Pharmaceutics-I Lecture No.01 By –Prof. Mr. Ritesh Vyavahare (M. Pharm)

08. Clarification and filtration Filtration: Its a process where particles are separated from liquid or gas by passing it through a porous medium which retain the solid but allows the fluid to pass. Clarification: when solids are present in a very small proportion (<1%) this process of separation is called as clarification. Filter medium :A porous medium used used to retain the solids is known as filter medium.

Filter cake: The solids which gets collected on the filter is called as filter cake. Filtrate : The clear liquid passing through the filter is known as Filtrate. Theory of Filtration It gives idea about factor influencing the rate of filtration. Factor influencing on rate of filtration were studied scientist Darcy .he expressed the equation called Darcy’s law.

The equation is V= KA P n l Where V: Volume of Filtrate K :Constant. A: Area of filter bed P: Pressure difference on the liquid n: Viscosity of the fluid l : thickness of the filter cake.

Factor affecting the rate of filtration 1)Pressure: Directly Proportional 2)Viscosity: Inversely Proportional 3)Surface area of Filter media : Directly Proportional 4)Temp. of liquid to be filtered : Directly Proportional 5)Particle Size: Directly Proportional. 6)Pore size of the Filering media : Directly Proportional.

7) Thickness of the cake :inversely Proportional to thickness. 8)Nature of the solid material: directly proportional to porosity of cake and porosity depends on nature of solid particles.

Filter Media: The surface upon which solids are retained in the process of filtration is known as filter medium. Ideal qualities of filter media: 1)It should not absorb constituents of the liquid preparation. 2)Should be resistant to corrosive action of liquid. 3)should have smooth surface. 4)Should allow free flow of liquid.

5)Should be resistant to chemical reaction. 6)Should have sufficient mechanical strength. Selection of filter media depends on – Quantity of material to be filtered. Nature of the product to be filtered. The size of the solid particles to be retained on the filter. Purpose of filtration.

Various filtering media used for filtration Filter paper Cotton wool Glass wool Asbestos Fine muslin Filter cloth Membrane filters Sintered glass filters.

Filter Aids These are the substances which reduces the resistance of the filtrate to flow. These are added to the preparation in the concentration range 0.1 to 0.5 % before filtration. Ideal qualities of filter aids : It should be able to remain suspended in the liquid.

2)It should be free from impurities 2)It should be free from impurities. 3)It should be inert to the liquid being filtered. 4)It should have uniform particle size distribution. 5)It should have structure that permits formation of porous cake.

Equipments used for filtration 1)Filter press/Plate and frame filter press. 2) Meta filters. 3)filter candles. 4)sintered filters.