Dissolution rate coefficient

Calculated dissolution rate coefficients have a range of 1 x... 

With the saturation solubility CggKj the organic solvent, the dissolution rate coefficient ks is dependent on the surface property and the degree of agitation. 

C = the aqueous saturation concentration = the dissolution rate coefficient evap = the evaporation rate coefficient OT = the mass of the compound in the slick M = the compound s molecular weight... 

More generally, the water-film dissolution rate coefficient for any compound, i, can be estimated from the reaeration rate coefficient, again by correcting for the differences in molecular diffusivities ... 

Hibbs and Gulliver (1999) recently found that when the turbulence responsible for mass transfer at the water surface is generated from the bottom, such as in a stream or in a stirred reactor, the near-surface turbulence that dominates the mass transfer process on the water side of the interface is essentially unaffected by the presence and/or the properties of an oil slick. Thus, the water-film dissolution rate coefficient can be estimated directly from the air-water liquid-film coefficient, corrected by a ratio of Schmidt number to the -V2 power. 

Figure 14. Effect of temperature on coal dissolution rate coefficient, indicating hydrodynamic influence...

Yagi and Wakao (1959) used mass transfer measurement results to estimate the heat transfer coefficient at the tube wall. Material was coated on the inner surface of the packed tubes and the dissolution rate was measured. 

Figure 4.52. Coefficients of variation that reflect both tablet to tablet and analytical variability. For formulation B, particularly strengths 2 and 3, the drop in CV with higher cumulative release (a - b) is marked, cf. Fig, 4.50. When the dissolution rate is high, individual differences dominate, while towards the end analytical uncertainty is all that remains. The very low CVs obtained with strength 3 of formulation A ( 0.7-0.8%, data offset by +10% for clarity) are indicative of the analytical uncertainty. Because content uniformity is harder to achieve the lower the drug-to-excipient ratio, this pattern is not unexpected.

It can be seen that the dissolution rate constant kD is equivalent to the diffusion coefficient divided by the thickness of the diffusion layer (D/h). 

Therefore, the final equation is relatively simple despite the fact that the derivation is complex. Equation (145) shows that the intrinsic dissolution rate depends on the diffusion coefficient and solubility of the drug, disk rotational speed, and the viscosity of the dissolution medium. The amount of drug dissolving per unit area is the same everywhere on the disk s surface. This makes the disk a powerful experimental tool in drug discovery and development. 

Heterogeneous conditions both in terms of hydrodynamics and composition prevails in the GI tract. Parameters such as D, Cs, V, and h are influenced by the conditions in the GI tract which change with time. Thus, time dependent rate coefficients govern the dissolution process under in vivo conditions. One of the major sources of variability for poorly soluble drugs can be associated with the time dependent character of the rate coefficient, which governs drug dissolution under in vivo conditions. 

Equation (43) describes the transport-controlled dissolution rate of a solid according to the diffusion layer theory in its simplest form. The mass transfer coefficient here is given by k, = kT = Dlh. 

This paper presents new data on dissolution kinetics. The effects of alkali concentration, size of the cation, and salt addition were studied. The influence of segmental mobility on dissolution was elucidated by measuring the temperature coefficients of the dissolution rates. Experiments were also carried out to study the relation between the chemical structure of a polymeric Inhibitor and Its effectiveness 1n retarding dissolution. Based on these results,... 

Once the diffusion coefficient is determined at a given concentration, the extent of fluorescence quenching can be predicted. Therefore, by working backward, one can determine the solvent diffusion coefficient and the solvent concentration in a polymer film from fluorescence quenching data. Consequently, if a polymer film dissolves in a solvent with a constant dissolution rate (DR), the solvent concentrations at different parts of the SCP can be determined. Finally, a SCP is constructed from these data. 

The diffusion coefficient is linked to the intrinsic dissolution rate constant ( i) as expressed by the term... 

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