Particle size analysis light diffraction

Submicron particle size analysis employs a scatter theory not completely described by Fraunhofer diffraction. The small particle range down to about 0.1 micrometer in diameter utilizes a combination of Fraunhofer diffraction and Mie theory for the forward scattered light and 90-degree Mie scatter at three (3) wavelengths and two (2) polarizations of each wavelength. Because of its need for a technology more involved than diffraction theory, submicron measurements are influenced by the index of refraction of the material making up the particulates to be sized. 

The theory of Mie " is used also in the laser diffraction method for particle size analysis. r In this method, the light scattered by the particles is collected over a range of angles (usually between 1° and 20°) in the forward direction. The corresponding experimental setup is usually... 

The first of the modem diffraction based instruments for particle size analysis is probably that produced by CILAS (France). This is described by Comillautf and used a moveable mask to detect light scattered at different angles. The Leeds and Northrup Microtrac dates from 1976, this was described by Wiess and Frock . 

Laser diffraction particle size analysis is based on the physical phenomenon that particles in a laser beam scatter laser light at angles that are inversely proportional to the size of the particles [64, 161, 223], Thus, larger particles scatter at small forward... 

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

The characterization of emulsions by particle size distribution analysis has been facilitated in recent years by a range of new instruments. Most of these instruments employ laser light diffraction principles, and have replaced older spectrophotometric methods. 

The solid-state properties like crystallinity, polymorphism (crystal structure), shape (morphology), and particle size of drugs are important in the stability, dissolution, and processibility of drugs. Some commonly used methods in solid-state studies include microscopy, hot stage microscopy with polarized light, x-ray powder diffraction (XRPD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared FTIR/Raman, and solid-state NMR. 

Third, in selecting a particle sizing technique, one must consider the size of the material itself. Most techniques have effective upper and lower limits of detection. Laser diffraction, for example, can measure particles from approximately 0.01 pm to several millimeters. With optical microscopy and image analysis, it becomes very difficult to resolve features that are smaller than a 0.3 pm because of the wavelength of light used in conventional optical microscopes.1... 

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