Clarification & Filtration (Pharmaceutics) notes

filtration and clarification pharmaceutics thepharmapedia

Terms used in Filtration

  • FILTRATION may be defined as the “Separation of solids from a fluid by means of a porous medium that retains the solids but allows the fluid to pass.
  • CLARIFICATION: When solid does not exceed 1.0%, filtration is termed as clarification & filtrate is the primary product.
  • STRAINING: The object of filtration is to remove large visible particles using a coarse filtering medium (muslin/cotton wool).
  • ULTRA-FILTRATION: Separation of inter-micellar liquid from solid by use of high pressure on a semi-permeable membrane
  • SLURRY/FEED: Suspension of solid in liquid to be filtered
  • FILTER MEDIUM: Porous medium used to retain/entrap the solids
  • FILTER CAKE/RESIDUE: Accumulation of solids on the filter medium
  • FILTRATE/EFFLUENT: Clear liquid passing through the filter medium
  • CAKE FILTRATION: If the recovery of the solid is desired, the process is called cake filtration.
Terms used in Filtration

Darcy’s Theory (Rate of Filtration)

V= Volume of filtrate
K= Permeability coff.
A=Area of filter bed
∆P= Pressure difference on liquid & below the filter medium
η= Viscosity of liquid
l= thickness of filter cake

Factor affecting the rate of filtration

  • Factor affecting the rate of filtration
    1. Filtration
    2. Viscosity
    3. Surface area of filter media
    4. Temp.
    5. Particle size
    6. Pore size of filter media
    7. Thickness of cake
    8. Nature of solid materials (porosity of filter cake)


    1. Filter paper (Grade-Coarse, medium & fine)
    2. Glass wool (Corrosive liquids)
    3. Cotton wool
    4. Asbestos(Al. silicate): Corrosive liquids, Alkalinity of filtrate)
    5. Sintered glass: borosilicate glass, Parenteral, corrosive liquid & Oxidising agents)
    6. Membrane filter
    7. Filter cloths

Substances that reduce the resistance of the filter cake & increase the filtration. (Added to the liquid slurry to be filtered)

Filter aids Should form a porous cake & Insoluble in liquid

Filter aids forms a fine surface deposit- prevent solid from contacting & plugging the supporting filter medium.

Filter aids added by 2 methods:

  • Pre-coating &
  • Body mix
CarbonCarbonFiltering strong alkaline solutionsCoarse grade only & Expensive
CelluloseCelluloseHigy purity & Excellent chemical resistanceExpensive
Diatomaceous earthSilicaWide range; Used for very fine filtrationSlightly soluble than diatomites in acid & alkali
AsbestosAluminosilicateGood retention on coarse screensMore soluble than diatomites in acid & alkali
PerliteSilica & AluminosilicateWide range; not capable of finest retentionMore soluble than diatomites in acid & alkali
Filter aids used in Pharmaceutical preparations

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