal systems were reported to be much more effective than immobilized or supported catalysts for photodegradation of ary hazardous molecule [72,73], Powdered materials exhibit an important inconvenience. The main difficulty in employing an insoluble, powdered semiconductor in aqueous dispersion is the need to remove the solids after treatment and subsequent redispersion in a second aqueous solution to be purified. However, in the case of colloids it was speculated that they may either be dispersed in the irradiated aqueous solution as a colloidal suspension, or attached to a suitable support as a fixed or mobile fluidized bed [72,73],... 

Impregnating a basic colloidal suspension (pH = 12) on alumina does not induce proton liberation, thus the pH is constant (Fig. 13.25b). The system keeps its initial properties, i.e. negative charges for alumina support and PdO particles. Repulsive interactions are created between the alumina surface and the PdO particles so that the particles deposited on the support are redispersed, and finally isolated from each other. 

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. 

Small-Volume Parenterals Color, clarity of solutions, particulate matter, pH, sterility, endotoxins. Powders for injection solutions include clarity, color, reconstitution time and water content, pH, sterility, endotoxins/pyrogens, and particulate matter. Suspensions for injection should include additional particle size distribution, redispersability, and rheological properties. Emulsion for injection should include phase separation, viscosity, mean size, and distribution of dispersed globules. 

The multivitamin suspension is prepared prior to application by shaking the granules with water. The uniform, yellow suspension thus obtained shows no sedimentation over a period of some hours. The redispersibility is very easy. 

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. 

Light-brown suspension showing no sedimentation during 24 hours and good redispersibility. The bitter taste of Azithromycin is almost completely masked. 

The redispersibility of the suspension is very easy after 14 days at room temperature. The viscosity is low. 

A homogeneous white suspension was obtained. It showed some sedimentation after 7 days but the redispersibility was very easy. The pH was 12. 

Ultrafilters can be used to permit sequential washing and filtering, after which the filter cake is redispersed into suspension, or continuous hollow-fibre ultrafiltration can be used to accomplish the same result (see Figure 7.6). 

Screen plates for the redispersion of the gas in the bed are placed at 1.2, 1.7, 2.2 and 2.7 m above the bottom. In the model the effect of the screen plates has been considered by mixing the gas of the bubble and suspension phases, respectively, and by restarting the bubble growth at the respective level of redispersion with an initial diameter of 4 cm. 

Figure 9.6. Schematic of repulsion or attraction forces (which vary with distance from the particle surface) between particles in suspension. Curves 1 and 6 are examples of repulsion and attraction curves, respectively, which vary with the colloid and the kinds and amounts of electrolytes. A summation of curves 1 and 6 for different conditions produces curves 2-5. In curve 2, the energy of repulsion predominates and a stable suspension is formed. Increasing electrolyte produces curves 3, 4, or 5 owing to suppression of the electric double layer. Curve 3 shows there is still an energy barrier to be overcome prior to flocculation. When the colloids surmount this energy barrier and approach closer than point C, flocculation occurs because the forces of attraction predominate. Curve 5 suggests spontaneous flocculation without redispersion unless there is a shift toward curve 2 by reexpanding the double layer through changing kinds and/or amounts of electrolytes (adapted from Kruyt, 1952).

Sediment volume and redispersion For sediment volume experiments a 50% w/v suspension was prepared using a 2% w/w of the polymer. 5g of the resulting suspension was added to 5 ml solutions of PEO to cover a wide concentration and the resulting suspension placed in stoppered cylinders and kept in constant temperature cabinets (25 1 C). The sediment height was followed with time for several weeks until equilibrium was reached. At this point the tubes were mechanically Inverted end-over-end and the number of revolutions required for redispersion was noted. 

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