Summary
Summary Pharmaceutical powders
- Institution
- University Of East Anglia
Industrial pharmacy - 1st semester Includes bullet points, key diagrams and images
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Pharmaceutical Powders Manufacture of dosage forms- flow properties determined by particle
size, shape and interactions
Bioavailability- determined by dissolution rate dm/dt=DA(c s-c)/h
Particle properties- polycrystalline systems are composed of aggregated
microcrystals
Particle size distribution- monodispersed means each particle is the same
size. Usually histogram of particle diameter vs % frequency is plotted to
determine average particle size (calculate mode, median and IQR)
Particle size analysis:
Sieve analysis- widest mesh at top and finest on bottom. Fine particles
wet sieving can be used where a suspension is passed through (down to
45um)
Air jet sieving- vacuum applied to pull particles through so is more
accurate, reproducible and quick
Microscopy- light microscope (10um) or scanning electron microscope
(100nm) but need a scale to use. Only 2D and need good dispersion
Electrical stream sensing zone method- particles suspended in electrolyte
solution, pass through an aperture of known diameter. Electrodes either
side of aperture register increase in resistance as particles displaces its
own volume of electrolyte. Use calibration standards (range of apertures
0.1-1000um). Fairly quick and easy but assume particles go through
individually (dispersion issue)
Laser light scattering method- suspension of aqueous or non-aqueous
medium. Large particle analyser (1-1000um and extent of diffraction is
inversely proportional to size) or photon correlation spectroscopy
(10nm-1um).
Bulk powder properties: adhesion, cohesion, inter-particle forces, surface
tension and electrostatic charge
Large particles flow better than small and round flow better than needle
Measurement of powder flow:
Angle response- pour powder on plate then measure angle towards
horizon. Powder flows until angle of inclination becomes too small to
overcome cohesive forces. High angle means high cohesion >50 o=poor
flow. Very cohesive particles may collapse- internal friction u=tan Φ
(Φ=angle)
Bulk density measurements- density of powder bed before and after
tapping. Hausner ratio=Df/Do where Df is final bulk density and Do is
initial density. Circe ratio 1.2 is good flow and higher than 1.6 is poor
flow. Density=m/v but m is constant so ratio=V o/Vf
Flow from hopper- particles flow through orifice through expanding
central channel until dead zones form.
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