Dissolution patterns

Test methods available are the free-running test (galvanic cell), galvano-static test (constant current) and potentiostatic test (constant potential). These are always run in conjunction with visual examinations with particular emphasis on dissolution pattern. 

Dissolution of Human Urinary Calculi in Vitro. Five human urinary calculi containing various proportions of Ca3(P04)2, Ca(C204), CaC03, and MgNH4(P04) were subjected to similar dissolution tests at pH 7 (Table 11). The same dissolution patterns as those of the model phosphate and oxalate calculi are found. That is, for phosphate calculi no. 1-4, X is more effective than [18]aneN6 or EDTA and for oxalate calculus no. 5, EDTA is best. 

The aim of the present study was to repeat the experiments of the previous study using a multiple-unit verapamil formulation instead of the single-unit tablet. The in vitro dissolution patterns of both formulations are approximately equal, thus allowing their biopharmaceutical properties to be compared. 

The verapamil pellets contained equal parts of verapamil hydrochloride (Fermion) and lactose (Ph. Eur.) plus 4% of gelatin as a binder. They were coated using a fluidized bed technique (Aeromatic Strea 1, Aeromatic AG). The coat consisted of ethyl cellulose (Ethocel N-50), Hercules) and 20% of dibutyl sebacate (E. Merck) as a plasticizer. The calculated amount of coating in the pellets was 10%. The density of the verapamil pellets was 1.13. The in vitro dissolution pattern was determined according to the USP paddle method 50% of the drug was dissolved at 4.2 h. 

In each test, 500 ml. of this solution were mixed with the silica powder and kept in suspension by continuous but mild agitation. The apparatus was thermostatically controlled to 25° dz 0.5°C. To facilitate comparisons of individual dissolution patterns, the particulates used in... 

Preliminary tests with samples of vitreous silica, quartz, cristobalite, and tridymite not treated with NaOH showed an effect which for quartz was previously described (7, 13) repeated tests on the same sample did not reproduce the dissolution pattern but gave reduced values. The example in Figure 8 shows three of four repeated runs on the same cristobalite sample. Although the surface area remained constant, the concentration increase with time was always slower than in the preceding... 

Figure 9. Dissolution patterns of vitreous silica of different quantities in suspension 0.44 grams = 5 sq. meters, 1.32 gram = 15 sq. meters and 3.95 grams = 45 sq. meters of a powder of 11.4 sq. meters/gram in 500 ml. of...

Figure 10 gives results obtained with quartz samples of various grain size as indicated by the different specific surface areas. Although these surface values differ by a factor of 20, the differences in the dissolution pattern for equal areas of exposed surface are barely significant. This indicates again that no difficulties in interpreting the data arise from special effects of disturbed surface layers or small particle sizes. 

Figure 10. Dissolution patterns obtained with quartz samples of different specific surface area. Total surface area suspended in 500 ml. of solvent is...

In view of this, the dissolution patterns of all other silica modifications were interpreted disregarding the condensation reaction. This seemed particularly adequate for stishovite, a high pressure, high temperature material, first produced in an autoclave by Stishov and Popova (17) in 1961 and detected at Meteor Crater one year later (6). The lattice... 

Figure 16. Dissolution patterns of different silica modifications 375 sq. meters of total surface area suspended in 500 ml. of a solution of 0.9% NaCl plus 0.1% NaHCOs at pH = 8.4...

In the petroleum industry, HC1 is routinely injected into carbonate formations in order to improve oil or gas production. It is known that the porous medium is not etched uniformly by the reactive fluid but that unstable dissolution patterns consisting of highly ramified, empty channels are formed. The channels are commonly called wormholes. As soon as a wormhole pattern develops, all the fluid will flow through it. Any local increase in the flow rate results in an increase in the local dissolution rate. A piece of porous medium in which a wormhole pattern has been created can be considered as composed of two parts the first part (wormholes) of very large permeability, and the second part keeping its original permeability. 

Residual Current-Voltage Curves and Dissolution Patterns in supporting Electrolytes. Anal. Chem. 26, 633 (1954). 

Non-uniform or incomplete coverage of tablets and beads results in different dissolution patterns... 

Dissolution, patterning pCP UPD on hybrid structure of hydrogen-bonded network and SAM... 

Figure 2.5.10 Typical dissolution pattern in the different regions of vesicle membranes the entrapped water volume 9 may contain an ionic dye, which can be separated from dyes in the bulk water phase by gel chromatography. The headgroups 3 and 7 may consist of redox systems, e.g., quinones in different oxidation states. The aqueous and membraneous surface regions 2,8 and 4,6 may enrich polar or charged compounds. Large and flat hydrophobic molecules (e.g., porphyrins) prefer the same regions. The central region 5 is thought take up some hydrophobic steroids and carotenoids.

Kawata M, Nakamura M, Goto S, Aoyama T. Preparation and dissolution pattern of Eudragit RS microcapsules containing ketoprofen. Chemical and Pharmaceutical Bulletin. June 1986 34(6) 2618-2623. PubMed PMID 3769077. 

It tends to have an uneven dissolution pattern, which adversely affects its efficiency. 

Fractal dimensions of some non-living and living systems including crystallization patterns, electro-deposited aggregates, polymers, chemical dissolution patterns, dielectric breakdown, sputter deposited film of NbGcj, retinal vessel and bacterial growth are given in Table 13.3. 

Daccord and Lenormand [36] have shown experimentally that the dissolution patterns obtained by injecting water through pure master were fractal. These results are of interest in different areas where chemical dissolution of porous media by a flowing fluid occurs. In nature, the formation of caves and the oil industry are examples of this process. In two dimensions, these dissolution patterns are remarkably similar to patterns associated with DLA, which includes dielectric breakdown. The two-dimensional dissolution patterns are remarkably similar to patterns associated with DLA. 

FIG. 8 Dissolution patterns of naproxen in JP first fluid at 37.0"C. (a) Naproxen-CPG 120 system (b) naproxen-CPG 1000 system. ( ) Naproxen crystals (O) fi esh mixture of 10% naproxen crystal and 90% CPG (O) same mixture after heating at 90°C for 3 h. Each point represents the mean value (n = 3). (From Ref 18.)... 

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