Laser diffraction

A laser diffraction spectrometer can measure particles as small as 0.2 pm and up to about 1000 pm. Some instruments allow the operation of the analyzer for... 

Particle Size Laser Refractometiy is based upon Mie scattering of particles in a liquid medium. Up until about 1985, the power of computers supplied with laser diffraction instruments was not sufficient to utilize the rigorous solution for homogeneous spherical particles formulated by Gustave Mie in 1908. Laser particle instrument manufacturers therefore used approximations conceived by Fraunhofer. 

Laser diffraction Population measure 0.1-800 Obscuration, sampling 54... 

J Ranucci. Dynamic plume-particle size analysis using laser diffraction. Pharm Technol 16 109-114, 1992. 

Iida Y, Ashokkumar M, Tuziuti T, Kozuka T, Yasui K, Towata A, Lee J (2010) Bubble population phenomena in sonochemical reactor I Estimation of bubble size distribution and its number density with pulsed sonocation - laser diffraction method. Ultrason Sonochem 17 473 179... 

For a given bulk solid, determine particle size distribution, median particle diameter dv50 (e.g., using a Coulter Counter or a Malvern Laser Diffraction Analyser) and ps. 

Vukjovic et al.199 recently proposed a simple, fast, sensitive, and low-cost procedure based on solid phase spectrophotometric (SPS) and multicomponent analysis by multiple linear regression (MA) to determine traces of heavy metals in pharmaceuticals. Other spectroscopic techniques employed for high-throughput pharmaceutical analysis include laser-induced breakdown spectroscopy (LIBS),200 201 fluorescence spectroscopy,202 204 diffusive reflectance spectroscopy,205 laser-based nephelometry,206 automated polarized light microscopy,207 and laser diffraction and image analysis.208... 

Laser diffraction equipment, in particle size measurement, 18 153—154 Laser diffraction methodology, 23 193—194 Laser diodes, 14 699 22 172, 173-176. 

This is a universally applicable instrument for determining particle-size distributions of all kinds of solids which can be analysed either in suspension in a measuring cell or dry by feeding through a solid particle feeder. In the Fritsch Analysette 22 laser diffraction apparatus the measured particle-size distribution is displayed on the monitor in various forms, either as a frequency distribution, as a summary curve or in tabular form and can be subsequently recorded on a plotter, stored on hard disk or transferred to a central computer via an interface. The time required for one measurement is approximately 2min. 

The scattering models employed in data processing invariably involve the assumption of particle sphericity. Size data obtained from the analysis of suspensions of asymmetrical particles using laser diffraction tend to be somewhat more ambiguous than those obtained by electronic particle counting, where the solid volumes of the particles are detected. 

The mass median diameter (MMD) is the most common descriptor of primary particle size and may be determined by sieving or centrifugal sedimentation. The volume median diameter, as determined by laser diffraction, may be used as an approximation of MMD, provided that the particle density is known and does not vary with size, and that the particle shape is near spherical. The MMD of a powder can be used as a predictor of aerodynamic diameter by Eq. (1),... 

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. 

Laser diffraction is a fast alternative for analysis of the size distribution of particles in an aerosol cloud. The theory of laser diffraction is well understood [124,125]) but this technique requires special measures to test inhalation devices and to interpret the results correctly. One of the major problems is that flow adjustment through the inhaler is not possible. Furthermore, the presence of carrier particles from adhesive mixtures may disturb the measurement of the fine drug particles and the size distribution obtained is of an unknown dehvered mass fraction of the dose. These practical problems and limitations have been solved by the design of a new modular inhaler adapter for the Sympatec laser diffraction apparatus (Figure 3.6). 

Figure 3.6. Schematic representation of a new inhaler adapter for laser diffraction characterization of the aerosol clond.

The apphcation of the laser diffraction technique is sometimes questioned becanse it measures geometric instead of aerod5mamic particle diameters. However, the aerod5mamic diameter can be calcnlated when the dynamic shape factor and density are known. Moreover, the dynamic shape factor (x) of micronized particles will often be only shghtly higher than 1 and so is the tme particle density (1.0 < pp < 1.4 g cm ). As a conseqnence, the aerodynamic diameter differs only slightly from the eqnivalent volume diameter (see Eq. 3.1). 

Wedd M.W., Particle sizing in the sub-micron range by laser diffraction, in Particle and Surface Characterization Methods, Muller R.H. and Mehnert W., eds.. Scientific Publishers, Stuttgart, 1997, 57. 

Figure 1. Effect of Binary Mixture Surfactant Concentration and Self-Emulsification Temperature on Emulsion Droplet Size for the Miglyol 812-Tagat TO System as Determined by Laser Diffraction. Bars Represent Standard Errors.

Table II. Proportion of Emulsion Droplets below 3 and 1 m as a Function of Increasing Surfactant Concentration of the Binary Mixture Tagat TO - Miglyol 812 as Measured by Laser Diffraction at a Self-Emulslflcatlon Temperature of 30 C,...

Laser diffraction of organic dispersion using weak ultrasonics 20 Detecting agglomerates... 

Surface Tension Determination through Capillary Rise and Laser Diffraction Patterns 41... 

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