Homogenization particle size reduction

IAEA/AL/095 1996). Both methods were suitable, but needed to be repeated several times to produce the small particle size that was required. The particle size reduction, e.g. of IAEA-395 from a median size of 30 pm to 3.5 pm, improved the homogeneity of elements. Sampling constants (the minimum mass that can be used to achieve a random error of i % at the 65 % confidence level) improved from a factor of 1.2 for Sc, up to a factor of 800 for Au. The average improvement was about a factor of 2-10. (Ni Bangfa et al. 1996). From these initial experiences, it is dear that preparation of reference materials is critical with respect to the final particle size distribution, which should exhibit a low maximum (<50 pm) and a narrow range in particle sizes. Milling techniques to meet such criteria are available today, and materials that show intrinsic uniformity are particularly suitable to achieve the desired properties. 

Obviously, the technology exists for obtaining analytical results without special preparation and analysis in a laboratory. However, at the present time there is no acceptable substitute for direct laboratory examination of samples if we want the kind of accuracy and confidence we have come to expect. All conventional methods for analysis of solid materials require one or more of the following preparation activities before an analytical method can be properly executed 1) particle size reduction, 2) homogenization and division, 3) partial dissolution, and 4) total dissolution. Let us briefly discuss each of these individually. 

Particle size reduction makes dissolving procedures more efficient and extracting procedures more accurate because of the improved contact of the solvent with the sample. If accompanied by thorough mixing, particle size reduction also results in more homogeneous samples, which are more representative. 

Disperse systems often necessitate particle size reduction, whether it is an integral part of product processing, as in the process of liquid-liquid emulsification, or an additional requirement insofar as solid particle suspensions are concerned. (It should be noted that solid particles suspended in liquids often tend to agglomerate. Although milling of such suspensions tends to disrupt such agglomerates and produce a more homogeneous suspension. 

Small particle sizes of raw batch materials accelerate melting and homogenization via an increase in the reaction area between raw materials. However, the use of very fine raw materials has an associated dusting problem along with the added cost of particle size reduction. In the following, simultaneous thermal analysis in conjunction with x-ray diffraction were used to determine the fusion path in a typical glass composition as a function of particle size. 

Fig. 6 Diagram of operation of a piston gap homogenizer. Turbulence and cavitation result in particle size reduction during the homogenization process. From Professor Douglas Goff, Dairy Science and Technology Education, University of Guelph, Canada www.foodsci.uoguelph.ca/dairyedu/ home.html (accessed September 2004).

Variations in assay results can be avoided by the preparation of homogeneous, well-mixed, or non-settling fine particle suspensions (size 1-10 pm). Particle size reduction results in slow, more uniform settling rates. The bioavailability of drugs is improved by reducing the size of suspension particles. Furthermore, drug particles smaller than 20 pm produce less pain and tissue irritation when injected parenterally. However, fine particles may have a deleterious effect on chemical stability because of their high dissolution rate. 

The resultant hot emulsion is allowed to cool to 60°C, at which point it is thoroughly homogenized using a recirculating homogenizer, homomixer, or other suitable equipment to provide a particle size reduction to a range of 5-20 pm for most particles. 

For the uniformity of content and dose accuracy. Particle size reduction increases the number of particles per tmit of weight and thereby the homogeneity of the mixture. 

The pre-emulsion was stable enough to remain intact during transfer to the Gaulin Sub-micron Disperser and Homogenizer. The emulsion was recycled until the desired particle size reduction was achieved. The Gaulin Homogenizer was operated at 3500 pounds per square inch of shear force. 

Particle-size reduction. To maximize the )neld of an extraction procedure, the lipid surface area exposed to a solvent may be increased by finely grinding the sample at low temperatures. This also affords a more homogeneous sample for solvent extraction. 

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