Particle size distribution is mainly estimated by analytical sieving or by application of other methods, and the powders are standardized according to the USP descriptive terms. The purpose of particle size analysis is to obtain quantitative data on drug and other components used in pharmaceutical formulations on the size, distribution and shape. Their main application is to extract drug compounds from botanical or zoological sources like animal pancreas which can be prepared into powder to extract insulin.
DEFINITION OF POWDERS OF VERGETABLE AND ANIMAL DRUGS
USP Descriptive Terms |
Maximum Diameter |
Fineness |
Very Course (No. 8) |
≤ 180 µm (≤ 0.180 mm) |
Not more than (nmt) 20% through a no. 60 sieve |
Course (No. 20) |
≤ 250 µm (≤ 0.250 mm) |
Nmt 20% through a no. 80 sieve |
Moderately course (No. 40) |
≤ 425 µm (≤ 0.425 mm) |
Nmt 40% through a no. 80 sieve |
Fine (No. 60) |
≤ 850 µm (≤ 0.850 mm) |
Nmt 40% through a no. 100 sieve |
Very Fine (No. 80) |
≤ 2360 µm (≤ 2.36 mm) |
No limit to greater fineness |
Designation | Maximum Diameter | Requirements |
Very Fine | ≤ 180 µm (≤ 0.180 mm) | passes through a No. 80 sieve |
Fine | ≤ 250 µm (≤ 0.250 mm) | passes through a No. 60 sieve |
Moderately Coarse | ≤ 425 µm (≤ 0.425 mm) | passes through a No. 40 sieve |
Coarse | ≤ 850 µm (≤ 0.850 mm) | passes through a No. 20 sieve |
Very Coarse | ≤ 2360 µm (≤ 2.36 mm) | passes through a No. 8 sieve |
Designation | Maximum Diameter | Requirements |
Very Fine | ≤ 125 µm (≤ 0.125 mm) | passes through a No. 120 sieve |
Fine | ≤ 180 µm (≤ 0.180 mm) | passes through a No. 80 sieve |
Moderately Coarse | ≤ 425 µm (≤ 0.425 mm) | passes through a No. 40 sieve |
Coarse | ≤ 850 µm (≤ 0.850 mm) | passes through a No. 20 sieve |
Particle Size Analysis
where dx/dt is the rate of settling in cm/s, d is the diameter of the particle in cm, ps is the density of the particles (g/cm^{3}), g is the added acceleration due to gravity (981 cm/s^{2}), and n_{o }is the viscosity of the medium in poise (g/(cm·s)).
• Bulk Density
• If more compressible bed of particles – less flowable powder or granules.P_{b = }M/V_{b}
• P_{b }– bulk density of granules• True or tapped Density
P_{b = }M/V_{b}
• P_{b }– bulk density of granules• Granular Density
Granular Density (D) = M/Vp-Vi
• Where, Vp – total volume of pycnometer
Vi – volume of intrusion fluid (mL), containing mass (M) in grams of granules required to fill pycnometer.
• Granular Strength and Friability
This affects the following:
Granule strength and friability are measured by:
• Flow Properties
It is an ability of the granule to flow from hopper to die cavity for tablet uniformity.
Flow property of material results from many forces:
Forces can also affect granule property such as particle size and shape, particle size distribution, surface texture, roughness and surface area.
Number | Angle of repose | Type of flow |
1 | < 25 | Excellent |
2 | 25-30 | Good |
3 | 30-40 | Passable |
4 | >40 | Poor |
% compressibility index = tapped density – bulk density/tapped density *100
or
l = (l – V/Vo) *100
where l is the % compressibility index
V is the volume occupied by powder/granules after tapping
Vo is the volume of powder/granules before tapping
Number | % Compressibility Index | Type of Flow |
1 | 5-15 | Excellent |
2 | 12-16 | Very Good |
3 | 18-21 | Good |
4 | 23-25 | Passable |
5 | 33-38 | Poor |
6 | >40 | Very Poor |
• Hausner’s ratio
% moisture content = initial weight – final weight/initial weight * 100
Percentage Fines