Particle size result interpretation
- 1. Particle Size Result Interpretation Elaheh Entezar-Almahdi, Pharm.D Ph.D Student of Pharmaceutics
- 2. What is a distribution? Number of particles in the different size bins Total volumes of particles in the different size bins How much light is scattered by the particles in the different size bins Number Distribution Volume Distribution Intensity Distribution
- 3. Number vs. Volume Distribution
- 4. Number vs. Volume Distribution (Cont’D)
- 5. Transforming Results Results from number based systems, such as microscopes or image analyzers construct their beginning result as a number distribution. Results from laser diffraction construct their beginning result as a volume distribution.
- 6. Example (TiO2) Mean (nm) Width (nm) Intensity 87 32 Volume 65 25 Number 50 14
- 7. Question: So Which is the Correct Size? Answer: All three are correct!!!
- 8. Z-Average Size The Z-Average size used in DLS is a parameter also known as the cumulant mean. It is the primary and most stable parameter produced by the technique. The Z-Average mean is the best value to report when used in a quality control setting as it is defined in ISO 13321 and more recently ISO 22412 which defines this mean as the ‘harmonic intensity averaged particle diameter”. It should be noted that the Z-average is a hydrodynamic parameter and is therefore only applicable to particles or molecules in solution. The Z-average size will only be comparable with the size measured by other techniques if the sample is monomodal, spherical or near-spherical in shape, monodisperse, and the sample is prepared in a suitable dispersant.
- 9. Polydispersity Index (PDI) • The Polydispersity Index is dimensionless. • It is scaled such that values ˂ 0.05 are rarely seen other than with highly monodisprse standards. • Values ˃ 0.7 indicate that the sample has a very broad size distribution and is probably not suitable for the DLS technique.
- 10. References: • Malvern Instrument (Technical notes) • HORIBA Scientific Guidebook