Particle size measurement with sieves

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

Various grades of sorbitol are available that differ in their pcuticle size distribution. Most of the particle size measurements reported for sorbitol are by sieve methods [1,7,26,27], and permit direct comparison with the vendor s specifications. For the samples used in this study, the vendor specified sieve limits for the various grades are listed in Table 1. 

In many industries, particle size measurements have been carried out historically by sieve analysis and light scattering instruments are increasingly replacing this. In order to correlate with historic data banks some manufacturers have software to manipulate the data so as to present the size distribution in terms of sieve diameter. 

Washington (1992) has discussed the concepts and techniques of particle size analysis and its role in pharmaceutical sciences and other industries. There are many different methods available for particle size analysis. The techniques most readily available include sieving, optical microscopy in conjunction with image analysis, electron microscopy, the Coulter Counter and laser diffractometers. Size characterization is simple for spherical particles, but not for irregular particles where the assigned size will depend on the method of characterization used. Table 6.2 lists particle size measurement methods commonly used and the corresponding approximate useful size range (Mullin 1993). 

Nakajima, Y. N., Whiten, W. J., and Withe, M. R. 1978. Method for measurement of particle size distribution by sieves. Transactions of the Institute of Mining and Metallurgy 87 C194-203. 

This last point is important in all particle size measuring techniques and it may be necessary to use a liquid sieving technique, together with dispersing agents, in difficult cases. 

The major gaseous components were analyzed by a gas chromatograph equipped with a TCD and a molecular sieve 13X column. The specific surface areas of carbon produced were measured by the BET method(ASAP 2010, Micromeritics). The morphology and particle size of the formed carbon were investigated by the scanning electron microscopy(S-4200, Hitachi... 

Corn stover was harvested from south Hungary in the fall of 2001. The selected and washed straw was air-dried to an average 90% dry matter (DM) content. The air-dried material was ground and sieved, and the fraction with a particle size of 2-5 mm was used. The composition of this material and also the washed, solid fibrous fraction remaining after pretreatment was determined using Kaar s (19) method. To measure the total ash content, approx 0.5 g of dried sample was placed in a crucible, ignited at 550°C for 3 h, cooled in a desiccator, and weighed. 

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