Laser diffractometry

By laser diffractometry, Okechukwu and Rao (1996a) found that ungelatinized cowpea starch granules had a unimodal distribution with a mean of 19 pm. In an unrelated method, Chuma et al. (1982) used photography, a digitizer, and a microcomputer to calculate the size, surface area, and volume of grains and soybeans. 

Microspheres intended for nasal administration need to be well characterized in terms of particle size distribution, since intranasal deposition of powder delivery systems is mostly determined by their aerodynamic properties and particle sizes. Commonly used methods for particle size determinations described in the literature are sieving methods [108], light microscopy [58], photon correlation spectroscopy [66], and laser diffractometry [25,41,53,93], The morphology of the microparticles (shape and surface) has been evaluated by optical, scanning, and transmission electron microscopy [66, 95],... 

A simple method of laser diffractometry has been described for sizing droplets with radii greater than 1.5 pm [75]. Under partially polarized laser illumination, at a 90° angle to a camera receiver, well-focused droplets appear as small circular dots. Out of focus droplets give large diffraction haloes crossed by a row of dark, parallel stripes, the number of which is indicative of particle size. 

Some work has shown a direct correlation between shape factor and the flow properties of powders. The flowability of fine powders, as measured by a shear-cell as well as by Carr s method, was found to increase with increasing sphericity, where the sphericity is indicated by a shape index approaching one, as measured by an image analyzer. Huber and co-workers derived an equuation in which flow rate was correlated to the volume specific surface as measured by laser diffractometry. Reasonable predictions were made for individual powders as well as binary and ternary mixtures. 

The measurement of particle size is a key issue in the formulation of many pharmaceutical products. Particle size distribution is known to directly influence physical properties of powders, such as dissolution rate, powder flow, bulk density, and compressibility. Conventional methods of particle size measurement include sieve analysis and laser diffractometry. ... 

FDA techniques (i.e.. fiber diameter analyser) which operate by a light scanning non-microscopical technique, or laser diffractometry. 

The validity of Princen s theory for concentrated water-in-oil emulsions was also investigated by Ponton et al. (2001), using the droplet size distribution determined by laser diffractometry based on the Mie theory model. Comparing the surface-volume diameter and the mass fractions of emulsions depicted an increase in the particle size with the volume fraction reduction. They showed that their experimental data (as obtained by oscillatory measurements and droplet-size distribution) corroborated the expression of the elastic shear modulus for the two-dimensional model proposed by Princen and Kiss (1986). In this model, G is proportional to (a/Rsv) l v ( l v- l c) where a is the interfacial tension, Rsv is the volume-surface radius (as obtained by laser diffractometry), and Oy and Oc are the volume fraction and the critical volume fraction, respectively (Ponton et al. 2001). The latter was found to be 0.714 experimentally, which is close to the value obtained by Princen ( 0.712) (Ponton et al. 2001). 

Figure 13.2. Particles diameters of the drug hydrocortisone acetate after 40 homogenization cycles applying the first generation process (left) and after 15 homogenization cycles applying the H42 process (homogenization pressure 1500 bar, laser diffractometry diameters D50%, D90% and D95%) (modified after Refs. 43 and 44).

Juppo AM, Yliruusi J, Kervinen L, Strom P. Determination of size distribution of lactose, glucose, and mannitol granules by sieve analysis and laser diffractometry. Int J Pharm 1992 88 141-149. 

Laser Diffractometry Phase Doppler Particle Analysis Systems (1) Broad measurement range for a given optical configuration (0.1 pm to several mm) (2) Excellent reproducibility between measurements of the same aerosol (3) No calibration required (1) Non-intrusive optical method (2) Measure the size or speed of spherical particles (liquid and solid) (1) Particles are assumed to be spherical (2) Bias due to high concentration or absence of the finest particles in the distribution... 

Laser diffractometry (LD) determines particle size (either solid particles or liquid droplets) indirectly from the interpretation of the pattern of light scattering intensity falling on the detector of the instrument [115]. Only the diffraction component of... 

Mitchell JP, Nagel MW, Nichols S, Nerbrink O (2006) Laser diffractometry as a technique for the rapid assessment of aerosol particle size from inhalers. J Aerosol Med Deposition Clearance Effects Lung 19 409... 

Baudet, G., Bizi, M., Rona, J. R, Estimation of the Average Aspect Ratio ofLamellae-Shaped Particles by Laser Diffractometry, Fart. iSci. Tech., 1993, 11,73-%. 

The size distribution of granules prepared from three different tablet excipients, lactose, glucose, and mannitol, in a high-shear granulator, were studied by both sieve analysis and laser light diffractometry (24). Both the shapes and the size distribution of the granules produced from the three excipients differed. 

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