- Particle Size and Distribution describe how particles vary in dimensions within a system.
- Particle Size and Distribution affect drug dissolution, bioavailability, and stability.
Particle Size
- Refers to the dimension of individual particles.
- Most pharmaceutical powders consist of irregularly shaped particles.
- Particle size is typically expressed as an equivalent diameter (the diameter of a sphere with similar properties, such as volume or surface area).
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Particle Size Distributions (PSD)
- Describes the range and proportion of different particle sizes in a sample.
- PSD is more meaningful than just the average size because pharmaceutical properties depend on both large and fine particles.
Types of Distributions:
- Monodisperse – particles of nearly the same size
- Polydisperse – particles of a wide range of sizes
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Methods to Represent PSD:
- Histogram
- Frequency and cumulative curves
- Log-normal or Gaussian distribution
Methods of Measurement
- Sieving: For particles > 50 µm
- Optical microscopy: Useful for 1–100 µm range
- Laser diffraction: Fast and suitable for wide size ranges
- Dynamic light scattering: For nanoparticles (<1 µm)
- Coulter counter: Measures electrical resistance changes
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