To obtain equivalent sphere diameters with which to characterize the particle size of a powder, it is necessary to perform a size analysis with use of one or more different methods. Particle size analysis methods can be divided into different categories based on several different criteria: size range of analysis; wet or dry methods; manual or automated methods; cost or speed of analysis.
Particle Size Analysis Methods
Commonly used methods for determination of particle size include:
- Sieve method
- Microscopic methods
- Sedimentation method
Electrical sensing zone method (Coulter Counter) - Dynamic light scattering
- Laser diffraction (low-angle laser light scattering)
Selection Of a Particle Size Analysis Method
The selection of a particle size analysis method may be constrained by the instruments available in a laboratory, but wherever possible the choice of method should be governed by the properties of the sample being investigated and the type of size information required.
For example, size analysis over a very wide range of particle diameters may preclude the use of a gravitational sedimentation method; alternatively, size analysis of tablet granules would not be done by DLS. As a general guide, it is often most appropriate to determine the particle size distribution of a powder in an environment that most closely resembles the conditions in which the powder will be processed or handled.
There are many different factors influencing the selection of an analysis method and should be considered together with information from a preliminary microscopy analysis and any other known physical properties of the powder, such as solubility, density and cohesiveness. Further analysis requirements should then be considered, such as speed of measurement, particle size data processing, initial and ongoing costs of equipment, and the physical separation of powders of different particle size for subsequent processing.
Reference:
- Aulton, M. (2018). Aulton’s pharmaceutics, the design and manufacture of medicines. Edinburgh. : Elsevier
