difference between volume based particle size vs number based particle size distribution in Malvern Mastersizer?how it will effects on Bioavaliability.
The particles are mostly not perfect spheres and, strictly speaking, cannot be defined by a single dimension unless it is about e.g. emulsion droplets). Therefore, the particle size is usually defined by the concept of equivalent spheres, which is the case when the measurement is done by laser diffraction applied in Malvern Mastersizer instruments. Here, the particle size is defined by the diameter of an equivalent sphere having the same volume as the subject particle. As the particles get less spherical in shape, this concept becomes less appropriate for their characterisation.
independent form the way the particle size distribution is represented (frequency distribution or cumulative distribution curve) it has to be done with respect to
the weighting of individual particles.
In volume weighted distribution, the contribution of each particle relates to its volume. For example, if the volume weighted cumulative frequency of a particle with the equivalent diameter of 1 μm is 26 %, it means that 26 % of total volume of the tested materials has an equivalent diameter lass than 1 μm. The laser diffraction used by Mastersizer gives this type of weighted distribution. You can find a frequency distribution diagram of this type in my article "Fracture behaviour of bitumen emulsion mortar", Figure1.
In number weighted distribution, all particles have the same contribution independent from their equivalent diameter. For example, the cumulative frequency of 26 % of a 1-μm particle means that it is has an equivalent diameter larger than the diameter of 26 % of all counted particles. This distribution is used when by instruments with automated particle imaging.
Lets make the assumption: 100 particles consist 90 with diameter of 10 nm and 10 with diameter of 100 nm. In volume base distribution the intensity of particle with diameter of 100nm is ~10 times than the particle with diameter of 10nm. So even 100nm is only 10 particles but they are much more in volume compare to 10nm with 100 particles. In number base the intensity is simply the amount of particles corespondence to its diameter, so it's kinda reverse order. Anyway both normalized to 100 %, just integrate it.
In general the smaller the particle the higher its surface area, as well as the surface energy. I cant tell which one is important in your research, analogues to spectroscopy; certain wavelength corespondence to certain effect for certain material.
I attach an older article that may help you see the differences. A volume-based distribution (equivalent to mass for constant density) may give an indication of the total amount of material. Bioavailability generally correlates with dissolution and dissolution rate. These are surface-area related properties and it may be that you need to look at surface area distributions (also available on the Mastersizer) and the Sauter Mean Diameter, D[3,2]. Also be aware that laser diffraction measures volumes of particles (actually, as correctly stated above, the equivalent scattering of spheres) and that conversions to other properties (surface, length, number) are based on a bunch of assumptions (Hatch-Choate). If numbers of particles are required use a technique that counts numbers. Further, USP Optical Microscopy states ‘For irregularly shaped particles, characterization of particle size must include information on particle shape’.
But how it will effects on bioavalability, do we need to match the both number based psd and volume based psd against Innovator to match Bioavaliability?
@ Shanker Read the attachment I sent earlier. The data can be expressed in a number of ways. How the data are expressed does not affect the bioavailability which is probably controlled or best expressed by surface area. Look at the D[3,2] as a marker of the surface area and the finer particles affect this value and this marker will be more sensitive to changes rather than volume-based considerations. So probably your answer is that neither volume or number are good markers for bioavailability. Again I stress, laser diffraction does not count or need to know the numbers of particles to generate its volume-based results. Other parameters are derived from the volume-based results and need to be treated with more caution.
Dear @Shanker,
I agree with @Alan sir. As per regulatory perspective; D10, D50, and D90 are often used as the acceptance criteria. For detail information, go to below link:
http://www.americanpharmaceuticalreview.com/Featured-Articles/36779-Particle-Size-Specifications-for-Solid-Oral-Dosage-Forms-A-Regulatory-Perspective/
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