Solubility particle size and

The relationship between particle size and solubility, originally derived for vapour pressures in liquid-vapour systems by Thomson (who became Lord Kelvin in 1892) in 1871, utilized later by Gibbs, and applied to solid liquid systems by Ostwald (1900) and Freundlich (1926) may be expressed in the form 

The quantity v represents the number of moles of ions formed from one mole of electrolyte (equation 3.30). For a non-electrolyte, z/ = 1. 

Confusingly, but for understandable reasons, equation 3.58 is referred to in the literature by a variety of names such as the Gibbs-Thomson, Gibbs-Kelvin and Ostwald-Freundlich relation. For consistency, however, the designation Gibbs-Thomson will be used throughout this work. 

As a result of the particle size solubility effect, solution compositions may exceed greatly the normal equilibrium saturation value if the excess solute particles dispersed in the solution are very small. For most solutes in water, however, the solubility increase only starts to become significant for particle sizes smaller than about 1 pm. 

For practical application to crystals, equation 3.58 could be more usefully redrafted in terms of particle size expressed as a convenient length parameter, L, coupled with an approximate overall shape factor, F  

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Although it is possible to control the dissolution rate of a drug by controlling its particle size and solubility, the pharmaceutical manufacturer has very little, if any, control over the D/h term in the Nernst-Brunner equation, Eq. (1). In deriving the equation it was assumed that h, the thickness of the stationary diffusion layer, was independent of particle size. In fact, this is not necessarily true. The diffusion layer probably increases as particle size increases. Furthermore, h decreases as the stirring rate increases. In vivo, as GI motility increases or decreases, h would be expected to decrease or increase. In deriving the Nernst-Brunner equation, it was also assumed that all the particles were... 

If very small solute particles are dispersed in a solution, the solute concentration may exceed the normal equilibrium saturation value. The relationship between particle size and solubility first applied to solid-liquid systems by Ostwai.d120 may be expressed as ... 

Ostwald (1900) was the L rst person to attempt to correlate particle size and solubility. This treatment was amended in 1909 by Freundlich and is written as... 

Braun, H. (1983) Particle size and solubility of disperse d s/,. Prog. Coloration, 13 62-72. 

This equation again demonstrates that particle size and solubility are the main parameters affecting dissolution kinetics of drug powders, which, in turn, could affect the release profile of dosage forms if dissolution is the rate-limiting step of in vivo absorption. Table 5.1 demonstrates several examples of dissolution times of spherical particles (assuming monodispersed systems) as a function of solubility and particle size. 

In wet deposition of airborne contaminants, the uranium is washed from the atmosphere by rain, sleet, snow or other forms of moisture. The rate of wet deposition depends upon particle size and solubility (chemical form). 

Field liming reactions are generally incomplete, because of incomplete mixing, and require considerable time. The reaction rate varies inversely with pH, limestone particle size, and solubility of the liming agent. Hence, the laboratory lime requirement value is often further multiplied by a conversion factor to better estimate the amount of lime needed to achieve a given field pH. 

Quantitative studies regarding absorption of zinc and zinc compounds after inhalation exposure in humans are limited. The absorption of inhaled zinc depends on the particle size and solubility. Elevated levels of zinc have been found in the blood and urine of workers exposed to zinc oxide fumes (Hamdi 1969). 

The choice of the type of dosage form will depend on the salt form, particle size and solubility of the substance. In principal there are three categories of semisolid eye preparations ... 

This section discusses the active substance (particle size and solubility), the bases and the excipients to obtain optimal release and absorption. Obviously these three components are closely interrelated. The active substance must be used in a chemical form, ionised or not, and with a particle size that are optimal for release and rectal absorption. In addition a base has to be chosen that optimises release, see also Fig. 11.1. Excipients can be added to improve dissolution and absorption or for technological reasons. However, excipients aimed at technological improvement may also influence the release of active substance. Whatever choice is made for active substance, base and excipients, their impact on the preparation process, the stability of the product and the shelf life must also be considered. 

Particle Growth. The monomer concentrations after points 1-L can be used to calculate the size of the colloidal particles versus time. In the molybdate test, the unrcactivc fraction corresponds to colloidal silica, and the reactive fraction is monomer or soluble silica. Using the graph of Figure 3.57 relating particle size and solubility (taken from Figure 3.32) the calculated particle size versus time is shown in Figure 3.58. 

Its ease of body contact and entry work method, particle size and solubility. 

Analysis of the particle size and solubility of samples of airborne radioactive material can assist in the development of biokinetic models for dose assessment (Section 6). Direct comparison of air samples with values of derived air concentrations (Section 2) can be used as an input to the evaluation of workplace conditions and to the estimation of doses. 

The body content of cadmium increases with age. In the newborn, the total body content is less that l xg, increasing to about 15-20 mg in cin adult human in the UK and Sweden. Cadmium enters the body mainly via the respiratory and gastrointestinal tracts. According to experimental data, after inhalation about 10-40% is absorbed. The absorption depends on the particle size and solubility, with higher values for small and highly soluble particles. ... 

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