Particulates large scattering

However, bringing the pH of the test solution to equilibrium with the atmosphere, in the brass tests 3 and 4, or carrying out the test with the standard solution in an enclosed vessel as in brass test 5, did not reduce what was admittedly an already low covariance in the results. A second explanation of large scatter could be the (random) presence of particulate matter (e.g. oxides) which is dissolved by the acidification of the test solution after the sample has been removed at the end of the test. 

Instruments that measure scattered light, such as the Photo-Nephelometer (Coleman Instruments, Oak Brook, IL), are used to evaluate and set clarity standards for parenteral preparations. It is not possible to establish an overall standard value for all products (e.g., 30 ne-phelos) because the value itself is relative and influenced by many factors, including concentration, aging, stopper extracts, and the solubility characteristics of the raw materials. Nephelometer readings are insensitive to contamination by large (visible) particulates. 

The measurement does not require particles to pass through the laser beam one at a time. In fact, there are normally large numbers of particles in the beam at any point in time. Each particle forms its own diffraction pattern, and the system sums the results from these patterns over the total measurement period. It is important that the particulate concentration be low enough so that multiple scattering does not occur. This happens when light which is scattered from one particle strikes another particle and is scattered further before it is collected. This phenomenon is easily detected, and the loading range is usually quite broad. 

The major contributors to radiation are soot, carbon dioxide, water vapor, inorganic particulates and other intermediate products whose concentrations depend upon the particular fuel. The presence of solid particles such as ash and carbonaceous material affects the radiation heat transport as they are continuous emitters, absorbers, and scatterers of radiation. Carbonaceous particles tend to be large relative to the wavelength of radiation and have surfaces with high absorptivity. 

The effort that leads to optimization of the particle morphology is largely one of trial and error, and there is no simple means to describe the distribution of components within individual particulates. Clearly, if the majority of an active component (API) is in the interior of a particle, then the dissolution or release characteristics are likely to differ from particles where the API is predominantly on the surface. The surface distribution of proteins and polymers within spray-dried particles has been studied using electron spectroscopy for chemical analysis that involves analyzing the energy signature of electrons scattered from surfaces while being bombarded by x-rays [11,28-31], Conclusions can then be drawn... 

Therefore, there is a quickly increasing emphasis on size enlargement of these finely divided particulate solids. Tasks are to increase the size of powders to particles that are large and heavy enough to avoid scattering by wind or water and to produce permanent bonds that are waterproof, survive freeze-thaw cycles, and, preferably, immobilize leachable compounds. 

At concentrations of interest in many applications, the particles are separated by distances large compared witli their diameter and are distributed in space in a random fashion. Light scattered in a given direction from an incident beam by different particles will be composed of waves of different pha.ses. The total energy of the scattered wave per unit area—that is, the intensity of the scattered wave in a given direction—will be equal to the sum of the intensities of the individual particles in that direction. This type of behavior is referred to as independent scattering, and it simplifies calculation of the total scattering by particulate systems. 

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