Percolation

Percolation

The term percolation has been derived from the Greek word percolare which means to pass through .

Percolation (or Process P) is also termed lixivation.

It involves extracting the constituents of granulated or powdered drug by slowly passing down through it a suitable menstruum.

The menstruum while travelling down the drug column under the influence of gravity, extracts the drug particles layer-wise, which are further replaced with the layers above as it moves downwards.

Percolation method achieves complete drug extraction.

Principle

Percolation is a short successive maceration or extraction by displacement method.

The powdered drug to be extracted is placed in a percolator (cylindrical or conical vessel) with a diaphragm at the base.

The menstruum is passed at a regulated rate through the drug column.

While passing down, the menstruum dissolves the active constituents and becomes saturated.

The gravitational force and the force of the above liquid column together make the saturated menstruum to move downward.

This movement is however opposed by the capillarity force.

Gravitational force, viscosity, adhesion, friction, osmosis, capillarity, surface tension, and dissolution rate are the physical factors important in percolation.

The various stages involved in the percolation are following:

(a) Size reduction:

• To assure the complete exhaustion of the crude drug, the drug should be suitably size reduced.

• Size reduction also increases the surface area of the crude drug and more surface area of the crude drug will be available to react with the menstrum.

• Size reduction also helpful of uniform packing of crude drug in percolator and reduce the moment of menstrum in the percolator.

(b) Imbibition:

• Imbibition is a process in which the powdered drug is kept along with menstrum for 4 hours in a well stoppered container.

• During this duration the menstrum penetrate into cell wall.

• This initial moistening of the crude drug powder is very important because it reduces the chances of choking of percolator though the dried drug swells when come into the contact of menstrum.

• The swelling of the drug reduces porosity of the powder and choke the percolator.

• Imbibitions replace the interstices air which can otherwise affect the flow of menstrum.

• Imbibitions also prevent the washing of fine particle of crude drug during percolation.

(c) Packing:

• After imbibition the lump of crude drug must be broken.

• The lower end of percolator should be plucked with cotton and then place the drug powder layer by layer.

• The packing should be perfect, neither too tight nor too loose which may affect the flow of menstrum.

• Two third of the percolator should be cover with the drug on which place the piece of filter paper and wash sand should be placed on the top of the filter paper.

• This prevents any type of disturbance of the crude drug by flow of menstrum.

(d) Maceration:

• Sufficient amount of menstrum should be added after packing the percolator.

• During the addition of menstrum the lower tap of percolator should be open so that air present in the percolator is displaced by the menstrum.

• When menstrum starts to come from lower tap close the tap and allowed to stand, the percolator for 24 hours as the primarily maceration take place.

• The menstrum level should be above the drug bed.

(e) Percolation:

• Open the lower tap after 24 hours of maceration and collect the menstrum from lower end until the three fourth portion of the final product is obtained.

• Meanwhile sufficient menstrum added over the powdered drug so that packed drug does not become dry.

• Completion of the percolation process should be check by various method like:

  • • 1. By checking the specific gravity of end few ml of percolate and compare with the specific gravity of fresh menstrum.

      2. Evaporate the last few ml of percolate to dryness and see that any residue comes after evaporation or not.

      3. Perform the specific chemical test for last few ml of percolate like tannins, glycoside, alkaloids etc whether it is positive or negative.

(f) Pressing the marc:

• In the last, the marc should be pressed and obtain liquid is added into the collected menstrum.

• More menstrum should be added to obtain the desired volume.

• Allow the liquid to stand and separate the suspended particles by filtration or decantation.

• Example- Strong tincture of ginger, tincture of belladona etc.